Risk Analysis And Its Application For Tunnel Works Based On Research Of Stratum And Soil Spatial Variability

Tunneling works were characterized by high degree of uncertainty. These uncertainties stem from two major problems: the geologic conditions are never known exactly and particular for deep and long crossing river tunnels; preconstruction information may be very sparse. And the first uncertain factor may have greater impaction on tunneling. It is known that the geologic uncertainty about spatial variability of stratum and soil is one of the biggest problems on which were focused by many researchers at home and abroad during the last three decades. Due to the inherent uncertainties including soil and groundwater conditions, there might be significant cost overrun and time delay risks in tunneling works. So the dissertation focused on the research of the spatial variability of stratum and soil, and established some theoretical models and calculating methods for application in risk analysis of tunneling works. The dissertation is supported by Shanghai Municipal Science and Technology Commission (Grant No.04dz12021) and its research achievement can be applied in the risk analysis on construction of Shanghai Yangtze River. Some main works and results about the dissertation were listed as follow.(1) Shanghai Yangtze River Tunnel is the biggest worldwide tunnel project. The dissertation firstly gave a brief introduction about the project and listed some most difficult construction problems in tunneling, such as the biggest diameter, high water pressure up to 0.6MPa, all long distance about 8.95km and multilayered shield excavation. Those key risk-induced factors were analyzed and discussed in detail by comparing with some other bigger tunnels all over world. Furthermore, all the important risks of the project were identified and summarized based on some engineering practice and experience.(2) Some uncertainties about geological site investigation were analyzed. And some terms about stratum like soil family and soil cluster were defined firstly. In order to calculate the stochastic distribution about strata, some methods were established to calculate probability of different soil clusters, soil families and soil types. Because of the co-existence of a soil type with many other soil types in a given site, the probability of co-existence of different soil types was measured against the soil with other soils under different clusters. Then we can get the probability of finding a soil type at a target point along tunnel alignment with respect to the clusters and soils that exist in the neighborhood of some boreholes. On the...