Mounded storage vessels presentation.pptx

Mounded storage has proved to be safer compared to above ground storage as it provides passive & safe environment & eliminates possibility of boiling liquid expanding vapor explosion.
This PPT provides some details regarding design guideline for mounded storage vessels.

1. Presentation on Mounded Bullets Reference – OISD, EEMUA PUBLICATION 190:1000, SMPV rules, relevant IS & IRC codes

2. Index – Part I – Guidelines for construction of mounded bullets based on OISD 150 – Slide 3 to 19 Part II – Guidelines for construction of mounded bullet based on EEMUA 190:1000 – Slide 20 to 65 Part III – Monitoring and inspection of construction of mounded bullet – Slide 67 to 102 Part IV – Pile foundation for mounded bullet – Slide 104 to 119 Part V – Ground improvement by vibro technique and vibro stone columns – Slide 121 to 155

3. Part I – Guidelines for Mounded bullet construction based on OISD 150

4. Part I –Guidelines for Mounded Bullet constn . Based on OISD 150 – Introduction - With a view of attaining the standardization in design philosophies, operation & maintenance coupled with the experiences of serious accidents in India & abroad Ministry of Oil & Natural Gas constituted, in 1986, Oil Industry Safety Directorate Design & safety requirements for LPG Mounded bullets – OISD 150 (First revision, amended edition Jul 2008) First Edition was published in 2000.

5. LPG handling has many challenges due to its dangerous properties. The conventional method of storing LPG in India is in a pressurized vessel above ground. Mounded storage has proved to be safer compared to above ground storage as it provides passive & safe environment & eliminates possibility of boiling liquid expanding vapor explosion. The cover of mound protects vessel from fire engulfment, radiation from fire & acts of sabotage.

6. Scope This standard lays down min. requirements of safety, design, layout, installation, operation, maintenance & testing for above ground fully mounded vessels of LPG storage in refineries, gas processing plants, terminals, bottling plants & auto LPG dispensing stations otherwise falling under the scope of other OISDs such as OISD 144, OISD 116, OISD 118, OISD 169, OISD 210 as applicable. This standard only supplement these standards for Mounded Bullet storage of LPG.

7. Definitions Mounded vessel – A storage vessel sited above ground and covered completely with mound of earth except nozzles, MH covers, inspection covers. Bullet – A horizontal pressure vessel for storage of LPG at ambient temperature. Compressed gas – Any gas, liquefiable gas or gas dissolved in liquid under pressure which in a closed container exerts a pressure exceeding two atmosphere at max. working temperature. Explosive mixtures – Mixture of combustion agent and a fuel Hazard area classification – Based zone/group wise based on flammability & explosive vapor-air mixture for purpose of selection of electrical eqpts .

8. Definitions -cont. Bulk vessels – Pressure vessels of more than 1000 lit water capacity for storage or transportation of compressed gas. Water capacity – Volume of water it can hold at 15-degree temperature.

9. Definition cont. Flammability limits – Range in % age by volume of flammable vapor which in admixture with air forms explosive mixture. Gas free – Condition when concentration of a flammable gas in eqpt. is well below threshold limits so that it is safe for a person to enter eqpt. Hot work – An activity which may produce enough heat to ignite flammable mixture. Kerb wall – wall of appropriate height and size of suitable material to contain spillage of LPG.

10. Definitions cont. LPG – Mixture of light hydrocarbons which are gaseous at ambient temperatures and atmospheric pressures but may be condensed to liquid state at normal ambient temperatures by application of moderate pressures. Purging – An act of replacing atmosphere within eqpt by inert gas to prevent formation of explosive mixture. Statutory Authority – Appointed under special act/regulation for specific function. CCOE is statutory authority to administer SMPV rules 1981. Source of ignition – Device/eqpt are capable of providing thermal energy to ignite flammable LPD-AIR mixtures.

11. Definitions cont. SMPV rules – The static & mobile pressure vessels (unfired) rules 1981 governing the storage, transport, handling of compressed gas in vessels exc. 1000 lit in volume. These rules are framed under Indian Explosive Act,1884. Shall – Indicates mandatory requirement. Competent Person – A person recognized by applicable statutory Authority for a job.

12. Why Mounded Bullets – Sand cover takes impact of external missile bodies BLEVE (boiling liquid expanding vapor explosion) is eliminated as no fire is possible below bullets Reduced fire cases as compared to spheres

13. Cl. 4.0 -Location & separation distances Location shall be as specified in cl. 4.1 of OISD 150 Separation distances shall be as per cl.4.2 of OISD 150 Features –

14. Cl. 5 -Mounded LPG storage facilities Storage vessels – horizontally placed cylindrical vessels shall be used for mounded storage. Mechanical design shall be based on : ASME Sec VII or PD -5500 or equivalent duly approved by CCE. Material shall be as per Cl. 5.1 (ii) Design temperatures, design pressure & other considerations shall be as per Cl. 5.1 (iii), (iv), (v)

15. Cl. 5.2 – Mound Mounded vessels shall be placed on firm foundation so as to prevent movement or floatation. Subsoil, rainwater should not be allowed to percolate in the mound. Foundation shall be constructed such that vessel slope of min 1:200 is maintained to facilitate draining. Soil condition shall be deciding factors for the type of foundation. The preferred type of foundation is a continuous sand bed, supporting the vessel over its full length. Foundation shall have sufficient load bearing capacity.

16. Cl. 5.2 – Mound contd. Following min factors shall be considered: Load of vessels during operations, during hydro test when sp. Gravity of liquid is 1 instead of that of LPG Earth/sand cover Settlement behavior of foundation as regards to overall settlement, differential settlement causing of bending of vessels & sloping of vessels. Sand bed beneath vessel shall be of min. 0.76 m to facilitate drainage from liquid outlet pipe by gravity. Bottom connections are permitted by providing an opening/tunnel & shall be designed to withstand forces acting on them.

17. Cl. 5.2 – Mound contd. Provision shall be made for encountering consequence of settlement of the vessel. The surrounding of bottom connection shall be such material that can absorb such settlement. Mound shall protect the vessel from effects of thermal radiation and jet flame impingement. Mound shall be of earth, sand or other non-combustible, non-corrosive material with min. 700 mm cover. Mound surface shall be protected against wind & rain by cover of stone, concrete tiles etc.

18. Cl. 5.2 – Mound contd. Water ingress shall be minimized by impervious layer of suitable material but continuous impermeable cover shall not be installed to avoid gas accumulation. Proper drainage and slope on top shall be provided. Longitudinal axis of vessels in a mound shall be parallel to each other with ends in line. Valves shall be accessible without disturbing the mound. Provision shall be made to monitor the settlement of mound by permanent reference points (min. 3) by which uniform/differential settlement and bending of vessel shall be monitored. (one each at ends and one in the middle)

19. Cl. 5.2 – Mound contd. Max. permissible differential settlement shall be determined at the project design stage. Regular monitoring shall be done of settlement throughout lifetime and records be maintained. The settlement of the vessel shall be monitored at least ½ yearly.

20. Cl. 7 – Hazardous area classification Shall be as per IS 5572 & OISD 113 Fire detection/protection system shall be as per Cl. 8 Gas detection system shall be as per cl. 8.2 Water requirement/storage shall be as per cl. 8.3 to 8.7 Operation, maintenance & inspection shall be as per cl.9

21. 9.4 – vessels shall be subjected to hydrotest once every 10 years or at every welding to the vessel (repairs or new connection) whichever is earlier. 9.5 – Vessels shall be tested every 5 years internally using visual and other techniques for the following: a) All the weld joints shall be examined through NDT such as radiography, wet magnetic particle test (WPT), Dye penetration test (DPT), ultrasonic flaw detection to ensure integrity of the joints. b) Wall thickness of the vessels shall be measured ultrasonically.

