مکانیک خاک-Soil mechanics
Soil
mechanics
The science that
applies laws and principles of physics, especially continuum and particulate
mechanics and hydraulics of porous media, to solve problems encountered in civil
engineering that are related to force-deformation behavior of soil and the flow
of fluids through soil. Civil engineers use the term soil for a naturally
occurring multiphase material consisting of gas or liquid and solid particles,
whether or not the material supports plant life. The term geotechnics or
geotechnical engineering refers to a subspecialty of civil engineering that
combines the disciplines traditionally known as soil mechanics, soil dynamics,
rock mechanics, earthwork engineering, and foundation engineering for the design
or analysis of natural or constructed facilities of, in, or on rock or soil. See
also: Rock mechanics
Fundamental
principles
Soil mechanics rests
on five fundamental relationships. The effective stress principle formulated by
K. Terzaghi in the early 1920s in relation to work on the consolidation of
clays, is given by Eq. (1),
(1)
where σ = total
normal stress, σ = effective normal stress, and u = pore water pressure. The
effective stress principle unifies and extends the applicability of other
fundamental relationships such as Darcy's law, Eq. (2),
(2)
where Q is flow rate,
k permeability, i hydraulic gradient, and A cross-sectional area; Coulomb
friction, Eq. (3),
(3)
where τ is shear
stress, σn normal stress, and φ friction angle; Newton's second law of motion,
Eq. (4),
(4)
where F is force, m
mass, and a acceleration; and Hooke's law, Eq. (5),
(5)
where σ is stress, E
modulus of elasticity, and ε strain. Most of the advances that have been made in
soil mechanics use these fundamental principles as their starting point. See
also: Friction; Hooke's law; Newton's laws of motion
Fig. 3 Relationship between pore water and
heads. (a) Relationship between heads in multilayered soil. (b) Placement of the
piezometers and well [he = elevation head; hp = pressure head (pore pressure);
ht = total head; zw = depth below the phreatic surface (water
table)].
Nature of
soil
Soil consists of a
multiphase assemblage of mineral or organic particles, as shown in the diagram
in Fig. 1. The voids within this solid soil skeleton contain gas (generally
air), liquid (generally water), or both. A saturated soil has its voids
completely filled with water. Various mathematical equations are used to
determine the relationships that exist among the three phases within a soil
element, an arbitrarily small volume within a soil mass.
Fig. 1 Diagram showing the three phases in a
thin section of a soil element.
When an element of
dry soil experiences a load (force F in Fig. 2), normal (N) and tangential (T)
forces develop immediately at the contact points of the soil particles. The soil
mass deforms as the air in the voids compresses or escapes. If the soil voids
contain water (Fig. 2b), an essentially incompressible liquid, the
spring–dashpot analogy helps visualize the load transfer process. Upon
application of the load, the pore fluid (water in chamber) cannot compress, and
the small size of the soil pores (valve orifice) restricts the escape of water.
The pressure in the pore water increases to counteract the applied force F.
Immediately after time t = 0, water slowly flows out through the tortuous path
formed by the microscopic pores. The soil skeleton (spring) begins to feel an
increased load, deforming as a load transfer from the pore water to the soil
skeleton occurs. After sufficient time has elapsed, pressure within the pore
water returns to zero, flow through the soil pores ceases, and the system
reaches an equilibrium position, with a compressed soil skeleton resisting the
applied force. The applied force imposes a stress F/A (force F per unit area A)
on the system, and a strain d/L in the vertical direction (deformation d per
unit length L in a given direction) in the equilibrium position. Geotechnical
engineers consider stresses and strains positive when compressive. A system with
large pores reaches equilibrium quickly, while a system with small pores
requires a long time to reach equilibrium.
Fig. 2 Load transfer and consolidation; the
effects of the application of a load (F) to soil. (a) Dry soil (N = normal
force; T = tangential force). (b–e) Soil containing water and the corresponding
spring and dashpot analogy from time = 0 until establishment of
equilibrium.
The spring–dashpot
system exhibits linearly elastic behavior. Doubling the force F doubles the
deformation. Upon removing the force F from the spring–dashpot system, the
compressed spring pushes the piston back to its original position as water flows
back into the chamber. In soils, crushing and slippage of particles results in
nonlinear behavior and unrecoverable deformations that prevent a total rebound
of the system to its original position. This nonlinear inelastic behavior means
that soils do not obey Hooke's law relating stress to strain.
