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某石化厂大化肥装置建在浙东海滨软土地基上,当地软基强度低,变形大。而装置区内露天构筑物多,重量轻,变形要求高。利用硬壳做成天然地基时,若按常规作法是先强度校核,后变形验算。对小面积基础,一般强度满足,变形不会过大。而基础稍大,即使强度满足,但压缩层厚度伸展到硬壳下面的淤泥质软土,变形就大大增加,超过了工艺要求。这时,基础的设计就由变形控制。我们在设计时,考虑硬壳层超固结土的前期固结压力P_e的影响。用硬壳层前期固结力与自重应力之差作为超固结储备,再反算基础外荷载,并将不同的基础尺寸和求得的相应外荷值,画成图表。设计时,直接选用。这样既满足强度要求,又控制变形要求,减少冗繁的变形计算。使压缩应力图形大部分在硬壳层,变形就能满足工艺要求。
A large-scale fertilizer plant of a petrochemical plant was built on the soft soil foundation of the east coast of Zhejiang Province. The local soft base has low strength and large deformation. There are many open-air structures in the installation area, light weight and high deformation requirements. When hard shells are used to make natural foundations, the conventional method is to check the strength first and then check the deformation afterwards. For a small area foundation, the general strength is satisfied and the deformation will not be too large. On the other hand, if the foundation is slightly larger, even if the strength is satisfied, the thickness of the compression layer is extended to the silty soft soil beneath the hard shell, and the deformation is greatly increased, exceeding the technological requirements. At this time, the basic design is controlled by the deformation. When designing, we consider the influence of the pre-consolidation pressure P_e of the hard-shell overconsolidated soil. The difference between the pre-consolidation force of the crust and the self-weight stress is taken as the over-consolidation reserve, and then the base load is reversed, and the different base dimensions and the corresponding load values obtained are plotted as a graph. Designed for direct use. This will not only meet the strength requirements, but also control the deformation requirements and reduce the tedious deformation calculations. Most of the compressive stress pattern is in the hard shell layer, and deformation can meet the process requirements.