Geotechnical and Geoenvironmental Engineering Handbook

The work of the geoprofessional has evolved and expanded enormously over the past two decades. The breadth of the discipline is reflected by the number of related international societies (e.g. International Society for Rock Mechanics, International Geosynthet-ics Society, International Tunnelling Association, International Association for Computer Methods and Advances in Geomechanics, International Association of Hydrogeologists, International Association of Engineering Geology and the Environment to name but a few) and even in the change of name for the International Society for Soil Mechanics and Foundation Engineering to the International Society for Soil Mechanics and Geotechnical Engineering. In particular, geotechnical practice has expanded far beyond the traditional areas of soil mechanics and foundation engineering to include what is now commonly referred to as“geoenvironmental engineering.”

The two major technical design considerations in geotechnical engineering are to: (1) avoid catastrophic failure, and (2) avoid excessive deformations (settlements, heave or lateral deformations). In the context of limit state design these are referred to as the ultimate and serviceability limit states, respectively. To perform the design, it is necessary to: (1) calculate the loads from the structure that need transmission into the ground;(2) obtain the behavior characteristics of the soils including, but not limited to, the stress-strain and strength behavior in order to perform the necessary analyses and detailed calculations; and (3) compare the stresses created in the ground by the structure with (a) the available shear strength to evaluate proximity to failure conditions, and with (b) the stress-strain behavior to evaluate deformations. Local building codes may place additional requirements on the design and construction procedures.

The purpose of this chapter is to provide simple correlations between engineering properties and index properties for soils. The most important index properties and the tests used for their determination are briefly described. Correlations are provided for: (1) hydraulic conductivity, (2) at rest stress state, (3) compressibility and consolidation, (4) swelling and shrinkage, (5) shear strength and (6) dynamic properties. References are given to the sources of all correlations presented.

Site characterization involves the determination of the nature and behavior of all aspects of a site and its environment that could significantly influence, or be influenced by, a project. Geotechnical and environmental aspects should be jointly considered and evaluated. The basic purpose of site characterization is to provide sufficient, reliable information of the site conditions to permit good decisions to be made during assessment, design and construction phases of a project, or as required by regulatory agencies. Site characterization involves determining information on previous and current land use, topography and surface features, hydro-geology, hydrology, meteorology, geology, seismology, geotechnical aspects, environmental aspects, biology, zoology, air quality, water quality, geochemistry and other factors.

Early theoretical soil mechanics dealt mainly with saturated soil from below the ground-water table, i.e. positive porewater pressures (see Chapter 2). The soil above the groundwater table has negative porewater pressures and is known as the vadose zone. Recent theories for unsaturated soil behavior have taken on the form of extensions of classical (saturated) soil mechanics theories. While parallels and similarities between saturated and unsaturated soil mechanics are present, variations exist that make the practice of unsaturated soil mechanics somewhat different in character from saturated soil mechanics. Differences lie primarily in the assessment of appropriate soil properties and soil property functions, and in the flux boundary condition between the soil and the atmosphere. This chapter presents the fundamental theories of unsaturated soil mechanics, and emphasizes those elements of unsaturated soil mechanics that differ from saturated soil mechanics. Unsaturated soil mechanics can be categorized into three classical areas of study: seepage, shear strength and volume change. Paradigm shifts in analysis associated with the assessment of soil properties become an important factor when moving from theory to practice of unsaturated soil mechanics.

The application of rock mechanics to solve engineering problems requires some knowledge of engineering geology and an appreciation of the difference between parameters measured in the laboratory and the design parameters used in field problems. This concept is particularly important in the practice of rock engineering because laboratory tests described in subsequent sections are performed on small specimens of intact rock. In contrast, the rock mass in the field is often dissected by variousdiscontinuities such as joints. Therefore, quantities of engineering importance measured in the laboratory, such as the elastic modulus and strength, can seldom be directly used in the field. However, the results of laboratory measurements do form an intrinsic component of the knowledge required for design. The parameters measured in the laboratory may serve as: (1) an index to correlate experience between different rock formations, (2) an index to represent the variation of material behavior over a proposed site, (3) upper bound values such as elastic modulus and strength, and (4) a component to which a “correction factor” may be applied to obtain the design value.

