Experimental Study On The Effect Of Humidified Swelling On The Shear Strength Index Of Expansive Soil

Expansive soil rich in hydrophilic minerals has the characteristics of swelling under water absorption and shrinking under water loss.It is prone to causing the engineering problem of shallow slope collapse.When the stability of its slope is analyzed,the stability coefficient is generally high,but the slope still collapses.The shear strength index is an important parameter for the slope stability analysis.For the shallow slope,the cohesion is the main source of shear resistance.Due to the effect of swelling,the dry density of test sample cannot be consistent during the consolidation process of direct shear test;The obtained effective cohesion and effective internal friction angle have certain test errors so that the stability of expansive soil slope cannot be accurately evaluated;Moreover,the dry density of shallow slope expansive soil is reduce,and its shear strength index is also attenuated.Therefore,the conventional direct shear test device was improved to eliminate the effect of swelling on the dry density,and a true cohesion test device was designed.In addition,the stability analysis of expansive soil slope was carried out,and the effect of swelling on the shear strength index was considered in this analysis.In this study,the conventional direct shear test device was improved.A piston and a pressurizing device were mainly added so that the dry density of test sample kept consistent during the consolidation process,thus eliminating the effect of swelling on the test result.Taking the medium-strength expansive soil in Baise,Guangxi as the research object,a comparative analysis of the results of conventional and improved direct shear test was conducted.The modified direct shear tests at different dry densities were carried out on the expansive soil in Baise,Guangxi and the weak expansive soil in Yichang,Hubei respectively.The law of shear strength index varying with the dry density was obtained,and the effect of swelling on the internal friction angle was analyzed by fitting the function.The undisturbed sample and remodeled sample of expansive soil were tested by the true cohesion device.The results show that the undisturbed sample of expansive soil has higher true cohesion while the remolded sample has no true cohesion.The effect of swelling of expansive soil on the true cohesion was studied by the water immersion test.The data show that the expansive soil with higher swelling potential has a greater influence on the cohesion,and the smaller the swelling potential,the smaller its impact.The closer the surface expansive soil on the slope of the first-class highway in Anchang,Yichang,Hubei,the smaller the dry density of slope.Considering the effect of swelling on the shallow slope,the shear strength index of test sample after the expansion was used in dry-wet cycle area,while the shear strength index of undisturbed sample was used for the stability analysis in non dry-wet cycle area.Calculation results show that the slope is instability.It is proved that due to the swelling of expansive soil,the dry density of shallow slope decreases,and its shear strength index attenuates,which causes the slope to collapse.The improved direct shear test device can eliminate the effect of swelling on the test and make the dry density of test sample keep consistent.The true cohesion device can remove the apparent cohesion and obtain the true cohesion of soil sample,thus providing more accurate parameters for the shallow slope calculation.Considering the effect of humidified swelling of expansive soil on the slope,the calculated slope stability results are more in line with the engineering practice.