The Numerical Analysis of Tunnel Traversing Piles and Its Seismic Response in Deep Soft Soil

The Ou River estuary deposits deep soft silt and silt clay, the pipe-jacking tunnel departures from Qidu island, then passes underneath north levee road, viewing platform, Ou River and Ou River road, finally reaches the received well. The net distance between tunnel segment and the viewing platform piles is only 230mm. In order to analyze the negative influence of large diameter pipe-jacking tunnel traversing piles of viewing platform, the numerical model is established, and the levee road settlement value is found which matches with observed settlement very well. The dynamic analysis is also conducted by EI Centro seismic wave, and the result reveals that the max displacement occurs on the segment between the rear row piles of viewing platform, and the max displacement reaches 68.6mm in the earthquake.

A Case Study of Vacuum Tube-Well Dewatering Technology for Improving Deep Soft Soil in Yangtze River Floodplain

Deep soft soil of the Yangtze River floodplain in Nanjing has a special interlayer structure, which provides favorable conditions for the application of vacuum tube-well dewatering technology. This paper focuses on the design, construction and treatment effect of vacuum tube-well dewatering technology. The hydrological parameters and the hydraulic connections between the various layers of the site have been ascertained through two simple single-well multi-holes pumping tests. Moreover, the layout of vacuum tube-wells and depressurization wells in a test site with 84m length and 84m width was designed based on the above parameters. Field tests of vacuum tube-well dewatering technology were conducted on the test site. And the changes of groundwater level, ground settlement and pore water pressure during the test was monitored. The CPTU test technology was used to quickly evaluate the engineering properties of the site before and after treatment. Finally, combined with the settlement monitoring data, the hyperbolic method was used to predict the final settlement. The results indicated that consolidation efficiency of vacuum tube-well dewatering technology has obvious advantages. Implications of this study can provide a reference for the construction design of the site's ground improvement consolidation and other similar projects.

The reinforcement effects of deep soft soil foundation with high degree of saturation under dynamic compaction

The dynamic compaction method is effective to reinforce soft soil foundation with a low degree of saturation. However, deep soft soil foundation with high degree of saturation has some different characteristics. It has been widely considered that dynamic compaction method is unsuitable to improve the characters of deep soft soil foundation with high degree of saturation. In this article, we will show that the dynamic compaction method with vacuum well-point dewatering is effective to deep soft soil foundation with high degree of saturation reinforcement. In situ and laboratorial experiments are used to assess the reinforcement effect of the deep soft soil foundation with high degree of saturation. Our results show that the dynamic compaction method causes long dissipation time of pore water pressure, and the dynamic compaction method with vacuum well-point dewatering makes construction time of a project 25% shorter. The effective depth of deep soft soil foundation with high degree of saturation reinforcement using the two experimental methods can reach to 8.0 m. In comparison with the total settlement and layered settlement of the dynamic compaction method with vacuum well-point dewatering, the dynamic compaction method settlement is relatively smaller. For soils with depth of 4 m, the reinforcement effect of dynamic compaction method with vacuum well-point dewatering is obviously superior to dynamic compaction method. Based on these results, we suggest construction procedures for different reinforcement depth of soils and construction time.