Geotechnical investigation

BY ABDUL MUTAKABER TAREEN THE UNIVERSITY OF LAHORE PAKISTAN

1. Group Members: Names: GROUP LEADER ABDUL MUTAKABER Umair Shams Muhammad Umar Ramzan Judge Muhammad Irfan Asadullah Shahid Ali Farooq Akram Mohsin Ali Zeeshan Zain ul Hassan Rana Shah Zaman Hafiz Mateen Arif Muhammad Noman Muhammad Junaid Muhammad Tariq Waqas Ali Registration Nos: BSCT01133006 BSCT01133002 BSCT01133009 BSCT01133015 BSCT01133018 BSCT01133028 BSCT01133033 BSCT01133034 BSCT01133039 BSCT01133079 BSCT01133158 BSCT01133200 BSCT01133235 BSCT01133220 BSCT01133222 BSCT01133116 BSCT01133074

2. PRESENTATION TOPIC: GEOTECHNICAL INVESTIGATION (SOIL EXPLORATION)

3. CONTENT OF PRESENTATION Introduction Purpose and objectives of soil exploration Investigation phases Phase I. Phase II. Phase III. Phase IV. Exploration methods Direct Methods. Indirect Methods. Geotechnical investigation

4. CONTENT OF PRESENTATION (Cont………) Soil sampling Disturbed Soil Sample. Undisturbed Soil Sample. 6. Amount of exploration 7. In-situ Tests 8. Planning an investigation Records and Reports Bore Hole/Test Pit Logs Data Sheets Of In-situ Tests 10. Conclusion Geotechnical investigation

5. INTRODUCTION Two very essential requirements for design and construction of any civil engineering facility: SOIL INVESTIGATION Also called site investigation. Provides data regarding subsoil conditions(i.e. underground conditions), ground water position and its fluctuations. TOPOGRAPHIC SURVEY Furnishes information regarding ground surface features of the site (i.e. surface conditions of the site). Geotechnical investigation

6. 1. INTRODUCTION(Cont…….) Soil Exploration Is Needed For: Planning, designing and constructing new facilities, Investigating the causes of distress or failure and developing remedial measures, Assessing quality and quantity of construction materials.(i.e. aggregates for concrete/asphalt mix etc) Geotechnical investigation

7. 2. PURPOSE AND OBJECTIVES To determine the stratigraphy of the site Primary Objectives: To assess sequence and thickness of strata. To assess quality of bedrock and depth of overburden soil. To determine position of GWT. To evaluate the characteristics of subsoil, rock, and GWT(ground water table). Geotechnical investigation

8. 3. INVESTIGATION PHASES In general can have Four Phases , as given below: Feasibility or reconnaissance Preliminary exploration pre-construction Detailed exploration phases Construction/post construction stage exploration For small projects, all pre-construction phases are combined into a single exploration operation and phase-4 may not be operated at all . Geotechnical investigation

9. 3. INVESTIGATION PHASES (Cont…..) phase-I Feasibility or Reconnaissance: Generally following information is collected in this phase: Project details(type of structure to be constructed, structural loads, intended use of the structure ) Surface and sub-surface conditions of the site (obtained through study of geological maps, aerial photographs, etc) Study of existing structures in the area.(behavior of existing structure adjacent to the site) Geotechnical investigation

10. 3. INVESTIGATION PHASES (Cont…..) phase II II. Preliminary exploration: During this phase Bedrock or hardpan is established Disturbed soil samples are recovered Position of GWT may also be established Geotechnical investigation

11. 3. INVESTIGATION PHASES (Cont……..) phase III III. Detailed exploration: This phase may include: Test pits excavation, boreholes, in-situ testing Collection of both disturbed and undisturbed samples for detailed laboratory testing GWT may also be monitored by installing piezometers. Geotechnical investigation

12. 3. INVESTIGATION PHASES (Cont………) phase IV IV. Construction/post construction stage exploration: Additional exploration may be required during construction stage to cope with the unexpected subsoil conditions. Monitoring of the movement of structure, Monitoring of groundwater fluctuations, both during and after construction, may be required. Geotechnical investigation

13. 4. EXPLORATION METHODS Indirect methods Establish boundaries between strata of different composition, Determine the quality by detecting changes in the electrical resistivity or wave velocity in the soil. II. Direct methods Soil samples are taken from the soil/rock strata by making actual excavations through probing, borings, test pits etc. Subsoil/GWT characteristics are determined by field /laboratory test performed on sample recovered. The indirect methods do not provide direct information regarding the characteristics of subsoil/rock and must be used in conjunction with direct methods. Geotechnical investigation

14. INDIRECT METHODS Also termed as GEO-PHYSICAL METHODS Used when soil exploration is to be carried out over large area and where speed is of prime importance. These soil exploration methods are based on principle that physical properties (like electrical conductivity, elasticity or seismicity, magnetic susceptibility, density etc) vary for different types of soils. Geotechnical investigation

