Module 1 - Jacking techniques.pptx

Box jacking and pipe jacking techniques for substructure construction under existing structures / facilities. Can be adopted for underground jacking and is a type of advanced construction technique. Advantages, limitations and problems encountered are also mentioned. Various figures and images are also added. Step by step procedure is also added. Computer aided system for remote controlling is also mentioned.

1. MODULE 1 – SUB STRUCTURE CONSTRUCTION CHINNU MARIAM NINAN ASSISTANT PROFESSOR DEPARTMENT OF CIVIL ENGINEERING TKM COLLEGE OF ENGINEERING, KOLLAM

2. JACKING UNDERGROUND STRUCTURES 2

3. JACKING CONCEPTS 3 Main jacking concepts Box jacking Box jacking (Tunnel jacking) Thrust boring (Pipe jacking) Modular jacking Advanced support structures 3

4. BOX JACKING / BOX DECK PUSHING Box jacking is a trenchless method of underpass construction (installed without breaking the ground or pavement surface, except at the entrance and exit point) that consists in pushing one or more prefabricated concrete boxes into the soil using high capacity hydraulic jacks . Need for box pushing Through traffic need not be disturbed Land constraints on either side for exploring other options become limited Compared to flyovers, it is economical Open cutting and filling involves huge earthwork volume 4

5. BOX JACKING It is the process in which a pre-cast R.C.C box or a rigid box is pushed into the soil with the help of hydraulic jacks It is non-intrusive method beneath the existing surface infrastructure. It is more often used when a subway or a aqueduct or a underground structure is to be constructed. It enables the traffic flow without disruption. 5

6. GENERAL PROCEDURE It involves the advancement of a site-cast / pre-cast box using high capacity hydraulic jacks. An open ended reinforced concrete box is cast on a jacking base. Then the high capacity jacks are placed at the back and it pushes the box into the ground. A purpose designed tunnelling shield is provided at its leading end, and thrust jacks are provided at its rear end reacting against a jacking slab/ thrust wall. The box is then jacked carefully through the ground. Excavation and jacking take place in small increments of advance. Measures are taken to ensure stability of the tunnel face and to prevent the ground from being dragged forward by the advancing box. When the box has reached its final position, the shield and jacking equipment are removed. 6

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8. ELEMENTS INVOLVED IN BOX PUSHING Thrust bed: It is an RCC member cast beyond the embankment. Upon the thrust bed, the precast/ cast-in-situ box elements are placed and pushed. Pin pockets: The pockets have been created to accommodate hydraulic jacks in the front (Approx. 0.5m × 0.5m) Auxiliary bed: It is used to facilitate the casting of units / placing of precast units and shift on to the main thrust bed. Front shield: It is a cutting edge provided in the front face of the first box Shear keys: These are provided in the base of thrust bed to avoid shear failure of thrust bed during box pushing operations. Drag sheets: It is used at the top of the box while pushing to minimize the rolling of soil above the top of the box (to reduce frictional force). In addition to these, jacking equipment are also required. 8

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10. JACKING EQUIPMENT 10

11. Jacking equipment comprises jacking rigs, cross beams with spacer pieces and power pack with operator’s console. Each jacking rig has a vertical structural member which rests on the floor at the rear of the box and bears against a thrust wall and anchorage is cast into the end face of the box floor and roof respectively. A cluster of six 1.2m stroke double acting hydraulic jacks is mounted on the lower end of the jacking rig. Jacks are rated at 200 tonnes , giving a maximum jacking thrust of 1,200 tonnes per jacking rig . Hydraulic power is provided by a diesel hydraulic power pack. The longitudinal and cross trench system is accurately constructed in the jacking base for each jacking rig. This permits the jack cluster to thrust against a cross beam located on the horizontal axis of the jacking base thus minimizing bending moments and simplifying base reinforcement. Thrust is transmitted through the jacking base into the surrounding ground. Spacers are inserted between the jacking cluster and cross beam as the box advances and then the cross beam is advanced incrementally. The number of jacking rigs required is determined from the jacking load calculation. Each rig is piped directly to the operator’s console so that he can advance the box using the required jacking thrust. 11 JACKING EQUIPMENT

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13. METHODOLOGY Excavation: Open excavation is to be carried out for the construction of thrust bed. Thrust bed: Required size of thrust bed to be constructed to facilitate the process of box pushing (Minimum M20 grade should be used). Casting of boxes: Precast / Cast in situ Fabrication of front and rear shields: Front shield is to be fitted on the first segment of the box through anchor bolts at the time of casting of the box. It pierces through the soil under the pushing forces of the jack (cutting the soil by front shields and manual excavation from inside the box). These cutting edges are to be designed based on the soil investigations. The rear shield is also fitted with anchor bolts at the rear end of each box segment to prevent soil caving in, at the junction. Drag sheets / epoxy coatings: Drag sheets are used at the top of the box while pushing to minimize the rolling of soil above the top of the box / Epoxy coating to be done on the top of the box to allow soil, free contact with top of the box as the box pushing progresses. Pushing of box segments: Initially the boxes are to be pushed by the hydraulic jacks which are provided in between the boxes and thrust wall. Shifting of succeeding box segments: After the first stroke of box pushing forward beyond first row of pins, the hydraulic jacks are to be placed in the space between the pins and the rear end of the box. Then the jacks are operated through the hydraulic system and the force generated by the jack pushes the boxes further. Pushing of succeeding box segments: When the box reached beyond the next row of pockets in thrust bed, the pins are to be removed from earlier row of pockets and placed in the exposed row of pockets. This process is to be continued until the first segment of the box is pushed beyond the edge of thrust bed. Completion: After every push, the level and alignment of the box is to be checked. 13

