Soil investigation

The thorough study of site investigation from map study to report preparation in Foundation engineering

1. Prepared By: Simarpreet Singh AP (CE) ACET Amritsar [email protected] SOIL INVESTIGATIONS

2. TABLE OF CONTENTS Objectives Stages in Sub-Surface Exploration Extent of Exploration Methods of Exploration Samplers Field Tests Geophysical Methods Soil Investigation Report

3. OBJECTIVES To classify the soil To check the properties of soil To select type and depth of foundation To check the water level beneath the ground To check the site preferred for “Borrow Pits” To identify the stratification of soil below ground surface To compute settlements To investigate safety of existing structures

4. STAGES IN SUB-SURFACE EXPLORATION Map Study Reconnaissance To know general topography and existence of drains To observe settlement cracks in existing structure To observe evidence of landslides Location of high flood marks To know about drainage pattern and type of vegetation Preliminary Exploration Detailed Exploration

5. EXTENT OF EXPLORATION The Depth of soil exploration is carried out upto “Significant Depth” i.e. where stresses due to the loading are reduced to 20%. Depth of soil exploration depends on: Type of structure Depth and type of foundation Height of embankment Scour Depth in case of flowing water Capillary Rise

6. EXTENT OF EXPLORATION Minimum 5 boreholes are required for an area of about 0.4 hectares that can be reduced to 1 in case of compact sites. The spacing of boreholes is kept as following: 10 to 30 m depending upon subsurface condition 150 to 300 m incase of highways 40 to 80 m in case of concrete dams

7. METHODS OF EXPLORATION Direct Methods Trenches and Pits Drifts and Shafts Boring Auger Boring Wash Boring Rotary Drilling Percussion Drilling Core Boring Indirect Methods Seismic Method Resistivity Method

8. METHODS OF EXPLORATION

9. METHODS OF EXPLORATION

10. METHODS OF EXPLORATION

11. METHODS OF EXPLORATION Rotary Drilling by MAIT Machine

12. METHODS OF EXPLORATION Trenches and pits provide the place for the engineer to minutely observe the stratification of soil or soil properties without taking the sample out of its natural state. Trenches and pits are normally preferred in case depth of exploration does not exceed 6m. On the other hand Boreholes are meant for exploring the soil where significant depth is more than 6m. In this method the sample of soil which is collected with the help of samplers, is tested in laboratory

13. METHODS OF EXPLORATION Auger Boring preferred for maximum depth of 12 m. Auger boring is not used when there are large cobbles, boulders or other obstructions are encountered. In wash boring hole is advanced by chopping bit and water jet. Wash Boring is not preferred in hard soils, rocks or soils containing boulders. Rotary Drilling make use of cutting bit by rotation Rotary Drilling is not preferred for soils containing large percentage of gravels as they start rotating along with bit.

14. METHODS OF EXPLORATION In Percussion drilling bore hole is advanced by lifting and dropping heavy chisel. Percussion Drilling is preferred where soils consist of rocks or boulders. Percussion Drilling is also used for constructing Tube Wells. Core Drilling is preferred to collect the core by rotating the hollow drilling rod.

15. SAMPLERS Terminology:

16. SAMPLERS Terminology:

17. SAMPLERS Types of Samples: Non Representative Soil Sample Representative Soil Sample Disturbed Soil Sample Undisturbed Soil Sample

18. SAMPLERS Requirement of Good Sampler: Considering different types of soil samplers available in the market to collect soil samples while boring, a good sampler should have following properties: The inside clearance should be 0.5% to 3% Sands, silts, soft clay should have 0.5% Stiff and hard clays below water table should have 1.5% Stiff expansive clays should have 3% The Area Ratio should be less than 10% The Outside Clearance should be less than 2%

19. SAMPLERS Requirement of Good Sampler: Maximum Inside diameter should be 75mm Cutting edge angle should be less than 20 o The sampler tube should be uniform and smooth Recovery Ratio should be 96% - 98% Inside wall should be properly oiled to reduce wall friction

20. SAMPLERS Types: Standard Split Spoon Sampler Scraper Bucket Sampler Shelby tubes and Thin Walled Sampler Piston Sampler Denison Sampler Hand-Carved Sampler

21. SAMPLERS

22. SAMPLERS

23. SAMPLERS Piston Sampler

24. SAMPLERS Scraper Bucket Sampler

25. FIELD TESTS Standard Penetration Test(SPT) https://www.youtube.com/watch?v=ZsxaMovxxGI Cone Penetration Test Static Cone Penetration Test (SCPT) Dynamic Cone Penetration Test (DCPT) Angle 50 o w/o Bentonite slurry Angle 65 o with Bentonite slurry Vane Shear Test

26. FIELD TESTS For Dynamic Cone Penetration Test, Cone resistance N cbr correlated with SPT 1.5N for depth upto 4m 1.75N for 4m to 9m 2N for more than 9m

27. GEOPHYSICAL METHODS Resistivity method Limitations Valid only for strata having different electrical resistivity Results are influenced by surface irregularities, wetness of strata Expertise is required Electrical resistivity changes gradually rather abruptly as assumed Seismic Method Limitations Cannot be used if harder surface overlies soft layer Cannot be used for areas covered by concrete or asphaltic pavement Cannot be used when surface is frozen Requires costly equipment Expertise is required

28. SOIL INVESTIGATION REPORT