多階加勁邊坡於泥岩邊坡保護數值分析

Numerical Evaluation of A Multi-tier Geosynthetic-reinforced Soil Slope for Mudstone Slope Protection

駱建澄(Chien-Cheng Lo)

指導教授 ： 楊國鑫

國立臺灣大學/工學院/土木工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903561

摘要

台灣西南部泥岩於地質上屬西部麓山帶古亭坑層，其形成時間介於上新世至更新世之間。泥岩材料力學性質特殊，泥岩處於乾燥狀態亦或濕潤狀態，其剪力強度下降幅度相當顯著，此和泥岩的成岩鍵結溶解化學反應作用有關，鍵結溶解時礦物間束制能力降低而產生回脹，本研究中將以非飽和土壤力學模擬泥岩吸水回脹特性。此外，台灣西南部氣候特性於乾季時經歷長時間乾燥，於汛季時轉變為高強度降雨，於本研究中汛季於三個月中累積降雨量達到3,000 mm。於泥岩邊坡中因表層土壤含水量達到縮性限度而開裂，開裂後之泥岩邊坡受高強度降雨作用而使開裂逐漸加深，最終邊坡由頂部開裂至底部學者們將此命名為侵蝕管道，中空的侵蝕管道無法提供邊坡剪力強度，因此隨著邊坡侵蝕管道不斷發展，邊坡剪力強度將弱化至小於等於驅動剪應力而發生破壞。
因此在泥岩邊坡的防護上，以不讓雨水入滲至泥岩中為最優先目標，而傳統的工法為噴漿，然而隨著環保議題關注現今已鮮少使用噴漿方式進行邊坡防護，取代噴漿的防護方式是掛網植生，但泥岩的表面沖刷特性使得此工法無法有效防護。本論文將探討採用加勁邊坡護坡方式是否能有效對泥岩邊坡進行防護，因加勁邊坡護坡本身自重可提供泥岩對抗回脹所需要之圍壓，再者加勁邊坡於建造過程中為防止回填材料流失，將鋪設土包袋及地工織物回包方式，可有效防止泥岩邊坡表面侵蝕問題。本論文將針對加勁邊坡護坡排水能力對邊坡穩定性之影響、加勁邊坡護坡抗表面侵蝕能力及泥岩邊坡回脹特性對護坡變形影響，以滲流與應力耦合分析及強度折減分析進行數值分析探討。

關鍵字

泥岩邊坡坡面侵蝕 ； 加勁邊坡護坡 ； 不飽和土壤 ； 滲流與應力耦合分析 ； 強度折減分析 ； 泥岩回脹特性

並列摘要

The mudstones in southwestern Taiwan belong to the ancient pavilion of the western Laoshan belt in geology. The formation time of mudstone formation was between the Pliocene and the Pleistocene. The mechanical properties of mudstone have some special characteristic. When mudstones transfer the water content form dry state into wet state, the shear strength would decrease significantly. This is related to the diagenetic bond dissolution chemical reaction of mudstone. When the bond is dissolved, the inter-mineral beam-forming ability is reduced. Inflated, the unsaturated soil mechanics will be used to simulate the swelling behavior of mudstone. In addition, the climatic characteristics of southwestern Taiwan experienced long-term dryness during the dry season and high intensity rainfall during the flood season. In this study, the accumulated rainfall reached 3,000 mm in June to August. The surface soil of mudstone slope water cracked due to reaching the shrinkage limit. The crack would develop because of the high intensity rainfall. In the end, the slope would develop the erosion pipe when the crack pass through the crust and the toe of slope. The erosion pipe cannot provide the shear strength for stability. Therefore, as the erosion pipes develops continuously, the shear strength of the slope will be weakened to less than or equal to the driving shear stress and cause failure.
Therefore, the top priority of mudstone slope protection is the prevention of rainfall infiltration. The most traditional method is shotcreting, but with the rising of environmental protection consciousness, it is rarely used nowadays. Therefore, the way to improve the mudstone slope protection is hanged-net with spraying seed. However, the characteristics of mudstone slope when undergoing high intensity rainfall is surface erosion, that make the method invalid to protecting. This paper will discuss whether the use of mechanically stabilized earth slope protection method can effectively protect the mudstone slope. Because the self-weight of the MSES can provide the confining pressure required to resist the swelling of mudstone. When design the MSES, the prevention of backfill material loss must be fully considered. The method of installation the soil bag and the geotextile returned-facing will be used to effectively prevent the erosion of mudstone slope surface. This paper will focus on whether the drainage system function will influence on the stability of the slope. The issue of surface erosion prevention will be discussed, concentrating on the difference of fully protecting MSES and the partially protecting MSES. In the end, to do the numerical analysis, the fully coupled analysis of seepage and stress and the strength reduction analysis would be executed.

並列關鍵字

Mudstone slope ； MSES ； unsaturated soil ； hydro-mechanical coupling analysis ； strength reduction ； swelling characteristic

參考文獻

AASHTO.（2002）. Standard specifications for highway bridges. American Association of State Highway and Transportation Officials, Sevententh Edition, Washington, D.C., with interms.

ASTM D1557-2000 Standard test methods for laboratory compaction characteristics of soil using modified effort. 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

ASTM D2166-2000 Standard test method for unconfined compressive strength of cohesive soil1. 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

ASTM D2850-1999 Standard test method for unconsolidated undrained triaxial compression test on cohesive soils. 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

ASTM D422-2007 Standard test method for particle-size analysis of soils. 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.