青藏铁路旱桥冻胀力的弹塑性分析

假设土体在冻结前已固结完毕,冻结过程中土体为具有弹塑性本构特征的各向同性体,土中的水分迁移符合达西定律,且土颗粒不可压缩。在给出冻土温度场、水分场基本方程及冻土弹塑性本构方程后,应用弹塑性有限元法,模拟旱桥施工过程。依次求出旱桥在围岩自重作用下的初始应力场、当前应力水平下围岩的温度场和体积膨胀引起的等效节点荷载,再求出上述荷载增量对应的应力增量和当前的围岩应力场,重复上述计算步骤直到规定年限。本文对青藏铁路旱桥单桩冻胀过程中在未来20年的应力场进行模拟计算,结果表明旱桥仅在靠近桥桩底部产生塑性应变,且塑性应变区很小,该旱桥是安全的。另外,本文提供分析寒区旱桥冻胀的理论与数值计算方法,可为类似工程设计提供参考。

Elastic plastic Analysis of Frost-heaving Forces of Land Bridges of the Qinghai-Tibet Railway

It is assumed that the soil body has already been consolidated before freezing,the soil body is considered an elastic-plastic isotropic body during the process of freezing,the water migration of the soil is assumed to obey the Darcy Law and soil particles cannot be compressed.The mathematical mechanical model and governing differential equations for solution to the coupled problem of temperatures,moisture migrating and stress fields with phase changes are derived from the theories of heat transfer,moisture migration and frozen soil mechanics.Using the elastic-plastic finite method and mechanics test data of soils,the construction process of the land bridge is simulated.The initial stress field of the surrounding soil subjected to its gravity load,the temperature field of the surrounding soil at the present stress level and the equivalent nodal load increments resulting from volume expansion are calculated successively.The stress increments corresponding to the nodal load increments and the present stress fields of the surrounding soil are worked out by FEM.The above calculation steps are reapeated until reaching the limit of the service life of the land bridge.Using the finite element formulas,nonlinear analysis is made for the frost-heaving process of the land bridge in the next 20 years.The results show that only soil at the foot of the pile generates plastic deformation and the deformation is quite small,therefore,the studied land bridge is safe.