管幕内顶进箱涵顶部管幕挠度分析

AN ANALYSIS OF THE DEFLECTION OF A PIPE-ROOF FOR BOX CULVERT JACKING

上海市中环线虹许路北虹路下立交工程是目前世界上在饱和含水软土地层中施工的截面最大的管幕法工程。按箱涵顶进土体开挖过程中前方土体的可能滑动的最不利情况分析了顶部钢管幕的挠度问题,以便在设计时对管幕的挠度以及地面的可能沉降有充分的认识。针对钢管不同部分的受力状况不同,主要按悬臂梁、两端固定梁以及弹性地基梁3种模型分情况对钢管的不同部分进行计算分析,并对该工程的情况进行了具体的分析。结果发现当管幕纵向两端自由时在开始进洞阶段钢管上会产生极大挠度,进而对后面顶进过程中钢管的挠曲产生重要影响,整个箱涵顶进过程中钢管的最大挠度出现在两端点处。当管幕纵向两端固定时,钢管挠曲有较大程度地减小,整个过程中最大挠度出现在钢管中点。

The subway project crossing under the Hongxu road employed pipe-roof to push a box culvert of the largest in the world at present cross section into the saturated soft soil stratum under the Beihong road located in the middle ring-road in Shanghai. In this paper, based on the worst potential sliding condition of the soil in front of the box culvert during excavation and push, deflection of the pipe-proof is analyzed to facilitate design and construction. Because different segments of these pipes are in different mechanical states, they are analyzed by using cantilevered beam model, supported beam model with fixed boundary and beam-on-elastic-foundation model. The results show that the largest deflection occras at the starting point of the pipe if its two ends are free when the two culverts being pushed vis-à-vis from the two working pits, respectively. The largest deflection of the pipe in the starting stage of the push significantly impacts the deflection of the pipe in later stages of the push. However, the largest deflection occurs at middle point of the pipe if its two ends are fixed and the deflection of the pipe is much smaller.