Since the early days
of modern soil mechanics, Hooke's law served as a benchmark to evaluate how far
soil behavior deviated from its simple generalization. Complex nonlinear
stress–strain relationships attempt to model more closely the deformation
characteristics of soil, but linear elasticity continues to provide a useful and
sufficiently accurate simplification for the solution of many engineering
problems.
Soil classification and index
properties
The discipline of
soil mechanics relies on the quantification of observed soil behavior. The
geotechnical engineer utilizes soil classification to organize soils that
exhibit similar behavior into groups. The table shows a simplified soil
classification based on the widely accepted Unified Soil Classification System
(USCS). Simple index tests such as grain size and plasticity help classify
soils.
Among the most common
index tests, the Atterberg limits that use the water content at the boundary
between states of consistency to correlate soils. The water content of a
remolded soil at which a ½-in. (13-mm) section of a 5/√64-in.-wide (2-mm) groove
closes from 25 successive shocks in a standard device corresponds to the liquid
limit. In effect, the test measures the water content required for an arbitrary
but constant shear strength of the remolded soil sample. Therefore, all soils
have approximately the same shear strength at the liquid limit. The plastic
limit corresponds to the water content at which a thread of soil with a diameter
of ⅛ in. (3.2 mm) crumbles when pressed together and rerolled. The shrinkage
limit corresponds to the minimum water content required to completely fill all
the voids of a dried soil pat (or similarly, the water content at which further
drying will not cause additional shrinkage of the sample).
Correlations between
fundamental soil properties (such as strength, permeability, compressibility,
and expansivity) and index tests help the engineer obtain approximate solutions.
The actual soil properties measured in laboratory or field tests can vary
greatly from the values suggested by the index property correlations.
Pore pressures and
heads
Water in the soil
pores exists at a measurable pressure—positive, zero, or negative. Zero pore
pressure corresponds to atmospheric pressure in the pore water. Figure 3 shows
the relationship between pore pressure and head. An instrument known as a
piezometer measures total head near its sensor. The elevation of the piezometer
sensor equals the elevation head, he. The dimensions of a piezometer sensor
generally do not exceed 4 in. (10 cm) in diameter and 3.3 ft (1 m) in length.
The total head, ht, equals the elevation to which water rises in a piezometer.
The height of water in the piezometer equals the pressure head, hp. The pore
pressure, u, is given by Eq. (6), where γw equals the unit
(6)
weight of water.
Wells can have long collection zones that penetrate different soil layers. This
characteristic makes total head data from wells difficult to interpret and use,
as shown in Fig. 3b.
Positive pore
pressures decrease effective stresses, which results in increased deformations
and decreased soil shearing resistance. In general, the higher the pore
pressure, the higher the possibility of encountering unsatisfactory performance.
For hydrostatic
conditions, the total head remains constant everywhere, no flow occurs and the
pore pressure, u, is given by Eq. (7),
(7)
where zw equals the
depth below the phreatic surface, the imaginary line where hp = 0. Most soil
deposits do not exist under hydrostatic conditions. A steady flow of water
through the soil results from a constant pattern of pore pressures, known as the
steady-state pore pressures or heads. Pore pressures different from steady-state
values, known as excess pore pressures, result from loading, unloading,
rainfall, increase in river or reservoir levels, leaks from pipelines or tanks,
and drying of the soil, among other causes.
Flow
Total heads determine
the direction of flow in soil. Water flows from a zone of higher total head
toward one of lower total head. Darcy's law [Eq. (2)] describes accurately the
flow of water through the soil pores. Figure 4a illustrates flow through soil
under conditions similar to those used by Darcy for his experiments. Rewriting
Darcy's law as Eq. (8), yields a
(8)
flow rate equal to
8.5 × 10−3 gal/s (3.2 × 10−5 m3/s). [Here Q is flow rate, k permeability or
hydraulic conductivity, i hydraulic gradient, ht1 total head at entrance end of
soil, ht2 total head at exit end of soil, L length of soil sample, and A
cross-sectional area of sample.] Darcy's coefficient of permeability varies more
than any other engineering soil property, as much as 10 orders of magnitude (or
109 times) between a clean gravel and a plastic clay. Furthermore,
discontinuities such as cracks or very pervious thin layers can greatly affect
the permeability of a soil deposit.
Fig. 4 Diagrams of flow through soil. (a) Flow
through a permeameter. (b) Simple flow net.