22. Guidelines on mounded bullet construction based on EEMUA 190:1000

23. Part II – Based on EEMUA 190:1000 Guidelines GUIDELINES FOR THE DESIGN, CONSTRUCTION AND USE OF MOUNDED HORIZONTAL CYLINDRICAL VESSELS FOR PRESSURISED STORAGE OF LPG AT AMBIENT TEMPERATURES - [ EEMUA PUBLICATION 190:1000, THE ENGINEERING EQUIPMENT AND MATERIALS USERS ASSOCIATION] [For guidance purpose. The final document to be referred to are tender provisions and the relevant codal provisions] ONLY CIVIL CONSTRUCTION PART IS COVERED HERE.

24. Scope – Guidance is provided covering the main requirements for the successful design, construction, and use of mounded facility: Criteria for selecting mounded storage ‘soil survey Foundation and mounded design Inspection and testing Inservice monitoring and inspection and maintenance

25. – Mounded Storage Mounded storage is employed because it provides additional safety compared with above ground storage of gases in sphere or bullets. Main advantage is that occurrence of BLEVE is virtually impossible [A boiling liquid expanding vapor explosion ( BLEVE , /ˈ blɛvi ː/ BLEV- ee ) is an explosion caused by the rupture of a vessel containing a pressurized liquid that has reached temperatures above its boiling point].

26. Other benefits are: Protection of vessels against Heat radiation from nearby fire A pressure wave originating from an explosion Impact by flying objects Sabotage Satisfies environmental and aesthetics Results in reduced site area due to less stringent inter-spacing requirements. The safety distance to the site boundary can be reduced considerably.

27. The design aspects of mounded bullets are in general more complicated than those above ground spheres or bullets. Particular attention to be given to the interaction between vessel and soil and to corrosion protection. Depending on site conditions, ground water level, the vessel may be installed either at grade levels or in an excavation. Vessels need to be installed above the highest known water table level and the soil cover therefore protrudes above grades as an earth mound – hence the term “mounded storage”.

28. Vessels in open underground vaults and excavations are not considered to be mounded. Mounded vessels are provided with connections through the top of mound. Designed for min. lifetime of 25 years. The min. distance between the vessels depends on activities such as welding, coating, backfilling and compaction of the backfill material. A distance of 1 m is considered to be practical min. Maximum diameter of 8 m is regarded as upper limit.

29. For vessels which are founded on a sand bed, the length of vessels should be no more than 8 times the diameter in order to prevent the designed shell thickness being governed by longitudinal bending of the vessel due to possible differential settlements or construction tolerances of vessels and foundations. The max. allowable length is determined by subsoil conditions (especially if the differential settlements are expected), size of site and economy of design. The above restrictions limits the max. volume to approx.. 3500 cu. M gross. No limitations on lower size.

30. FOUNDATION & EARTH MOUND For soil investigation the purchaser shall have to give following details to the contractor: Details of construction site Orientation of vessels relative to plant north. Prevailing wind direction Site development plan Ground levels and ground water table Seismicity of the area Depending on the history, chemical survey of the sub soil and ground water shall be also considered.

31. Fieldwork The heterogeneity/stratigraphy of the subsoil shall be investigated by cone penetration tests (CPT) and borings. If CPT is not possible the number of borings shall be increased. All borings shall be combined with recovered undisturbed samples and SPTs, both at average intervals of 1.5 m and at changes of strata. The min. number of field tests is set out as below:

32. With CPTs CPT CENTRE TO CENTRE 20+/- 5M   BH AT LEAST 1 OR 1 PER 2 VESSELS.   USS/SPT EACH BH   SCT AT LEAST 1 OR 1 PER 2 VESSELS.   DCT 1 BH LOCATION   PM AT LEAST 1   BH+ USS/SPT CENTRE TO CENTRE 20+/- 5M   SCT AT LEAST 1 OR 1 PER 2 VESSELS.   DCT 1 BH LOCATION   PM AT LEAST 1

33. Positions of CPTs and BH shall be evenly distributed over the length of vessels.  The testing locations are indicated below: One vessel Along the center line of the vessel Two vessels Both outside edge of the vessels in the longitudinal direction. Three vessels or more For outer vessels along the outside edges and for the inner vessels along the centre line

34. The scope of soil investigation may be reduced if reliable information in the form of electromagnetic survey, geo-electrical survey is available. Depending on the knowledge of site, specific geohydrology [e.g. presence of aquifers - An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials. Groundwater can be extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology, phreatic ground water level - The  phreatic  zone, or zone of saturation, is the area in an aquifer, below the  water table , in which

35. relatively all pores and fractures are saturated with water . ... The  phreatic  zone size, color, and depth may fluctuate with changes of season, and during wet and dry periods, piezometric levels from aquifers - For  groundwater  "potentiometric surface" is a synonym of " piezometric  surface" which is an imaginary surface that defines the  level  to which water in a confined  aquifer  would rise were it completely pierced with wells, piezometric levels from aquifers and level variations) the number of open standpipe piezometers shall be determined.

36. – laboratory work Tests shall be carried out on recovered samples (undisturbed and disturbed). Classification tests: On all samples Visual Wet & dry unit weight Water content Particle size analysis Atterberg limit Consolidation tests (seven loading steps + one unloading step) Drained and/or undrained triaxial tests to obtain strength and stiffness parameters of soil. Chemical analysis of soil and ground water samples. Optimum moisture content Electrical resistivity of soil

37. Reporting – Factual data – Topography and geodetic levels of the site Ground water levels including fluctuations Results from field work and lab work Stratigraphy along with axis of the vessels (indicating position of CPTs and BH)

38. Engineering data – Discussion of factual data against site geology Possible subsoil variation Recommendation of installation level of vessel relative to ground water levels. Evaluation of load conditions during mound construction and operational lifetime, e.g. including horizontal loads on piled foundations as a consequence of mound construction. Discussion of recommendation of type of foundation 9see 3.2 to 3.8)

39. Bearing capacity Selection of governing load conditions for the critical stages of construction and for the operational lifetime of the mounded storage facility. Susceptibility of the subsoil to liquification, if relevant. For soil bearing foundation, subsoil bearing capacity during various stages of mound construction and during lifetime of the mounded storage facility. For piled foundations with raft or saddles, axial pile bearing capacity taking in to account positive/negative skin friction and end bearing, group effect and lateral bearing capacity.

40. Settlement Settlement analysis to be executed shall specify elastic, consolidation and creep components. Selection of governing operational load. Settlement of vessel during hydrotesting (during construction and during retest conditions. Minimum and maximum long-term subgrade (bedding) modulus along the vessel’s axis.

41. Stability analysis Of mound slope for various load cases during construction and during operational lifetime Construction of mound, provide advice on: Suitability of fill material for foundation bed and construction of mound Compaction of vessel foundation bed and fill material surrounding the vessel Remedial measures to overcome severe erosion during construction

42. 2Types of foundation – 3.2.1 – Soil bearing foundation A soil bearing foundation which supports the vessel over its full length, on a sand bed, is preferred. This type of foundation provides continuous support, which allows an economic structural design of vessel, an economic foundation method and optimal cathodic protection. In order to reduce settlements, it may be necessary to employ soil improvement methods. A preload embankment, preferably consisting of the fill materials to be used in mound construction, is an economic solution. The duration of preload period depends on subsoil condition, specially the period required for drainage of water from subsoil. In some cases, additional fill material may be required to minimize the preload period. During construction of embankment and subsequent preload period, settlement shall be monitored and recorded. Monitoring of settlements during construction and the preload period allows for foundation design verification.

