Research On Consolidation Effect Of Ultra-soft Soil Under Static-Dynamic Drainage

The Static-Dynamic Drainage Consolidation Method (SDDCM) is widely used in the saturated soft soil as well as other poor foundation for its fast and efficient treatment effect. Many domestic and foreign scholars studied the dynamic characteristics of the soil samples with lower water content, and got some significant conclusions, however, the ultra-soft soil under the impact loading of the internal law of mechanical response and the research on impact consolidation effect are still rarely reported, which static and dynamic response remains to be discussed. Especially the influence of different impact loading frequency (including high frequency) to the mechanical response of different depth.In this paper, using the improved SPAX-2000 true triaxial testing system, the conventional triaxial and true triaxial static and dynamic drainage consolidation test for muck was carried out. And then investigated the mechanical responses of muck under the action of different impact loading frequency(1Hz,8Hz,16Hz), different confining pressure (200kPa,250kPa,300kPa) and different intermediate principal stress(250kPa,300kPa,350kPa). Combined with triaxial shear tests study the undrained strength development of muck under different consolidation conditions. The experimental results are as follows:Using true triaxial tests to simulate the static-dynamic consolidation method, and research on the regularity of the mechanical response such as the impact of stress, pore water pressure and soil deformation changes during the process. The work involves several aspects as follow:1. For conventional triaxial test:(1) The axial strain of the specimen will change with the impact loading frequency changes, under the same confining pressure, there is a impact loading frequency threshold, when frequency is lower than the threshold, with the improvement of impact loading frequency, the axial strain should be gradually become smaller, whereas increases gradually.(2) At the instant of the impact, the volume strain is negative, characterized by volume expansion, and it is identical with the in situ test lamping moments of pore water pressure curve, thus verified the high water content of muck under the impact of negative pore pressure.2. The true triaxial test:(1) In the process of impact loading, the curves of deviatoric stress-axial strain forming a lower end of the opening and non-enclosed hysteresis loop, and the surrounding area size and shape of the plastic ring are variational, as shown in Figure 5-12. In the initial phase, the area of the hysteresis loop and not closing degree is larger, plastic deformation and energy dissipation are relatively large as well, gradually decreases with the increase of the impact loading times, all of them become smaller gradually. In the initial unloading phase the deviatoric stress is reduced, and it is too fast for the axial strain to change, so it remains to continue to increase the maximum. The largest moment of deviatoric stress is not the largest time of the deviatoric strain, indicates that there is strain hysteresis of the muck specimen in loading and unloading transition section.(2) Under the same impact loading frequency, hysteretic curve is more and more steep with the increase of intermediate principal stress, That is to say the dynamic modulus of deformation increases constantly with the increase of intermediate principal stress. Under the same intermediate principal stress, as the impact frequency increased, the area of hysteresis loop constantly decrescent, namely the maximum shear strain restricted and smaller impact energy loss under the effect of high impact loading frequency.(3) After the impact consolidation effect, in the initial shear phase, the incremental energy versus time AEv-T curves increased rapidly under the same intermediate principal stress, then the energy curve of high impact loading frequency first to stabilize and energy reach saturation status. It shows that under the same impact energy action, the impact of high frequency micro-tremor such as blasting and quake on the soft clay foundation of buildings is greater, and it is easy to make the energy of foundation soil reaches saturation, capacity dissipating and causes building destruction. Under the same impact loading frequency and different intermediate principal stress, the △Ev-T curves rises gradually in the shear phase, along with the increase of intermediate principal stress, the greater the intermediate principal stress is, the faster the energy grows, and the greater the energy increases.