The relationship among the surface fissure ratio,moisture content,seepage coefficient and deformation modulus of field unsaturated expansive soil in Nanning,Guangxi Province,China,was obtained by a direct or indirect method.Digital images of expansive soil of the surface fissure with different moisture contents were analyzed with the binarization statistic method.In addition,the fissure fractal dimension was computed with a self-compiled program.Combined with in situ seepage and loading plate tests,the relationship among the surface fissure ratio,moisture content,seepage coefficient and deformation modulus was initially established.The surface fissure ratio and moisture content show a linear relation,"y=0.019 1x+1.028 5" for rufous expansive soil and "y=0.071x+2.610 5" for grey expansive soil.Soil initial seepage coefficient and surface fissure ratio show a power function relation,"y=1×10-9 exp(15.472x)" for rufous expansive soil and "y=5×10-7 exp(4.209 6x)" for grey expansive soil.Grey expansive soil deformation modulus and surface fissure ratio show a power function relation of "y=3.935 7exp(0.993 6x)".Based on the binarization and fractal dimension methods,the results show that the surface fissure statistics can depict the fissure distribution in the view of two dimensions.And the evolvement behaviors of permeability and the deformation modulus can indirectly describe the developing state of the fissure.The analysis reflects that the engineering behaviors of unsaturated expansive soil are objectively influenced by fissure.
The pile soil system interaction computational model in liquefaction-induced lateral spreading ground was established by the finite difference numerical method.Considering an elastic-plastic subgrade reaction method,numerical methods involving finite difference approach of pile in liquefaction-induced lateral spreading ground were derived and implemented into a finite difference program.Based on the monotonic loading tests on saturated sand after liquefaction,the liquefaction lateral deformation of the site where group piles are located was predicted.The effects of lateral ground deformation after liquefaction on a group of pile foundations were studied using the finite difference program mentioned above,and the failure mechanism of group piles in liquefaction-induced lateral spreading ground was obtained.The applicability of the program was preliminarily verified.The results show that the bending moments at the interfaces between liquefied and non-liquefied soil layers are larger than those at the pile’s top when the pile’s top is embedded.The value of the additional static bending moment is larger than the peak dynamic bending moment during the earthquake,so in the pile foundation design,more than the superstructure’s dynamics should be considered and the effect of lateral ground deformation on pile foundations cannot be neglected.
