Soil Exploration: 1. Topographic Survey
Soil Exploration: 1. Topographic Survey
Soil Exploration: 1. Topographic Survey
1. Topographic Survey
TSs provides information regarding ground surface feature of the
site (i.e., surface condition of the site)
– Project Details
• Type of structure, intended use of structure, construction method, etc.
– Surface and Subsurface Conditions of the site
• Study of topographic/geologic maps, aerial photographs, data from previous
investigations, satellite imagery, etc.
– Study of existing structures in the area
Investigation Phases
2. Preliminary Investigation
– Location of bedrock is established by drilling a few holes. Position
of GWT may also be established.
3. Detailed Investigation
– This phase may include test pits excavation, boreholes, in-situ
testing and collection of both disturbed and undisturbed soil
samples for detailed laboratory testing/analysis. GWT may also be
monitored by installing piezometers.
4. Construction/Post Construction Investigation
– Sometimes monitoring of movement of structure and monitoring
of groundwater fluctuations, both during and after construction,
may be required.
Amount of Exploration
1. Test pits
2. Boring or drilling
1. Test Pits
If the pit is to be extend below the GWT, some form of dewatering is necessary.
Block samples can be cut by hand tools and tube samples can be taken from the
bottom of the pit.
Test pits are suitable for investigations in all type of soil, including those
containing cobbles or boulders.
1. Test Pits
Walls of the test pit indicate four layers (1) Clayey silt (2) Sandy
silt (3) Clean sand (4) Sandy gravel
2. Boring or Drilling:
1. Hand Augar:
• The hand augar (also called post-hole or Iwan augar) is a very simple hand tool
used for drilling into soft soils down to maximum of 5-6m in small projects.
• Hand-augered holes can be made up to about 20m depth, although depth
greater than about 8-10m is usually not practical.
• For hard soil and soil containing gravels boring with hand auger becomes
difficult.
• The auger is rotated until it is full of soil, then it is withdrawn to remove the
soil and the soil type present at various depths is noted.
• They can be used for soil exploration work for highways and small structures.
• The soil samples collected in this manner are disturbed but they can be used
for classification test in laboratory such as grain-size determination and
Atterberg limits.
• Auger boring may not be possible in very soft clay or coarse sand because the
hole tends to collapse when auger is removed.
Hand Augar
Rotary Drilling
ii. Rotary Drilling
There are two forms of rotary drilling, open-hole drilling and core
drilling.
Open-hole drilling, which is generally used in soils and weak rock, uses a
cutting bit to break down all the material within the diameter of the hole.
Open-hole drilling can thus be used only as a means of advancing the
hole: the drilling rods can then be removed to allow tube samples to be
taken or in-situ tests to be carried out.
In core drilling, which is used in rocks and hard clays, the diamond bit cuts
an annular hole in the material and an intact core enters the barrel, to be
removed as a sample. However, the natural water content of the material
is liable to be increased due to contact with the drilling fluid.
iii. Wash Boring
1. Disturbed Sample:
A disturbed sample is one having the same particle size distribution as the
in-situ soil but in which natural moisture content is disturbed and soil
structure has been significantly damaged or completely destroyed.
Disturbed samples, which are used mainly for soil classification tests,
visual classification and compaction tests, can be excavated from trial pits.
Soil Sampling
2. Undisturbed Sample:
Undisturbed samples are obtained by techniques which aim at
preserving the in-situ structure and water content of the soil.
It is impossible to obtain a sample that is completely undisturbed, no
matter how elaborate or careful the ground investigation and sampling
technique might be.
Undisturbed samples are used to determine the shear strength,
compressibility and permeability of the materials.
All samples should be clearly labelled to show the project name, date,
location, borehole number, depth and method of sampling.
Special care is required in the handling, transportation and storage of
samples prior to testing.
Common Sampling Techniques:
Sample Disturbance
The degree of disturbance of the sample collected by various method can
be expressed by a term called the area ratio, which is given by
Ar = (Do2 – Di2) / Di2
where Di and Do are inside and outside diameter of sampler respectively.