Research On Mechanism Of Dynamic Replacement Method For Thick Soft Soil Subgrade

Due to complex geological and topographical conditions in China,constructing highway in coastal areas of thick marine sediment is inevitable,which has brought a lot of challenges to the quality and later operation of highway construction.Dynamic replacement method,as an effective method in dealing soft soil with high saturation,low permeability,low strength,high compressibility,has been developing for 30 years since last century and been widely used in coastal areas.At the same time,the research on mechanism and process parameters of dynamic replacement method usually relied on field test and summary of engineering experience.So far,complete and reliable theory and design criteria for process parameters has not been formed.In this thesis,we choose the dynamic replacement method as research object,which has been applied in soft soil subgrade treatment of a highway engineering in Yuhuan,Zhejiang Province,indoor model test and numerical analysis were organized to study the mechanism and effect of main process parameters in dynamic replacement method.Main research contents include following parts.Firstly,the characteristics of impact load and energy transferring during dynamic compaction were introduced and analyzed basing on wave and collision theory in physics.Then,an indoor model test was organized according to similarity law,which was in order to simulate the process of dynamic replacement.In the end,moving rules of rock and soil were summarized by experimental data and image data.The influence of reinforcement on soft soil due to different process parameters,such as diameter,spacing and falling distance of hammer,were studied as well.As confirmed,the results of numerical simulation and model test were in good agreement.Secondly,basing on reasonable assumptions,different discrete element models were established to simulate the process of dynamic replacement and movement laws of rock and soil under single-point and multi-point dynamic replacement were calculated and analyzed.As a supplement,results of numerical simulation and indoor similarity test were compared.In addition,in order to discuss the influence of reinforcement on soft soil due to different process parameters,such as diameter,spacing and falling distance of hammer,different discrete element and finite element numerical model were established.The relationship between main process parameters and effect of dynamic replacement method in dealing with soft soil was obtained,and which was consistent with indoor similarity test as well.Finally,according to relevant data of the entity engineering,the whole process of dynamic compaction replacement treatment on soft soil subgrade was obtained.The results can be theoretical reference and design guidance for treatments on soft soil foundation in coastal areas in future.