Geosynthetics are polymeric materials that are used in below-grade construction in a broad and ever-increasing range of applications. The majority of the applications generally fall into the areas of geotechnical, environmental, transportation and hydraulic engineering. A number of specific applications using geosynthetics will be described in Chapters 13–19, 25–27 and 29, 30. Before dealing with applications, however, it is necessary to present the salient characteristics of the various geosynthetics and the most relevant test methods and properties. This chapter is focused on providing that type of background material. While the literature is abundant with references on geosynthetic properties and test methods, this review is quite brief. It follows the general description in Koerner (1998), which is more detailed.

Each year thousands of projects require some type of groundwater control. Whether it is minor seepage or a complex groundwater flow, a proper assessment of the conditions at the site and the selection of an appropriate groundwater control system is essential to the successful completion of the project. This chapter will describe procedures that can be of assistance in the assessment, selection, design, installation, operation and removal of groundwater control systems.

Shallow foundations can be classified as those that are constructed on the ground surface or at shallow depth beneath the ground surface. A foundation is usually termed “shallow” if it is at a depth that is less than its breadth.

A major function of piles is to transmit foundation loads through relatively weak or loose strata to stiffer underlying soil or rock strata. Piles may also be used to carry uplift loads, to carry loads below scour level in marine situations, to resist lateral loadings, and to reduce the settlement of shallow pad or raft foundations. Resistance of piles to vertical loads is supplied by a combination of pile shaft friction and end bearing, and even with nominally end bearing piles, significant resistance can be derived from shaft friction. Piles subjected to lateral loads rely mainly on the resistance developed near the ground surface. The soil in this region is often disturbed or else subjected to seasonal moisture changes that may affect the soil strength and stiffness significantly. Thus, prediction of the lateral behavior of piles may be even more difficult than vertical behavior.

This chapter covers two main topics. The first deals with the design principles for foundations on rock specially those for tall buildings (Section 11.2): both shallow footings and piles socketed in rocks are addressed. The second topic deals with the safety assessment of concrete dams on rock foundations (Section 11.3).

Geotechnical engineers encounter problems related to the dynamic loading of foundations when designing foundations for machinery and vibrating equipment or designing foundations for structures subjected to seismic loading. This chapter will focus on the former case and the latter will be treated in Chapter 21.

The study of slope movements is complicated because they can take very different configurations and mechanisms ranging from rock topple to mudflow, can involve a variety of materials ranging from hard rock to sensitive clay and loess, and can result from a variety of phenomena ranging from rapid snow melt or heavy rainfall to earthquake. Leroueil et al. (1996b) defined four different stages of slope movement (Fig. 14.1): (a) the pre-failure stage, including deformations associated with changes in stresses, viscous deformations, and strains and displacements associated with progressive failure; (b) the onset of failure characterized by the formation of a continuous shear surface through the entire soil or rock mass or by the separation of an unstable rock mass from the slope (rock fall or toppling); (c) the post-failure stage, which includes movement of the soil or rock mass involved in the landslide, from just after the onset of failure until it essentially stops; and (d) the reactivation stage, when the soil or rock mass slides along one or several pre-existing shear surfaces. This reactivation is generally occasional. Continuous movements with seasonal variations of the rate of movement (active landslides), which are the rule in some countries and geological environments, represent a peculiar situation that might be associated with reactivation since these movements occur along well-defined shear surfaces.

If during the design of a foundation, the geotechnical engineer finds, for example, that the bearing capacity of the soils at the site are inadequate or if estimates of the total and differential foundation settlements are intolerable, then alternate approaches to the design must be considered (Holtz 1991; Munfakh 1997a). The project may be abandoned as being infeasible or too expensive, or it may be possible to relocate the facility to a more suitable site. For buildings and some bridges, an alternate shallow foundation type such as a mat or raft may be appropriate, or in some cases, a compensated foundation is a feasible alternative (see Chapter 9). Probably the most common alternate foundation to be considered for structures is a deep foundation of one type or another. Pile foundations and drilled shafts are discussed in Chapter 10 and in Kulhawy (1991). The design and construction of embankments on soft soils and peat pose special problems, and these are discussed in Chapter 16.

