风化残积砂土相对密实度及含水率对抗剪强度的影响

Effects of moisture content and relative density in weathering residual sand soils on shear strength

全风化花岗岩回填土的抗剪强度受其含水率与相对密实度的影响。优化回填土含水率与相对密实度来提高土体抗剪强度是实现中缅油气管道龙陵段管道作业边坡坡面侵蚀治理的手段之一。以管沟回填的全风化花岗岩回填土为研究对象,通过室内直剪试验和人工降雨模型试验,研究该类土体抗剪强度参数随着含水率和干密度的变化规律以及其抗冲刷能力。结果显示:1)干密度为1.30 g/cm^(3)的土样的最佳含水率为15%,此时其黏聚力和内摩擦角分别为20.33 kPa和34.59°,当土体含水率增加至25%时,其黏聚力降低至3.63 kPa,内摩擦角减小到32.42°;2)通过击实方式将土体的相对密实度从0.06提高至0.83,土体的黏聚力和内摩擦角分别提高53%和18%,相对密实度为0.50时,对土体抗剪强度参数的改善效果最佳;3)人工模拟降雨实验结果显示,坡面侵蚀模数与土体的抗剪强度有关,尤其与内聚力呈负相关关系。综上,相同含水率条件下,提高土体的相对密实度,能有效改善土体的抗侵蚀能力。

[Background]In the granite distribution area of Longling section of China-Myanmar oil and gas pipeline,the slope soil erosion of pipeline operation slope is very serious.The previous treatment experience shows that the conventional soil and water conservation measures have poor effect on the fully weathered granite backfill soil.For this,pertinence treatment measure research needs to develop.The shear strength of fully weathered granite backfill soil is affected by its moisture content and relative density.Optimizing themoisture content and relative density of backfill soil to improve the shear strength of soil is an important measure to control the erosion on the slope of Longling section of China-Myanmar oil and gas pipeline.[Methods]In this paper,the fully weathered granite backfill soil from the pipe trench of the China-Myanmar oil and gas pipeline in Longling county was selected as the test soil.The moisture content and relative density were measured by ring knife method.The shear strength parameters were determined by direct shear test with quadruple direct shear apparatus.Slow shear method was selected according to specification.The slope erosion modulus was measured by artificial simulated rainfall test.Two groups of soil samples were equipped according to the interval of 5%moisture content and 0.2 relative density,respectively,and the effects of moisture content and dry density on shear strength were analyzed.[Results]1)With the dry density of 1.30 g/cm^(3)soil samples as a benchmark,when the soil moisture content is 5%,10%,15%,20%and 25%,the cohesion C is 9.15,13.67,20.33,8.87 and 3.63 kPa,respectively,and the internal friction angleφis 36.83°,33.11°,34.59°,34.85°and 32.42°,respectively.The 15%moisture content is the optimal moisture content.2)Taking the soil sample with 15%water content as a reference,the cohesion C of soil with density ratio at 0.06,0.27,0.51,0.72 and 0.83 are 20.00,20.33,26.75,26.96 and 31.12 kPa,respectively,and the internal friction angleφare 31.77°,34.59°,36.97°,39.07°and 41.88°,respectively.When the relative density of the soil increases from 0.06 to 0.83,the cohesion and internal friction Angle of the soil increase by 53%and 18%,respectively.When the relative density is 0.50,the improvement effect of soil shear strength parameters is the best.3)The results of artificial simulated rainfall experiments show that the slope soil erosion modulus is related to the shear strength of soil,especially negatively correlated with cohesion.[Conclusions]The results show that the moisture content of fully weathered granite backfill soil increases,and the cohesion increases first and then decreases rapidly,and the internal friction angle decreases gradually,under the same dry density.Under the same moisture content,the cohesion and internal friction angle increase with the increase of relative density.Under the same moisture content,increasing the relative density of soil can effectively improve the anti-erosion ability of soil.