Fig 5. Analysis of flow through soil of an earth dam. (a) Profile of flow through the dam. (b) Flow parallel to the slope. Piezometric line is a line located at a vertical distance hp from a surface of interest; uppermost flow line represents the phreatic surface (water table). (c) Flow toward a fully penetrating well.
A flow net provides a
graphical representation of flow through soil, particularly useful for
evaluating complex conditions. For two-dimensional flow through isotropic soil,
the flow net consists of a set of flow lines and orthogonal equipotential lines
that divide the soil into curvilinear squares. A flow line traces the flow path
through the soil for a drop of water. While an infinite number of flow lines
exist, a flow net utilizes an arbitrary selection to divide the soil into a
convenient number of flow channels, nf. Equipotential lines, drawn through
points of equal total head, divide the flow net into a number of uniform head
drops, nd. The flow per unit length, l, perpendicular to the page is given by
(9)
Eq. (9), where Δh =
total head drop = ht1 − ht2, and sint = shape factor = nf/nd
The flow net for the
Darcy permeameter (Fig. 4b) has a shape factor equal to 4/5, which yields a flow
equal to that computed by using Darcy's equation. The gradient between two
points in the net equals the head drop divided by the distance between them.
Since the net in Fig. 4 has equally spaced equipotentials, the gradient in the
direction of flow remains constant.
Figure 5a shows a
flow net for an earth dam with the following characteristics: Δht = 88 ft(27 m),
nf = 9.9, nd = 18, sint = 0.55 and Q/l = 0.014 ft2/day (0.0013 m2/day) for k =4
× 10−8 in./s (1 × 10−7 cm/s). The gradient in the direction of flow varies
throughout the flow region, increasing as the flow approaches the drain. (Note
that the distance between equipotentials decreases in Fig. 5a.) Areas of
uncontrolled high gradients can experience instability problems from low
effective stress and internal erosion. The graded filter shown on the upstream
side of the drain ensures that the fine particles of the compacted fill do not
get washed into the drain. Filters generally consist of layers of selected soil
with particle sizes chosen to prevent migration of fines. Geosynthetic filters,
rapidly growing in acceptance, consist of one or more layers of fabric
engineered to retain soil fines. See also: Dam; Geosynthetic
A flow net provides
information on the pore pressure throughout the flow region. Rather than using
the entire flow net for some analyses, engineers can obtain the information
applicable to a surface of interest (for example, a potential shear surface) and
portray the heads obtained from the net in terms of a piezometric line. Figure
5b shows that the piezometric line does not necessarily coincide with the
phreatic surface. Under conditions of horizontal flow or no flow, the
piezometric line and phreatic surface coincide.
Figure 5c shows a
simplification that permits evaluation of the flow into a fully penetrating well
using Darcy's law. The Dupuit assumption to Darcy's law states that the
hydraulic gradient remains constant from top to bottom in the pervious formation
and equal to the slope of the water surface, as in Eq. (10).
(10)
Then, the flow rate,
q, out of the well using any set of consistent units is given by formula (11),
where
(11)
q is water quantity
per unit time (Q/t). The values for h1, h2, r1, and r2 are measured (Fig. 5c) at
observation wells 1 and 2, respectively. Pumped wells have many uses in projects
involving civil engineering, including water supply, reduction of pore pressures
to increase effective stresses and thus strength, and control of contaminants in
the groundwater.
Stress in
soil
Figure 6 illustrates
the concept of stress in soil. Geotechnical engineers frequently work with
normal stresses acting perpendicular to a surface of interest, shear stresses
acting parallel to a surface of interest, and pore pressures (sometimes known as
neutral stresses) acting equally in all directions, expressed as stress vectors
(Fig. 6b). See also: Shear
Fig. 6 Stress in soil represented by (a) soil
element beneath loaded surface and (b) free-body diagram with stress vectors. τ
= shear stress. Friction angle (θ) is measured counterclockwise from direction
of normal stress (σ1).
The effective stress
principle [Eq. (1)] states that the total normal stress experienced by an
element of soil consists of the effective normal stress, which controls strength
and deformation, and the pore water pressure. Since water can not sustain shear,
pore water pressures do not affect shear stresses. A bar over the symbol
identifies a stress as effective or a property as related to effective stresses
(for example σ, φ, c.
The stress history of
a soil greatly influences its behavior. Two powerful mathematical tools used to
understand and make use of stress history are Mohr's circle of stress and stress
path (Fig. 7). Mohr's circle provides a graphical representation of the stresses
in any direction acting at a point. A distance equal to the magnitude of the
pore pressure separates the circle for total stresses from that representing
effective stresses. Each point along the circle represents the normal and shear
stresses acting on a particular plane. The pole of the Mohr circle relates the
stresses to the physical planes on which they act. A line through the pole and
point σθ, τθ will lie parallel to the plane on which σθ and τθ act.
