台灣西南部泥岩地區植生護坡之根系力學模式應用性探討

The Suitability of Root Mechanical Model Applied on Vegetative Slope Protection for the Mudstones in Southwestern Taiwan

蔡光榮(Kuang-Jung Tsai)

《地工技術》 48期 (1994/12) Pp. 49-61

https://doi.org/10.30140/SG.199412.0004

摘要

台灣省西南部泥岩坡地，分佈面積廣達1014平方公里，惟泥岩岩性軟弱恐水，以坋土粒為其主要組成，極易遭受水蝕崩解而流失成災，又因其本身富含高濃度鹽基納離子（Na^+），常使其經風化之土壤呈中至強鹼性反應（pH≥8.5），故對於農業上實值利用性偏低，加以植生撫育不易，每遇雨季遭受颱風豪雨侵襲時，即產生地表逕流之激烈沖蝕而形成裸露陡峭惡地形，尤以本省西南部之丘陸坡地為甚。其主要分佈範圍密集於高雄縣和台南縣境內海拔50公尺至799公尺間之坡地，且以曾文溪與二仁溪等二大集水區為其主要區域，據近20年來之統計得知，崩坍裸露面之擴增倍數，高達1.51倍，由民國58年之2532.58公頃，擴大至民國76年之3836.28公頃，且以坡度30－45°間之南向坡最為嚴重，因此泥岩地區之植生復舊工作，將成為未來泥岩坡地保育利用之重點。本研究重點首先推導出泥岩地區之根系力學理論模式，再著重於野外試驗儀器之開發設計及泥岩地區各類植生根系之現地抗剪試驗與統計檢定分析，進而據以檢討根系力學模式之適用性與限制性。本試驗分析結果顯示，泥岩地區經根系補強後之土壤抗剪強度增加量，大多取決於根系補強後之土壤凝聚力（C）之變化，而受其內摩擦角（ø）之影響較小，若依不同植生根系補強之功能分析，發現根系補強度後之土壤抗剪力增加量依序為銀合歡＞白茅≥百喜草＞五節芒＞百慕達草，至於經以根系力學理論模式之檢測修正與根系補強係數之校正後，發現植物根系基本固土功能，乃以主根系之防坍止滑功能，結合側根或鬢根系之增加土壤團粒穩定度與防沖抗蝕作用為主體而發揮功效，至於主根系對邊坡安定之補強功能，依據野外試驗結果顯示，其抗剪強度平均值幾可達全根系補強教應之85%以上，惟因根系固土力學特性之研究，在國內尚屬啟蒙時期，故不論在基礎理論之發展，新儀器之開發設計與理論模式之適用性探討與地域性限制因素之克服，均有待進一步之深入研究。

關鍵字

泥岩 ； 護坡 ； 根系力學

並列摘要

The first year of this study is to concentrate on developing the rootmechanical model based on the principle of equilibrium theory of mechanicsand the rule of dimension analysis. To evaluate the function of soil-rootreinforced model, in situ root tests were executed el during the period of this project.A new apparatus with a shearing box of 20cm × 20cm × l0cm has been developed forconducting the direct shear test of reinforced soil in the field. Fivedifferent varieties of biological root systems were chosen as sample examinedin mudstone areas. Also, the judgement of soil-root reinforced coefficient foreach variety of vegetation would be necessary. The limitations andsuitability of this model had been studied in detail at the end of thisresearch. All the parameters are going to be figurized, tablized andcomputerized through the information systems developed from this project. Thetape root has been found to take over more than 85% of shear strengthincrements on the soil-root reinforced systems.The increment of shear strength was identified to be much more significant on the soil cohesion force (C) than on the internal friction angle (ø) in the soil-root reinforecd system. It is expected that this research canoffer an index used to select right species of vegetation for side-slopeprotection based on their root bonding function in the soil-root reinforcedsystems located at the mudstones in southwestern Taiwan.

並列關鍵字

mudstone ； slope protection ； root mechanics