He is a member of the Chinese Society for Rock Mechanics and Engineering and the Shaanxi Society for Rock-Soil Mechanics and Engineering. He is a member of the American Society of Civil Engineers (ASCE) and the International Society for Soil Mechanics and Geotechnical Engineering (ISSMG).
Introduction
The basic variables are the height of the wall H and the burial depth D, together with the strength and stiffness of the wall and the forces in any anchors or supports. The basic design requirements are complex and include overall stability, ground movement limitation, and the wall's bending and shear resistance.
Soil Composition and Phase Relationships
The following relationships are defined according to figure 1) The water content (w), or moisture content, is the ratio between the mass of water and the mass of solids in the soil. The unit weight (γ) of a soil is the ratio of the total weight (a force) to the total volume, i.e. 3) The specific gravity of the soil particles (ds) is given by ds= ms. where is the particle density.
Soil Fabric
This kind of soil is quite unstable and will cause large deformation under water immersion or external force. The soil grains of this kind of material arrange randomly and have large pores, consequently it will show low strength and high compressibility, meanwhile it is sensitive to disturbance.
Particle Size Analysis
Thus, the honeycomb tissue is created, which has large cavities, as can be seen in fig. The particle size corresponding to any specified value on the "percent less" scale can be read from the particle size distribution curve.
Density Properties for Granular Soils
This method is based on Stokes' law, which controls the rate at which spherical particles settle in a suspension: the larger the particle, the greater the sedimentation rate and vice versa. the technical properties of this type of soil. The wider the range of particle sizes present, the greater the maximum density (i.e. the voids between the larger particles can be filled with smaller particles).
Plasticity Properties of Soils
The liquid and plastic limits of the water content range are defined as the plasticity index Ip, that is, the same process is carried out in other samples, and the average water content is indicated as the plastic limit of the soil.
Soil Compaction
Note that A is the cross-sectional area of the soil perpendicular to the direction of flow. The additional stress at the center of the foundation is calculated by the following equation, viz. Find the additional stress distribution under points O and A on the foundation (the calculation depth is 3b, b is the width of the foundation).
Engineering Classification of Soils
Permeability of Soil and Seepage Force 31
Capillary Phenomena
The water particles are suspended in the soil particles and have no connection with the capillary water in the middle and lower part. The rise of capillary water is therefore one of the main factors that cause damage to the road surface.
Groundwater Movement and Darcy’s Law
Based on the above flow characteristics, the flow is commonly called laminar flow. Based on the above flow characteristics, this flow is commonly referred to as turbulent flow.
Determination of Permeability Coefficient
When all the variables on the right side of Eq. 2.5) has been determined from the test, the permeability coefficient of the soil can be calculated. The reference values for the coefficient of permeability for some soil types are given in Table 2.1. Other factors remaining the same, the coefficient of permeability decreases with increasing thickness of the diffuse double layer.
Flow Nets
Assume that the flow elements are square (b = l) and assume that dq denotes the flow through the flow channel per unit length of the hydraulic structure (ie, perpendicular to the section shown). Assume that there are no potential points and flow channels in a flow network, then the drainage rate per unit length of the hydraulic structure is 2.18) In addition, if the values of the flow net are given, the hydraulic head, hydraulic gradient, seepage amount, pore water pressure and seepage force at any point in the seepage field can be calculated.
Seepage Force
As the flow direction changes, the drainage force will have different effects on the soil, as shown in Fig. When upward drainage occurs, the direction of the drainage force and gravity is completely opposite, reducing the effective stress. When lateral drainage occurs, it is convenient to calculate the pore water pressure using the flow net.
Critical Hydraulic Gradient
Stress Distribution in Soil 55
Stresses Due to Self-Weight
Tensions in the soil are caused by the external loads exerted on the soil and by the soil's own weight. If the soil is stratified and the unit weight is different for each layer, the vertical stress can be easily calculated by the summation, as shown in a) Geologic Section and (b) Geostatic Stress Distribution. If the unit weight of the soil varies continuously with depth, the vertical stress can be evaluated using the integral.
Effective Stress Principle
The total vertical stress (ie the total normal stress on a horizontal plane) at depth C is equal to the weight of all the materials (solids + water) per area unit above this depth, i.e. Calculate and plot the total normal stress distribution, pore water pressure distribution and the effective normal stress distribution of the soil along the depth direction. The distribution of the total normal stress, pore water pressure and effective normal stress of the soil along the depth direction is shown in Fig.
Contact Pressure between the Foundation
The magnitude and distribution pattern of the contact pressure has an important influence on the stress increment induced in the soil. When the resulting displacement e is equal to l/6, pmin is zero and the contact pressure distribution curve is triangular. Iy=lb3/12 represents the moment of inertia for the area of the underside of the foundation around the Y–Y axis.
Additional Stress in Ground Base
Additional stress coefficient αc under the angle of the bottom of a rectangular foundation due to a vertical load. Rectangular foundation subjected to a triangularly distributed load. 3.29) where this is the coefficient of the additional stress under the corner of the bottom of a rectangular foundation due to a vertical triangular load. Additional coefficient of stress at the angle of the bottom of a rectangular foundation due to a vertical triangular load.
