The Deformation Character Test And Numerical Simulation Research For The Soft Clay In The Unloading Condition

The deformation character of the soft clay in the unloading condition is very important for the geotechnical engineering deformation calculations,such as in the bottom heave calculatioin caused by the excavation in the foundation ditch engineering,and the resillience calculation caused by the surcharge preloading in the heap preloading treated foundation,and so on.Compared with the loading indoor test ,the unloading indoor test is excuted in order to anlayse the deformation character of the soft clay in the unloading condition,and based on this,the numerical similation research to the indoor test and a engineering example is done.The displacement-time relationship curve is got from the indoor test for the deformation character analysis of the soft clay in the unloading condition,and the following conclusions are gained from the anlaysis of the test results:(1)in the intial period of the whole unloading process,the resillience amount is very small,and when the unloading amount is big enough,the resillience amount rise up rapidly ;(2)in every level of unloading process,the instantaneous resillience is produced in the very moment of the unloading action,and then the resillience deformation rate decreases,until no more resillience increases;(3)the unloading resillience amount increases with the increase of the amount of the initial preloading.The finite element analysis software ABAQUS is used to simulate the indoor test,and the displacement-time relationship curve is got from the numerical simulation analysis,what revealed the following results:(1)the numerical calculated deformation increment is bigger than the deformation increment got from the indoor test in the initial and last period of the whole unloading process,but fit well in the whole period;(2)in every level of unloading process,the displacement-time relationship curves from the numerical sumulation analysis fit well with the displacment-time relationship curve from the indoor test,which produces a huge amount of instantaneous resillience,and then the deformation rate decreases with the time,and tends to be stable at last;(3)With the same loading-unloading amount,the deformation in the unloading condition is much smaller than that in the loading condition,which is about one tenth of the that.The numerical simulation of the deformation in the effect of the unloading of the surcharge preloading in the heap preloading treated foundation in the Sixin South Road in the New District in Wuhan is done through the finite element analysis soft ABAQUS,and the following conclusions are displayed:(1)on the surface of the foundatioin,the settlement decreases with distance from the center of the surface,that is ,in the center ,the biggest settlement is produced ,and at abount 20m away from the center,the heave is produced ;(2)after unloading,the resillience emerges in the palces where the settlement was produced,and the heave which was produded drops too.(3)The deformation of the center of the surface and the nodes not far away from the center suits well with the loading-unloading curve;(4)after unloading,the resillience is produced on every node on the vertical axial cord,and similar to the doformation regular pattern ,which is smaller and smaller from up to down.