Effect Of Sratic Load On Pore Pressure Variation Of Sandy Soil

In this paper,the independent developed high-precision pore pressure monitoring facility is used to monitor the total suction of unsaturated soil and the total pore water pressure of saturated soil.The test plan is to conduct coupling design for water injection,drainage,static observation,application of different loads(three levels of load in total)and change of loading mode(pre load or post load at static water level)of soil in the sand box,and monitor the pore pressure and soil settlement in the whole process.Studying the variation law of pore pressure in the process of water level rise and fall under the coupling conditions of load and no load,and the response of soil settlement to the change of pore pressure.The research conclusions mainly include:(1)It is the first time to(propose and)prove the existence of unsaturated soil stress field.The pore gas pressure(suction)with gradient change is measured in the dry sand area above the water level that exceeds the rising height of capillary water,which reveals that the pore pressure in the field is not limited to the combination of pore pressure sub items determined by geotechnical test parameters.(2)The adaptability of Terzaghi’s one-dimensional consolidation theory to sand(medium sand)is questioned.The pore pressure is synchronized and stable after loading at the high water level(submerged state)with stable load or after loading at the stable high water level.The excess pore water pressure remains unchanged after standing for20 to 30 minutes,and maintains a high value.According to the basic assumption of Terzaghi’s one-dimension consolidation theory,the stable excess pore water pressure should be zero.(3)The negative pore pressure is the effective stress.The essence of effective stress is the stress that can produce soil deformation.In vacuum preloading of saturated soil,since the total stress is zero,the effective stress is equal to the negative pore pressure.In this paper,there is a corresponding relationship between the settlement of unsaturated soil and the negative pore pressure,that is,when the negative pore pressure in unsaturated soil exceeds the historical negative pore pressure,the compression settlement will inevitably occur.