Fig. 7 Mohr's circle (a) for state of stress at
a point and (b) stress path to failure for the soil element shown in Fig.
6.
Two particular points
prove very helpful in portraying stress history—the point for stresses on the
failure plane, often taken as the point of maximum obliquity (maximum value of
τ/ σ), and that for maximum shear stress τ (identified by
coordinates p and q). The total stress path (TSP) and effective stress path
(ESP) provide a locus of stress points representing successive states of stress
in the history of the soil. For clarity, Mohr circles usually do not appear in
stress path plots, although one could reconstruct the circle at any point along
the stress path. Failure occurs when the effective failure-plane stress path
reaches the strength envelope (also known as yield surface) or when the p-q
stress path reaches the Kf line as in Fig. 7.
The stress path can
reach the strength envelope because of a loading, an unloading, an increase in
pore pressure, or a combination of these. Stress paths help engineers identify
mechanisms and select methods and soil parameters for solving a problem. See
also: Stress and strain
Strength
Soil behaves as a
frictional material; that is, it resists shear stresses by the frictional action
between particles. Figure 8 shows a strength test where a sample under a
constant normal force gets sheared along a predetermined horizontal plane. The
displacement-versus-shear stress plot (Fig. 8b) shows two important
characteristics—a peak shear strength and a residual value obtained after large
deformations. A series of these tests at different values of normal stress
yields the peak and residual strength envelopes shown. These strength envelopes,
unique for practical purposes, remain valid for a wide range of effective stress
paths to failure. Some soils exhibit a monotonically ascending
displacement–versus–shear stress curve where the peak strength equals that at
large deformations.
شکل ۸
Fig 9. Consolidation settlement. (a) Clay layer with double drainage, no lateral strains. (b) Oedometer test to obtain soil parameters. (c) Oedometer test results; each data point represents the end of a load increment; and left broken line represents 10 metric tons/m2 and right broken line represents 100 metric tons/m2. 1 metric ton = 1.1 ton; 1 m2 = 10.8 ft2.
Soils generally do
not have true cohesion, that is, when σ = 0, strength = 0. Since strength
envelopes can be curved, use of the linear Coulomb friction equation (3)
requires care in the selection of parameters that are valid for the stress range
of interest.
Consolidation and
swelling
Consolidation refers
to a process during which a saturated soil experiences a decrease in water
content due to a decrease in the volume of voids. The opposite process, swelling
(heave) results in an increase in water content due to an increase in the volume
of voids. Consolidation and heave involve flow of water into or out of the soil,
and a corresponding change in volume. Changed pore pressures (for example, from
a change in load or heads) establish a hydraulic gradient, since the pore
pressure near the drainage boundary remains essentially unchanged. In soils with
low permeability, the water flows slowly, and a time lag exists between the
event that changed the pore pressures and the completion of consolidation. The
compression of a partially saturated soil involves compression, solution, or
expulsion of air until the soil becomes nearly saturated. The spring–dashpot
example in Fig. 2 illustrates the mechanism of consolidation.
Figure 9a shows a
layer of clay with double drainage subjected to a uniform load. After
application of the load, pore pressures near the center of the layer increase by
an amount equal to the magnitude of the load. The high permeability of the sand
permits rapid dissipation of excess pore pressures, and deformations occur
almost instantaneously. The total head difference between the center of the clay
and the sand layers creates a hydraulic gradient, which produces a flow from the
center outward in two directions. Figure 9b shows a consolidation test (known as
an oedometer test) that models the one-dimensional compression experienced by
the clay layer. The expression for final settlement shown in Fig. 9d remains
valid for fine- as well as coarse-grained soils.
The oedometer tests
provide information to predict both the magnitude and rate of deformation. In
coarse-grained soils, deformations occur very rapidly. In fine-grained soils,
the theory of consolidation helps predict the rate of deformation using the
coefficient of consolidation, a parameter influenced mostly by the permeability
of the soil. The theory of consolidation permits computation of more detailed
results, including distribution of pore pressures and deformations throughout
the deposit at any time.
