碎石桩复合地基是目前土木工程中广泛应用的地基处理方式之一，但有关碎石桩复合地基的理论研究相对滞后，尤其是碎石桩复合地基沉降的计算值，与现场实测值相差较大，承载力计算仍是半经验、半理论的公式，计算结果的准确程度很大程度上决定于计算者的实践经验以及现场试验参数可靠性的高低。因此，关于碎石桩复合地基的性状分析研究是目前工程地质学科的主要研究内容之一，也是工程应用之急需。 本文以赣大高速公路K38+150～K38+300段软土地基采用碎石桩处理的工程实例为依托，采用FLAC3D数值模拟软件对软土地基的沉降机理和碎石桩复合地基的作用机理进行研究探讨。 首先，介绍了赣大高速公路软土地基工程地质特征，分析物理力学性质，计算了软土地基在路基荷载作用下的沉降值和固结时间，再采用数值模拟软件分析软土地基在路基荷载分层加载的情况下应力应变变化规律，并进行理论解释和稳定性评价。 其次，分析了碎石桩复合地基加固机理、破坏模式，讨论了碎石桩复合地基承载力和沉降计算思路及设计理论，再采用数值模拟软件分析碎石桩复合地基在路基荷载分层加载的情况下应力应变变化规律，并进行理论解释和稳定性评价。 第三，运用数值模拟软件模拟不同设计参数的碎石桩复合地基在路基荷载作用下应力应变情况，并对模拟结果进行对比评定，提出碎石桩处理软土地基的最佳方案。

The gravel pile composite foundation is widely used in the foundation treatment in current project, but the theoretical research on which is still lagging behind. In particular the gravel pile composite foundation subsid calculations, and the scene of the subsid value of the measured difference between the relatively large; The calculation of bearing capacity is still semi-empirical, semi-theoretical, and the accuracy of the calculation results is mostly decided by the calculator's practical experience and the quality of parameter quality provided in the field trials. Study on numerical simulation of soil stress and strain have some advantages, And is gradually used to guide the practice of engineering in recent years. This thesis adopting the project which use the gravel pile to deal with the soft soil foundation in the section of K38 +150 ~ K38 +300 in GanDa expressway, deeply discuss the mechanism of soft soil subsid and gravel pile composite compound, and focus on the numerical simulation. Firstly of all, it is introduced that the GanDa expressway soft engineering geological characteristics and analyzed its physical and mechanical properties. it is calculated the subsiding value and consolidation time of soft soil foundation under the road bed load,and adopting numerical simulation software analyzed the stress-changing laws of soft soil foundation when the road bed loads and loads hierarchically,and then explained the theory and appraisaled of stability. Secondly, it is analyzed that the gravel pile-compounding the foundation and strengthens mechanism, and destroys the mode. it is discussed that the thoughts of the loading strength and subsiding calculations and design theory when the gravel pile-compounding the foundation. and adopting numerical simulation software analyzed the stress-changing laws of the gravel pile-compounding foundation when the road bed loads and loads hierarchically, and then explained the theory and appraisaled of stability. Thirdly, adopting of numerical simulation software it is simulated the stress-changing states of gravel pile-compounding the foundation under road bed load using different design parameters.and compare the imitating results with evaluating, put forward a best scheme of dealing with soft soil foundation by gravel pile.