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现有的平面应变试验仪都不能很好地解决接触摩擦的问题,试验中土样与约束面板之间存在较大的摩擦力影响变形测量的准确性。在总结平面应变仪发展历程的基础上,根据加载方式将平面应变仪分为4类,分析了现有的平面应变试验仪的特点和存在的问题;介绍了一种改进的平面应变仪的压力室。改进后的压力室在前、后约束面板与土样之间分别增设一层厚约3 mm的密封水膜。在试验过程中,包裹土样的橡皮膜与密封水膜的硅胶膜紧密贴合而不直接与面板贴合,可以消除土样与面板之间的摩擦。同时,新型的压力室还可应用于土样变形数字图像测量系统,实时测量土样表面的变形分布,可以比较精确地测量土样的表面变形、剪切带的形成过程及特征。分别使用改进的压力室和未改进的压力室对福建标准砂进行平面应变试验,前者测得的应力-应变关系曲线的峰值比后者低约60%。制备相同干密度的土样分别进行不同围压条件下的三轴试验和平面应变试验测取土样的抗剪强度,使用改进压力室得到的抗剪强度参数与三轴试验测得的结果很接近,而使用未改进的压力室测得结果则明显不合理。
The existing flat strain tester can not solve the problem of contact friction very well. In the experiment, the larger friction between the soil sample and the restraint panel affects the accuracy of deformation measurement. On the basis of summarizing the development history of the plane strain gauge, the plane strain gauges are divided into four categories according to the loading method, and the characteristics and existing problems of the existing plane strain tester are analyzed. An improved method of pressure room. The improved pressure chamber is provided with a layer of sealing water film with a thickness of about 3 mm between the front restraint panel and the soil sample respectively. During the test, the rubber-coated rubber membrane and the water-sealed silicone film closely fit the panel, which can eliminate the friction between the soil sample and the panel. At the same time, the new pressure chamber can also be applied to digital image measurement system of soil deformation, real-time measurement of soil surface deformation distribution, can more accurately measure the soil surface deformation, shear zone formation process and characteristics. Fujian normalized sand was subjected to a plane strain test using an improved pressure chamber and an unmodified pressure chamber, respectively. The former measured a stress-strain curve with a peak value of about 60% lower than the latter. Preparation of the same dry density of soil samples were carried out under different confining pressure triaxial test and plane strain test to measure the shear strength of soil samples obtained using improved pressure chamber shear strength parameters obtained with the triaxial test results are very Close to, and the use of unmodified pressure chamber measured results are obviously unreasonable.