Subsurface Exploration Techniques

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Questions and Answers

What is the primary aim of a preliminary exploration in sub-surface exploration?

To determine soil stratum characteristics (correct)

To evaluate drainage patterns in the area

To assess the surface vegetation at the site

To identify the presence of underground water mains

Which method is used in detailed explorations to assess the properties of soil?

Radar imaging techniques

Geophysical surveys

Plant root analysis

Field tests including vane shear tests (correct)

Which of the following features is NOT typically identified during the site reconnaissance stage?

Depth of ground water

Existence of springs and swamps

Drainage pattern

Thickness of soil layers (correct)

For which type of projects might detailed investigations not be necessary?

Small projects with uniform strata Signup and view all the answers

What informs the design for a small project if detailed investigations are not conducted?

Data from reconnaissance and preliminary exploration Signup and view all the answers

Which of the following aspects is typically included in site reconnaissance?

Assessing the existence of vegetation Signup and view all the answers

What is a common characteristic of soils encountered in nature?

Mixture of sand, silt, and clay Signup and view all the answers

Which tests are typically conducted in detailed explorations to understand soil conditions?

Vane shear, permeability, and plate load tests Signup and view all the answers

What is one of the purposes of site investigations in subsurface exploration?

To determine the bearing capacity of soil Signup and view all the answers

Which factor does NOT influence the planning of a subsurface exploration program?

Aesthetic preferences of the architect Signup and view all the answers

What stage in subsurface exploration involves visiting the site and studying relevant maps?

Site reconnaissance Signup and view all the answers

Which aspect is NOT typically evaluated during site reconnaissance?

Material costs for construction Signup and view all the answers

Why is it advised to invest in subsurface exploration for building in a newly developed area?

To prevent overdesign and excessive costs Signup and view all the answers

Which of the following is a potential aim of subsurface exploration?

To predict and solve potential foundation problems Signup and view all the answers

During site reconnaissance, which feature is likely to indicate past geological activity?

Existence of settlement cracks Signup and view all the answers

Which principle should guide subsurface exploration regarding cost-efficiency?

Maximize information gained at minimum cost Signup and view all the answers

What characterizes coarse-grained soil?

Particle size larger than 0.075mm Signup and view all the answers

Which sampling method preserves the structure of the soil?

Undisturbed sampling Signup and view all the answers

What is the primary function of the shell method in soil sampling?

To cut and obtain soil samples from dense deposits Signup and view all the answers

Which factor does NOT influence the amount of soil sampling needed?

Weather conditions Signup and view all the answers

What is one laboratory test that can be conducted on disturbed soil samples?

Shear strength testing Signup and view all the answers

Which method stops boring to obtain undisturbed soil samples?

Wash boring Signup and view all the answers

What is a disadvantage of wash boring?

It can only be used in sand and clay soils Signup and view all the answers

Which tool is typically used to collect undisturbed soil samples?

Shelby tubes Signup and view all the answers

Which soil types can rotary drilling effectively operate in?

In sand, clay, and moderately fissured rocks Signup and view all the answers

Which type of soil sample captures soil conditions in situ?

Undisturbed samples Signup and view all the answers

What is a primary method used for basic geotechnical investigations?

Using backhoes to create test pits Signup and view all the answers

What is used in rotary drilling to help advance the borehole and remove cuttings?

Water or drilling mud Signup and view all the answers

In which scenario is percussion drilling most appropriate?

For making holes in very hard rock formations Signup and view all the answers

What type of sampler is NOT effective in gravel or sand?

Piston samplers Signup and view all the answers

What characteristic distinguishes the shell method from other drilling techniques?

It uses a flat valve that opens only inside Signup and view all the answers

What is a key feature of the rotary drilling technique?

It creates boreholes of various diameters with a single method Signup and view all the answers

What is the primary purpose of the Standard Penetration Test (SPT)?

Determines soil density and strength Signup and view all the answers

How does the Cone Penetration Test (CPT) measure soil properties?

By pushing a cone-shaped probe into the ground Signup and view all the answers

What aspect of soil does the Plate Load Test primarily determine?

Soil bearing capacity and settlement Signup and view all the answers

During the Vane Shear Test, what is being measured?

Shear strength of soft, cohesive soils Signup and view all the answers

What information does the Pressuremeter Test (PMT) provide?

In situ stress-strain behavior of soils Signup and view all the answers

What is the main application of the Field Permeability Test?

Evaluating permeability of soil or rock Signup and view all the answers

In what context is the Dynamic Cone Penetrometer (DCP) Test typically used?

In evaluating soil strength for road construction Signup and view all the answers

What does the Electrical Resistivity Test mainly determine?

Soil moisture content, salinity, and structure Signup and view all the answers

What is a primary disadvantage of hand operated augers when used below the water table?

They are not suitable for very stiff to hard clay Signup and view all the answers

What is the depth capability of power driven augers?

Up to 60 m Signup and view all the answers

Which type of soil can power driven augers be used in below the water table?

Sandy soils Signup and view all the answers

What is the function of the flights in power driven augers?

To convey the soil to the surface Signup and view all the answers

What must engineers look for in samples collected from soil explorations?

