climate-change – vulcanhammer.net

A couple of years ago our bookstore was reorganised to put our offerings in wider distribution. Some of the discontinued titles are being put back into print, directly from the printer. Click on the title or image to to order.

Bearing Capacity and Settlement

This is actually two books in one. We also offer for download two software packages described in the book:

Bearing Capacity of Soils

This manual presents guidelines for calculation of the bearing capacity of soil under shallow and deep foundations supporting various types of structures and embankments. Principles for evaluating bearing capacity presented in this manual are applicable to numerous types of structures such as buildings and houses, towers and storage tanks, fills, embankments and dams. These guidelines may be helpful in determining soils that will lead to bearing capacity failure or excessive settlements for given foundations and loads. Consideration should be given to obtaining the services and advice of specialists and consultants in foundation design where foundation conditions are unusual or critical or structures are economically significant.

Settlement Analysis

This manual presents guidelines for calculation of vertical displacements and settlement of soil under shallow foundations (mats and footings) supporting various types of structures and under embankments. Vertical displacements and settlement caused by change in stress and water content are described in this manual. Limitations of these movements required for different structures are also described. Various types of settlement are discussed in detail, including settlement due to elastic deformation, consolidation, secondary compression and creep, settlement due to dynamic loads, and expansive and collapsible soils. Solutions to soil movement problems are discussed and detailed. Deep foundations and landfills are also discussed.

Retaining and Flood Walls

This book presents information on the design of retaining walls and inland and coastal flood walls. Retaining walls are defined as any wall that restrains material to maintain a difference in elevation.

A floodwall is defined as any wall having as its principal function the prevention of loading of adjacent land. Not specifically covered in this book are seawalls which are defined as structures separating land and water areas, primarily designed to prevent erosion and other damage due to wave action. They are frequently built at the edge of the water, but can be built inland to withstand periods of high water.

Seawalls are generally characterized by a massive cross section and a seaward face shaped to dissipate wave energy. Coastal flood walls, however, are generally located landward of the normal high water line so that they are inundated only by hurricane or other surge tide and have the smooth-faced cantilever stems shown in this book. This book also describes procedures for the design of retaining and flood walls on shallow foundations, i.e., those bearing directly on rock or soil.

Seismic Design of Waterfront Retaining Structures

This book deals with the soil mechanics aspects of the design of waterfront retaining structures built to withstand the effects of earthquake loadings. It addresses the stability and movement of gravity retaining walls and anchored sheet pile walls, and the dynamic forces against the walls of drydocks and U-frame locks. It also contains one of the most complete descriptions of lateral earth pressure theory available anywhere.

The effects of wall displacements, submergence, liquefaction potential, and excess pore water pressures, as well as inertial and hydrodynamic forces, are incorporated in the design procedures. Several new computational procedures are described in this report.

The procedures used to calculate the dynamic earth pressures acting on retaining structures consider the magnitude of wall displacements. For example, dynamic active earth pressures are computed for walls that retain yielding backfills, i.e., backfills that undergo sufficient displacements during seismic events to mobilize fully the shear resistance of the soil. For smaller wall movements, the shear resistance of the soil is not fully mobilized and the dynamic earth pressures acting on those walls are greater because the soil comprising the backfill does not yield, i.e., a nonyielding backfill. Procedures for incorporating the effects of submergence within the earth pressure computations, including consideration of excess pore water pressures, are described.

Military Soils Engineering

Originally written to supply engineer officers and noncommissioned officers with doctrinal tenets and technical facts concerning the use and management of soils during military construction, Military Soils Engineering is one of the most practical guides to basic engineering geology and soil mechanics available. It provides guidance in evaluating soil conditions, predicting soil behavior under varying conditions, and solving soil problems principally related to military operations but applicable to the construction of a wide variety of foundations and earth structures.

Construction in a military theater of operations is normally limited to roads, airfields, and structures. This manual emphasizes the soils engineering aspects of road and airfield construction. The references included in the manual give detailed information on other soils engineering topics that are discussed in general terms.

In addition to this, the manual:

Provides a discussion of the formation and characteristics of soil and the Unified System of soil classification, used by the United States (US) Army and most geotechnical engineers;
Gives an overview of classification systems used by AASHTO and the Department of Agriculture;
Describes the compaction of soils and quality control, settlement and shearing resistance of soils;
Describes the movement of water through soils, frost action, and the bearing capacity of soils that serve as foundations, slopes, embankments, dikes, dams, and earth-retaining structures; and
Has a detailed description of the geologic factors that affect the properties and occurrences of natural mineral/soil construction materials used to build a wide variety of structures.

Military Soils Engineering is an indispensable reference for geotechnical engineers, engineering geologists and laboratory and field technicians.

Dam Safety

This is a combination of two authoritative documents on this vital subject.

Federal Guidelines for Dam Safety (FEMA 93): These guidelines apply to management practices for dam safety of all Federal agencies responsible for the planning, design, construction, operation, or regulation of dams. They are not intended as guidelines or standards for the technology of dams. The basic principles of the guidelines apply to all dams. However, reasonable judgments need to be made in their application commensurate with each dam’s size, complexity, and hazard. Federal agencies have a good record and generally sound practices on dam safety. These guidelines are intended to promote management control of dam safety and a common approach to dam safety practices by all the agencies. Although the guidelines are intended for and applicable to all agencies, it is recognized that the methods of the degree of application will vary depending on the agency mission and functions.

