Geotechnical Investigation Basics

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Questions and Answers

What is the primary purpose of drilling fluid in rotary drilling?

To provide support to the derrick

To increase the speed of the rotary drive

To cool and lubricate the drilling tool and carry debris to the surface (correct)

To reduce the downward thrust on the drilling rods

What is the primary difference between open-hole drilling and core drilling?

Open-hole drilling produces a continuous core sample, while core drilling does not.

Open-hole drilling is faster than core drilling.

Open-hole drilling uses a coring bit, while core drilling uses a cutting bit.

Open-hole drilling is used in soils, while core drilling is used in rocks. (correct)

Which type of soil is the Standard Penetration Test (SPT) most commonly used to evaluate?

Organic soils

Clayey soils

Silty soils

Granular soils (correct)

What is the primary function of the winch in a rotary drilling rig?

To hoist and lower the drilling rods (C) Signup and view all the answers

Which of the following field tests is NOT directly related to soil properties?

Pressure Meter Test (PMT) (C) Signup and view all the answers

In core drilling, what is the primary function of the diamond or tungsten carbide bit?

To extract a continuous core sample (B) Signup and view all the answers

What type of drilling bit is typically used in open-hole drilling?

Cutting bit (A) Signup and view all the answers

What is the main function of the drilling head in a rotary drilling rig?

To provide downward thrust to the drilling rods (D) Signup and view all the answers

What is the main purpose of Phase III, 'Detailed Soils Exploration', in a site investigation?

To determine the geological structure, groundwater conditions, and obtain soil samples for testing. (A) Signup and view all the answers

What is the significance of the preliminary reconnaissance or site visit (Phase II) in a site investigation?

To get a general understanding of the topography, geology, and existing conditions of the site. (D) Signup and view all the answers

What information from Phase I is crucial to compare with the current conditions during the site visit (Phase II)?

The detailed soil profiles and groundwater levels from previous investigations. (D) Signup and view all the answers

Which of the following is NOT a primary objective of detailed soil exploration (Phase III)?

Assessing the potential for seismic activity in the area. (A) Signup and view all the answers

Which of the following is NOT a crucial component of the soil exploration program outlined in the given content?

Analyzing the chemical composition of the soil to determine its suitability for construction. (A) Signup and view all the answers

Why is it necessary to include information about unusual soil conditions, water-bearing strata, and potential construction challenges in the final report (Phase IV)?

To guide the design and construction process, mitigating potential risks and complications. (C) Signup and view all the answers

Why are sampling instructions often modified after the first borehole is completed?

To address unexpected soil conditions or changes in the geological structure encountered in the first borehole. (A) Signup and view all the answers

What is the primary purpose of conducting in situ tests during soil exploration?

To assess the soil's strength, compressibility, and other engineering properties in its natural environment. (D) Signup and view all the answers

Which of the following is a potential issue with continuous flight augers?

They can mix different soil types together during sampling. (D) Signup and view all the answers

What is the primary function of the water jet in wash boring?

To loosen and break up the soil. (B) Signup and view all the answers

Why are hollow stem continuous flight augers preferred for obtaining undisturbed soil samples?

They allow for the insertion of a sampler below the auger. (B) Signup and view all the answers

How is the change of strata detected when using continuous flight augers?

By the combination of drilling speed and sound produced. (C) Signup and view all the answers

What is the main disadvantage of wash boring for obtaining soil samples?

It mixes the soil samples together, making identification difficult. (C) Signup and view all the answers

When is wash boring considered appropriate for subsurface exploration?

When the primary goal is to advance the borehole for further testing. (A) Signup and view all the answers

What is a key advantage of wash boring compared to continuous flight augers?

It causes less disturbance to the soil immediately beneath the hole. (D) Signup and view all the answers

Continuous flight augers are not suitable for soil boreholes that require casing. Why is this the case?

The casing must be removed to drive the auger into the ground. (C) Signup and view all the answers

What is the maximum depth that can be achieved with a hand auger?

20m (B) Signup and view all the answers

Which method of soil investigation is considered non-destructive?

Auger boring (A) Signup and view all the answers

What is a significant limitation of test pit excavation?

It is difficult to obtain undisturbed samples (D) Signup and view all the answers

Which type of auger is best suited for boring in soft, cohesive soils?

Hand auger (C) Signup and view all the answers

What is the main purpose of the downward pressure applied during mechanical auger boring?

To prevent the borehole from collapsing (C) Signup and view all the answers

Which of the following IS NOT a type of mechanical auger?

Hand Auger (B) Signup and view all the answers

Which of these is a benefit of using test pits for soil investigation?

Provides in-situ data and visual inspection. (D) Signup and view all the answers

Which statement accurately describes the samples obtained from hand auger boring?

Disturbed samples, suitable for classification tests. (C) Signup and view all the answers

What is the standard weight of the hammer used in the SPT (Standard Penetration Test)?

63.5 kg (C) Signup and view all the answers

What is the specified maximum overall weight for the drive assembly (or trip hammer) in the SPT?

115 kg (D) Signup and view all the answers

What is the maximum permitted curvature for bent rods used in the SPT, expressed as a relative deflection?

1/1000 (A) Signup and view all the answers

What is the minimum depth required before an SPT can be performed?

1 m (B) Signup and view all the answers

What is the SPT N value recorded if the penetration under the dead weight of the rods and hammer exceeds 450 mm?

