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Underwater Sampling of Soils

John Poullain, P.E.


Course Outline

This three hour online course discusses the commonly used equipment for soil sampling and recovering soil samples in nearshore environments such as harbors, channels, rivers, and wetlands. The course is a guide for providing the soils information for marine construction projects, dredging of channels, harbors and reclamation of wetlands. Visual examination and other measures used during sampling and sample recovery are considered. The types of equipment and methods covered in the course include common available sampling equipment, boomerang, diver, box, and gravity corers. Guidelines for grab, dredge and drill string samplers are discussed. Special attention is given to the handling, storage, and selection of samples and the procedures used for soil sampling. Basic soil types and factors such as the type of sediment, depth of water, and availability of vessels are considered in the selection of the appropriate sampling methods. Chemical and deep water sampling are not addressed herein.

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:


Intended Audience

This course is intended for civil engineers and air quality professionals.


Benefit to Attendees

The student will become familiar with the commonly used equipment for soil sampling and recovering soil samples in nearshore environments such as harbors, channels, rivers, and wetlands.


Course Introduction

The design of nearshore foundations, excavation, and fills requires an understanding of underwater soil sediments, soil characteristics and consideration of problem soils. Samples provide the information necessary for laboratory tests and for in-situ field-testing. Sampling soils underwater is similar to onshore procedures but is more difficult to perform because of factors like the wind, tides, currents, and water depths. It is important to follow the guidelines so the appropriate sampling methods are selected especially since underwater exploration is expensive and difficult to perform and requires special precautions for quality samples.

Nearshore sediment samples are required for a variety of projects. The type of sediment must be determined for harbor and channel dredging in order to properly dispose of the material and to size disposal areas.  Harbor dredging may entail designing dryland expansions of the harbor facilities. Because soils in dredge slurries settle at different rates when placed in confined or unconfined areas future development is determined by the rate of soil consolidation. Samples obtained for laboratory testing help to predict the engineering properties, constructability, consolidation rates, and the physical, chemical and biological characteristics of the sediment. Other sampling needs include foundation investigations for drilling platforms, control of underwater earthwork at dams, offshore wind farms and other underwater construction.

Sample data is required to evaluate the disposal alternatives and dredge plant requirements, possible beneficial uses such as for wetland habitats, island and barrier island protection for coastal areas, aquatic developments and for industrial and residential developments. Because of the large variety of soils and a large variety of applied soil mechanics problems there is also a large variety of soil sampling methods for determining the engineering properties of soils. Before the sampling program can be requested the design engineer must define the purpose for the exploration program and the testing program for field and laboratory personnel. Accurate observations and operations of the exploration equipment are of great importance and the equipment must be properly maintained.

Not only must exploratory personnel be well trained and conscientious; the 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, 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 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, 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. 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-10 and F-13 of the US Army Corps of Engineers manual EM 1110-1-1804, “Geotechnical Investigations”, (2001 Edition, 49 pages), PDF file and the course paragraph “Course Introduction”.

The links to the US Army Corps of Engineers manual Chapters are:

“Geotechnical Investigations”, Chapters F-10

“Geotechnical Investigations”, Chapters F-13

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 selecting proper sampling methods needed to determine the nearshore characteristics of soil sediments for marine construction projects, harbors, channels, harbor expansions, barrier islands, evaluation for beneficial use of dredged material and wetland reclamation. The advantages and limitation of soil sampling equipment and coring equipment discussed. Photographs and diagrams are presented to highlight the key features of the equipment and procedures are discussed. Basic soil types and sources are discussed to select the type of soil sampling method. The importance of following proper procedures for sampling is stressed and considers the proper storage, handling and selection of soil specimens for testing programs.


Related Links

For additional technical information related to this subject, please refer to:
 

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.conepenetration.com/case-studies
Onland, offshore and nearshore site investigation with case studies.

http://www.visittgi.com/environmental.html
Describes soil and rock underwater sampling techniques and equipment.

 

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.