Anirudhan I.V. Geotechnical Solutions, Chennai

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Carmella Bond
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1 Anirudhan I.V. Geotechnical Solutions, Chennai

2 Often inadequate In some cases, excess In some cases, disoriented Bad investigation Once in a while good ones

3 Depends on one type of investigation, often exploratory boreholes with SPT and sampling at 1.50m to 5.00m depth intervals Static Cone Penetration tests and Pressure meter tests are conducted as ritual and never used in the strength and compressibility assessments. No attempt to correlate the shear strength and compressibility parameters from different tests No concentration on foundation bearing stratum

4 In many large projects large number of boreholes are executed in a very short time, often producing data not consistent Rock drilling for very large depths, whereas no concentration on the foundation bearing stratum such as intermediate geo-material Large number of plate load tests in weak soil where main foundation system is pile Many numbers of ERT tests for earthing purpose

5 Boreholes with SPT at large depth intervals where liquefaction assessment is necessary Boreholes and other test locations are decided before deciding a plant layout Trial pits are not considered where weathered rock at very shallow depth is expected Very deep trial pit excavations when the soil is loose

6 Often because of lack of respect for the work (70%) Faulty specifications and scheduling (30%) Done in a hurry (20%) Lack of sensible supervision (70%) Unethical practices (30%)

7 Have a very specific specification for the work Have good supervision Sensible investigation programme

8 Specification shall be drawn based on some idea about the soil profile in the site. Pilot boreholes shall be drilled before finalizing the specification for investigation Depth of investigation and surface extent of investigation shall be clearly drawn Shall call for detailed procedure for each and every tests to be carried out in the site and laboratory. For example, the procedure of dropping of SPT hammer shall be clearly mentioned.

9 Often the borehole termination criteria is unscientific. Sometime SPT refusal is given as N>50 and anything beyond this is rock In some cases SPT refusal is N >100 Some specifications call for chiseling for 2 hrs in borehole when SPT N >50 or N>100 without mentioning chisel size, weight, etc. Most specifications do not recognize the existence of 1.0m to more than 10.0m thick intermediate geomaterial where rock core sampling is not possible Not allowing mud circulation in stiff soil and sand soil above water table

10 This is a must for any medium to large size projects. Geotechnical Engineers shall understand and respect the job of supervision of geotechnical investigation The supervising team can have one or two geotechnical engineers and experienced technicians The first step of supervision shall be calibrating all the testing tools. Periodic measurements and records will ensure good supervision

11 The state of art approach is continuous sampling and probing. It is long way to reach this status in India. However, it can be achieved by the following. Instead of 50 to 100 exploratory boreholes with SPT at 1.50m to 5.00m interval, make 20 to 40 exploratory boreholes with SPT at every 0.75m to 1.00m depth interval. This will amount to continuous sampling. Obtain NMC profile from the continuous samples.

12 Conduct static cone probing of piezo cone probing for every alternate borehole and establish correlation for soil profile and the cone resistance and other parameters Conduct cone penetration tests at more locations and use the correlation Make more boreholes for exploring more on intermediate geo-material and rock formation.

13 Take the help of pressure meter tests for intermediate geo-material Include large number of Field Vane Shear Tests in soft clay deposits But, always fear for variations and cater for more investigations Leave the interpretation of the good data to a sensible geotechnical engineer

Geotechnical Measurements and Explorations Prof. Nihar Ranjan Patra Department of Civil Engineering Indian Institute of Technology, Kanpur

Geotechnical Measurements and Explorations Prof. Nihar Ranjan Patra Department of Civil Engineering Indian Institute of Technology, Kanpur Lecture No. # 13 (Refer Slide Time: 00:18) So last class, it was