Soil
improvement
For many centuries,
builders have tried to make soil stronger, denser, lighter, less compressible,
less pervious, more pervious, or more resistant to erosion. One of the most
common soil improvement techniques compacts the soil with a heavy roller or
tamper. Compaction of fine-grained soils generally takes place in layers no more
than 12 in. (30 cm) thick. Compaction densifies the soil, and it can increase
its strength and decrease its compressibility and permeability. The key to
obtaining the desired dry density lies in achieving a preselected water content
in the soil undergoing compaction. Compaction at the optimum water content
yields the highest dry density for a given compactive effort. Soil compacted at
or near the optimum water content has negative pore pressures.
Other techniques use
to improve engineering properties of soil include preloading; dewatering;
stabilization with chemical admixtures; and reinforcement with rods, strips,
grids, and fabrics made of natural of synthetic materials.
Slope
stability
In earth slopes, the
force of gravity pulls the soil mass downward. The internal friction between
soil particles resists this force. As long as the resisting forces exceed the
driving forces, the slope remains standing. A stability assessment of a slope
involves a comparison of the stresses acting on the sliding mass and the
strength of the soil along which sliding occurs. This assessment requires
evaluation of the geometry and pore pressures, which together determine the
stresses, and the strength of soils involved in a potential slide.
Geotechnical
engineers use the term factor of safety (FS) to indicate the level of stability
of a slope. Using forces, FS is the ratio of the shear resistance on a shear
surface to the net shear force along a shear surface; or, using stresses, FS is
the ratio of the shear strength along a shear surface to the average shear
stress on a shear surface. When FS decreases to 1, failure occurs. Figure 10
shows the forces acting on a wedge of soil. To increase FS would require an
increase in shear resistance, S, or a decrease in shear force, T.
Fig. 10 Free-body diagram showing forces on a
slope wedge.
The following actions
would increase S: (1) Increase W. (2) Increase c (densify, replace soil
chemicals, temperature). (3) Increase φ. (4) Decrease Us (drain).
The following actions
would decrease T: (1) Decrease UL (drain). (2) Decrease W (excavate, replace
with lighter soil). (3) Decrease PL (unload above slide). (4) Increase UR (raise
reservoir level). (5) Increase R (install tiebacks, piles, berm retaining wall).
Slope stability
analyses generally use the principles of force and moment equilibrium, a
technique known as limit equilibrium. In general, a free body bounded by the
slope surface and a potential failure surface is isolated, and the stresses are
determined by solving the static equilibrium equations. The ratio of the
determined stresses and the shear strength of the soil yields the factor of
safety. Repetition of the analysis with other possible failure surfaces yields
different factors of safety because both the driving and resisting forces can
vary from surface to surface. The most critical surface has the lowest factor of
safety. Computer programs allow the rapid investigation of hundreds of potential
failure surfaces along cross sections with different soil layers. See also:
Statics
More sophisticated
numerical techniques consider the stress–strain properties of the soil, and
allow the analysis of slopes composed of soils with complicated
stress–strain–strength properties. Finite-element stress–deformation analyses
can provide a detailed description of the stresses acting throughout the slope.
The engineer calculates the factor of safety by integrating the acting shear
stress along a potential failure surface and comparing the result to the
available shear strength along the surface. See also: Finite element method
The principles of
stability analysis outlined above apply for natural slopes as well as for earth
structures such as earth dams and highway embankments. With constructed
facilities, the engineer has more detailed knowledge and some degree of control
over the material properties. An earth structure must satisfy all the criteria
needed to perform its intended function. These may include overall stability,
limited deformation, weight limitations, specific flow characteristics, or
particular dimensions. See also: Highway engineering
Foundations
Nearly every large
structure derives its support from contact with the earth. The foundation,
whether of a building, tower, highway, retaining wall, bridge, or storage tank,
transfers live and dead loads from the structure to the ground. Besides
providing support, or adequate bearing capacity, the foundation must keep
settlements within an acceptable range for the structure. Foundations vary from
the simple preparation of a patch of ground to elaborate arrays of long steel
piles driven to great depths. Other foundation types include rafts, footings,
caissons, many types of piles, stone columns, grouted soil, frozen soil,
mechanically reinforced soil, and hybrid combinations of these.
The bearing capacity
of a foundation element depends on its ability to resist a shear failure, that
is, a loss of stability. The principles of static equilibrium that govern
stability of slopes also control foundation stability. The sum of the resisting
forces must exceed the sum of the driving forces. See also: Foundations
Shallow
In practice,
engineers design most shallow foundations by using semiempirical formulas that
combine the concepts embodied in the theories with the experience gained by
measuring the performance of actual foundations. Most shallow foundations have a
large factor of safety against a general shear failure (3 or above) because
restrictions on allowable settlement usually prove much more stringent and
result in low allowable bearing stresses.