0 (A) Signup and view all the answers

When should an SPT test be terminated? (Select all that apply)

When 75 mm penetration cannot be achieved after 100 blows (B), When the total number of blows, excluding the seating drive, reaches 200 (C) Signup and view all the answers

What is one of the key advantages of the SPT compared to other in-situ tests like the Cone Penetration Test?

It is a simpler and more versatile test that can be done with standard exploration equipment (A) Signup and view all the answers

What is the main reason for the widespread use of the SPT?

Its low cost, simplicity and versatility. (D) Signup and view all the answers

Which of the following is NOT a type of boring mentioned in the text?

Sonic boring (D) Signup and view all the answers

Why are test pits and trenches considered limited in their application for soil investigation?

They only provide information about the surface layer of soil. (C) Signup and view all the answers

What is the primary purpose of boring or drilling in soil investigations?

To obtain soil and rock samples for laboratory analysis. (A) Signup and view all the answers

Geophysical methods are considered indirect methods because they ...

rely on interpretations of data rather than direct observation. (C) Signup and view all the answers

Which of these is a key advantage of geophysical methods compared to traditional boring methods?

They provide information over a larger area in a shorter time. (A) Signup and view all the answers

What is the main reason why both geophysical and boring methods are considered important for soil investigations?

They complement each other by providing different types of data. (D) Signup and view all the answers

Which of these is NOT a commonly used geophysical technique mentioned in the text?

Magnetic Resonance Imaging (MRI) (D) Signup and view all the answers

Why are geophysical techniques often used alongside traditional boring methods?

To provide a more comprehensive understanding of the soil conditions. (B) Signup and view all the answers

Study Notes

Site Investigation

The first step in foundation investigation is obtaining preliminary information to plan the project.
The next step is subsurface exploration to understand soil and rock properties, impacting the foundation.

Specific Items Discussed

Document review
Purpose of subsurface exploration
Borings (soil samplers, sample disturbance, field tests, boring layout, depth)
Test pits and trenches
Preparation of logs
Geophysical techniques
Subsurface exploration (geotechnical earthquake engineering)
Subsoil profile

Prior Development

If a site had previous development, information on fill, septic systems, leach fields, storage tanks, and man-made structures is crucial.
This information is essential to understand possible impacts on the new development (utilities, pipelines, etc.).

Aerial Photographs and Geologic Maps

Aerial photographs are taken from aircraft at specific altitudes.
Engineering geologists interpret these photos, offering a three-dimensional view.
Geologic maps provide additional reference materials.

Purpose of Soil Investigations

Evaluate the site's suitability for the proposed project.
Enable adequate and economical design.
Disclose potential construction difficulties.

Phases of Soil Investigation

Phase I: Gather information (pile plan, structure type/size, loading conditions, previous reports, maps, and clippings).
Phase II: Reconnaissance visit, using Phase I information to compare current site conditions.
Phase III: Detailed soil exploration, determining geological structure, groundwater conditions, and collecting samples for lab tests.
Phase IV: Comprehensive report including soil description, exploration methods, profiles, and groundwater locations.

Soil Exploration Program

Involves test pits or borings.
Determine the need and extent of geophysical exploration;
Locate/number boreholes/test pits.
Plan depth of boreholes/test pits.
Methods of advancing boreholes.
Sampling instructions (number and possible location) for at least one borehole.
Indicate requirements for groundwater observations and in situ tests.

Methods of Soil Investigation

Geophysical methods: Seismic, electrical resistivity (variations in sound waves or electrical resistivity of soil formations). Test pits/trenches (shallow). Augers (shallow), Wash Boring, Rotary rigs (detailed soil investigations)
Boring or Drilling: used to obtain representative samples for lab tests and assess groundwater conditions
Geophysical Methods: Nondestructive technique providing information on soil, rock, hydrological, and environmental conditions; boring and test pits provide definite but time-consuming and expensive results.

Geophysical Techniques Indirect Methods

Ground Penetrating Radar (GPR)
Electromagnetic (EM)
Magnetic
Utility Locating
Seismic
Electrical Resistivity
Gravity
Very Low Frequency (VLF)

Advantages of Geophysical Techniques

Quick and cheaper than borings or test pits
Provide thorough area coverage
Provide less definitive results

Advantages of SPT

Low cost and easy-to-use, versatile.
Provides simple, universally applicable testing method.
No sophisticated equipment necessary.
Can provide information for hard-to-sample soils.

Field Tests

Standard Penetration Test (SPT): Used to determine density and compressibility of granular soils; used to check consistency of stiff cohesive soils and weak rocks; useful for evaluating liquefaction potential.
Cone Penetration Test (CPT): Electric probes with a 60° tip, high-speed continuous sampling and accuracy compared to drilling, low cost, reduces laboratory sample requirements; not for hard samples, only unconsolidated sediments.

Test Methods and Standards

Procedures for drilling, driving weight, anvil mass for SPT.
Incremental penetration, blow counts for seating and test drive (to determine N-value).
Total blow counts, increments of penetration.

Wash Boring

High-pressure water jet loosens soil and carries it to the surface.
Can be used in various soil types.

Rotary Drilling

Used mainly for rock investigations
Drilling tools (cutting or coring bit) which is attached to hollow rods.
Water or drilling mud lubricates the drilling tool.

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Description

This quiz covers the fundamentals of site investigation for foundation projects, focusing on subsurface exploration, document review, and geophysical techniques. Key topics include boring methods, test pits, and interpreting aerial photographs. It's essential for understanding soil and rock properties crucial to foundation design.