Print this page Geotechnical Report Guidelines
John Poullain, P.E.
Course Outline
This three-hour online course discusses guidelines and recommendations for developing geotechnical reports. GTRs consist of preliminary (data) reports and final (design and P&S) reports. This course primarily covers data reports and the specific information required for subsurface soil, rock and water conditions to be presented in a project report. Also presented are review checklists useful for preparing accurate reports, which include elements such as site investigations, embankments and excavations, structural foundations and material sites. The student will gain an understanding of the types of subsurface investigations and the requirements for the minimum number of borings, depths, and spacing of borings, samplings and for testing for various types of construction projects and types of soil.
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 have reviewed the following topics:
- Guidelines and recommendations for preparing concise and accurate geotechnical reports;
- Review checklists which aid in preparing geotechnical reports with guidelines for site investigation, embankments, excavations, structure foundations and material sites;
- Sources for existing data useful in the planning and preparation of subsurface investigations and GTRs;
- Basic types of subsurface investigations, borings and methods for sampling;
- Requirements for the minimum number of borings, depths and spacing of borings, samplings and testing pertaining to different types of construction in order to produce adequate subsurface data for construction;
- Criteria for geotechnical engineering analysis such as slope stability, F.S. and settlement analysis as they pertain to different types of construction;
- Essential data for presentation in a report for boring logs, plan views and subsurface profiles;
- Examples of GTR Table of Contents outlining the features covered in data and design reports;
- Difficult subsurface conditions such as boulders, high P.I. and high ground water tables and their effect on subsurface investigations; and
- The effects of soil types on geotechnical engineering analysis for embankments, structure foundations, retaining structures and landslide corrections.
Intended
Audience
This course is intended for civil engineers and project engineers.
Benefit to Attendees
The student will become familiar with the guidelines for geotechnical report.
Course
Introduction
The course covers the development of geotechnical reports for the preliminary and design stages of a project. The importance of the GTR and thorough subsurface investigations is stressed. Additional costs may result if the investigations are inadequate and the presentation or interpretation of subsurface conditions is incomplete in the report. The design of foundations for buildings, roadways, excavations, and embankments requires a complete understanding of soil strength; soil characteristics, problem soils and how soil behaves under imposed loads. Drilling and coring provide the necessary samples for laboratory tests, for in-situ field-testing and for the detailed subsurface record, the boring log and profile presented in the GTR.
From the initiation of a project, subsurface investigations progress through several phases from the concept to construction and to operation and maintenance. Initially the investigations are general and cover data gathering for subsurface conditions. As the project develops from the planning and concept phases to plans and specifications for construction the reports are more detailed for design and interpretation of subsurface conditions. It is important to follow established criteria and guidelines in order to select the appropriate drilling, sampling and testing methods given the expense of subsurface exploration.
Planning for subsurface investigations can be broken into these steps:
a. Historical and Geological Studies.
Geological maps, topographical maps, aerial photographs, site histories and adjacent property developments are reviewed to gather data. Proposed construction features are studied for access and to plan investigations. Land use, problems areas, subsoil information; terrain conditions will indicate the necessary subsurface investigations.
b. Site Reconnaissance.
Existing surface features and topography of the site with the data gathered from prior historical and geological studies are compared. Telltale signs of problem areas, presence of soft terrain, wet areas, outcrops and changes in topography like cut or fill developments will be noted.
c. Subsurface Investigations Requirements.
Extent of investigations will depend on available subsurface data, geological data, groundwater variability, adjacent development and the proposed construction. Investigations progress from generalized and large areas to more specific and detailed studies. Conceptual or preliminary subsurface investigations require limited laboratory and sampling work and are used to prepare possible routes or structures layout for evaluation. More detailed subsurface investigations including borings, samplings and testing are performed in order to design for the selected route or structure location.
Boring logs are prepared from subsurface information encountered while drilling 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.
Exploratory personnel must be well trained and conscientious; the drilling and sampling data provide accurate samples and recorded accurately for the reports. Soil and rock samples must be handled and stored with care and should be inventoried, examined and tested as soon as they are received. If samples are stored for a long 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.
Downhole Logging
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, 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:
- downhole logs give a continuous record of subsurface formations, especially if sample recovery is limited
- downhole logs can reveal a more realistic stratigraphy of fractures, fissures etc and in real time
- LWD’s tools record the logs in memory devices which are downloaded for assessment when returned to the surface after a drilling run
- downhole log measurements present in-situ conditions as compared to recovered cores
- 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.
There are also software solutions for preparing reports, which help to reduce the time to generate reports, and also a variety of related reports. Predesigned questions in template form are used to cover different types of projects, shallow and deep foundations, embankments, cuts and retaining walls. The computer software templates incorporate review questions similar to those of the course text.
Course Content
The course is primarily based on Chapter 11 of the US Dept of Transportation FHWA publication FHWA NHI-01-031, “Subsurface Investigation-Geotechnical Site Characterization”, (2001 Edition, 9 pages), PDF file. The course is also based on pages 1 to 29 of the FHWA publication FHWA ED-88-053, “Checklist and Guidelines for Review of Geotechnical Reports and Preliminary P & S”, (2003 Revised Edition, 33 pages with index), PDF file.
The links to the those documents are:
pages 1 to 29 of the FHWA publication FHWA ED-88-053, “Checklist and Guidelines for Review of Geotechnical Reports and Preliminary P & S”
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Course Summary
This course should serve as a guide for preparing a geotechnical report and the requirements for data and design reports for subsurface investigations. The course provides the basics for selection of spacing of drilling, depths and number of borings needed to determine the condition of subgrade soil and rock formations. Guidelines for site investigation and sources of existing geological and historical data are presented. Review checklists are presented to protect from omissions or inadequate data for report features such as site investigation, embankments, excavations, and structure foundations, retaining structures and material sites.
Related Links
For additional technical information related to this subject, please refer to:
USACE Geotechnical Investigations - Chapters 1 and 3 (PDF)
Information and applications describing subsurface investigations, borings, map studies, remote sensing methods, geotechnical reports and field reconnaissance.
Logging while Drilling (HTML)
Discusses logging during drilling in order to provide real time information by using various resistivities, nuclear and acoustic means to define the subsurface conditions.
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.
