含根土壤剪力強度增量評估－簡易法與蒙地卡羅模擬

Simplified Method and Monte Carlo Simulation on Prediction of Shear Strength Increment for Soil-Root System

游新旺(Hsin-Wan Yu) ； 陳主惠(Chu-Hui Chen) ； 陳致向(Chih-Hsiang Chen)

《中國土木水利工程學刊》 21卷3期 (2009/09) Pp. 351-363

https://doi.org/10.6652/JoCICHE.200909_21(3).0010

摘要

本文依據根之彈性變形、斷裂現象及土－根間產生握裹滑移等力學行為，建立含根土壤之根力模式，經由模式分析配合試驗結果，探討五節芒根系對含根土壤剪應力增量之影響。首先取不同剪力帶厚度，藉由根力模式分析計算土壤剪應力增量與剪變位關係歷程，經與試驗結果比較後，得到含根土壤試體受剪時，剪力帶厚度有隨著剪位移量之增加而變大之情形。研究中發現，當土－根間力學行為由握裹滑移控制時，根系埋置長度增加，可提高含根土壤之剪力強度增量，但當土－根間力學行為係由斷裂破壞控制時，根系埋置長度增加對含根土壤剪力強度增量貢獻甚少。由於同等級根徑下，其根長度及土－根界面握裹強度之變異係數均甚大，如使用簡易法，以定值代入根力模式，將與根之實際力學行為不符，本研究將根長度及土－根界面之握裹強度均假設為對數常態分配，以蒙地卡羅法模擬尋求含根土壤之剪應力增量，經與試驗結果比較後，確能得到較接近之評估結果。

關鍵字

根力模式 ； 剪力強度 ； 蒙地卡羅模擬

並列摘要

An analytical model responsible for the loading of root stretching, root breaking, and soil-root slipping was established in this study. From a comparison between the analytical simulation and experiments data, the effect of the roots of the silver grass on the shear strength of the soil mass was discussed. This study investigates the relationships between the shear stress increments and displacements due to changes in thickness of the shear zone. By comparing the results of the numerical simulations and experiments, we can find that the thickness of the shear zone increases with the lateral shear displacements. The soil shear strength increases with the root embedment length when the soil-root mechanism is dominated by the root slipping before breaking occurs. By contrary, the root embedment length gives slight contribution to the increment of the soil shear strength when the soil-root mechanism is dominated by the root breaking. There is a large variation in the root lengths and soil-root bonding strength even in the same root-diameter system. If we substitute the definite values into the root strength model in a simplified method, the results will not correspond to real mechanical behaviors. The study thus assumes the root length and bonding strength to be independent respectively and follows the log-normal distribution. According to observation and comparison between the data obtained from different analytical models and lab experiments, we found that the Monte Carlo Simulation method has a close relationship to the results of the assessments for shear strength increments on the soil-root system.

並列關鍵字

root strength model ； shear strength ； Monte Carlo simulation