43. In addition, at specific locations soil improvement may be required by replacing the subsoil. Although a soil bearing type of foundation is preferred, it may not be always possible. If for example long term settlements are too large, a sound and/or economic structural design of the vessel may not be possible. Also, seismicity may affect the selection of foundation type.

44. 3.2.2 Sand bed on piled concrete slab If for settlement reasons, the project does not allow the use of a soil bearing foundation, a piled foundation supporting a concrete slab may be considered. The vessel shall be then be installed in a sand bed having a minimum thickness of 1 m, on top of concrete slab. 3.2.3 Vessels on saddles In some designs the vessels are placed on saddles and subsequently on piled foundations as an alternative to above foundations. This foundation is completely different to above foundations. In fact, a conventionally supported vessel is created but covered with a layer of soil.

45. An undesirable side effect occurs with piled saddles, i.e. the subsoil will settle but saddles will not. This causes the mound to separate from underneath the vessels. It is for this reason that the design philosophy described in this document is not valid for mounded vessels on piled saddles. Due to the complexity in the design, construction and long-term cathodic protection, piled saddles are not recommended as foundations. 3.3 Settlement of soil bearing foundations 3.3.1 Immediate settlements Settlements of the vessels and/or preload embankment occurring immediately during construction shall be analyzed and compared with predicted settlement (trending).

46. 3.3.2 Long term settlements Settlement analysis should also address long term settlements during operational life time. Predicted long term settlements shall be used to derive a subgrade modulus required for vessel design process. 3.3.3 Total and differential settlements In settlement analysis both shall be addressed. The maximum allowable total settlement of the vessel depends, amongst other things, on connecting piping and/or whether a tunnel is to be built to house a bottom discharge pipe.

47. Differential settlements of the vessel will affect its longitudinal slop and uniformity of support. Settlements may be reduced by the application of soil improvement. 3.4 Settlement monitoring 3.4.1 Settlement monitoring during preloading Prior to installation of a preload embankment, settlement plates shall be installed on the original ground level. They shall be of 1 X 1 m base plate with 25 mm diameter vertical rod. The rod shall extend above the preload embankment for measuring purpose. These plates shall be removed after preloading period. Frequency of settlement shall be as follows:

48. phase Frequency preloading Month 1 & 2 Weekly preloading Month 3 & 4 Fortnightly preloading Month 5 onwards Monthly Vessel installation weekly

49. In cases of doubt on the stability of preload embankment and/or mound as consequence of the presence of top clay. Excess pore water pressures should be monitored during preload period and/or mound construction. 3.4.2 settlement monitoring during operation Permanent reference points shall be located longitudinally on top of the vessel to monitor the vessel settlements. The maximum spacing of the points should be approximately twice the vessel diameter. Minimum 3 points shall be installed to be able to identify possible vessel bending (i.e. two near the vessel ends and one in the middle). Nozzles/domes can be used for this purpose.

50. Settlements shall be monitored during the life time. Frequency shall depend on the predicted settlements and on the associated period. The results shall be compared with preload settlements. If the actual settlements exceed that preload and/or the rate of settlement increases, corrective action based on specialist shall be taken. During the hydrostatic pressure test settlement monitoring should be performed for site fabricated vessel which usually undergo this test on their foundation. The occurring settlements shall be monitored for the relatively high hydrostatic loads at 0,25,50,75 and 100% filling and after 48 hours with vessel completely filled. The settlement rate during this testing period to diminish with the time as otherwise there should be danger of instability. If the rate does not diminish adequately, client shall be informed immediately. The vessel shall be (partly) emptied and a geotechnical engineer and mounded vessel specialist should be consulted.

51. 3.5 Foundation design 3.5.1 General Shall be designed, constructed and monitored as per applicable standards. The vessels should be installed at least 0.6 m above the highest ground water level on a sand bed of at least 1 m thickness in order to obtain proper bedding-in. The foundation of the vessel shall be constructed such that during the operational life time of the vessel, its longitudinal slope shall be between 1:200 minimum and 1:50 maximum. The former is the minimum for effective drainage whilst the later is intended for minimizing the dead stock. Hence in the design phase the predicted immediate and long-term settlements along axis of each vessel shall be taken in to account in determining the slop.  

52. 3.5.2 Operational phase of vessel In operational phase it is assumed that the vessel is supported over an angle of 120 degrees. The minimum safety factor during operations shall be 2. 3.5.3 Construction phase of vessel During construction, it may be assumed that the vessel is supported over an angle of less than 120 degrees (with minimum of 60 degrees). In the case of on-site vessel assembly, the maximum foundation loading will occur during hydrostatic pressure testing. The maximum load will consist of the weight of the vessel and the water. The bearing capacity of the foundation shall be verified for this load condition. Special attention shall be given to presence of welding trenches.

53. The minimum safety factor for the bearing capacity and overall vessel stability during the hydrostatic pressure test shall be 1.5. 3.6 Mound design 3.6.1 Geometry The slope of mound shall not exceed the natural slope of the fill material and should be 1:1.5 maximum. Following the results of the soil investigation, a slip rate analysis shall be performed to perform the stability of mound. When performing the calculation, it should be noted that the angle of friction along the vessel-soil interface and the effective stress in a zone next to the vessel is lower than in an “all soil condition”.

54. 3.6.2 External loads The purpose of the mound is to protect the vessels against the external events such as radiation in case of fire, flying objects and sabotage. Hence the thickness cover shall be at least 0.5 m. temporary loadings on the vessels by construction equipment on the mound shall be avoided when the thickness of the cover is less than 1 m.

55. 3.6.3 Erosion protection The slopes and top of the mound shall be protected against erosion. To prevent the possibility of gas accumulation inside the mound, continuous impermeable coverings should not be used. Open drain channels shall be constructed along side the toe of mound. The mound top shall have slight downward slope to have effective drain off. Only minimal rain water percolation shall be allowed through the erosion protection. Rain water accumulation shall be avoided inside the mound.

56. 3.7 Foundation and mound material Consideration shall be given to following while selecting the material. In the case of multiple vessels there is limited accessibility for mechanical fill and compaction equipment to the area in between the vessels. In these cases, fill material should be chosen for ease of handling. The fill material shall be compactable in order to minimize settlements. The fill material shall be suitable to allow proper functioning of cathodic protection system. However, sea sand and other unsuitable fill materials undesirable for corrosion reasons shall not be used.

57. Although it is not the intention to remove any mound for inspection, excavation of the vessels may be required (by govt regulations). For the above reasons sand should be used for both the sand bed and mound. It shall fulfill following criteria: It shall be clean. The maximum silt content (particles smaller than 0.063mm) shall not exceed 10% by weight and the maximum organic material content shall not exceed 3% by weight.

58. The maximum sulphate content shall be 0.02%. The maximum chloride content shall be 0.02%. The maximum particle size shall be 2 mm Grain size distribution shall have a uniformity coefficient (D60/D10) of between 4 & 10. In areas where sand is difficult to obtain, at least 0.3 m sand shall be placed around vessel to protect coating.

59. 3.8 Construction of foundation and mound 3.8.1 Foundation The sand bed foundation, that is the bedding associated to the 120 degrees bottom support angle, shall be prepared in layers of maximum 0.3 m thick. Each layer shall be compacted to at least 95% of MDD. ( Here we shall have to abide by the Indian context and the relevant contract and codal provisions.) The in-situ density shall be either by cone penetration testing or the replacement method. The cylindrical bottom profile of the vessel should later be cut in the sand-bed by excavation. A steel template with curvature of the vessel should be used to shape the sand-bed to the required profile. Over excavation should be avoided.