14. PRECAUTIONS TO BE CONSIDERED Adequate cushion between track structure and the boxes (not less than 1m) is to be provided to avoid lateral and vertical disturbance of road / track. Protection of track structures from vertical and lateral disturbances Suitable speed restriction – caution order to be decided and displayed ( Eg : 20 kmph max.) Not to be done in rainy season & / extreme hot season Jacking must be stopped while passing of train in case of tracks. Level and alignment of the box is to be checked immediately after every push. Deploy lookout men round the clock to track the track parameters after every passage of train and the records to be maintained Sufficient number of sand bags / soil filled bags and ballast should be stacked near the tracks. 14

15. ADVANTAGES PROBLEMS ENCOUNTERED Traffic need not be disturbed Best alternative in terms of overall economy Speed in construction Greater efficiency in case of busy routes Less volume of earthwork excavation Settlement of the above ground. Seepage of ground water. Caving in of soil etc. 15 DISADVANTAGES Skilled personnels are required Safety precautions to be done properly

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17. THRUST BORING METHOD It is a process of simultaneously jacking the pipe through the earth while removing the earth inside the pipe by means of a rotating auger. Unstable conditions- the end of auger is kept retracted inside the encasement so as not to cause voids. Stable conditions- the auger can be successfully extended beyond the encasement. This can be successfully used in any kind of soil conditions. 17

18. Pipe jacking is a special tunnelling technique for installing underground pipelines by assembling the pipes at the foot of an access shaft and pushing them through the ground with the minimum of surface disruption. 18 PIPE JACKING

19. PIPE JACKING TECHNIQUE It is generally referred as “Micro tunneling” Pipes are pushed through the ground behind the shield using powerful jacks. Simultaneously excavation takes place within the shield. This process is continued until the pipeline is completed. The method provides a flexible, structural, watertight, finished pipeline as the tunnel is excavated. No theoretical limit to the length of individual pipelines. Pipes range from 150mm to 3000mm diameter can be installed in straight line or in curvature. Thrust wall is provided for the reaction of the jacks. In case of poor soil, the thrust wall may punch inside the soil. Then piles or ground anchoring methods can be used. 19

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21. PIPE JACKING PROCEDURE The thrust pit and the reception pit are excavated at the required places. Then the thrust wall is set up in the thrust pit according to the requirement. In case of mechanized excavations, a very large pit is required. But in case of manual excavation, a small pit is enough. Thrust ring is provided to ensure the even distribution of stress along the circumference of the pipe. The number of jacks vary depending upon the frictional resistance of the soil, strength of pipes etc., The size of the reception pit is to be big enough to receive the jacking shield. To maintain the accuracy of alignment a steer-able shield is used during the pipe jacking. In case of small and short distance excavations, ordinary survey method is sufficient. But in case of long excavations, remote sensing and other techniques can be used. 21

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23. EXCAVATION SYSTEMS A number of excavation systems are available including manual, mechanical and remote controlled Shields, excavation and face support can be provided for a wide variety of ground conditions. To install a pipeline, thrust and reception pits are constructed, usually at manhole positions. The dimension and construction of a thrust pit may vary according to the specific requirements of any drive. Mechanised excavation may require larger pits than hand excavated drives. 23

24. THRUST WALL A thrust wall is constructed to provide a reaction against jacking force. In poor ground, piling or other special arrangements may have to be employed, to increase the reaction capability of the thrust wall. Where there is insufficient depth to construct a normal thrust wall, the jacking reactions has to be resisted by means of a structural framework constructed above ground level having adequate restraint provided by means of piles, ground anchors (or) other such methods for transferring horizontal loads. 24

25. DESCRIPTION OF JACKS High-pressure jacks driven by hydraulic power packs required for jacking concrete pipes. Thrust ring is provided depending on the number of jacks Jacks are interconnected and the jacking forces are distributed around the circumference of the pipe to be inserted into the ground. The ram diameter and stroke of the jack varies: Short stroke jacks with multiple space blocks Medium stroke jacks with shorter length pipes Long stroke jacks to push a full length pipe. 25

26. COMPUTER GUIDANCE SYSTEM The computer system enables us to control the work remotely. 26

27. APPLICATIONS OF PIPE JACKING New sewerage and drainage constructions Culverts Gas mains Water mains Oil pipelines Electricity - cable installations Telecommunication cable installations Special applications include the installation of Rectangular / circular sections for pedestrian subways Road underpasses Bridge abutments 27 Note: The technique can be used to negotiate obstacles such as motor ways, railways, rivers, canals, buildings and airfields in the path of pipe laying projects.

28. FACTORS CONSIDERED FOR PIPE JACKING Following factors are to be considered when selecting a pipe jacking system The type of pipe The size of pipe (diameter and length) Soil conditions Pit restrictions Length of push Price 28

29. ADVANTAGES OF PIPE JACKING Inherent strength of lining Minimal surface disruption Less risk of settlement Reduced requirement for diversion of utilities in urban areas Smooth internal finish Gives good flow characteristics Prevents good water ingress by use of pipes with sealed flexible joints Virtually maintenance free construction Economic when compared to open cut trenching in urban areas Reduced environmental disturbances 29

30. AD VANTAGES OF PIPE JACKING It avoids the excavation of trenches. So it is also called as “Trench less Technique”. There won’t be any leak problems in the future. Timely finish of projects. DISADVANTAGES OF PIPE JACKING Very costly method Skilled personnel is required PROBLEMS ENCOUNTERED IN JACKING Settlement of the above ground. Seepage of ground water. Caving in of soil etc. 30