研究目的: 为确定水泥土搅拌桩对湿陷性黄土地基的加固效果,以太焦高速铁路某工段为背景,首先,试验测试该路段黄土的物理力学特性,确定其湿陷性指标和湿陷等级,分析其力学特性的变化特点;其次,设计该黄土地基的加固方案以及水泥土搅拌桩的试桩参数,抽芯检测试验桩体的成桩质量;再次,通过复合地基承载力试验并结合数值分析,研究不同试桩参数的水泥土搅拌桩复合地基的承载力特征值;最后,在地基加固试验段铺筑试验路基,采用现场监测、理论计算及数值模拟相结合的手段研究路基的沉降变形规律。
研究结论: (1)3种水灰比试验桩的成桩质量良好,测得试验桩体无侧限抗压强度分别为1.6 MPa、1.8 MPa和2.0 MPa,均大于1.0 MPa的工程设计要求,最终确定该工程施工所用水灰比为0.50;(2)现场试验所得单桩复合地基承载力特征值为261~266 kPa,理论计算及数值模拟所得其特征值分别为282.87 kPa和209 kPa;(3)现场监测、理论计算及数值模拟所得试验段路基的最终沉降量分别为21.17 mm、31.25 mm和26.14 mm,该复合地基强度满足工程设计要求;(4)本研究成果可为高速铁路软土地基加固方案设计提供一定参考。

Research purposes: To determine the reinforcement effect of cement-soil mixing pile on collapsible loess foundation, taking one section located at Taiyuan-Jiaozuo high speed railway engineering as an example, firstly, physical and mechanical properties of the loess were tested, the collapsibility indexes and grades were determined, and mechanical characteristics and change law were also analyzed. Then the reinforcement plans and the parameters of tested piles were designed, and the pile quality was tested by core pulling test. Thirdly, the characteristic value of bearing capacity of composite foundation reinforced by cement-soil mixing pile with different parameters were all studied using bearing capacity test of composite foundation as well as numerical simulation method. Finally, the test subgrade was paved on the foundation reinforced by cement-soil mixing pile, and the settlement laws were determined by means of field monitoring, theoretical calculation and numerical simulation.
Research conclusions: (1) The quality of the three kinds of water-cement ratio test piles was great and the unconfined extrusion strength was 1.6 MPa, 1.8 MPa and 2.0 MPa respectively which were larger than 1.0 MPa, and the water-cement ratio in this foundation construction is 0.5. (2) The characteristic value of bearing capacity of single pile composite foundation from field monitoring was 261~266 kPa, and they were 282.87 kPa and 209 kPa respectively obtained from theoretical calculation and numerical simulation. (3) The field monitoring subsidence, theoretical calculation subsidence and numerical simulation subsidence were 21.17 mm, 31.25 mm and 26.14 mm, respectively. All of these indicated that the strength of composite foundation could meet requirement of engineering design. (4) The research results can provide reference for the design of reinforcement scheme on soft foundation of high speed railway.