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Laboratory Testing of Soils

John Poullain, P.E.

Course Outline

This four hour online course discusses guidelines and criteria for laboratory testing of soils. Basic concepts of soil behavior and the selection of appropriate tests for the design of earthwork structures and foundations are considered. Frequently used soil tests include those used to establish index properties of soils, determine strength tests, permeability and consolidation of soils. Test for index property range from moisture content, specific gravity and unit weight to liquid limits and densification of soils. Strength tests include unconfined compressive, triaxial, shear, R-value and CBR. Also considered is quality assurance for laboratory testing which includes the storage, handling and selection of specimen samples. The AASHTO and ASTM designations for the most frequently used laboratory tests are provided.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:

Intended Audience

This course is intended for civil engineers and project engineers.

Course Introduction

The design of building foundations, excavation, fills and slopes requires an understanding of soil strength; soil characteristics and consideration of problem soils and how soil behaves under imposed loads. Laboratory soils tests and in-situ field-testing provide this information. These criteria and guidelines are important so the appropriate tests are selected especially since the laboratory tests can be expensive but not nearly as expensive in case of a project failure.

Because there of the large variety of soils and a large variety of applied soil mechanics problems there is also a large variety of soils tests, laboratory and on site, for determining the engineering properties of soils. Before the laboratory tests can be requested the design engineer must define the purpose for a testing program for himself and the laboratory personnel. Accurate measurements are of great importance and the test equipment must be properly maintained, otherwise the test results will be valueless and misleading. Poorly constructed and maintained equipment such as maladjusted liquid limit devices and proving rings, worn liquid limit cups, grooving tools or consolidometer rings will produce serious test errors.

Not only must laboratory personnel be well trained and conscientious, laboratory facilities must also provide for a variety of tests with well-maintained testing equipment and samples fulfilling these specific needs. Soil samples must be handled and stored with care following established standards. Samples should be inventoried, examined and tested as soon after receipt. Sometimes especially for large testing programs it may become necessary to store the samples for days or weeks, but not longer than 15 days If possible. If samples are stored longer then undisturbed samples should be protected against damage or changes in water content by maintaining at temperatures close to those required at the project. Rewaxing and relabeling may be required. Nevertheless the stored samples may undergo physical and chemical changes when stored too long no matter how carefully stored and resealed.

Soil particles are rearranged and densified to improve the soils' engineering properties of strength, permeability and compressibility. The existing subgrade may have poor strength or instability due to excess clay, expansive clays, silts, fine sands, voids, collapsing soils or high watertables. The existing soil properties must be known to protect against potential settlement with the required bearing capacities. There are problem soils such as loess, hydraulic fills and tailings, which have collapsing or low-density structures, and when saturated have large decreases in volume and loss of strength. Other soils, which contain clays such as bentonite, can expand and increase in volume when exposed to water. Expansive soils however can shrink or decrease in volume when water is not present. There are also dispersive clays so named because the soil particles are not structurally sound and can easily disperse or detach and erode in still water.

Compaction or mechanical stabilization is one of the oldest means of soil stabilization.

Mechanical stabilization may achieve the desired results by blending two soils and/or mixing with admixtures. If suitable soil was located within a feasible haul distance, blending the soils together could effect an improvement in the existing soil. However the soil blending would introduce ROW, hauling and handling issues to consider. Using chemical or bitumen additives to improve a soil is another possibility but handling and excavation of the existing soil would also have to be considered. Certain soils because of their chemical nature, organic or high acid compounds may not be responsive to these stabilization methods and may be corrosive to steel reinforcement. Often the soils are not readily distinguished by their classification or physical properties. Corrositivity and pH tests will determine the chemical and organic content of the soil if these are suspected problems.

The variety of methods used for earthwork construction include compaction or densification, admixture stabilization, soil replacement, dewatering and drain systems and also deep densification, explosive compaction, soil reinforcement and grout injection methods. Selection of the most suitable method will depend on the type of soil, soil problems, degree of improvement and depth and extent of treatment required.

The following text errors should be noted:
a. Page. 7-17. Figure 7.4 should be 7.5

Course Content

The course is based on Chapter 7 of the US Dept of Transportation FHWA publication FHWA NHI-01-031, "Subsurface Investigation-Geotechnical Site Characterization", (2001 Edition, 40 pages), PDF file and the course paragraph "Course Introduction".

The link to the US Dept of Transportation FHWA publication is "Subsurface Investigation-Geotechnical Site Characterization", Chapter 7.

Subsurface Investigation-Geotechnical Site Characterizationv

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

Course Summary

This course should serve as a guide for testing soils in the laboratory and to better understand the variety of tests, purposes, and the advantages and limitations of each. Basic concepts of soil behavior are discussed to better understand the purposes of the soil tests and the measurements of various values for soil indexes, characteristics and strengths. Laboratory test data is necessary to meet the needs of the type of construction and plan the measures to provide the necessary strength, slope stability and bearing capacity with the existing soils. Tests for index properties include moisture content, specific gravity, unit weight and liquid limit. Strength tests include triaxial, compressive, shear, and CBR. The importance of quality assurance for laboratory testing is stressed including the proper storage, handling and selection of soil specimens for testing programs. This course should serve as a guide for selecting laboratory tests needed determine the characteristics of subgrade soils in order to protect against potential settlement, liquefaction or ground movement.

Related Links

For additional technical information related to this subject, please refer to:
Information and applications describing construction methods for ground improvement, structural support and earth retention and necessary materials. Provides solution tools for problem soils and project applications. 
Describes lab tests for pervious and fine-grained cohesive soils and the soils characteristics tested for.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.