P r e p a r e d B y : S i m a r p r e e t S i n g h A P ( C E ) A C E T A m r i t s a r
s i m a r p r e e t _ b a t r a @ y a h o o . c o m
SOIL INVESTIGATIONS
TABLE OF CONTENTS
Objectives
Stages in Sub-Surface Exploration
Extent of Exploration
Methods of Exploration
Samplers
Field Tests
Geophysical Methods
Soil Investigation Report
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
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
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
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
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
METHODS OF EXPLORATION
METHODS OF EXPLORATION
METHODS OF EXPLORATION
METHODS OF EXPLORATION
Rotary Drilling by MAIT Machine
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
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.
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.
SAMPLERS
Terminology:
SAMPLERS
Terminology:
SAMPLERS
Types of Samples:
Non Representative Soil Sample
Representative Soil Sample
Disturbed Soil Sample
Undisturbed Soil Sample
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%
SAMPLERS
Requirement of Good Sampler:
Maximum Inside diameter should be 75mm
Cutting edge angle should be less than 20o
The sampler tube should be uniform and smooth
Recovery Ratio should be 96% - 98%
Inside wall should be properly oiled to reduce wall friction
SAMPLERS
Types:
Standard Split Spoon Sampler
Scraper Bucket Sampler
Shelby tubes and Thin Walled Sampler
Piston Sampler
Denison Sampler
Hand-Carved Sampler
SAMPLERS
SAMPLERS
SAMPLERS
Piston Sampler
SAMPLERS
Scraper Bucket Sampler
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 50o w/o Bentonite slurry
Angle 65o with Bentonite slurry
Vane Shear Test
FIELD TESTS
For Dynamic Cone Penetration Test, Cone resistance Ncbr correlated with SPT
1.5N for depth upto 4m
1.75N for 4m to 9m
2N for more than 9m
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
