反压施加是提高土体饱和度的常用有效方法，但易引起土体强度参数表观偏离。采用标准球形玻璃珠砂，开展基准固结不排水（consolidated undrain，CU），固结排水（consolidateddrained，CD）及干样试验，对偏应力与孔压（或体积应变）数据进行实时精准测记与对比分析，借助p'-q应力路径图，显著呈现并定量分析了反压施加对土体力学特性的影响规律，初步厘清了反压施加对土体强度的影响机制。反压设置对CU试验结果影响显著，孔压发展形态控制着偏应力发展的形态，最终影响强度参数的确定，但应力路径始终约束在修正类剑桥模型的框架范围内。孔压发展模式和速率主要受限于反压设置大小及试样相对密实度，反压越大，孔压潜在变化幅度越大，进而导致偏应力变化区间增大；相对密实度越大，孔压发展速率越大，偏应力增速渐大。初始状态相同时，CU试验孔压发展与CD试验体积应变发展趋势高度一致，展示了试样体积应变势在不同边界条件下的共同本质。初步给出了临界状态时CU残余强度定量预测公式，根据相对密实度及反压值可初步定量评定残余孔压值，进而可确定CU残余强度。 The back pressuresaturation method

a widely adopted and efficient technique for enhancing soilsaturation

can nonetheless introduce notable deviations in soil strengthparameters. Standard spherical glass bead sand was utilized for conductingbenchmark consolidated undrained (CU)

consolidated drained (CD)

and drysample tests. Real-time accurate measurements and comparative analyses ofdeviatoric stress and pore pressure (or volumetric deformation) data wereperformed. Utilizing the p'-q stress path diagram

the influenceof back pressure application on soil mechanical properties was significantlydemonstrated and quantitatively analyzed

thereby preliminarily elucidating themechanism of back pressure influence. The setting of back pressure significantlyimpacts the results of CU tests

where the shape of pore pressure developmentgoverns the shape of deviatoric stress development

ultimately influencing thedetermination of strength parameters. However

the stress path remainsconstrained within the framework of the revised Cam-Clay model. The mode andrate of pore pressure development are primarily constrained by the magnitude ofthe back pressure setting and the relative density of the sample. As backpressure increases

the potential change in pore pressure also increases

resulting in a greater amplitude of deviatoric stress change. Similarly

ahigher relative density leads to a faster development rate of pore pressure andan increased rate of deviatoric stress. Under identical initial conditions

thedevelopment of pore pressure in CU tests exhibits high consistency with thedevelopment of volume deformation in CD tests

revealing the common essence ofthe sample’s volumetric deformation potential across different boundaryconditions. A quantitative prediction formula for the residual strength of CUtests at the critical state is presented. The residual pore pressure value canbe initially quantified based on the relative density and back pressuremeasurements

subsequently leading to the determination of the residualstrength of CU.