真空预压与真空井点降水用于软土处理的机理差异

真空预压与真空井点降水两种工艺均可用于软土地基处理，表观上两者都是通过抽真空使土体内孔隙水排出并使软土沉降，但目前对两者的工艺和机理等关键差异的认识不深入，难以有效指导现场施工。真空预压和真空井点降水在抽真空设备、竖向排水通道和密封边界等设备与工艺方面有显著差异；两者的的排水机理也有着本质区别。真空预压的加固机理是负压作用下土体发生塑料排水板水平向排水固结，同时塑料排水板内的水向上流动与重力无关；真空井点降水的加固机理是群井抽水引起地下水位降低，土体的浮重度变为湿重度导致荷载增大使土体沉降，同时井点管内的水向上流动受重力影响。在工艺和机理的差异分析的基础上，进一步明确了真空预压和真空井点降水在10个关键方面的差异，包括加固机理、影响深度、不同深度的真空传播、土体水平变形、竖向排水与重力的关系、抽真空位置影响、与外界是否连通、影响区成因、地下水位变化、是否形成非饱和带。

Mechanism difference between vacuum preloading and vacuum well dewatering for soft soil treatment

Both vacuum preloading and vacuum well dewatering can be used for the improvement of soft soil foundation.Apparently，both of them drain out pore water through vacuum and make the soft soil consolidate.However，if the understanding of the key differences between the two technologies and mechanisms is not clear，it is difficult to effectively guide the on-site construction.There are significant differences between vacuum preloading and vacuum well dewatering in vacuum pumping equipment，vertical drainage channels and sealing boundaries.The drainage mechanism of the two is also fundamentally different.The mechanism of vacuum preloading is that the soil mass is consolidated horizontally towards prefabricated vertical drains(PVD) under negative pressure difference，and the upward flow of water in the PVD is independent of gravity.The mechanism of the vacuum well dewatering is that the groundwater level decreases due to the pumping of group wells，thus makes the soil unit weight to change from buoyant unit weight to the wet unit weight，resulting in additional loading and consolidation，and the water inside the well pipe is affected by gravity.On the basis of the difference analysis of process and mechanism，the differences between vacuum preloading and vacuum well dewatering in 10 key aspects are further clarified，including reinforcement mechanism，influence depth，vacuum propagation at different depths，soil horizontal deformation，relationship between upwards water flow and gravity，influence of vacuum pumping location，connectivity state with the outside environment，cause of influence area，changes in groundwater level，and formation of unsaturated zone.