Signs of disturbance during collection Signup and view all the answers

Why might a hollow stem auger be preferred over a solid stem auger?

It allows for testing without removing the auger Signup and view all the answers

What is the normal diameter range for holes drilled by hand operated augers?

10 to 20 cm Signup and view all the answers

Which method is NOT suitable for sampling soils mixed with gravel while above the water table?

Hand operated augers Signup and view all the answers

Study Notes

Soil Exploration

Soil exploration is the process of identifying subsurface layers and their characteristics.
It's crucial for designing structures and planning construction techniques.
It involves field and laboratory investigations to gather information on the subsoil.

Subsurface Exploration: Purposes

Selecting the suitable type and depth of foundations for a given structure.
Determining bearing capacity of soil.
Estimating probable maximum and differential settlements.
Establishing ground water levels and determining properties of water.
Predicting lateral earth pressure against retaining walls and abutments.
Choosing appropriate construction techniques.
Identifying and solving potential foundation problems.
Assessing the suitability of soil for construction materials.
Investigating the safety of existing structures and suggesting remedial measures.

Planning a Subsurface Exploration Program

The program depends on the type of structure, variability of strata at the site, and cost of investigation.
A small house in a developed area may require less extensive exploration, whereas a complex structure in a new area would need more extensive exploration.
The goal is to gather maximum useful information at minimum cost.

Stages in Subsurface Explorations

1. Site Reconnaissance

It involves site visit, studying maps and records.
Determining general topography, existence of settlement cracks, landslides, creep in slopes, shrinkage cracks, location of high flood marks, depth of ground water (wells), existence of springs, swamps, drainage patterns, vegetation, and presence of underground water mains, power conduits.

2. Preliminary Exploration

Aims to determine the depth, thickness, extent, and composition of different soil strata.
Performed with a few borings, test pits, and using cone penetrometers or sounding rods to understand the soil's strength and compressibility.

3. Detailed Explorations

This stage involves an extensive boring program and sampling, followed by laboratory testing of soil samples.
For complex projects like bridges, dams, and multistory buildings, detailed investigations are essential.
For smaller projects with uniform strata, reconnaissance and preliminary exploration data might suffice.

Sampling in Soil

Natural soil is a heterogeneous mixture of sand, silt, and clay in varying proportions.
Soil can be classified into coarse-grained and fine-grained based on particle size.
Sampling methods can be either undisturbed or disturbed.
Undisturbed samples are representative of the in-situ conditions; methods like piston samplers are used for undisturbed samples.
Disturbed samples are collected for general analysis and may not accurately reflect the structure of soil; methods like split-spoon samplers are used.
Factors influencing sampling amount include time constraints, topography, cost factors, and the purpose of sampling.
Techniques for disturbed soil sample collection include backhoe, hand augers, and drill rigs.
Undisturbed soil sample collection methods include piston samplers, long split-spoon samplers, and pitcher barrel samplers.
Selection of sampling method depends on soil type, depth, and nature of information required.

Exploratory Borings in the Field

Hand operated augers are suitable for shallow depths and above the water table.
Power driven augers can be used in all types of soils below water tables.
Shell and auger methods use heavy-duty pipes with cutting edges.
Wash boring is suitable for sand, silt, and clay; methods include pressure water to drill to specific depth.
Rotary drilling uses rapidly rotating bits and is suitable for varied formations (sand, clay, or rock).
Percussion drilling employs a heavy chisel often used on rocks, boulders and hard strata
Core drilling is for obtaining rock cores and uses diamond-studded bits.

Soil Exploration Report

The report summarizes soil and rock sample analysis, visual observation, and laboratory tests.
It includes scope of investigation, general description of the structure, geologic conditions, drainage facilities, boring details, subsoil descriptions, and groundwater tables from boreholes.
The report also includes details of foundation recommendations, anticipated construction problems, and limitations of the investigation.
Essential supplemental data such as maps, boring logs, and laboratory test results should be included in the report.

In-Situ Tests

In-situ tests directly assess soil properties at the site without disturbing the soil. Common methods include:
Standard Penetration Test (SPT): Measures soil density and strength using a hammer and split-spoon sampler.
Cone Penetration Test (CPT): Measures soil resistance to penetration with a cone-shaped probe.
Plate Load Test: Determines soil bearing capacity and settlement under load by incrementally applying load to a steel plate.
Vane Shear Test: Measures the shear strength of soft, cohesive soils by inserting and rotating a vane into the soil.
Pressuremeter Test (PMT): Measures in-situ stress-strain behavior.
Field Permeability Test: Assesses soil or rock permeability by injecting or pumping water and measuring flow rate.
Dynamic Cone Penetrometer (DCP): Evaluates soil strength, especially for road construction.
Electrical Resistivity Test: Determines soil moisture content, salinity, and structure.
The benefits of in-situ tests include reflecting real soil behavior and minimizing soil disturbance.

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Description

This quiz assesses your understanding of subsurface exploration methods, including preliminary exploration and site reconnaissance details. Test your knowledge on soil properties, design considerations for projects, and testing methods used during detailed investigations.