15. METHODS USED IN INDIRECT METHODS(Cont…….) Seismic refraction method. Electrical resistivity method. Magnetic measurements method. Gravitational measurements method. NOTE: Here we will discuss only those methods which are being widely used. Geotechnical investigation Widely used methods

16. METHODS USED IN INDIRECT METHODS(Cont…….) Seismic refraction method. This soil exploration method is based on the principle that sound waves travel faster in rock than in soil. shock waves  (or sound waves of vibration) are created into the soil at ground level or at a certain depth below it, either by striking a plate on the soil with the hammer or by exploding small charge in the soil. The shock waves so produced travel down in the sub-soil strata and get refracted after striking a hard rock surface below. Geotechnical investigation

17. METHODS USED IN INDIRECT METHODS(Cont…….) Seismic refraction method.(Cont…….) The refracted or radiated shock waves are picked up by the vibration detector (also known as geophone) where the time of travel of the shock waves gets recorded. Knowing the time of travel of the primary and refracted waves at various geophones, tune and distance graphs are drawn based on which it is possible to evaluate the depth of various strata in the sub-soil. Geotechnical investigation

18. Fig. Seismic refraction method. Geotechnical investigation

19. METHODS USED IN INDIRECT METHODS(Cont…….) ii. Electrical resistivity method This soil exploration method is based on the principle that each soil has different electrical resistivity, depending upon the type of soil, its water content, compaction and composition 4 electrodes are driven in the ground at equal distance apart and in a straight line. A current is passed between the two outer electrodes and the potential drop between the inner electrodes is measured by use of potentiometer. Thus on knowing the values of change in resistivity of sub soil strata at site, it is possible to establish the nature and distribution of different type of soils in the formation. Geotechnical investigation

20. Fig. Electrical resistivity method Geotechnical investigation

21. II. Direct Methods A more detailed description of underground conditions at specific locations are revealed with direct investigation methods which obtain information by physically sampling or testing soil, rock and groundwater. The sampling or testing devices are inserted into a borehole advanced into the ground by drilling methods, and either samples are returned to the surface for evaluation and testing, or the properties of the underground profile are measured by in-place testing Methods used in DIRECT METHODS Tests pits, trenches, shafts, tunnels Probing or sounding Test boreholes Geotechnical investigation

22. METHODS USED IN DIRECT MTHODS Test pits, Trenches, Shafts, Tunnels: Also termed as open excavations . The most satisfactory method of inspecting soil stratification through visual observations and recovering both disturbed and undisturbed samples. Excavations may be made by hand by using manual labor or by using earth moving equipments (i.e. backhoe, trencher or dozer) Geotechnical investigation

23. METHODS USED IN DIRECT MTHODS(Cont………) MERITS Visual inspection of stratification. Suitable for best quality disturbed and undisturbed sampling. Difficulties of excavating can be assessed. DEMERITS Limited to a depth of about 3 m as the cost beyond limit increase rapidly. Suitable for exploration only above GWT. Limited to shallow exploration only. Geotechnical investigation Test pits, Trenches, Shafts, Tunnels(Cont……...)

24. METHODS USED IN DIRECT MTHODS(Cont………) b. Probing or sounding Probing or sounding is made by driving a steel rod about 25 mm diameter into the ground. The soil type and its properties are related to the driving resistance to the rod and from particles adhering to the rod when it is pulled out. Sometime some small grooves are made along the rod to collect some traces of soils through which it passes during probing. Geotechnical investigation

25. METHODS USED IN DIRECT MTHODS(Cont………) MERITS Suitable to locate the thickness of loose overburden soil. Rapid method and relative cost is very low. Very cheap and rapid method of exploration. DEMERITS A boulder may be mistaken for bedrock. Method is of limited use as soil sample for identification are not recovered. Suitable for depth about 10 to 20 m. Geotechnical investigation b. Probing or sounding(Cont………)

26. METHODS USED IN DIRECT MTHODS(Cont………) C. Test Boreholes: Boreholes in soil/rock may be drilled using: Auger Boring, Percussion rig, Wash boring rig and Rotary drilling rig. Auger Boring: Hand augers are used only for boring above GWT to a maximum depth of about 10m. The range of diameter of holes is from 50mm(2inch) to about 300mm(12 inch) drilled by different augers. Geotechnical investigation

27. METHODS USED IN DIRECT MTHODS(Cont………) Auger Boring (Cont ………) Fast and economical, using simple, light, instruments for large to small holes. Soil removed by this is disturbed but it is better than wash boring, percussion or rotary drilling. It is not suitable for very hard or cemented soils, very soft soils. Geotechnical investigation

28. METHODS USED IN DIRECT MTHODS(Cont………) Fig. Augers Geotechnical investigation

29. METHODS USED IN DIRECT MTHODS(Cont………) Percussion rig: In case of hard soils or soft rock, auger boring or wash boring cannot be employed. For such strata, percussion drilling is usually adopted. Here advancement of hole is done by alternatively lifting and dropping a heavy drilling bit which is attached to the lower end of the drilling bit which is attached to the cable. Geotechnical investigation

30. METHODS USED IN DIRECT MTHODS(Cont………) Fig. Percussion Drilling Geotechnical investigation Lifting, dropping, cutting by drilling bit.