In the analysis of the behavior of embankments on clay foundations it has commonly been assumed that the behavior is perfectly undrained during construction and that drainage and consolidation start only after the end of construction. This approach has been widely used and has generally performed well for conventional design situations. However, observations during construction have shown that while this approach may often provide reasonable designs, the actual behavior may be more complicated and that conventional undrained analyses may overpredict pore pressures and lateral displacements. Thus, if one wishes to predict the actual behavior of an embankment on clay, it is essential to have a good knowledge of the mechanical behavior of natural clays, as described in Chapter 2, and to understand what may happen under an embankment during construction as described in Section 16.1.1.

For many years engineering practice for earth retaining structures emphasized earth pressures and their application in choosing an appropriate design and support system. In the last 25 years there has been a dramatic growth in new construction technologies and products for retaining soil. In particular there has been increasing use of reinforcing elements, either by incremental burial to create reinforced soils or by systematic in situ installation to produce soil nailing. Rapid developments in polymer manufacturing have led to a wide range of polymeric products (geosyn-thetics) (see Chapter 7). These materials are now routinely used to reinforce the soil in retaining wall and slope applications, and to control soil drainage. Reinforced soils and soil nailing have changed the ways built-up and in situ walls are constructed by providing economically attractive alternatives to conventional methods. The use of these products in reinforced soil applications has led to many different earth retention systems.

A variety of buried pipe infrastructure is needed to service the needs of our communities and resource industries for electrical, water, gas and oil supply, power development, storm-water and sanitary sewer systems, and highway and railway culverts. The conduit surrounded by soil is both loaded and supported by the earth and porewater: and geotechnical engineers are frequently called upon to provide advice regarding various design and construction issues. This chapter describes issues associated with pipe loading and load capacity, and the construction of buried pipeline infrastructure. Other chapters contain related material associated with trenchless pipe-laying technologies (Chapter 19), slope stability (Chapter 14) and frost and thermal effects (Chapter 20).

Permafrost underlies about one-quarter of the world’s land surface and most of the engineering aspect has been well-covered in Andersland & Anderson (1978), Johnston (1981) and Andersland & Ladanyi (1994). This chapter considers more specifically the problems associated with seasonal freezing and thawing of soils in which there is no perennially frozen ground. Frost action may cause extensive damage to buildings, infrastructure such as roads and utility lines and other civil-engineering structures. All such facilities should be designed and constructed to avoid serious functional problems, costly maintenance and unduly short service life. The behavior of soils is strongly influenced by temperature and, therefore, an appreciation of heat transfer in soils is of utmost importance to cold region engineering.

This chapter presents the concepts and procedures used by geotechnical earthquake engineers to design safe structures in a seismic environment. Geotechnical engineers tackle a wide range of problems; establishing design ground motions, the seismic design of foundations, analysis of soil-structure interaction, estimating seismic pressures against retaining and basement walls, evaluation of liquefaction potential, seismic response analysis of earth structures, post-liquefaction behavior of soil structures, evaluating the design of remediation measures and seismic risk analysis for critical facilities such as embankment dams with seismic liquefaction hazard potential.

The issue of contaminated land carries with it significant environmental and economic implications. A key question is how best to fulfill the interests of all those with a stake in contaminated land (owners, potential vendors/purchasers, consultants, the public, the regulators and so on) while ensuring that the land is returned to a condition that is protective of the users and does not present a long-term environmental liability.

While advances into understanding the complexities of contaminant migration through porous media and fractured rock are continually being made, nothing is more important to understanding contaminant migration, and designing remedial systems, then a complete model of the hydrogeological environment. One must understand the hydrostratigraphy and other factors that control fluid flow at a site before one can hope to understand or control contaminant migration.

