多年冻土区管道地基土开式冻胀试验

摘要

In the Da Hinggan Mountains,the safe and smooth operation of shallowly buried oil pipelines is threatened greatly by the frozen-heave damage derived from frozen soil.At present,a closed frozen-heave simulation test is often carried out in China,with water content and dry density of samples being assumed to be constant.However,an open frozen-heave test,all the factors of which change as the test goes on,can reflect the real frozen-heave damage more accurately.In this paper,the open frozen-heave test was carried out on five types frozen soil along the China-Russia Crude Oil Pipeline to measure the frozen-heave factor and water content of each soil sample and accordingly analyze their relationship.Besides,its test results were compared with that of the closed frozen-heave test.Then,the normal frozen-heave force was measured by using the displacement limiting method,and this measurement was compared with the result of the static equilibrium test.Finally,a difference significance test was conducted.It is shown that the frozen-heave factor of the open test is higher than that of the closed test;the frozen-heave factor of fine grained soil has a significant effect on the frozen-heave factor of soils,and the frozen-heave factor increases as the capillary effect or the swabbing action of soil increases;the frozen-heave factor of coarse grained soil is mainly dependent on the mud content,and it is lower than that of fine grained soil;the value of frozen-heave force is in close relation with the test methods and the sample height;it is indicated that the open frozen-heave test is more applicable to the investigation on the frozen-heave of the foundation soils of pipelines in the Da Hinggan Mountains.It is concluded that the soils for the cushion and digging/packing layers of the pipelines in the permafrost regions shall be acted by the gravel or detritus with lower mud content,and waterproof and draining pipeline jetty shall be made from the clay soils with a higher plasticity.%大兴安岭地区冻土冻胀型冻害对浅埋式石油管道的安全稳定运行威胁很大.目前国内有关研究多采用闭式冻胀模拟试验,试样的含水率、干密度等因素是假设不变的,相比之下,采用各因素随试验进展而不断变化的的开式冻胀试验更能反映实际冻胀型冻害.为此,对中俄原油管道沿线5种冻土进行了开式冻胀模拟试验,测定了各种土料冻胀率与含水率,并据此分析了二者的关系,同时与闭式冻胀试验结果进行了对比分析,还应用限制位移法测定了法向冻胀力,并与静力平衡法试验结果进行了比较和差异显著性检验.试验结果表明:①开式冻胀试验的冻胀率大于闭式冻胀试验的冻胀率;②细粒土的冻胀率对土料冻胀率的影响十分显著,并且土料的毛细管作用或抽吸作用越强烈,冻胀率就越大;③粗粒土的冻胀率主要受含泥量的影响,其冻胀率比细粒土小;④法向冻胀力的大小与试验方法和试样高度的关系密切;⑤开式冻胀试验方法更适用于大兴安岭地区管道地基土的冻胀研究.结论认为:该区多年冻土区管道垫层和挖填层的土料应选用含泥量较少的砂砾或碎石,且需要采用塑性较大的黏性土做好防排水管堤.