Boring Log Preparation
John Poullain, P.E.
This four-hour online course discusses the procedures used for preparing soil boring and rock coring logs for subsurface exploration. A boring log is described as the record of exploration procedures and subsurface conditions encountered during drilling and sampling. Guidelines for the completion of boring logs and the preparation of classification of soil and rock are described. Also presented are the techniques for determining subsurface information by visual examination and other methods while drilling. USCS, the most commonly used system for geotechnical work and the AASHTO classification system, used for highway subgrade materials, are discussed and include guidelines for samplers as well as the storage, handling and selection of samples. Quality assurance for log preparation and measures for accurate identification of subsurface materials are stressed. The AASHTO and ASTM designations for the most frequently used drilling methods, equipment and tests 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, how soil behaves under imposed loads and consideration of problem soils. Drilling and coring provide the necessary samples for laboratory soil and rock tests, for in-situ field-testing and for the detailed subsurface record, the boring log. It is important to follow established 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 caused by inaccurate or incomplete boring data.
Boring logs are prepared from subsurface information encountered while drilling, coring and sampling. Information is derived from measurements such as the energy required for drilling per foot of borehole, monitoring rock and soil debris, drilling mud and return water pumped from the borehole, sample recovery percentages and loss of drilling mud, to mention a few. It is very important to complete the logs in the field and not the laboratory and that the field observations and lab test results are differentiated to make clear the source of information. When more comprehensive information is desired, downhole logging may be performed.
Downhole logging uses tools, such as wireline logging, where electronic instruments are lowered down the borehole or logging-while-drilling (LWD) where the instruments are in the drill pipe behind the drill bit itself. Other tools take measurements while drilling and measure inclinations, tool temperatures and optimize casing selection. Although they may be used to complement standard boring measurements and sampling methods, they have these advantages:
a. downhole logs
give a continuous record of subsurface formations, especially if sample recovery
b. downhole logs can reveal a more realistic stratigraphy of fractures, fissures etc and in real time
c. LWD's tools record the logs in memory devices which are downloaded for assessment when returned to the surface after a drilling run
d. downhole log measurements present in-situ conditions as compared to recovered cores
e. material cored may physically swell or slake when no longer under pressure at depth and give an erroneous presentation of the actual underground conditions
Other devises such as borehole cameras and TV cameras are used to prepare logs and serve to record subsurface conditions that may not have been obvious while boring and therefore not recorded on the log. They can be reviewed many times to assure the subsurface conditions are as presented on the original exploration.
Because of the large variety of soils and 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 prepared 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. 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 should not be 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 determined to protect against potential settlement from 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 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 which allows them to easily disperse or detach and erode in still water.
The methods used for earthwork construction include compaction or densification, admixture stabilization, soil replacement, dewatering and drain systems and also deep densification, 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.
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 course is primarily based on Chapters 2, pages 2-8 thru 2-16,
and 4 of the US Dept of Transportation FHWA publication FHWA NHI-01-031, "Subsurface
Investigation-Geotechnical Site Characterization", (2001 Edition, 43 pages),
PDF file. The course is also based on Chapter 5, Sections II and III, of the
US Army Corps of Engineers Engineer Manual EM 1110-1-1804, "Geotechnical
Investigations", (2001 Edition, 8 pages), PDF file.
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 preparing soil boring and rock coring logs for subsurface exploration programs. The course provides basics for preparing boring logs and selection of spacing of drilling and the depths needed to better determine the condition of subgrade soil and rock formations. Basic concepts for soil description and classification are discussed to understand the types and conditions of formations as encountered initially in the field while drilling. The importance of quality assurance for subsurface exploration, sampling and for recording of data in the field is stressed. Proper procedures must be followed and information must be recorded in the field while drilling in order to provide as complete a picture of subsurface conditions as possible. Often logs have information of the subsurface conditions that may not be apparent from cores.
technical information related to this subject, please refer to:
Information and applications describing subsurface investigations, boring, sampling methods, soil identification, coring rock, preparation of logs and borehole viewing means.
Logging while drilling provides real time information while drilling by using various resistivity, nuclear and acoustic means to define the subsurface conditions.
Lists over 50 software packages, shareware or commercial as noted, for soil boring logs and subsurface profiling.
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.