土木工程岩土外文翻译

1 Basic mechanics of soils

Loads from foundations and walls apply stresses in the ground. Settlements are caused by strains in the ground. To analyze the conditions within a material under loading, we must consider the stress-strain behavior. The relationship between a strain and stress is termed stiffness. The maximum value of stress that may be sustained is termed strength.

1.1 Analysis of stress and strain

1）Special stress and strain states

2）Mohr circle construction

3）Parameters for stress and strain

Stresses and strains occur in all directions and to do settlement and stability analyses it is often necessary to relate the stresses in a particular direction to those in other directions.

normal stress σ = F n / A

shear stress

τ = F s

/ A normal strain ε = δz / z o

shear strain

γ = δh / z o

Note that compressive stresses and strains are positive, counter-clockwise shear stress and strain are positive, and that these are total stresses (see effective stress).

1.1.1 Special stress and strain states

In general, the stresses and strains in the three dimensions will all be different.

There are three special cases which are important in ground engineering:

General case princpal stresses

Axially symmetric or triaxial states

Stresses and strains in two dorections are equal.

σ'x = σ'y and εx = εy

Relevant to conditions near relatively small foundations,

piles, anchors and other concentrated load s.

P lane strain:

Strain in one direction = 0

εy = 0

Relevant to conditions near long foundations,

embankments, retaining walls and other long structures.

One-dimensional compression:

Strain in two directions = 0

εx = εy = 0

Relevant to conditions below wide foundations or

relatively thin compressible soil layers.

Uniaxial compression

σ'x = σ'y = 0

This is an artifical case which is only possible for soil is

there are negative pore water pressures.

1.1.2 Mohr circle construction

relate to a particular plane within an element of soil. In

general, the stresses on another plane will be different.

To visualise the stresses on all the possible planes,

a graph called the Mohr circle is drawn by plotting a

(normal stress, shear stress) point for a plane at every

possible angle.

There are special planes on which the shear

stress is zero (i.e. the circle crosses the normal stress

axis), and the state of stress (i.e. the circle) can be described by the normal stresses acting on these planes; these are called the principal stresses '1 and '3 .

1.1.3 Parameters for stress and strain

In common soil tests, cylindrical samples are used in which the axial and radial stresses and strains are principal stresses and strains. For analysis of test data, and to develop soil mechanics theories, it is usual to combine these into mean (or normal) components which influence volume changes, and deviator (or shearing) components which influence shape changes.

In the Mohr circle construction t' is the radius of the circle and s' defines its centre. Note: Total and effective stresses are related to pore pressure u:

p' = p - u s' = s - u q' = q t' = t

1.2 Strength

The shear strength of a material is most simply described as the maximum shear stress it can sustain: When the shear stress is incre ased, the shear strain increases; there will be a limiting condition at which the shear strain becomes very large and the material fails; the shear stress f is then the shear strength of the material. The simple type of failure shown here is associated