Drilling and Sampling of Soil and Rock
John Poullain, P.E.
This four hour online course discusses the commonly used equipment and procedures for drilling, methods for sampling and recovering soil samples and rock cores. Visual examination and other techniques used during drilling and sample recovery are considered. The types of equipment and drilling methods covered in the course include solid stem, hollow stem augers, rotating wash, bucket augers, hand auger boring and exploration pit excavations. Guidelines for a wide variety of samplers including split barrel, thin wall Shelby tubes, continuous push, pitcher tube and continuous soil auger are discussed as well as the storage, handling and selection of specimen samples. Basic soil behavior and factors such as water table are considered in the selection of appropriate drilling and sampling methods to satisfy a project's design requirements. Also considered is quality assurance and safety requirements for drilling and sampling operations The AASHTO and ASTM designations for the most frequently used drilling methods and equipment are provided.
This course includes
a multiple-choice quiz at the end, which is designed to enhance the understanding
of the course materials.
At the conclusion of this course, the student will:
This course is intended for civil engineers and project engineers.
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. Drilling and core samples provide the necessary samples for laboratory soil and rock tests and for in-situ field-testing. It is important to follow the criteria and guidelines so the appropriate drilling methods are selected especially since subsurface exploration is expensive but not nearly as expensive as for a project failure.
Because of the large variety of soils and a large variety of applied soil mechanics problems there is also a large variety of soil and rock 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 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. Soil and rock 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, 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 samples are stored for a longer time the undisturbed samples should be protected against damage or changes in water content by maintaining at 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, 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 course is based on Chapters 2 (selected parts) and 3 of the
US Dept of Transportation FHWA publication FHWA NHI-01-031, "Subsurface
Investigation-Geotechnical Site Characterization", (2001 Edition, 45 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", Chapters 2 and 3.
The links to the parts of both documents are as follows:
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.
This course should serve as a guide for soil and rock exploration to assure that the required samples and other geological data are properly obtained for various types of construction projects. The advantages and limitation of soil and rock drilling equipment, coring equipment and samplers are discussed and sketches are presented to better understand the equipment and component functions. Basic concepts of soil behavior are discussed to understand the selection of the soil and rock drilling methods. The importance of quality assurance for subsurface exploration and sampling is stressed and considers the proper storage, handling and selection of soil and rock specimens for testing programs. This course should serve as a guide for selecting proper drilling methods needed to determine the characteristics of subgrade soil formations and rock in order to protect against potential problems, settlement, liquefaction, ground movement and litigation.
technical information related to this subject, please refer to:
Information and applications describing construction methods for structural support and earth retention. Provides solution "tools" for problem soils and applications for projects.
Describes lab tests for pervious and fine-grained cohesive soils and the soils characteristics tested for.
Lists over 50 software packages, shareware or commercial as noted, for soil boring logs and subsurface profiling.