Soft clays,which have been commonly encountered in real construction projects,are widely distributed in the deltas of major rivers and coastal area of the southeast China.The construction of buildings,roads,bridges,canals,harbours and railways in soft clays has always been associated with settlements,water gushing and stability problems.Grouting technology and pre-stressing grouting method are known to improve the mechanical characteristics of the soil clay and plug water gushing,but little information available on principle causes of grouting treatment in soft clays.The research described in this thesis focuses on the grouting diffusion mechanism,reinforcement mechanism and their applications in soft clay stratum.Literature consultation and theoretical analysis were performed to investigate the grouting diffusion mechanism in soft clay stratum.Numerical study was conducted to identify the critical controllable factors of pre-stressing stratum control grouting for optimizing the compaction effectiveness.Simulation test and laboratory test were used to study the mechanism of grouting reinforcement.Field test was carried out to improve the understanding of the key technology of water gushing treatment on soft clay.Firstly,in order to study the diffusion mechanism of shallow surface grouting in soft clay,the theoretical analysis and literature consultation were carried out to obtain the influence of physical mechanical properties of soil,groutability and crustal stress on grout diffusion direction in soft clay.Moreover,the comparative analysis between the deep crustal stress and shallow crustal stress was proposed,which particular attention was paid to the dynamic relationship between horizontal stress and vertical stress during grouting period.In addition,the governing equation of hydro fracture grouting was presented,and the analysis on hydro fracture diffusion was stated.Secondly,finite element analysis was adopted for the simulation of pre-stressing stratum control grouting method in soft clay.The main focus was to investigate the development of stresses,strains along the radial distance from the mold bag and the deformation around the mold bag due to injection and expansion of mold bag.For the sake of this,numerical simulation was carried out to simulate the behavior of pre-stress grouting tests in soft clay stratum.After that,the effective influence scope and the optimum interval on the results were studied.Thirdly,a series of simulation and laboratory tests were carred out to obtain the basic grout body properties including elastic modulus,cohesion,internal friction angle and permeability coefficient.The effects of volume ratio and grouting pressure on the improvement of properties were studied.Meanwhile,the quantitive relationship between reinforcement effects and grouting factors were illustrated.Furthermore,the disparate impact of grouting factors on different mechanical indexes of soil was investigated.Moreover,the conversion rate of material strength was also studied.In addition,the simple excavation criterion of reinforcement stratum ξ due to pre-stressing grouting was defined.Fourthly,to investigate the key technology of grouting treatment,Shangyuanmen metro station was selected as the test site.Using fine prospecting method,multi-geophysic exploration,which includes the cross-hole resistivity CT,high density resistivity,transient electromagnetic method and geological radar method,were carried out to detect the water conducting structure.Moreover,field test and theoretical analysis were performed to study the disaster synergistic control technology during the construction period,the results of disaster synergistic control technology demonstrate the optimum grouting volume and water plugging ratio.Furthermore,the life-cycle theory was investigated,whereas,the selection of materials and key borehole theory were presented.Finally,a series of field tests was carried out for the application of grouting in soft clay of Shangyuanmen metro station foundation pit.The engineering problems and comprehensive treatment principle were presented.Nevertheless,the grouting theory which was proposed in Chapter 3,the pre-stressing grouting method which was stated in Chapter 4,the selection of grouting parameters which was illustrated in Chapter 5,the key technology of water gushing treatment which was demonstrated in Chapter 6,were applied in this field test.The governance results showed that the grouting technology system has proven to be effective.