Study On The Material Properties Of TRD Mixing Wall And The Environmental Impact Of Its Construction

With the high-growth of economy and the continuous progress of urbanization in China,the urban population keeps increasing rapidly,and traffic congestion is becoming more and more serious.In order to find a solution to the transportation problem and make full use of underground space,China has accelerated the pace of urban rail transit construction since the 1990s.So far,there are 35 cities with operating rail transit,and another 14 cities have carried out the construction work for urban rail transit.Urban rail transit station is generally constructed by open-cut method,which requires reliable techniques of supporting,dewatering,waterproofing and earthwork excavation for the foundation pit.Triaxial mixing pile is a common form of waterproof curtain.However,the machine stand is high and the construction depth is relatively small,which limit the usage of triaxial mixing pile as waterproof curtain where there are high-voltage wires overhead or thick aquifer layer.The procedures of TRD(Trench cutting Re-mixing Deep wall)are as follows:the chain cutter is inserted into soil,and then moves and advances horizontally to form a continuous groove,at the same time,the solidified mortar is ejected from the end of the cutter and mixed with the surrounding soil to form a continuous cement soil wall.This method was introduced into China from Japan in 2005.Because of its strength in stand height,stability,continuity and uniformity of wall,waterproof and construction depth,TRD method has been gradually adopted to deep foundation pit engineering in China.In this paper,the mechanical properties of mineral powder cement soil were investigated by mix proportion design and laboratory test.Taking the foundation pit engineering of Maopeng Road Station of Suzhou Metro Line 5 as a study case,the influence of TRD mixing wall construction on surrounding environment was analyzed by combining field measurement with numerical simulation.The main research contents and achievements are listed below:1?The compressive strength and its variation law,stress-strain characteristics and permeability characteristics of cement-soil with different proportion of cement and mineral powder were studied under the condition that the total ratio of curing agent(30%)was constant.Orthogonal test was used to further analyze the influence weight of cement mixing ratio,mineral powder mixing ratio and curing time on mineral powder cement soil,and to determine the optimal mixing ratio.Meanwhile,the compressive strength data obtained from orthogonal test were fitted,and the strength prediction formula of mineral powder cement soil was launched.2?During the construction of TRD waterproof curtain for foundation pit of Maoping Road Station of Suzhou Metro Line 5,the surrounding surface settlement,horizontal displacement of deep soil were measured,and the influence of TRD waterproof curtain on the surrounding surface settlement and horizontal displacement of deep soil was investigated.3?Using the finite element numerical simulation analysis software Abaqus,combined with the measured data,the numerical simulation of TRD waterproof curtain excavation into wall was carried out.The simulated and measured values of surface settlement and horizontal displacement of deep soil under different scenarios were investigated and compared.The result shows that the simulated values are in good agreement with the measured values,and the numerical calculation model and parameter selection are satisfactory.