Additional Stress in Plane Problem
The additional stress on the center of the foundation due to each load can be calculated and the calculation process is shown in Table 3.9. The shear strength of the sandy soil is determined by the normal effective stress and the angle of internal friction. The slope will slide easily when the shear stress of the soil mass exceeds its shear strength.
Compression and Consolidation of Soils 101
Compressibility Characteristics
Since the change in the pressure range caused by external loading is small, eg, from p1top2 (see Fig. 4.3), the curve M1M2. The compression index (Cc) is the slope of the linear part of the e-lgp plot (see Fig. 4.4) and is dimensionless. For any two points on the linear part of the graph, Cc is given by:
Calculation of Settlement of Foundation
The shortcomings of the layer-by-layer summation method can be analyzed from the following factors: calculation and distribution of additional stress, selection of compression indicators and soil layer thickness. In addition, there is no strict theoretical basis for measuring the thickness of the compression layer. The determination of the thickness is based on a semi-empirical method, which is verified only by engineering measurements.
One-Dimensional Consolidation Theory
The slope is unstable due to the increase in unit weight and soil shear stress. Therefore, the angle of repose of the slope of unconsolidated soils is equal to the angle of friction of the soil. For a unit of soil mass, the effective unit of soil weight is the floating weight γ.
Shear Strength 123
Mohr–Coulomb Failure Criterion
A stress state can be represented either by a point with coordinates τ and σ(σ) as shown in Fig. For a given stress state, it is clear that, because σ1 = σ1−u and σ3=σ3−u, the Mohr circles for the total and effective stresses have the same diameter, but their centers are separated by the corresponding pore water pressure u . To determine the stresses in an arbitrarily inclined section a–a through the sample shown in Fig.
Shear Strength Tests
Effective Stress Paths
The horizontal distance between the effective and total stress path is the value of the pore water pressure. The effective and total voltage paths (denoted by ESP and TSP, respectively) for the triaxial tests are shown in figure. The detailed shape of the effective stress paths for the CU tests depends on the pore water pressureu.
Characteristics of Shear Strength of
The nature of the change in void ratio with deformation for loose and dense sands is shown in Fig. The concept of critical void ratio was first introduced by Casagrande in 1938 to study the liquefaction of granular soils. If the initial void ratio is small and the surface of the soil particles is rough, then the angle of internal friction of the well-graded soil is larger.
Characteristics of Shear Strength of Cohesive Soil . 135
Thus, the Mohr–Coulomb envelope equation can be given by τf = σtanϕ. The slope of the collapse envelope will give us the angle of soil friction as follows:. After the excess pore water pressure generated by the confining pressure is completely dissipated, the deviatoric stress increases, causing the specimen to fail. The overall stress failure envelope for an overconsolidated clay will be of the nature shown in Fig.
Introduction
In the state of local shear failure, there is a significant compaction of the soil under the footing and only partial development of the state of plastic equilibrium. The punch shear failure occurs when there is compression of the soil under the footing, accompanied by displacement in the vertical direction around the edges of the footing. There is no heaving of the ground surface away from the edges and no tilting of the footing.
Critical Edge Pressure
It can be seen that pcr depends on ϕ, γ0, c and d, and is independent of the width of the foundation. It is generally accepted that the maximum depth of the plastic zone under a central load can reach a quarter of the width of the foot. Under a small eccentric load, the maximum depth of the plastic zone is allowed to reach 1/3 of the width of the foundation.
Prandtl’s Bearing Capacity Theory
The slope of cohesionless soils is stable if the slope angle is smaller than the soil friction angle. Determining the slope of the failure surface is one of the key requirements in slope stability analysis. The slope of cohesive soil does not slide on the failure surface of the slope without cohesive soil.
Modification of Prandtl’s Bearing Capacity Theory . 150
Slope Stability Analysis 161
Factors and Engineering Measures that Influence
Therefore, additional attention should be paid to the influence of external influencing factors for greater stability and safety of the slope. If the slope of the foundation pit is too gentle, it will increase the working load and affect the adjacent buildings. If the building is far from the slope, the slope is not affected.
Stability Analysis of Cohesionless Soil Slope
Thus, the stability of the slope of homogeneous cohesionless soil depends only on the angle of inclination and is independent of the height of the slope. A rapid lowering of the water table will cause a seepage force in the soil of the slope surface, making the slope unstable without soil cohesion. Therefore, when seepage is along the slope, the slope safety factor of non-cohesive soils is halved.
Stability Analysis of a Cohesive Soil Slope
Thus, the factor of safety for slope calculation can be simplified by using the assumption of the circular arc failure surface. The formula for the factor of safety can be established using the static force equilibrium conditions for each disc. The sum of the sliding moment generated by the body force Wi for each disk is. 7.14).
Stability Number Method
Earth Pressure and Retaining Walls 187
Earth Pressure on the Retaining Wall
Calculation of the At-Rest Earth Pressure
Rankine’s Earth Pressure Theory
Coulomb’s Earth Pressure Theory
Design of Earth-Retaining Structures
