Study of Pipe-Jacking Force in Gravel Formation

[[abstract]]由於在都會區之地底下早已管線密佈，為避免因管線施工造成鄰近居民生活受影響，使得推進工法成為免開挖工法之主軸，但現地推進過程中仍多仰賴施工人員之施工經驗，係因推進力在實務與經驗計算公式尚未相互印證所致，為使推進工程推進力之估算能符合現地之需求，本文蒐集台電公司大口徑曲線推進工程，在卵礫石地質之施工案例，利用日本下水道管渠推進技術協會建議之經驗公式與實際發生之推進紀錄，進行推進力之回饋分析，並探討推進工程在卵礫石地質中，直線推進在銜接曲線段推進時，推進管壁與土壤間之摩擦力折減係數及面盤切削抵抗係數之變化，以供未來在相同區域或類似地質區域進行推進工程時，估算推進力時之參考。 本研究係以台電公司大口徑曲線推進工程在卵礫石地質之施工案例為根據，藉由各案例之地質鑽探報告書、曲線推進工程之設計資料及實際施工推進力監測資料，採用最小平方差方法來進行推進力回饋分析，並將各卵礫石地質所回饋出之參數進行分析、整理及修正，進而達到在相同卵礫石地質條件情形下，產生之管壁與土壤間之摩擦力折減係數及面盤切削抵抗係數，能於推進工程施工初期提供有利於選擇適當之推進機組來施工。 依據回饋分析結果，面盤切削抵抗係數（α），大部分高於經驗公式所設定之數值（0.5）；推進力折減係數（β）則全數低於經驗公式所設定之數值（0.6），即現地土壤摩擦力並未如經驗公式高，於實地施工時可適時減少元押及中押千斤頂之使用數量，可達節省成本之目的。[[abstract]]Nowadays the underground life-lines have been densely distributed in metropolitan area. Pipe-jacking has become the main-stream of non-excavation methods in order to minimize the influence of nearby residents and environment caused by pipe-line construction. As a matter of fact the on-site process of pipe-jacking is still more dependent on the experience of construction workers, since the pipe-jacking forces from design formulas are not authenticated with in-situ performance. In order to improve the estimation of pipe-jacking force, this study collects construction information of large-diameter curved pipe-jacking in gravel formation of Tai-Power Company projects. The authors employ the empirical formulas proposed by the “Japanese Association of Pipe-Jacking Technology in Sewer Pipes”, and perform feedback analysis of the friction parameters between the pipe-wall and the soil. This study also discusses the variation of the friction parameters around pipe surface and the pressure-resistance coefficient of the shield head of conjunct curved-segment of straight-line sections of pipe jacking in gravel formations. The authors wish the result of this study provides useful reference for estimating pipe-jacking forces in similar regions and/or geological conditions. This study firstly compiles the geological investigation reports, design information, as well as monitoring data during pipe-jacking construction from practical cases of large-diameter curved pipe-jacking in gravel formations of Tai-Power Company. Secondly, the least-squares method is utilized to perform feedback analysis of pipe-jacking force. Then the feedback-parameters are analysed and modified to obtain the reduction coefficient of frictions between the pipe-wall and the soil, as well as the pressure-resistance coefficient of the shield head. Accordingly, the result is expected to be useful for selecting appropriate jacking machines in advance of construction work. Based upon the feedback analysis, the pressure-resistance coefficients of the shield head (α) are mostly higher than the value 0.5 as suggested in empirical formula. The reduction coefficients of pipe-jacking force (β) are all lower than the value 0.6 as suggested in empirical formula. The result indicates the fact that the in-situ soil friction is not as high as predicted in empirical formula. Therefore the amount of jacks could be properly reduced, so as to save the construction cost