场地断裂活动效应的风险分析与评价——以宿迁三线船闸为例

断裂研究是区域和场地稳定性评价以及工程抗震设计中的一项重要的基础性工作。对于有断裂通过的工程场地,从断裂、场地土层和工程三者相互作用的角度出发,开展有针对性的场地断裂活动效应及地震稳定性研究,对保证工程的安全建设和可靠运行有着极为重要的现实意义。本文试以宿迁三线船闸的建设为例,对场地断裂活动效应的风险进行分析与评价。

Risk Analysis and Evaluation of Site Fault Activity Effects--A Case Study of Suqian Ship Lock Group

Suqian ship lock group locates in the mid-south segment of famous Tancheng-Lujiang Fault, where a large earthquake of M8. 5 once occurred in history. From the view of interaction among fault, site and construction, the fault activity and seismic stability in the site of Suqian ship lock group are studied for the risk analysis and evaluation of site fault activity.The geological survey of the site shows that the main site fault across Suqian ship lock group affects the soil layers to a depth of 20 m or more which is 5 ?5 m under the base of lock chambers. The fault will not be exposed when the soil is excavated for building lock, whereas the distribution of faults provides a favourable tectonic condition for earthquake occurence. When the buried depth of fault exceeds a critical value, the surface dislocation caused by earthquake can be neglected. The survey data shows that the top of main fault of the site is 15 m below the base of lock chambers, therefore the possibility of surface dislocation and its influence on ship locks are relatively little.In the further analysis and evaluation of the risk of site fault activity effects, the elaspse rate and activity (in terms of average rate and seismic period) of fault and the seismic fragility of geological factors are taken into account. The formula for evaluating the risk of site fault activity effects is given as follows:HD = E×M/8 × (x1+…+xn)/n]where HD is hazard degree of site fault activity effects, E is elapse rate of fault (ranging from 0 to 1) , M is the activity of fault represented in earthquake magnitude (M≥8) , .r, is the seismic fragility of geological factor represented in index of earthquake hazard (ranging from 0 to 1), and n is the number of considered geological factors. HD ranges from 0 to 1, the larger the value of which is, the higher the risk of fault activity will be.Although the geological background of ship lock group and the global environment of the site are not favourable, it is found after the analysis of the mode of interaction among fault, site structure and ship lock group that the upper site soil layers connected the most closely with the ship lock have not been affected by main fault, which will ensure the ship lock running in safety. It is found after the synthetical analysis of the large amount of borehole data that there are stable silty clay and clay layers at the depth of 5. 5 m to 8. 5 m. It is suggested that the foundation of ship locks should lay on such layers, in order to obtain higher degree of safety.