黏性背填土壤之力學性質對加勁擋土牆變形之影響

The Effect of Mechanical Properties of Cohesive Backfill on Deformation of Geosynthetic Reinforced Earth Wall

吳仁傑(Ren-jie Wu)

指導教授 ： 李崇正 ； 陳慧慈

國立中央大學/工學院/土木工程學系/碩士(2007年)

摘要

加勁擋土牆的設計規範多規定以滲透性高的顆粒性土壤作為背填材料，但實際上施工現場常用現地非顆粒性土壤或黏土回填，這種作法勢必影響加勁擋土牆牆體之變形行為，因此引起了諸多研究。過去國外以離心機探討黏性背填土加勁擋土牆的行為時，大都使用高嶺土，而國內的研究則使用中大紅土。雖然皆屬黏性土壤，但對加勁擋土牆的變形研究所獲致的結論是否一致，實有必要進行探討。
本研究以地工離心機進行離心模型試驗，探討以低強度高嶺土為背填土壤的加勁擋土牆於不同加勁材的配置下的各種變形行為，並與先前以低強度中大紅土為背填土壤的加勁擋土牆的結果進行比較，期望能闡明不同黏性背填土壤之力學性質對加勁擋土牆變形之影響。
研究結果顯示： 1.影響高嶺土試體與中大紅土試體之加勁擋土牆變形行為的差異，最主要因素為土壤的彈性模數不同，顯示土壤力學性質對牆體變形行為的影響甚鉅。2. 當加勁間距縮短為20mm、加勁材長度增長為0.85H時，高嶺土試體與中大紅土試體皆可有效的減少牆體的沈陷量及前傾量，兩者前傾改善率都能達到90%，但高嶺土試體沉陷改善率為74%而中大紅土試體沉陷改善率為92%，這表示高嶺土試體壓縮性大於中大紅土試體。3.在兩者牆體變形行為方面，加勁間距為30mm時，牆面變形行為呈肚凸狀；加勁間距為20mm時，牆面變形行為呈前傾狀；在加勁間距為40mm時，牆體變形行為不同，高嶺土試體牆面變形行為呈肚凸狀，而中大紅土試體牆面變形行為呈前傾狀。4.在裂縫發展方面，因高嶺土具有延展性，故牆頂裂縫產生不易；但高嶺土試體與中大紅土試體裂縫發生位置卻相同，而裂縫發生時機與狀態相異。整體而言，若欲以離心模型試驗來探討特定地區的大地工程結構的行為時，有必要使用現地土壤製作試體，方能得到更確切的結果。

關鍵字

高嶺土 ； 離心模型試驗 ； 加勁擋土牆 ； 中大紅土

並列摘要

For the backfill materials of the geosynthetic reinforced earth walls (GREWs), the design and construction guidelines usually require the use of high quality granular. In practice, nevertheless, the cohesive soil or clay is frequently used to cut down the cost. Over the past years, centrifuge modeling technique has been adopted to investigate the effect of cohesive soil on the deformation of GREWs, where either the kaolin or the laterite was chosen as the backfill. However, even under the category of clayey soil, different kinds of clayey soil exhibit different mechanical properties which may affect the wall behavior significantly. Therefore, in this study, a series of centrifuge modeling tests was performed to investigate the deformation of the vertical geosynthetic reinforced earth wall (VGREW) with low strength kaolin backfill and the improvement on the wall deformation was also studied by using the different arrangement of reinforcement. The obtained results were then compared with those using laterite as backfill.
From the test results, conclusions can be drawn as follows. (1) The secant modulus, E50, of the cohesive backfill is the most important factor to influence the deformation of VGREWs, implying that the in-situ soil should be used as the backfill to simulate the wall behaviors. (2) It is more effective to reduce the settlement and the horizontal displacement of VGREW by decreasing reinforcement spacing with better effect being for laterite backfill than for kaolin backfill. (3) From the deformation point of view, the deformed shape of wall face changes form bulging to tilting when the reinforcement spacing is decreased. (4) For two types of backfill soil compared in this study, with the same arrangement of reinforcement, the positions of the crack on the wall top are identical, while the timing for crack occurrence is totally different.

並列關鍵字

geosynthetic reinforced earth wall ； centrifuge modeling

參考文獻

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