Safety of Dams—Policy and Procedures (U.S. Army Corps of Engineers ER 1110-2-1156): This regulation prescribes the guiding principles, policy, organization, responsibilities, and procedures for implementation of risk- informed dam safety program activities and a dam safety portfolio risk management process within the United States Army, Corps of Engineers (USACE). Risk is defined as a measure of the probability and severity of undesirable consequences or outcome. The purpose and intent of this regulation is to ensure that responsible officials at all levels within the Corps of Engineers implement and maintain a strong dam safety program in compliance with “Federal Guidelines for Dam Safety.” The program ensures that all dams and appurtenant structures are designed, constructed, and operated safely and effectively under all conditions, based on the following dam safety and dam safety program purposes, as adopted by the Interagency Committee on Dam Safety (ICODS).

Part of Soils in Construction‘s presentation of dewatering is this topic. I cover it in my treatment of flow nets in Soil Mechanics: Groundwater and Permeability II; however, Soils in Construction uses a less computationally intensive approach. In this piece I’ll explain that, give some better graphics than the book had available at the time of publication, and compare them with the flow net/FEA results I discussed in my Soil Mechanics course.

Let us consider the problem of a braced cut, which is commonly used for “cut and cover” construction. Such a construction is shown at the right. One of the challenges of temporary works such as this is to insure that a) there is sufficient pumping capacity to keep the “steel trench” dry, and b) the hydraulic gradient of the water coming up into the trench is sufficiently low to avoid soil boiling and bottom heave due to that soil boiling. (Bottom heave can take place due to other factors as well.) An example of that (showing a flow net) is below to the left.

Because the cut is internally braced, it is usually possible to make the sheeting walls simply penetrate to just below the bottom of the trench. However, in order to mitigate the effects of water flowing from around the cut into the bottom, the sheeting can be extended. The idea is that, the longer the extensions, the longer distance the water has to flow, the increased resistance of the soil to flow, and the lower the hydraulic gradients, which both reduce the flow overall and the possibility that the soil at the bottom of the trench will boil, i.e., enter into a quick condition.

Soils in Construction shows two methods of dealing with this problem:

A “rule of thumb” for sheeting extension; and
Charts to determine the minimum extension of the sheeting. These were developed by Marsland (1953). In the book they were taken from NAVFAC DM 7.01, but since the book’s publication NAVFAC DM 7.1 has redone the graphics, and you can see that below (and click on it to download). It is important to note that there is an error in the lower part of this figure; I checked it against Marsland (1953) and have modified it a bit to restore it to Marsland’s original formulation, the following example will show how it is supposed to be used.

Example Problem

I have used this example for many years and feature it in Soil Mechanics: Groundwater and Permeability II. Consider the braced cut shown below.

The parameters for this problem are as follows:

Braced Sheet Piling Excavation
- Depth of excavation = 38’
- Width of excavation = 32’
- Impervious layer 20’ below the toe of the sheeting
- Length of Sheet Piling = 66’
Water table at the excavation level on the excavation side
Water table 6’ below the top of the sheeting on the soil side
Variables for chart above
- H_w = 38 – 6 = 32′
- D = 66 – 38 = 28′
- H_l= 20′
- H = D + H_l = 28 + 20 = 48′
- W = 16′
- Even though the graphic for the problem doesn’t show it, the problem statement indicates an impervious layer below the excavation; thus, we will use the lower chart for this problem.
Soil Conditions
- Uniform medium sand, k = 0.0003 ft/sec
- Saturated Unit Weight = 115 pcf

We need to, one way or another, insure that the design does not experience soil boiling.

The “rule of thumb” in Soils in Construction states that “the depth of penetration of the cut-off wall below the bottom of the excavation should be a third of the “length” computed. For this wall, the ratio is 28/66 = 42%, which means the rule of thumb is achieved.

Turning to the chart above, we must compute three quantities:

The x-axis ratio of half width of excavation to net hydrostatic head, or W/H_w = 16/32 = 0.5;
the y-axis ratio of penetration required to net hydrostatic head, or D/H_w = 28/32 = 0.875; and
the ratio of the depth between the bottom of the excavation and the impervious layer to the net hydrostatic head, or H/H_w = 48/32 = 1.5.

In this case we only have two values of H/H_w to work with: 1 and 2. For H/H_w = 1, FS ~ 2.5 (this is a very rough extrapolation.) For H/H_w = 2, FS = 1.75. Since H/H_w = 1.5 is in the middle between the two, the FS = (2.5+1.75)/2 = 2.125.

If we want to check our results by neglecting the impervious layer, we use the upper chart, and assuming the soil is closer to being a loose sand, FS ~ 1.4.

So how does this all compare to a flow net/FEA result? Same is given below.

At the right is a flow net generated by the finite element program SEEP-W. At the left is a chart showing the direction of the water flow (arrows) and the hydraulic head (coloured bands.) An in-depth explanation of these can be found at Soil Mechanics: Groundwater and Permeability II. The results are as follows:

Gradient at bottom of excavation = 0.48
Factor of safety = 1.77
Total flow = 1.02 gpm/ft of wall

The critical hydraulic gradient, computed by the methods shown in Computing Pore Water Pressure and Effective Stress in Upward (and Downward) Flow in Soil, is 115/62.4 – 1 = 0.843, which checks with the factor of safety for the actual gradient.

The factor of safety from the chart ignoring the presence of the impervious layer is the closest to the FEA/flow net result. For the chart with the impervious layer, the extrapolation for the lower factor of safety should perhaps be ignored.

A couple of other charts (based on Marsland (1953)) are shown below.

References

Marsland, A.R. 1953. “Model Experiments to Study the Influence of Seepage on the Stability of a Sheeted Excavation in Sand.” Geotechnique, 3(6), 223-241.