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为增加试样饱和度而采用反压饱和是室内三轴试验中普遍采用的技术手段,但现行规范对试样中反压取值没有具体规定。通过对福建标准砂的一系列固结不排水和固结排水三轴试验,分析了不同反压、围压下饱和砂土的应力–应变关系、孔压发展规律,并分析了几种常用破坏取值标准下土体强度指标的差异。试验结果表明固结不排水三轴试验中,反压对砂土应力应变关系、孔压发展有明显影响,从而影响强度取值;而在固结排水试验中,施加不同的反压对于砂土抗剪强度则基本无影响。在不排水剪切中,建议反压设为300～500 kPa,且在同一组试样中采用统一的反压对试样进行饱和。在破坏标准上,建议采用最大有效主应力比(1/3)max对应强度作为砂土的不排水抗剪强度;而在考虑土体残余强度时,建议采用超静孔压下降为零为破坏标准。
In order to increase the sample saturation and the use of backpressure saturation is commonly used in indoor three-axis test techniques, but the current norms of the sample back pressure value is not specified. Through a series of three-axis tests of undrained and consolidated drainage of consolidated sand in Fujian, the stress-strain relationship and pore pressure of saturated sands under different backpressure and confining pressure were analyzed, and several commonly used damages Difference of soil strength index under the standard value. The test results show that in the consolidated undrained triaxial test, the back pressure exerts a significant influence on the stress-strain relationship of sand and pore pressure and affects the strength value. In the consolidated drainage test, different backpressures are applied to the sand Shear strength is basically no effect. In undrained shear, it is recommended that the backpressure be set at 300 to 500 kPa, and the sample should be saturated with uniform backpressure in the same group of specimens. In terms of failure criteria, it is recommended that the maximum effective principal stress ratio (1/3) max be used as the undrained shear strength of sandy soil. When considering the residual strength of soil, it is recommended that the excess pore water pressure be reduced to zero to destroy standard.