球形模板压入仪在冻土长期强度测试中的应用

Application of spherical template indenter to long-term strength tests for frozen soil

球形模板压入仪(球模仪)在前苏联和俄罗斯等冻土区土力学性质测试中得到广泛应用。在60多年的工程实践中,试验理论、方法等方面都得到了完善。因其试验简单易行且测试结果能较好地反映冻结土的力学性质,特别是在冻结土黏聚力的长期强度评价及预测方面广泛应用。简要介绍该试验理论、试验方法、试验仪器。以莫斯科郊外冰碛粉质黏土作为研究对象。在恒定-7～20℃温度条件下,在封闭状态下分别进行3、6、20、40次冻融循环试验。对各试验阶段土样进行物理性质测试,之后用球模仪对冻结土样进行强度测试。冻融循环后土样的各物理指标均有不同程度的减小,随着冻融次数的增加,其强度降低。冻融过程中,土样中水体积的变化使其密度减小、孔隙率增大是造成这一结果的原因。

Spherical template indenter（ball mode device） has been widely used in the mechanical properties of permafrost soil testing in the former Union of Socialist Soviet Republics（USSR） and Russian Federation.In the past 60 years of engineering practice,the test method,test theory,etc.were improved.It is simple,easy to test.And the results reflected the mechanical properties of frozen soil better.So,it widely used in long-term strength＇s evaluation and forecast of the cohesion for the frozen soil.This paper made a brief introduction to the equipment,the test theory,and test methods.Moraine clayey loam in the outskirts of Moscow city was used as the object of study.In constant temperature（from-7 ℃ to 20 ℃） conditions,in a closed state,the freeze-thaw cycle tests were conducted,3,6,20,40 times,respectively.Physical properties of soil were tested in different experimental stages;and strength was tested on the frozen soil with spherical template indenter after the freeze-thaw cycle.After freeze-thaw cycle test,soil＇s physical properties indicators reduced in varying degrees.With the increase in the number of freeze-thaw cycle,soil strength decreases.The volumes of water in soil change in the freeze-thaw process,which caused soil density decreases and the porosity increases.This is the reason for the reduction of soil strength.