60. Due to construction tolerances, the axis of vessel shall only deviate from straight line up to 0.3% of the vessel. The construction procedure for foundation depends on the fabrication method for the vessel but shall provide uniform vessel support. If the vessel has been assembled elsewhere, the deviations of the vessel axis from straight line shall be measured and the sand bed shall be shaped accordingly to obtain good fit of the vessel in sand bed and hence an even support.

61. If the vessel is assembled on its foundation, the shape of the sand bed should be made in sections with length equal to length of vessel section to be placed on it. Each foundation section shall be completed just before the corresponding vessel section is placed on it and after the previous section has been at least tack welded in place. This procedure shall help in obtaining uniform support of the vessel.

62. It may be necessary to dig trenches in the sand bed for welding and inspection of circumferential seams of the vessel sections. The sides of the trenches shall be properly supported e.g. with sand bags. After the weld inspection and hydrostatic pressure test is successfully carried out and the coating applied, the trenches shall be carefully backfilled with properly compacted sand. Coatings of the welds shall be only applied after hydrostatic pressure testing. The number and sizes of the trenches shall be restricted to minimum because of the restriction in achieving full compaction. The method of backfilling shall be approved by the client.

63. Depending on the distance between the trenches, the local code requirements (which might require full vessel support during hydro static testing) and the calculations, it may be required to temporarily backfill the trenches prior to hydrostatic pressure test. In this way the maximum load on sand bed is reduced. To avoid too much disturbance to the foundation during construction, the shoulders of the foundation should have a horizontal part of at least 2 m wide before sloping down to grade.

64. After completion of the vessel but prior to the hydrotest, the foundation shall be repaired and recompacted where required. 3.8.2 Mound Horizontal support of the vessel by the mound is not assumed in the vessel design and is therefore not required. Too much compaction during installation of the mound may in fact impose excessive loads on the vessel. In view of this, it is advised that the mound should be compacted to 90% of MDD to prevent excessive settlements of sand only, having due regard for the material stability from stability and cathodic protection point of view. ( Here we shall have to abide by the Indian context and the relevant contract and codal provisions.)

65. If during construction a foundation with a reduced angle of support has been used, it shall be built up with well compacted sand (95% of MDD - ( Here we shall have to abide by the Indian context and the relevant contract and codal provisions.) to an angle of support of 120 degrees before compacting the mound.     5. Inspection, testing and certificates [ only civil part is considered]

66. 5.1.2 Hydrostatic pressure test The vessels shall be tested at 1.25 times maximum design pressure, unless stipulated otherwise. The test may be carried out in the shop or at site on the foundation. For shop tested vessels the pressure will be measured with a gaige having a range of 1.5 times the test pressure and an accuracy of +/- 0.6% or finer. For field tested vessels a pressure recorder of the same accuracy as that of gauge shall be used. In both the cases the temperature of the test water and ambient temperature shall be continuously recorded.

67. The pressure need not be repeated if the entire vessel was pressure tested in the shop. However, the vessel shall still be used for foundation preloading. The pH of the water shall be kept between 6 & 7. The vessel shall be completely drained, cleaned and dried by hot air. 5.1.5.2 Settlement Shall be monitored during its operational life.

68. 5.2 Mound The erosion protection layer shall be inspected for damage at regular intervals (every 6 months) in combination with settlement measurements. Dropping vegetation may indicate presence of gases inside the mound. Local vegetation may be expected at damaged locations.

69. Part III – Monitoring & inspection of construction of mounded bullet

70. Part II - Monitoring/inspection of construction of Mounded Bullets Reference documents - Material specs, construction methodology as provided in main tender Approved QAP Approved drawings & design Soil investigation report and recommendations OISD 150 – Design & safety requirements for LPG mounded storage facility SMPV Rules-1991 – Static & mobile pressure vessels (unfired) rules 1991 – To regulate the construction, fitment, loading, transport & inspection of unfired vessels in service of LPG with capacity exceeding 1000 lit.

71. Output documents Inspection reports Record of inspection Calibration certificates of testing equipment at field, at plant and the plant itself The evidence of NABL accreditation of calibrating agency The accreditation of testing labs, whether NABL or not Whether all the MTCs and independent test certificates available & reviewed? Whether all the tests carried out and witnessed/reviewed as per approved QAP?

72. Whether record summary is being maintained for actual sampling frequency v/s required sampling frequency? Whether sampling frequency matches with the quantity of material procured lot wise as required as per QAP? Whether all the test results are within the acceptance criteria? Approved methodology of construction is reviewed and available?

73. Site registers to be maintained – Mix design & trial mix – review and approval Site instruction register Cement consumption Cube test and slump test Standard deviation of cube test results Steel acceptance register showing the details of invoice lot wise, MTC and details of independent tests

74. Summary of testing requirement and that actually carried out as per approved QAP, whether accepting criteria has been met for all the tests for materials like water, coarse aggregate, fine aggregate, cement, admixture, concrete cubes compressive strength, steel reinforcement physical and chemical requirements, murum brought from borrow pits, pebble stones, soling, sand for fillings in different layers, pea gravels, geotextile sheets, UPVC sheets, showing the quantity received lot/cast wise, sampling frequency, whether adhered to, acceptance criteria and actual results thereof.

75. Bar bending schedule – bar bending schedule shall be checked as per IS recommendations of IS 2502, IS 5525 and SP 34 -1987. The welding shall be carried out if recommended by the Eng in Charge as per IS 2751 – 1998. The physical and chemical requirements shall be checked as per IS 1786. Material approval register – Each material when approved shall be noted in the register with details such as contractors’ letter/dt, the tender specs and the approval by the Eng in Charge.

76. Stage passing register/Requisition for Inspection – shall be maintained for each stage passing before the next stage begins. Level register – original ground levels and levels of each fill layer wise shall be recorded. These shall be marked with the locations of the FFD tests. MDD and OMC lab reports Record of Hydrostatic test and settlements Testing manual (already circulated) External lab reports /independent test reports for all the materials

77. Preamble to schedule of works – Contractor to give detailed construction methodology prior to commencement of work along with sequence of construction Contractor to submit BBS approved from client/TPIA Cement shall be tested daily at site @ 0.5% for each lot of cement received before consumption. Initial setting, final setting, compressive strength of cement for 3-day duration.  

78. What to look for – Soil investigation report – Which agency has carried out the investigation and is it approved one? How many bore holes were required to be investigated and how many were investigated and to what depth? Which tests were required to be carried out and whether they have been carried out and witnessed/reviewed as the case may be? The recommendations – What are the findings for SBC of underside subgrade of bullet? Whether any recommendations given for soil improvement and details of it? What are the findings for SBC of underside raft of retaining wall? Whether any recommendations given for soil improvement and details of it?

79. Design mix review and approval – Please go through the detailed step wise checks to be exercised as per IS 10262 given in enclosed appendix A and then only review/approve the design mix. Please go through the following step before we review and approve the design mix: A1 – Stipulations for proportioning Grade, cement, aggregate size, min. cement content, max w/c, workability, exposure, placing, degree of supervision, type of agg , max. cement content, admixture.

80. A2 – test data for materials Cement used, sp. Gravity of cement, CA, FA, admixture, water absorption of CA, FA, free surface moisture of CA and FA, sieve analysis of CA & FA A3 – Target mean strength – Fck (target) = fck + t X s A4 – selection of w/c ratio from table 5 of IS 456, max w/c ratio of 0.45, then adopt requisite w/c ratio.

