Sampling from Test Pits, Trenches and Stockpiles - a PDH Online Course for Engineers, Architects and Surveyors

Sampling from Test Pits, Trenches and Stockpiles

Course Outline

This three hour online course provides guidance for the procedures used for sampling soil and materials in support of geotechnical investigations from sources including test pits, trenches, tunnels, stockpiles, trucks and conveyor belts. It covers “accessible” explorations that are made with excavation equipment and conventional drilling equipment. Information on the methods for recovering, handling and storage of samples is discussed. Visual examination and other practices used during drilling and sample recovery are considered. Guidelines for the storage, handling and shipping of specimen samples are discussed. Soil types and factors such as the groundwater table are considered for sampling methods. Because of the risks inherent in accessible explorations the course addresses safety and health problems that are encountered during sampling operations and general precautionary measures to take.

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:

Be knowledgeable about the precautions and procedures required for obtaining, handling and storing samples;
Understand the basic sampling practices and procedures accessible excavations such as test pits and trenches;
Be familiar with procedures for obtaining representative samples from stockpiles and trucks;
Understand how undisturbed samples are obtained and when specialized procedures are required;
Be familiar with how undisturbed and disturbed samples are obtained and how they are handled and stored;
Understand the methods used to stabilize boreholes and how samples are obtained from accessible boreholes;
Consider the importance of visual observations and information of subsurface conditions that become available during accessible excavations;
Be informed of designated ASTM pertaining to the sampling and preservation of samples from test pits, trenches and stockpiles;
Understand the advantages and limitations of sampling methods and the most suitable to use for soil formations and groundwater conditions commonly encountered;
Be aware of the inherent risks affecting personnel safety and health problems encountered during sampling operations and general safety measures to take; and
Be aware of the importance of recording data in field logs. A checklist for recommended information to include is presented.

Intended Audience

This course is intended for civil engineers and project engineers.

Course Introduction

The design of building foundations, roadways, excavation, fills and slopes requires an understanding of soil strength; soil characteristics and consideration of problem soils and how soil behaves under imposed loads. Samples provide the necessary soil and materials for laboratory tests and for in-situ field-testing. It is important to follow the procedures and guidelines so the appropriate samples are selected especially since subsurface exploration is expensive but not nearly as expensive as for a project failure.

Test pits, trenches, accessible borings and tunnels if economically feasible may be the best way to obtain the necessary subsurface information for projects. If they are economical to perform they fill in information gaps that is not always possible with conventional boring. Accessible excavations have advantages because they permit direct inspection of in situ subsurface conditions, formation stratification, recovery of large undisturbed samples and allow evaluation of certain excavation methods.

Because of the large variety of soils and large variety of applied soil mechanics problems there is also a large variety of soil exploration and sampling methods for determining the engineering properties of soils. Before the boring program can be requested the design engineer must define the purpose for the exploration program and the testing program for his self and for field and laboratory personnel. Accurate observations and operations of the exploration equipment are of great importance and the equipment must be properly maintained, otherwise the sampling results will be valueless and result in poor design and construction.

Not only must exploratory personnel be well trained and conscientious; the drilling and sampling equipment must also provide accurate samples and data for a variety of tests. Samples must be handled and stored with care following established standards. Samples should be inventoried, examined and tested as soon as they are received. Sometimes however, especially for large testing programs, it may become necessary to store the samples for days or weeks, but no longer than 15 days If possible. If they are stored for a longer periods of time the undisturbed samples should be protected against damage or changes in water content by maintaining the storage temperatures close to those required for 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, and 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.

Course Content

The course is based on Chapters F-11, F-12 and F-13 of the US Army Corps of Engineers manual EM 1110-1-1804, “Geotechnical Investigations”, (2001 Edition, 30 pages), PDF file. The course is also based on paragraphs 2.8 and 2.9 of the US Department of the Interior “Earth Manual Part I”, (1998 Edition, 5 pages), PDF file.

The link to the documents are as follows:

US Army Corps of Engineers manual EM 1110-1-1804, “Geotechnical Investigations” Chapter F-11

US Army Corps of Engineers manual EM 1110-1-1804, “Geotechnical Investigations” Chapter F-12

US Army Corps of Engineers manual EM 1110-1-1804, “Geotechnical Investigations” Chapter F-13

US Department of the Interior “Earth Manual Part I”

Terms

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Course Summary

This course should serve as a guide for the equipment and procedures used for sampling from accessible excavations such as test pits, trenches and large borings and from unique sources such as stockpiles and trucks. The advantages and limitation of the sampling methods for determining the characteristics of subsurface soils and formations are discussed. Basic soil types are covered as they pertain to the procedures for sampling and storage of soils and materials. The importance of following proper procedures for sampling is stressed and considers the proper storage, recording of data, handling and shipping of soil and material specimens for testing programs. Personnel safety and health concerns are considered.

Related Links

For additional technical information related to this subject, please visit the following websites or web pages:

http://www.haywardbaker.com/
Information and applications describing construction methods for structural support and earth retention. Provides solution “tools” for problem soils and applications for projects.

http://www.usace.army.mil/publications/eng-manuals/em1110-2-1913/c-3.pdf
Describes lab tests for pervious and fine-grained cohesive soils and the soils characteristics tested for.

http://www.ggsd.com
Lists over 50 software packages, shareware or commercial as noted, for soil boring logs and subsurface profiling.

Quiz

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.