| The rapid development of urbanization construction and the shortage of urban land resources are a major contradiction in current project construction.The development of underground space has become a hot spot,and the deep foundation pit project has begun to develop toward a high-depth,high-difficult and large-scale trend.Three-axis mixing piles and high-pressure jet grouting piles are widely used in deep foundation pit support systems to improve the strength and durability of foundations,reduce the deformation of soft soil foundations,and prevent groundwater flows into the sidewalls or the bottom of foundation pits as underground structures,and they finally forms a continuous anti-seepage curtain.The basic material of the anti-seepage curtain is composed of cement soil,therefore,it is often called the anti-seepage curtain cement wall in engineering field.In engineering construction,the most important mechanical index of the anti-seepage curtain is its permeability coefficient.Water seepage is the most important problem during the construction,use and delivery of deep foundation pits.In recent years,the problem that the sewage entered the soil and the ecological environment was affected has been widely concerned.The function of the anti-seepage curtain can enclose the contaminated soil and make polluted soil isolated from the external environment,to prevent the spread of pollutants has received increasing attention.However,in engineering practice,due to a series of problems such as complex site conditions,there is no clear judgment standard for anti-seepage effect.Therefore,in order to study the water-stopping effect of anti-seepage curtain,it is usually through studying the strength of cement soil of anti-seepage curtain foundation material indexes,side analyse and assess the function of the anti-seepage curtain,then use these research to guide practical engineering.According to different use needs and actual needs,the ratio of anti-seepage curtain cement soil can be said to be invincible.In order to study the optimization research of the anti-seepage curtain cement content of deep foundation pit under different soil conditions,this paper relies on several engineering projects in Hangzhou.On the one hand,soft clay is used as the representative basic soil to design different cement soil allocation schemes to simulate different soil quality,and conduct indoor unconfined compression test and direct shear test,explored the strength and its change of cement soil in different configurations at different ages;On the other hand,the composite soil is used as the representative base,and carry out the penetration test of the cement soil at the engineering site,and summarize the permeability coefficient of the soil after reinforcement.In addition,the replacement rate formula of replacement soil was proposed for the first time,and based on a project in Huangshan,the theoretical replacement rate formula was used to compare the theoretical and measured values of the engineering replacement rate,and the rationality and reliability of the derivation formula were verified,then can help the engineer to have more comprehensive understanding of the construction site.In the context of combining practical engineering projects,this paper has obtained the following conclusions through experimental research:?1?The water-cement ratio and the change of cement content will directly affect the mechanical strength of cement soil.In the research scope of this paper,the mechanical strength of cement soil is inversely related to the water-cement ratio,and is positively correlated with cement content.?2?Incorporating admixtures into cement soil,the strength of cement soil can be enhanced within the scope of this study,such as bentonite,zeolite powder and standard sand,and its strength is further increased with the addition of admixture,but the reinforced action mechanism of different admixtures is different,and the reinforcing effect on cement soil is also different;?3?A large number of mathematical models have been established through unconfined compression test and direct shear test to deepen the understanding of the performance changes of cement soil under different configuration conditions;?4?Within the scope of this study,under the technical conditions of the TRD method,the permeability coefficient of the anti-seepage curtain cement soil wall of the project construction can reach the order of 10-7cm/s;?5?Through theoretical analysis,the relationship between the replacement rate of the displaced soil at the project site is derived:???... |
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