81. A5 – selection of water content Table 2, max water content = 186 lit for slump of 25 to 50 mmfor 20 mm agg Work out water content for requisite slump. Add or deduct for slump required by applying correction factor (3% for each 25 mm slump) If superplasticizer used reduce water content by 20% A6 – calculation of cement content from given w/c ratio and quantity of water derived. Check it for exposure content.

82. A7 – proportioning of volume of CA and FA asper table 3 which gives CA + FA for given w/c ratio A8 – Mix calculation Volume of concrete = 1 m3 Volume of cement = mass of cement/ sp gravity of cement X 1/1000 m3 Volume of water = mass o/ sp gravity X 1/1000 m3 Volume of admixture = mass t/ sp gravity X 1/1000 m3 Volume of all in aggregate = vol of concrete – [ vol of cement + vol of water + vol of admixture] Mass of CA = [ vol of all in agg X vol of CA X sp gravity of CA X 1000] Mass of FA = [ vol of all in agg X vol of FA X sp gravity of FA X 1000]

83. A9 – Mix proportion for TM 1 A10 – 2 more TMs having variation of +/- 10% w/c ratio shall be carried out & graph between w/c ratio & corresponding strength shall be plotted to work out mix proportion for given target strength.  

84. Specifications of materials The detailed specification of each of the material to be incorporated shall be checked against the contract provisions before approval. Mainly the materials are: Murum as fill material below FGL – Gravel/ murum fill below the tank or wherever required: BS 1377 Liquid limit Plasticity index Gravel max size 10 mm) Sand 20% FDD of compacted layer – 98% Shall be free from organic and harmful chemicals  

85. Sieve % mass passing 75 mm 100 37.5 mm 85-100 10 mm 45-100 5 mm 25-85 600 micron 8-50 63 micron 0-25

86. Sand for tank bed, tank surround, filling between tanks – Max. organic content – 3% Max. silt – 10% Max particle size – 5 mm Grain size distribution uniformity coefficient – 2 to 8 Pea gravels – 8 to 10 mm round stone Non-woven geotextile – Terram 1000/NELTON S1 – 401 (thickness 1000 microns) as specified in the tender UPVC sheets – Shall be as per IS 2076-1981 and thickness shall be 1000 micron. Shall be stitched water tight at joints. Perforated PVC pipes – as per relevant BIS specs/tender specs Stones for pitching – hard granite of 230 mm thick  

87. ] Construction methodology – 1. Check the clause of precedence in the tender in the event of conflicting provisions. 2. Design and engineering – Soil investigation – check whether the work is being carried out by a specialized and approved agency Check who is responsible for design, engineering and construction drawings and whether they have been approved by client/ TPI Check whether tender provides for design and drawing review from IIT

88. Tentative construction methodology for the mound – These are generic methods, please check with respective tender provisions. Excavate and remove all fill material up to formation level. Fill materials shall be as per specs recommended in soil investigation report. Formation shall be compacted with 10 T roller. Back fill with soling (depth 400 mm) packed with murum /sand. Compact with 10 T roller. Spread 50 mm thick sand and compact Provide TERRAM 1000/NETLON SI – 401 , thickness 1000 micron/1mm, non-woven geotextile sheet over fine sand.

89. Lay sand bed in max 200 mm layers compacted to 98% of MDD, up to level of 60 degree from center line of tank. Provide stone drains as per drawing Use template form to give exact shape & size of bullet in compacted sand bed Excavate required number of trenches of width 1.5 m in the locations given in drawing for field welds. These are for providing access for welding the tank sections. Pace the bullet in the grove and carry out welds Lay the sand surround and general mound fill, compact it specified density (93% for sand surround of 500 mm thickness by hand compaction and 95% for general mound fill compacted with hand or light compacting machine) [here the relevant tender provisions shall apply] up to 120 degrees from center line of tank

90. Hydro test shall be conducted & bullets shall be kept filled with water for 15 days to observe settlement Complete all the mechanical requirements Retaining wall shall be constructed in required heights before start of construction of boulders and sand Construct 230 mm thick stone pitching from top of retaining wall to within 1 m of drainage layer Lay 1mm thick UPVC membrane over mound filling Lay 150 mm dia PVC perforated drainage pipe with pea gravel surround Lay Geotextile sheet over drainage pipe Complete 300 mm thick concrete apron up to top of mound Cover geotextile layer with 100 mm thick pebble finish (size 10 to 50 mm) round in shape Lay 150 mm stone layer over pebbles The mound should have toe wall & drain along three sides

91. sand bed – Sand fillings/beds shall be laid to falls & to the levels and full depths as per drg 5. sand surround between the bullets – sand filling between the tanks and line extending out of 45 degrees from the tank above the tank center line shall be hand compacted to 95% of MDD Sand fillings shall be in max. 200 mm layers (or as specified) compacted thickness on each side of tanks to avoid lateral displacement/rotation of tank 6. Pea gravel – shall be clean, washed, single size 8 mm round in shape

92. Non-woven geotextile – Used for separating two different layers One layer between soling & compacted sand at bottom of bullet Second layer between pebble finish & UPVC layer Lap shall be minimum 300 mm 8. UPVC sheet – To be provided over sand mound to prevent water percolation in to mound. Thickness shall be min. 1000 micron as per BIS 2076 – 1981 laid to slope.

93. It is laid at the mound slope. The joints shall be stitched water tight. Manufacturers TC to be checked. 9. Perforated PVC pipes – As per relevant IS codes. Shall be placed to collect water. To be laid above UPVC sheet. Min. slope 1:100. Pipe to be surrounded with pea gravel of size 10 to 20 mm 10. stone pitching – 230 mm thick over 75 mm thick PCC 1:3:6. Flush pointed. Stones shall be hard granite of 230 mm thick. 11. stone finish – Top layer of mound shall be finished with 150 mm thick, clean gravel of size 10 to 50 mm over 100 mm pebble sand laid over geotextile sheet.

94. The compaction requirements – Fill to underside of bullet – specification of material, the thickness of compacted layers and the depth shall be as soil investigation recommendation/tenders’ specifications. The sampling of FDD test is 1 number of FDD test for each 500 sq. m. each test to have minimum 5 samples. Tank surround 300 mm/500 mm – specification of material, the thickness of compacted layers and the depth shall be as per tenders’ specifications. shall be hand compacted to min 93%.

95. Sand fill around - specification of material, the thickness of compacted layers and the depth shall be as per tenders’ specifications. shall be hand compacted or compacted with light compacting machine to min 93%/95% Filling between tanks - specification of material, the thickness of compacted layers and the depth shall be as per tenders’ specifications. shall be hand compacted or compacted with light compacting machine to min 93%/95%

96. 8] HYDROTESTING & SETTLEMENT a) Hydrotesting All completed equipment shall be tested hydrostatically as per the requirements of specifications/codes & approved hydrotest procedure in presence of the inspecting authority. Prior to hydrotest, all weld splatter, weld studs, scale, dirt, etc. shall be removed from the vessel. The vessel is to be supported while hydrotesting on sand bed which is to be laid & completed up to a level of 120 degree taken from the center of vessel to the edge of vessel. Entrapped air near dome shall be completely removed by suitable means during hydrotest.

97. Contractor shall submit a detail procedure for Hydrostatic testing for approval by Owner/TPIA prior to commencement of testing time. Pressure-Time graph shall also be submitted. All necessary precautions shall be taken to safe guard against the risk of brittle fracture during hydrostatic test at site. It is suggested that the temperature of the testing medium shall not be less than 15°C. PH of water used for hydrotest shall be between 6.0 – 7.0. After hydro testing water shall be drained in NRL drains.

