Formation, Evolution, and Stability of Coastal Cliffs–Status and Trends

The Ocean Studies Board of the National Research Council recently reviewed the U.S. Geological Survey’s Coastal and Marine Geology (USGS-CMG) program (National Research Council, 1999). One of the Board’s primary recommendations was that CMG prepare comprehensive assessments of the nation’s coastal and marine regions, drawing on expertise not only from within the USGS, but also from outside agencies and academic institutions. In response to that recommendation, this report assesses the status and trends of coastal cliffs along the shorelines of the conterminous United States and the Great Lakes. By “status” is meant the present distribution and character of coastal cliffs, as well as their current relevance to social issues such as coastal development. By “trends” is meant the changes in status caused by both geological forces and human activities.

Coastal cliffs are steep escarpments at the coastline. They commonly form during times of rising sea level, such as the present, as the shoreline advances landward and erodes the elevated landmass. Coastal cliffs are a common landform, particularly on the west, northeast, and Great Lakes coasts of the United States, as well as within large estuaries. The land adjacent to coastal cliffs has been heavily developed along much of the coast, particularly in urban areas where the natural instability and progressive retreat of the cliffs pose a threat to life and property. Coastal land is permanently lost when coastal cliffs collapse and retreat landward, which is an important national issue in coastal planning, management, and engineering.

Strength of Materials for Embankment Dams

This white paper presents the results of a survey initiated by the Committee on Materials for Embankment Dams to determine the “state of the practice” for selecting fill strength parameters used in static and pseudostatic analyses of earthfill embankment dams. A
questionnaire was sent to federal and state agencies, consulting firms, and private consultants experienced in the design and safety evaluation of embankment dams. Among the federal and state agencies contacted were: U. S. Army Corps of Engineers(USACE); U. S. Bureau of Reclamation (USBR); Federal Energy Regulatory Commission (FERC); U. S. Department of Agriculture, National Resources Conservation Service (NRCS); Tennessee Valley Authority (TVA); and California Department of Water Resources, Division of Dam Safety (DSOD).

The questionnaire asked each respondent to provide information as to their practice in determining the static strength of embankment materials and analyzing the static stability of embankment dams. The information provided included: approach to static stability analyses, loading conditions, shear strength parameters, field and laboratory testing used to determine shear strength parameters, procedures for interpreting test results, factors of safety, and methodologies used for static analyses.

The information provided by the respondents is summarized in this white paper, which is divided into the following sections:
~ Loading Conditions for Embankment Dams, including End of Construction, Steady-State Seepage, Rapid Drawdown, and Earthquake.
~ Determination of Shear Strengths, including subsections describing total and effective stresses, selection of shear strengths, and the use of cohesion. The information provided in this white paper regarding the determination of shear strengths applies primarily to earthfill materials: soils with a grain size less than 20 mm.
~ Static Analyses of Embankment Stability, including subsections on the limit equilibrium method of slope stability analysis, types of potential failures surfaces evaluated, location of potential failure surfaces for analyses, and recommended factors of safety.

STATE-OF-THE-ART SHEET PILING FOUNDATION

Analysis and Design of Drilled Shaft Foundations Socketed into Rock

A Comprehensive investigation has been made of the behavior of drilled shaft foundation shocked into rock. Methods of analysis have been presented to predict the ultimate capacity and the load displacement behavior under axial load (compression or uplift), lateral load or moment, and torsion. Simple approximate models have been developed which allow closed form predictions for all of these loading modes.. The models for axial loading have been used in the interpretation of 25 load tests from the literature to deduce the likely range of design parameters. Only two load tests were available for lateral load analysis, and no torsional load tests were available. More data are needed from these loading modes for model verification. A detailed design example also is included to illustrate the use of the design equations presented.

Practical Aspects of The Design Of Diaphragm Walls

The design of diaphragm walls has always been treated as something of a mystery. Although this is not exactly a happy situation, the misconception is justified to some extent. The design of diaphragm walls does have some aspects, theoretical as well as practical, which must be well appreciated before a designer who is new to the subject can delve into it. The attempt here will be to demystify the subject while indicating the problems as well as the practical solutions that a designer comes across in the noble practice of the diaphragm wall design.

The Deflection of Earth Retaining Diaphragm wall during Deep Excavation

The technique of constructing reinforced concrete diaphragm wall together with internal bracing or tie back system in deep excavation has been practiced for many years. It has become on of the most popular earth retaining schemes for deep excavation nowadays, yet the analytical methods on the lateral displacement and deflection of the diaphragm wall are still in vague and a sort of art.

This report describes a simple spring model method to predict the lateral displacement and deflection of the diaphragm wall in according to sequence of excavation. A scheme of selecting proper soil strength parameters and earth pressure diagram as well as determination on the soil spring constants is introduced.

Direct measurements on the lateral movement of the diaphragm wall has been carried out in site during deep excavation. The results demonstrated that the prediction for lateral movement of the diaphragm wall by the spring model method has a reasonably fail accuracy.

Design of Diaphragm walls for the TRTS Deep Excavations

The diaphragm wall designed of more than 100 sections of the Taipei Rapid Transit Systems are reviewed and analyzed collectively with emphasis on wall depth, strut reaction, wall bending moment and wall deflection. The subsoil conditions, methods of analysis, methods of construction, ground improvement and groundwater pressure assumptions used in the design are discussed.