less disparity in soil strength, soil mechanical and physical indicators in the Ultimate Bearing Capacity formula could be a weighted average?、
cand? of sliding within the depth of layers of soil, And the following
formula to estimate the maximum depth of the bearing stratum
zmax??b?
λ——Subsoil average angle of internal friction and load ramp rate, look-up table 5.6 we have.
5.9.3 Meyer Hove Formula
The ultimate bearing capacity formula put forward by Meyer hoff is derived on the basis of the shape of the sliding surface in Figure 5.33.He assumes that when the overall shear failure occurs, the local base sliding surface of the foundation not only below the underside of the foundation, but also extends upward.For shallow foundations, extending to the ground g point, but for deep foundation, does not extend to the ground surface, and intersect at the side of the foundation.Figure 5.33 (a) the sliding surface shape is composed of three parts, namely linear me, logarithmic spiral ef, straight line fg,Wherein me and the horizontal angle of 45???2
Figure 5.33
When computing, take cmefg for out of the body, take the role of the ultimate load on the cm surface,Interaction between soil and foundation side BC and the influence of foundation soil on both sides of CGB weight W, can be taken place of the equivalent stress σ0 and shear stressτ0 on the plane CG .Its value should be determined by trial.In considering the balance of the soil can be removed CGB soil with equivalent free surface CG instead. Assume that CG surface and horizontal plane Angle for the beta, it increases with embedded depth of foundation deepen,The normal stress σ0, based on the side sigma 0 by the static
earth pressure distribution, Angle between CG and cf for the η.First calculate,σ0、τa andηvalue, again by the balance condition of basal triangular wedge cme ,respectively,calculated bearing capacity due to the cohesion c and Weight of Soil
pu?cNc??oNq??bNr （5.45）
12 σ0——Equivalent on the free surface normal stress ?0??d(Kosin2??Kotan?sin2??cos2?)1212 KO——Coefficient of earth pressure at rest；
（5.46）
μ——Poisson's ratio;
δ——Angle of friction between the side of the foundation and soil； β—— the equivalent free surface and horizontal Angle In figure 5.34;
Nc、Nq、Nγ——Bearing capacity factor, as shown in figure 5.34
Figure 5.34
Meyer Hoff proposed the foundation sliding surface shape of the deep foundation as shown in Figure 5.34 (b) below.For this sliding surface shape, it can be used to calculate the axial bearing capacity of single pile.
In addition to the above two types of ultimate bearing capacity calculation methods,Skye Town apply to the ultimate bearing capacity formula.of saturated soft clay (??0) Assume that the sliding surface shape in the plastic balance area,Prang del derived,The logarithmic spiral degenerate arc,So the basal surface and slip surface changed
from45???2 to 45 ° Angle.Out of sliding surface and the horizontal
?2plane Angle is from 45?? to 45 °,As shown in Figure 5.35.Therefore,
Skye Town solution can be regarded as one of the special case of the prandtl -Reissene solution.
Figure 5.35
Skye Town semi-empirical formula is as follows:
bdpu?5c(1?0.2)(1?0.2??od)lb
b、l——width and length of basis,m；
d——Foundation depthm；
c——The cohesive force of soil，Taken on the basis of the following 0.707b within the depth of the average，kPa；
γo——The average of severe soil above the base ，kN/m3。