98. At the time of hydro test, the adjacent bullets on either side of the bullet under test pressure shall be kept water filled, i.e., minimum three adjacent bullets shall remain completely filled with water anytime during hydro test. A method of measuring the water height in the bullet is also to be established. Water shall be filled / emptied in stages 25%, 50%, 75% and full with 2 hours holding period at stages.

99. Loading rate shall be monitored such that the loading rate does not exceed 2.0M/day subject to a pumping rate of not more than 20cm/hour. Minimum 2 nos. Dial gauges, dial graduated over the range of not less than 1.5 times and not more than about 2 times the test pressure and an accuracy of +/- 0.6 percent or finer, shall be used. All pressure gauges / pressure recorders (the same accuracy or finer) used in testing shall have a calibration record showing values of standard indicated pressure and validity period.

100. Inspector shall verify that calibration tag is displayed on the pressure gauge/recorder. Pressure pumps, pipe / hose pipe, fittings and other accessories shall be capable of developing and withstanding the test pressure. Hydro Test pressurization shall be developed in stages i.e. 0 Working Pressure, Design Pressure, Hydro test Pressure with holding period of two hours minimum at stages. Depressurization shall also be done in stages i.e. Hydro test Pressure, Design Pressure, Working Pressure with holding period of two hours minimum at stages.

101. All visible weld joints / connections shall be visually inspected for any leakage/sweating at various stages. After successful hydrotesting, test water shall be transferred to the other Bullet ready for hydro testing. Unless otherwise stated, gaskets used during testing shall be same as specified for operating conditions. Sweet potable water shall be used for hydrotesting. Minimum duration to hold hydraulic pressure shall be 4 hours

102. Settlement – Their initial levels of equidistant points (bench marks) placed on top of the bullet shall be taken with respect to minimum 3 numbers permanent bench marks for settlements readings which shall be provided as near to bullet as possible but not more than twice the vessel diameter from the periphery of the mound. The settlement shall be monitored & recorded during construction period, preload period, hydro test period for foundation design verification. Some tenders specify minimum 4 permanent reference points to be installed on top of vessel to monitor vessel settlement of which 2 points shall be installed near ends.

103. Further bench marks shall be painted as per vessel specifications. Standard reference level for comparison of future readings with current measurements shall be provided. Mound settlement shall be recorded / checked after allowing 24 hours’ time at different filling/emptying stages of hydrotesting of each bullet and after 48 hours with the bullet completely filled. Also, after completion of hydro-testing, settlement recording shall be continued by the contractor during construction of mound, and till successful commissioning of bullet once in a week.

104. Settlement recording shall be done preferably when atmospheric temperature is not more than 30° Celsius. IMPORTANT The settlement rate during this testing period needs to diminish with time as otherwise there would be a danger of instability. If the rate does not diminish adequately, the client/inspecting authority shall be informed immediately. The bullet shall be (partly) emptied, and a geotechnical / specialist should be consulted.

105. The maximum differential settlement allowed is 25 mm. Total settlement allowed is 60 mm. (but individual tender specifications shall be gone into). Vessel settlement shall be monitored during operational times. Pointer markers with measuring scale shall be installed for all vessels in the inspection tunnel for monitoring settlements.   CALIBRATION – Contractor shall prepare & submit a LPG Mounded Bullet calibration procedure including Calibration Chart in accordance with IS:2009 & IS:2166. Contractor shall obtain necessary approval for calibration from statutory authority CPWD / Weight & Measurement Dept. or competent authority.  

106. Pile foundation

107. Part IV – Pile foundation RCC bored cast in situ pile – [wherever applicable] Referral codes – IS 2911 all parts Grade of concrete – M-25 with min cement content of 400 kg/m3 Slump – 100-180 mm in case bore hole is water free and unlined 150-180 mm in case of water filled bore and tremie is being used Reinforcement – Min. longitudinal reinf . – 0.4% of cross-sectional area Cover 50 to 75 mm C/C distance between two main bars – 100 mm min Lateral ties – not closer than 150 mm Vertical reinf – shall project 40 times dia above cut off level

108. RQD % Rock quality 25% Poor 25 to 75 Medium 75 good RQD % Rock quality Poor 25 to 75 Medium good

109. Liner to be provided in soft soil to ensure stability to protect concrete where high hydrostatic pressure exist in sub soil or underground flow of water exists. Provide welding to reinforcement for stability ties shall be tack welded as per Eng in Charge’s direction

110. Concreting – Ensure necessary socketing as per design/drawing (1/2d, 2D,5D) is provided depending upon rock type, RQD, CR, energy values, in case of chiseling, & pile penetration rate in case of auger boring. Concreting shall not proceed if sp. Gravity of fluid near bottom exceeds 1.2 Laitance shall be 750 mm above cut off Recording of data Date, diameter, mark of pile Reinforcement details and calculation Boring method Time and period of boring/chiseling/auguring Penetration in given time Hard rock touch level/soft rock touch level Socketing of pile Termination of pile Cut off level Concrete and cement consumption Tremie details Liner details

111. Typical data sheets of recording piling data shall be as per Appendix D of IS 2911 ( pt I/sec 2) The tolerances of verticality, eccentricity shall be as per relevant tender specs or IS code. For any deviation from designed location, alignment or load carrying capacity shall be reported to Eng in Charge. The standard specifications of materials required for piling shall be as per relevant IS codes and contract specs. Welding – field welding will not be permitted without written consent of Eng In Charge. wherever welding is permitted, it shall be in staggered locations. Tests to show that joints are full strength of bars shall be conducted. Welding shall be conducted as per IS 2751. Hot bending of bars shall not be permitted.

112. 7] Testing of piles – these are applicable to all types of piles except sheet piles. (when IS codes are refereed it shall always be the latest revision including amendments. Referral code is IS 2911 ( PtIV ). Requirements – Load tests shall be required to provide data regarding load deformation characteristics of pile up to failure or otherwise specified and safe design capacity. Minimum period of 2 weeks for precast piles and 4 weeks for cast in situ piles, shall be allowed to pass between installation and tests. The record shall include plot of load time settlement of piles.

113. Vertical load test (compression) – Test pile to be decided by Eng in Charge. can be working pile or separate test pile. Load is to be applied in 1/5 th increments of rated capacity of pile or as specified. Settlement readings shall be taken before and after application of each new load increment and at 2, 4, 8, 30, 60 min and at every 2 hrs until application of next load increment. Each stage load shall be maintained till rate of movement of pile top is not more than 0.2 mm/ hr or until 1 hr has elapsed whichever is later.

114. Further loading shall be continued in above manner till one of the following occurs: Yield of soil-pile system occurs causing progressive settlement of pile exc. 1/10 th of pile di Loading on top equals twice rated capacity or as specified in case of separate test pile and 1.5 times capacity in case of working pile. Where yielding of soil does not occur, full test load shall be maintained for 24 hrs & settlement readings at 6 hrs interval or as specified. Unloading shall be done as per loading steps. Final rebound shall be recorded 6 hrs after entire test load has been removed. If directed by eng in charge, loading & unloading cycles shall be carried out for all load stages within assumed working load.

115. Assessment of safe load – Safe capacity shall be least of the following: Load corresponding to settlement specified. 50% of final load at which total displacement equals 10% of pile dia in uniform dia & 7.5% of bulb dia in case of under-reamed piles.

116. Cyclic loading test – Load shall be applied in increments of 1/5 th of estimated safe capacity of pile or as specified. Settlement reading shall be taken before & after the application of each new load increment at 2, 4, 8, 15, 30, 60 minutes & at every 1 hr till rate of settlement is 0.2 mm/ hr until application of the next load increment. Alternate load & unloading shall be carried out at each stage and the total & net settlements be recorded. Each stage of loading & unloading shall be maintained till the rate of movement of pile top is not more than 0.2 mm/ hr for loading period of 1.5 hr & unloading period is 1 hr.

