By nonlinear calculation and analysis of additional stress caused by pre-load in soft clay subgrade,various factors are considered and analyzed comprehensively,such as section size of subgrade,load(height) of filled clay,etc.And the compensated fill volume due to settlement for soft clay subgrade is obtained.

According to the present national standards,the square of the ratio of longitudinal wave(P-wave) velocity of rock mass to that of rock block is defined as intactness index of rock mass.It is well known that the P-wave velocity of in-situ rock mass is believed to be lower than that of relevant rock block commonly.The more broken the rock mass is,the lower its P-wave velocity than that of rock block is.Acoustic logging and wave velocity measurement of rock cores are applied to bedrock of Nanjing subway engineering.It is found that most wave velocities of rock mass are greater than those of rock cores;and the cause is unloading-disturbance influence on rock cores.In order to analyze the acoustic responses of rock core unloading-disturbance more availably,wavelet transformation method is applied to decompose the rock core acoustic signals into wavelet components belonging to various frequency channels;and weight spectrum parameters are given after time-frequency analysis of the channel signals.There are good relationships between the data of rock core acoustic signals and rock core sensitivity degree of unloading-disturbance.It indicates that the wavelet transformation method is superior for rock cores unloading-disturbance analysis.

Combining with an engineering case of soft ground treatment about the experimental segment of expressway of the south shore connecting line of Hangzhou Bay spanning bridge,the technology of surcharge preloading is studied.To comprehend the treatment effectt,he in-situ monitoring has been conducted for more than two years.The following results can be drawn.The post-construction settlement is less than 15 cm,meeting the design requirement that the post-construction settlement should be less than 30 cm.The deep compression of soft soil mainly occurs in the scope of the prefabricated vertical drains.The horizontal displacement of soil mainly takes place in the range below the roadbed with depth of 16 m;and the direction of the horizontal displacement below the roadbed with depth of 7 m points to the improvement area,but the one between 7–16 m below the roadbed deviates to outside of improvement area.In the preloading anaphase,the cross-section settlement appears obvious pot bottom shape;and the pore water pressure changes obviously and sensitively in the shallow soil layers,but the one in deep region responds slowly.The results of both vane shear test and laboratory soil test show that the physical properties of soil have been improved obviously after improvement;and the engineering mechanical properties have also been strengthened obviously.These indicate that the surcharge preloading method is very effective for treatment of the soft clay ground of the ordinary expressway section and feasible in the similar road segments in this area.

For the foundation treatment of the experimental segment of the south shore expressway of the Hangzhou Bay Cross Sea Bridge,the in situ monitoring has been conducted for more than two years by use of vacuum-surcharge preloading.Through analyzing and comparing the experimental data and the in situ measured data before and after improvement,it can be seen that the vacuum surcharge preloading technique is successful in dealing with the deep soft base.

Concrete-cored sand-gravel pile as a new technique for improvement of soft foundation is briefly introduced.Based on the squeezing effect in the process of pile sinking,the squeezing behaviour of concrete-cored sand-gravel piles is analyzed by applying cavity expansion theory and consolidation theory.Results of calculation show that dissipation of excess pore water pressure due to squeezing effect of concrete-cored sand-gravel piles is faster than that of the ordinary CFG piles.