Barrier systems are intended to minimize the movement of liquids and/or gases from one location to another. Typical example applications include the use of liners for canals, ponds, dams, waste disposal facilities and spill protection around tanks. The liquids to be “contained” may range from water (e.g. in canals, ponds and dams) to contaminated water (e.g. in landfills; sewage lagoons; brine ponds; or contaminated groundwater) to relatively pure chemicals (e.g. hydrocarbons) stored in tank farms. In these applications the primary objective is to limit the physical escape of the liquid to either surface water or groundwater. In situations where the liner is in contact with contaminated water over long periods of time (e.g. lagoons, landfill liners, etc.), a secondary objective may also be to limit chemical migration by the process of diffusion (Section 24.3.1) whereby contaminants migrate from a point of high concentration (e.g. in the retained fluid) to points of lower concentration (e.g. in groundwater).

The liquid-containing structures considered herein are those constructed with soil; thus, concrete dams, concrete reservoirs, cavities excavated in rock and steel tanks are not considered. The liquid-containing structures considered include: structures used for liquid storage (e.g. embankment dams, liquid impoundments excavated in soil or surrounded with dikes), structures used for liquid conveyance (canals) and structures used to prevent liquid from migrating into the ground (lined landfills). This chapter addresses analysis and design methods for liquid-containing structures. Required geosynthetic material properties and engineering parameters are addressed. The geosynthetic materials themselves are not discussed, however, and the reader is referred to Chapter 7 for information on this subject.

Cover systems are used at landfills and other types of waste management units (e.g. waste piles, mine tailings piles, surface impoundments) to contain waste and any waste byproducts (e.g. leachate, acid mine drainage, gas), to control moisture and air infiltration into the waste, and to prevent the occurrence of odors, disease vectors, and other nuisances. Cover systems are also used to meet erosion, aesthetic, and other end-use criteria for waste management sites. Cover systems for waste sites may involve only a single soil layer, placed over a mine waste rock pile, for example, or a multicomponent system of soil and geosynthetic layers, placed over a hazardous waste landfill, for example.

Groundwater monitoring is a critical component of activities performed at a site where the groundwater may have been adversely impacted by chemicals (i.e. contaminated). The specific purposes of groundwater monitoring will vary depending on the stage of impact identification. The elements of monitoring include:

Full restoration of contaminated zones in the subsurface, such that unrestricted use of the land or groundwater resources can occur, has proven to be a challenging, costly and often elusive goal. This has been a consequence of the limitations of available remedial technologies, incomplete investigation and definition of the contaminant problem, and the complex and heterogeneous nature of the subsurface. A remedial program for subsurface contamination arising from widespread non-point sources such as the use of agricultural chemicals and fertilizers generally needs to be approached through the implementation of better management practices, such that the introduction of contamination to the subsurface over extensive areas is either reduced or eliminated. For point-source contamination, however, it may be feasible to implement specific programs to reduce or remove contaminants from the subsurface.

With the advent of legislation prescribing the handling of contaminated soil and ground-water, the typical scope of a modern site investigation includes consideration of both engineering properties of the soil and ground-water and how to manage any contaminated soil and groundwater in a manner consistent with law, protective of human health and the environment, and in the most cost-effective manner possible. Construction in most urban areas and in some rural areas can lead to the discovery of contaminated soil or groundwater. Linear construction features, such as excavation for pipelines, in an urban area are typically adjacent to numerous sites capable of contaminating soil and groundwater at the construction site, as shown in Fig. 30.1. A business, commercial or industrial building may occupy a site that is the former location of a gas station, dry-cleaning facility, or paint manufacturing or distributing center. The innocent-looking warehouse building in a rural town may be the former site of pesticide storage or formulating facility. An environmental investigation is required if new construction requires excavation of soil or dewatering where there is reason to believe contamination may exist. The discovery of contaminated soil initiates what can be a complex legal, regulatory and engineering process if the proposed project is to move forward. The engineer must manage the handling of the contaminated soil in a manner that is consistent with good engineering practice, consideration of the legal and regulatory environment of the project, and the cost efficiency and schedule goals of the client.