117. The following loading stages shall however be maintained for longer periods as below: At load of 1.5 times assumed safe capacity (Routine test only) – 24 hrs At load of twice assumed safe capacity ( for initial test only) – 24 hrs The loading shall be continued till one of the following occurs: Yield of soil-pile system occurs carrying settlement exc. 1/10 th of pile dia The loading on pile equals twice estimated safe load in case of separate test pile & 1.5 times the rated capacity of pile for working pile. Assessment of safe load – Shall be least of the following: Load corresponding to settlement specified ½ of final load at which total settlement equals 1/10 th of pile dia

118. Lateral load test – Test pile to be decided by eng -in-charge & may be working pile or separate test pile. Loading in increments of 1/5 th of safe capacity or as specified Each stage shall be maintained till rate of movement of pile is not more than 0.2mm/ hr or 1 hr whichever is greater Loading shall be continued till Deflection of pile head exc. 12 mm Apllied load is twice the assumed lateral load capacity of pile in case of separate test pile & 1.5 times the rated capacity for working pile.

119. Assessment of safe load – Shall be smaller of following: ½ of final load for which total deflection is 12 mm Load corresponding to 5 mm total deflection Note – deflection is at cut off level of pile

120. Pull out capacity of piles – Loading shall be applied in increments of 1/5 th the rated capacity of pile. Each stage shall be maintained till rate of movement of pile is not more than 0.2 mm/ hr or 1 hr , whichever is greater. Loading shall be continued till one of the following occurs: Yield of soil-pile system occurs causing movement of pile exc. 12 mm Loading equals twice the estimated safe load or s specified.

121. Assessment of safe load – Shall be least of following – 2/3 rd of load at which total displacement is 12 mm or load corresponding to specified permissible uplift. ½ the load at which load-displacement curve shows clear break (downward trend)    

122. Combined vertical & lateral loading test – Pile shall be first subjected to full vertical load. Lateral load shall commence after all settlements due to vertical loads have ceased while full vertical load is in position. Assessment of safe load shall be as per lateral load testing.

123. Part V - Ground improvement by vibro technique & vibro stone columns

124. Part V – Ground Improvement by Vibro technique and Vibro stone columns Illustrated example of ground improvement method by M/S Keller at MSV, Motihari . Name of work – MSV at Motihari Client – IOCL Subproject – Ground improvement Subcontractor – Keller Contractor – Fabtech Details of mound – Diameter – 7.26 m, height -7.26 m, length - 66.834 m, capacity 1200 MT Relevant codes – IS 15284 part I – 2003, Design and construction for ground improvement IS 8009, 1993 – part 1 – calculation of settlement of foundations

125. List of annexures submitted – Method statement for soil investigation Method statement for ground improvement by deep vibro technique Field quality plan Design basis & field trials Method statement for load test Method statement for granular blanket works Method statement for settlement monitoring & hydrotest guidelines Technical specifications for ground improvement Method statement for vibro stone columns Method statement for load test for single columns Method statement for load test for single column & 3 group columns Initial soil investigation report by M/s Engicons

126. Aim – To achieve required bearing capacity & to limit total and differential settlements within limits. To mitigate liquefaction potential of loose to medium dense sand in the event of earthquake. Soil improvement by providing stone columns Soil improvement by vibro compaction Soil improvement through most significant compressible strata that contributes to settlement of foundations.  

127. Scope of work – Pretreatment soil investigation works Design, supply & construction of vibro stone columns S & L min. 500 mm thick load distribution granular blanket layer Conducting trial works, initial load tests, routine load tests Post treatment soil investigation Monitoring settlement during hydro test stage & operational stage

128. ISSPL to check – Whether all the above aspects are covered & method statement & QAP is submitted and to make a review. To verify whether design concept & calculations for columns & compaction works are vetted and approved by IIT To check whether refereed technical documents as per clause 3.3 are available or not. To check whether contractor has carried out soil investigation prior to commencement of works.

129. Land to be filled & compaction up to av. Height of 1.5 m from OGL in MSV area prior to Ground improvement works. To check all the design considerations. Soil investigation – Pretreatment and post treatment Liquefaction analysis & to establish that min. factor of safety of 1.1 is available throughout the depth. This shall be vetted and approved by IIT  

130. Construction methodology – Ground improvement to be carried out as per guidelines issued by IIT Soil investigation report to be approved by IIT prior to commencement of works Construction methodology to be approved by IIT Ground improvement to be monitored by automated real time monitoring system. Depth of treatment – A per IIT recommendations, remediation can be achieved with stone columns for first 5 m from NGL with min. replacement ratio of 20% & beyond 5 m with vibro compaction. Treatment depth to be achieved for critical structures, is minimum 23 m below EGL & 20 m below EGL for non-critical structures. Design treatment depth should take in to account the consideration the influence of pressure bulbs.

131. Post ground improvement test – To check if soil is safe against liquefaction. Power consumption shall be the basis for determining adequacy of compaction of stone columns. Uniform settlement shall not exceed 50 mm Differential settlement shall not exceed 1:2500 of length of vessel. Density of sand & gravel under moist condition – 1.80 T/sq. m Design basis & field trial proposal using deep vibro technique –

132. Scope of field trials Carrying out field trails with combination of vibro compaction and vibro stone columns based on confirmatory soil investigation data. Conducting initial field load tests. Conducting post ground improvement soil investigation test at field trial locations.

133. Design basis as specified in the IOCL tender - Loading intensity – Hydrotest – 200 KPa SBC – 270 KPa Pascal (Pa) – unit of pressure and stress in MKS. 1 Pa = 1 Newton/m2 equivalent to 1 Kg/m/seconds 2 1 KPa = 1000 Newtons/m2 Long term permissible settlement (50) years) Uniform settlement of vessel to not exceed 50 mm Differential settlement not exceeding 1:2500 of length of vessel

134. Seismic Earthquake zone – zone IV Earthquake magnitude – 7.6 Peak ground acceleration – (PGA) – 0.24 g Combination of ground improvement scheme comprising of vibro compaction and vibro stone columns is employed here as top 5 m soil below WPL is observed with fines >15% hence the vibro stone column technique and below 5 m, percentage of fines is less than 15% and hence the vibro compaction is proposed.

135. Considering the interface zone of clay strata and sand layer, stone columns were installed for a depth of 7m by vibro compaction for the required treatment depth.  

136. Treatment scheme – Grid pattern – equilateral triangular pattern Grid spacing – 2.75 m center to center Diameter of vibro stone column – 1300 mm Area replacement ratio (ARR) – 20% for bibro stone columns Depth of vibro stone columns – top 7.00 m from working platform level Depth of vibro compaction – below 7. 0 to 24.5 /30 m from WPL

137. The actual depth of treatment shall be based on factual soil conditions at the treatment area. The column shall be terminated in medium dense layer which can be detected by the vibrator through power resistance against soils. Evaluation of liquefaction potential – The proposed location falls in earthquake zone IV (IS 1893) and as the subsoil comprises of loose to medium dense sand layer below 5 m depth from WPL, which is susceptible to liquify in an event of earthquake. The liquefaction potential assessment is done considering bore hole (strata, depth, no. of blows, penetration, N values, grain size analysis, liquid limit, plastic limit, plasticity index, bulk density, dry density, moisture content, sp. Gravity, shear strength characteristics like cohesion & angle of friction, void ratio, compression index, pre-consolidation pressures and chemical analysis), eCPT (electronic cone penetration test), DMT (dilatometer test)& CHST (cross hole seismic test).

