An open frozen–heave test on the pipeline foundation soils in the permafrost regions

Abstract

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. Keywords: Open frozen–heave test, Closed frozen–heave test, Displacement limiting method, Static equilibrium method, Frozen–heave factor, Normal frozen–heave force, Regression analysis, The t test