干密度与含水率对标准砂抗剪强度的影响研究

Experimental research on the influence of dry density and moisture content on the shear strength of standard sand

抗剪强度是土的重要力学性质之一,是决定工程稳定性的关键因素。为研究砂土的强度特性,选取标准砂为试验材料,设计不同含水率与干密度水平的直剪试验,明确干密度与含水率对标准砂应力-应变曲线的影响,揭示其对标准砂抗剪强度特性的影响规律。研究结果表明:标准砂试样达到相同应变所需的应力随着标准砂的干密度及试验法向应力的增加而增加、随着标准砂含水率的升高而减少。在干密度为1.45cm^(3)与含水率为20%和25%的直剪试验中标准砂的应力应变曲线呈现出应变软化的特点,进一步分析表明标准砂的应力-应变曲线随着试样干密度增加、法向应力减小呈现出由硬化型应变向软化型应变转换的趋势。标准砂的抗剪强度随着干密度的增大而增大,随着含水率的增大而降低,其抗剪强度主要来源于材料颗粒之间的内摩擦角。在控制含水率不变的试验中内摩擦角随着干密度的增加依次增加0.54°,2.17°,1.99°和0.21°,呈现出平缓-陡峭-平缓的上升趋势;在控制干密度不变的试验中内摩擦角由含水率每降低1%降低0.5°降低至含水率每降低1%降低0.3°,随着含水率的升高呈现出陡峭-平缓的降低趋势。研究结果可以为与砂土相关工程的防灾预警等研究提供参考。

The shear strength is not only one of the important mechanical properties of soil,but also a key factor to determine the stability of engineering.The standard sand was selected as the experimental material in order to explore the strength characteristics of sand.Direct shear tests with different levels of moisture content and dry density were designed to clarify the effects of dry density and moisture content on the stress-strain curves of standard sand,and to further reveal the influence law of the two factors on the strength characteristics of standard sand.The results show that the stress required to achieve the same strain of the standard sand in the test increases as the dry density and normal stress of the standard sand increase,while it decreases with the increasing moisture content in each test group.In the direct shear test with the dry density of 1.45 cm^(3) and the water content of 20%and 25%,the stress-strain curve of standard sand shows the characteristics of strain softening.Further analysis shows that the stress-strain curve of standard sand shows a trend of transition from strain hardening to strain softening with the increase of dry density and the decrease of normal stress.The shear strength of standard sand increases with the increase of dry density and decreases with the increase of moisture content,which is due to internal friction angle.With an increase in dry density,the internal friction angle increases by 0.54°,2.17°,1.99°and 0.21°in the experiment with constant water content which shows a gentle-steep-gentle upward trend.The change of internal friction angle decreases from 0.5°for every 1%decrease of water content to 0.3°for every 1%decrease of water content in the experiment with constant dry density which shows a steep-gentle decreasing trend with the increase of moisture content.The results of the research can provide a reference for the study of disaster prevention and early warning of sand-related engineering.