138. Liquefaction potential is assessed based on Seed & Idriss approach which is used as described in NCEER summary report, 2001. The depth of liquefaction assessment has been limited to 30 m below WPL. The target FOS of 1.1 is considered for mitigation of liquefaction as per tech specs and this will be verified by post soil investigation. As per IS 1893, part 4, 2016, if N cor values are greater than value below, subsoil is not prone to liquify.

139. Seismic zone Depth below GL N values Remarks III, IV, V ≤ 5 15     ≤10 25   II ≤5 10     ≤10 20  

140. Based on the liquefaction assessment using CPT approach of NCER (2001) and above guidelines of IS 1893 -2002 for SPT, the depth of liquefaction is varying from 21 m to 30 m below WPL in MSV area. It shall be noted from the typical calculations of liquefaction analysis based on CPT, BH, DMT, CHST, that top subsoil is having fines> 15% and liquid limit > 35%, hence the same is considered as non-liquefiable layer based on the guidelines of NCER summary report.  

141. Lateral extent of treatment – It is necessary to improve the ground beyond the structure area to provide a lateral confinement and mitigate liquefaction in the event of earthquake. The lateral extent shall be based on the following: Based on Japanese geotechnical guidelines, the lateral extent of treatment (L) beyond structure footprint shall be 5 m ≤ L ≤ 10m Lateral area corresponding to an angle of 30 against the vertical axis starting from the edge of the foundation (i.e. 0.5777 times H, where H is liquefiable depth below the founding level) (2/3) * liquefiable depth Hence, lateral extent of treatment of 10 m is provided from the edge of retaining wall.

142. Settlement analysis – Carried out by GGU-Settle software. The estimated settlements are lower than allowable settlement. It shall be noted that subsoil is predominantly sandy, hence majority of post improvement settlements will occur during construction stage leaving tolerable minimal settlement for long term. Bearing capacity check – Carried out using improved composite parameters KID – Keller improvement designer and soil parameters derived from soil investigation.

143. Post ground improvement testing – To check the efficacy of the improved ground post improvement the following tests shall be carried out in the concerned area: Post sounding tests – By means of eCPTs /BH/CHST after 15 days of ground improvement works. Post soil investigation shall be carried out near pre-soil investigation locations. Routine plate load tests – Total 8 nos of routine load tests shall be carried out in proposed MSV area. Out of them 6 shall be single column load tests and 2 shall be group column load tests. Assessment shall be based on results of post soil investigation works and load test on improved ground.

144. Summary and conclusions – Location is in seismic zone IV. Subsoil consists of loose to medium sand susceptible to liquefaction in the event of earthquake. Top soil up to 3 m from WPL is of mixture of sandy silt which is not susceptible to liquefaction. However, bearing capacity and settlement of this layer shall be addressed. To meet the performance requirements, ground improvement with combination of vibro stone columns and vibro compaction is proposed. vibro columns provides improved shear strength, compressibility and effective drainage path to ensure rapid dissipation of excess pore water pressure besides in increasing the rate of settlement of top sandy soil. Densification of loose sand is achieved by vibro compaction and mitigation of liquefaction potential.

145. Subsoil conditions- Initially carried out by m/s Engicons Confirmatory test carried out by m/s Keller in MSV footprint area. 3 – BH, 3 – CPT (cone penetration test), 1 CHST, 2 DMT. Ground water table – 2 to 4 m below the GL. Silt clay – 2 to 3 m at top. Loose/medium dense sand – rest Max. SPT in BH 3 at 68 m RL (20 m below GL), is 65 and BH 2 at 86 m RL (10 m below GL) is 68.

146. Grain size analysis is done. This is done to determine % age of different size grains in a soil. Significance is, it affects engineering properties of soil and is required in classification of soil. Cone resistance – To understand soil properties such as relative density of soil, soil behavior and how ground is likely to behave in an earthquake shaking. Helps in design of foundation and ground improvement.

147. Geotechnical concerns – Mitigate liquefaction Reduce post construction long term settlements to permissible limits Bearing capacity Location is in earthquake zone IV Soil is loose & has potential to liquify in earthquakes Top soil is weak & has low SBC to support MSV

148. Hence ground improvement is required. Hence field trials using combination of vibro compaction & vibro stone columns are proposed in MSV area to arrive at suitable patterns to suit tech. specs.

149. Ground improvement techniques – To compact & densify the loose sands up to design depth which are prone to liquification and having clayey silty layers with large quantity of fines at top, stone aggregates shall be used for compaction back fill during column construction. Concept of vibro compaction – Designed to induce compaction of granular materials. Basic principle is that non-cohesive particles can be rearranged in to denser state by vibration.  

150. Concept of vibro stone columns – This technique introduces a coarse-grained material as load bearing element consisting of stone aggregate as a backfill medium.

151. Construction methodology – Use of depth vibrator as an equipment, to compact & improve subsoil. Depth vibrator is a long, heavy tube enclosing eccentric weight driven by electric motor. Field trials – Layout showing locations for field trials for ground improvement is to be submitted.  

152. Depth of treatment - Trial no VR/VC Dia in m Spacing in m Grid pattern Treatment depth in m 1 VR (clayey silt/sandy silt) 1.3 2.75 Triangular 7 m from av. Ground level   VC (sand) - 2.75 Triangular 7 to 30 m

153. As per tender, min. depth of treatment – 23 m below NGL (RL 95.5 m). clause 5.2 of TS of tender. Based on confirmatory soil investigation data & technical analysis, depth of treatment shall be min. 24.5 m to max. below av. GL (97 m). Depth of vibro columns is considering min. area replacement ratio (ARR) of 20% for vibro stone columns. Following guidelines shall be followed – Lifting weight – 0.4 m to 0.75 m Compaction time – 25 sec to 50 sec Installation procedure shall be finalized based on results of trial works.

154. Liquefaction mitigation – Liquefaction assessment is done considering BH, CPT, CHST and based on it, depth of liquefaction is varying as per table given. The assessment is limited to 30 m below GL. Summary of liquefiable depths –

155. Confirmatory sl Depth BH 28 m CCPT 30 m CHST 21 m DMT To be performed  

156. The proposed treatment depth for trial works shall be min. 24.5 m to 30 m below WPL (97 m). Target factor of safety of 1.1 is considered to mitigate liquefaction as per tender specs and shall be verified by post soil investigation. The top subsoil is having fines >15% & liquid limit >35% & hence non-liquefiable as per NCER summary report. Bearing capacity – Check by general shear failure criteria (IS 6403) Settlement – Settlement analysis based on hydrotest load intensity shall be carried out. After obtaining improved composite parameters, settlement evaluation is done by software “GGO-settle”.

157. Performance of GI works – Field trials – load tests & soil investigation will be carried out to check the efficacy of field trials. Post soil investigation tests will be conducted at trial location after completion of ground improvement works. Field investigation consist of CCPT & BH locations. Testing shall be carried out 15 days after GI works. Stone column tests – Initial load tests on improved ground to replicate design loads & required bearing capacity as per section 4 Shall be conducted after 7 days of GI works Method statement shall be reviewed.  

158. Ground improvement using vibro compaction shall be resorted to mitigate liquefaction when sand is having percentage of fines less than 15%. Basic principle is that particles of non-cohesive soils can be rearranged into a denser state by means of vibration. When the sandy silt has percentage of fines higher than 15% then ground improvement can be done by way of vibro stone columns. This technique introduces a coarse-grained material as load bearing elements consisting of stone aggregates as a backfill medium.