桩基沉降计算的几个问题

针对密桩桩基、疏桩桩基两类桩型沉降计算方法，分析了沉降压缩层的分层原则、沉降计算点、应力计算点的选取原则；探讨了附加应力、沉降计算深度、压缩层厚度等指标的影响因素、计算指标取值，并给出了压缩层厚度计算公式；对长桩疏桩桩基，分析了沉降量的变化规律，提出了减少桩基沉降的建议和应对措施。

Numerical Analysis of Highway Subgrade above an Elliptical Karstic Rock Cavern

This paper presents the numerical analysis results of the stability of highway subgrade above an elliptical karstic rock cavern. The factor of safety, development of the potential failure plane, which defined as the connection of the plastic zones and the shear strain rates, are used as the failure criteria. The thickness of the overburden material, shape, horizontal distance of the embankment toe to the cavern on the stability of the highway subgrade above the elliptical karst rock cavern are investiga ted. The results indicate that the settlement shape of the subgrade is a cone type and the magnitude of the settlement is reduced with the increase of the overburden material. The factor of safety will also increase and tends to stable. The failure patterns of the subgrade above the cavern are： tensile failure of the overburden rock and shear failure of the embankment above. For ellip soid karstic rock cavern, the roof thickness was less than that for horizontal cavern roof.