31. METHODS USED IN DIRECT MTHODS(Cont………) Wash boring rig: It is a popular method due to the use of limited equipments. Here first an open hole is formed on the ground so that the soil sampling or rock drilling operation can be done below the hole. The hole is advanced by chopping and twisting action of the light bit. Cutting is done by forced water and water jet under pressure through the rods operated inside the hole. Geotechnical investigation

32. METHODS USED IN DIRECT MTHODS(Cont………) Fig. Wash Boring Geotechnical investigation

33. METHODS USED IN DIRECT MTHODS(Cont………) Rotary drilling rig: Rotary drilling method of boring is useful in case of highly resistant strata. It can conveniently be used in sands and silts also. Here, the bore holes are advanced in depth by rotary percussion method which is similar to wash boring technique. Geotechnical investigation

34. METHODS USED IN DIRECT MTHODS(Cont………) Fig. Rotary Drilling System Geotechnical investigation

35. 5. SOIL SAMPLING A sample is said to be a representative sample when it truly represents the characteristics of the stratum from which it is recovered. In geotechnical engineering, generally following types of samples are retrieved. Disturbed Soil Samples (DS). Undisturbed Soil Samples (UDS). Geotechnical investigation

36. 5. SOIL SAMPLING(Cont………) Disturbed Soil Samples: In disturbed soil samples the natural structures of soils gets partly or fully modified or destroyed, Although with suitable precaution the natural water content may be preserved. Disturbed sample can be obtained by direct excavations by augers. Undisturbed Soil Samples: In undisturbed soil samples the natural structure and properties remain preserved. These samples are used to tests for shear, consolidation and permeability. Geotechnical investigation

37. 5. SOIL SAMPLING(Cont………) Causes Of Sample Disturbance: Volume disturbance. Side friction between the sampler and the soil. Moisture content changes. Loss of hydraulic pressure. Working environment. Improper shearing of the sample. Failure to shut-off the drilling fluid during sampling operation. Geotechnical investigation

38. 6. AMOUNT OF EXPLORATION By amount of exploration is meant to decide about the extent of investigation i.e. to determine the number, location, and depth of open excavation and boring soundings. The extent of exploration depends upon : Site conditions Nature and extent of the project. Availability of time, funds, equipment for exploration Geotechnical investigation

39. 7. IN-SITU TESTS Following are the different tests performed in soil exploration: Standard Penetration Test (SPT). Static Cone Penetration Test (CPT). Field Vane Shear Test (FVT). Plate Load Test (PLT). Pressure meter Test (PMT). Dilatometer (DMT). Geotechnical investigation

40. 8. PLANING AN INVESTIGATION The aim of planning an investigation programmed is to gather adequate data regarding surface and subsurface conditions of the site necessary for the design and construction of the new facilities for evaluating the causes of distress and developing remedies for the existing facilities. Investigation program must include; Amount and extent of exploration: Spells out number of boring and test pits Geotechnical investigation

41. 8. PLANING AN INVESTIGATION (Cont............) b. Method of exploration: Based on the information gathered from a critical review of the background data of the site. It may be split into following phase: Feasibility or reconnaissance Preliminary exploration Detailed exploration Construction/post construction stage exploration c. Sampling method: Types of method should be specified in the program. the program should also specify the labeling, packing, transporting procedures etc, of the samples from the site to the laboratory. Geotechnical investigation

42. 8. PLANING AN INVESTIGATION (Cont……..) d. Laboratory testing program: should include the number and types of tests required for the investigation. e. In-situ tests: should specify the number and types of in-situ tests needed for collecting information essential for the adequate design of the works. f. Recording of Field Data and Preparation of the Geotechnical Report It should specify the procedure of recording field data and should include specimen boring logs or data recording sheets. g. Time and cost of exploration It should make estimates for the time and cost of investigation. it must include the bill of quantities of the investigation.(BOQ) Geotechnical investigation

43. 9. RECORDS AND REPORTS Borehole/Test Pits Logs: should be prepared in the field providing all necessary information about the site. II. Data Sheets of In-situ Tests: A geotechnical report should include: Introduction Brief project description Purpose and scope Techniques and geophysical survey record Boring logs and in-situ and laboratory test result Comments , Conclusion , and Recommendation Geotechnical investigation

44. 10. CONCLUSION OF PRESENTAION For any construction the soil that it’s built on is of great importance. If the foundation is not set on solid ground it can have disastrous impact on the building. Necessary for the design and construction of the new facilities for evaluating the causes of distress and developing remedies for the existing facilities. Geotechnical investigation