For either drained or
undrained conditions, elastic theory predicts the stress change at any depth
below a loaded area. The change in stress produces a strain in accordance with
Hooke's law. The sum of the individual strains from the footing base to some
depth where the stress change becomes negligible equals the settlement of the
footing. In the case of shallow foundations on fine-grained soils, additional
settlement will occur because of time-dependent consolidation under the applied
load. Difficulties arise in selecting the appropriate elastic parameters,
Young's modulus and Poisson's ratio, for the anticipated drainage and stress
conditions. The stress path method, which attempts to simulate the anticipated
changes in the state of stress with soil samples in the laboratory, can aid the
engineer in selecting correct parameters. See also: Elasticity; Young's modulus
Deep
Where soils of
adequate strength do not lie sufficiently close to the ground surface, deep
foundations can transfer the loads to stronger soil strata or distribute the
loads throughout a greater mass of soil. Deep foundation elements, such as
caissons or piles, can develop support along their entire length as well as at
their base or tip. See also: Caisson foundation
Friction piles
develop resistance primarily through shear resistance (skin friction) along
their length. End-bearing piles develop resistance primarily at their tip by
bearing on firmer soil or rock. Most piles combine the characteristics of the
two pile types. Pile equipment has evolved that can drive the piles into the
ground with powerful hammers, vibrate the piles through soil, or place the piles
in predrilled holes. Pile widths or diameters range from about 4 in. (10 cm) for
minipiles to several feet for offshore oil platforms, with lengths up to several
hundred feet. Common pile materials include steel, concrete, and wood.
Caissons or drilled
piers usually have greater diameters than piles and rely on end-bearing support.
Their construction involves excavation instead of driving, and it often allows
visual inspection of the ultimate bearing surface.
Tests and
properties
Field and laboratory
tests are used to determine soil properties. Those conducted in the field
measure density, permeability, shear strength, penetration resistance,
compressibility, and deposit boundaries. Those done in the laboratory measure
water content, expansion index, grain size distribution, permeability, shear
strength, dynamic stress, resonant frequency, and mineral composition.
The broad range of
geotechnical instrumentation includes piezometers for measuring ground-water
pressure, earth pressure cells for measuring total stress in soil, settlement
plates for measuring vertical displacements, extensometers for determining
deformation, tiltmeters for measuring inclination, inclinometers for measuring
lateral deformation versus depth, piezoelectric transducers for measuring
acoustic emissions, load cells for measuring load in a structural member, strain
gages for measuring strain in a structural member, and various devices for
measuring temperature.
Other soil engineering
problems
A naturally occurring
material such as soil presents geotechnical engineers with several particularly
difficult problems. In addition to the complexities of working with a
nonhomogeneous material with nonlinear anisotropic stress–strain
properties, the strength varies from point to point, may vary with time or
deformation, and remains difficult to measure precisely. The simple examples
that have been discussed illustrate the fundamentals of soil mechanics.
Engineers routinely extend and apply these fundamentals to the complicated
conditions encountered in the field. Some of these applicationsinclude two- and
three-dimensional problems; dynamic loading of soil; construction of
earthquake-resistant facilities; earth pressures and retaining walls,
tunnels, and excavations; subsidence; problems involving expansive soils; field
exploration; probability and reliability; and the use of synthetic materials
such as fabrics, membranes, and superlight fills. See also: Clay; Construction
methods; Engineering geology; Retaining wall; Sand; Soil; Tunnel
Bibliography
American Society for
Testing and Materials, Annual Book of ASTM Standards, sect. 4: Construction,
vol. 04.08: Soil and Rock; Building Stones, Geotextiles,
1989
H. R. Cedergren,
Seepage, Drainage and Flow Nets, 3d ed., 1997
R. F. Craig, Soil
Mechanics, 6th ed., 1997
B. M. Das,
Fundamentals of Soil Dynamics, 1983
J. Dunnicliff,
Geotechnical Instrumentation for Monitoring Field Performance,
1988
T. W. Lambe and R.
V. Whitman, Soil Mechanics, 1969
J. K. Mitchell,
Fundamentals of Soil Behavior, 2d ed., 1993
K. Terzaghi and R.
B. Peck, Soil Mechanics in Engineering Practice, 3d ed.,
1996
U.S. Navy, Soil
Mechanics, Design Man. 7.01, 1986
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