Study On The Reliability Of Using Vacuum-surcharge Preloading Instead Of Cement-soil Mixing Pile Method For The Soft Soil Subgrade Of Wetlands And Lakes

This paper is based on the test section in Hengshui of Xingtai-Hengshui expressway(the Ⅰ period). This test section is located in the wetland of south Hengshui Lake. Thespecial character of soft soil of wetlands and lakes can cause significant after constructionsedimentation to the highways constructed on the soft soil. The special character of soft soilof wetlands and lakes can cause significant after construction sedimentation to thehighways constructed on the soft soil. The author makes a comprehensive research on thatreplacing cement-soil mixing pile with vacuum-surcharge preloading. The main results areas follows:1. Introduce two kinds of methods calculating soft soil foundations’ sedimentation,vacuum-surcharge preloading and cement-soil mixing pile; and estimate the foundations’sedimentation.2. Perform numerical simulation on using cement-soil mixing pile method to deal withthe soft soil subgrade. Analyze from four aspects: pile-soil stress ratio, sedimentation ofsubgrade reinforcement section, subgrade substratum sedimentation and pile bodydecrement. We can get that pile-soil stress ratio increases as the highways’ embankmentload increases, and the sedimentation of substratum is relatively large.3. Perform numerical simulation on using vacuum-surcharge preloading to deal withthe soft soil subgrade. Compare the simulating result with the measured result and make ananalysis. The general developing trend is almost the same. Analyze the following aspects:pore water pressure, sedimentation of subgrade’s surface and layered sedimentation, it canbe concluded that pore water pressure increases as the road embankment load rises, thesubgrade sedimentation mainly happens during the loading period, and it tend to be stableduring the preloading period.4. Comparing the two methods and make an analysis, we can get that when usevacuum-surcharge preloading to deal with the soft soil subgrade, the after constructionsedimentation is less than that when use cement-soil mixing pile method. Calculate the afterconstruction sedimentation’s reliability index, the reliability index of cement-soil mixingpile is1.85, the vacuum-surcharge preloading7.31. Therefore, vacuum-surchargepreloading is more reliable to deal with the soft soil subgrade sedimentation.