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将应用于围垦工程中的底部抽真空技术同传统的上部抽真空方法进行对比试验,研究底部抽真空的优点。经过改进的仪器能够对试样施加80kPa的真空压力,同时能够量测不同土层深度下土体的孔隙压力、沉降及体积随时间的变化情况。试验用土取自南京秦淮河,研究结论表明:底部抽真空方法对土体的加固效果优于上部抽真空方法。与上部抽真空方法相比,底部抽真空方法加固后土体含水率低10%,干密度大11%,不排水剪强度提高35%,最终沉降则增加22%。除此之外,试验结果还显示底部抽真空方法固结更快,不同深度土层加固效果差异较小,底部法还能够有效保持真空度的恒定。底部抽真空方法与上部抽真空方法的最大区别就在于:上部抽真空过程中,土体内部水位不会发生变化,因此总保持饱和状态。相反,采用底部法时,真空压力的施加使得排水板内的水位快速下降到土层底部,土体中水位也因此随时间增加而逐渐下降,土体不再被水浸没,可以由饱和态转变成为非饱和态。
The bottom vacuuming technology used in reclamation project is compared with the traditional upper vacuuming method to study the advantages of bottom vacuuming. The improved instrument can apply vacuum pressure of 80kPa to the sample and measure the pore pressure, settlement and volume change with time under different soil depths. The test soil was taken from Qinhuai River in Nanjing. The research results show that the method of vacuum pumping at the bottom of the soil is better than that of the upper vacuum pumping. Compared with the method of vacuum pumping, the soil moisture content is 10% lower, the dry density is 11% higher, the undrained shear strength is increased 35% and the final settlement is increased by 22%. In addition, the test results also show that the bottom vacuum method consolidation faster, different depths of soil reinforcement effect difference is small, the bottom method can effectively maintain the degree of vacuum constant. Bottom of the vacuum method and the upper part of the vacuum method is the biggest difference is: the upper part of the vacuum process, the soil inside the water level will not change, so always remain saturated. On the contrary, when the bottom method is applied, the water pressure in the drainage board rapidly drops to the bottom of the soil layer due to the application of vacuum pressure. As a result, the water level in the soil body gradually decreases with time, and the soil is no longer immersed in water. Into the unsaturated state.