應用簡易貫入試驗及大地比電阻法推估崩積地土壤岩層界面

Applying Cone Penetration Testing and Electrical Resistivity Tomography to Estimate the Soil-bedrock Interface in Colluvium

10.29417/JCSWC.201412_45(4).0003

呂宗烜(Tsung-Hsuan Lu)；梁偉立(Wei-Li Liang)

簡易貫入試驗 ； 大地比電阻法 ； 鑽探法 ； 土壤岩層界面 ； Cone Penetration Test ； Electrical Resistivity Tomography ； Geological Boring ； Soil-bedrock Interface

中華水土保持學報

45卷4期（2014 / 12 / 01）

234 - 242

繁體中文

淺層崩塌為臺灣常見的土砂災害之一，其規模及範圍受土壤層厚度、基岩面位置（土壤岩層界面）等地形、地質條件影響，因此如何有效地探測基岩面的位置，為推估淺層崩塌的規模或範圍前需要克服的問題。本研究於具有崩積地層的三樣區進行，首先於面積較小的淺層崩塌樣區進行大地比電阻法、簡易貫入試驗及鑽探法三種試驗，確認三種試驗法於基岩面位置之探測能力；接著應用簡易貫入試驗及大地比電阻法於面積較大的二新植造林樣區，探討大地比電阻法對於廣域基岩面位置的判釋能力。對照鑽探資料，本研究證明簡易貫入試驗對於推測土壤厚度、基岩面位置皆具有良好精度；由大地比電阻法所得的資料顯示，基岩面所在位置比電阻變化急遽，故可利用此現象來判斷基岩面位置。就廣域探測而言，在崩積地層中基岩面的比電阻值變化差異較大，不易從固定比電阻值範圍來推斷基岩面的位置，且比電阻值易受電極排列方法、崩積地層複雜性之影響，偶有難判釋土壤岩層界面之情況，因此本研究建議實施大地比電阻法時，可搭配較經濟、易於坡地環境施行的簡易貫入試驗，以增進大地比電阻法判釋廣域崩積地層中基岩面位置之精度。

Shallow slope failure is one of the common sediment disasters in Taiwan. The size and range of a shallow slope failure depend on topographic and geological conditions, such as soil depth and bedrock topography (soil-bedrock interface). Thus, the methods for detecting the soil-bedrock interface need to be established before predicting or estimating the size and range of shallow slope failure occurrence. In this study, we selected three sites on colluvial slopes. First, we verified the applicability of electrical resistivity tomography (ERT), cone penetration testing (CPT), and geological boring methods for detecting the soil-bedrock interface at a site with a shallow slope failure. Then, we applied ERT and CPT to investigate the bedrock topography at two large-scale sites. Based on the information of the boring cores, we confirmed that CPT can effectively detect soil depth and the soil-bedrock interface. Moreover, the characteristic of electrical resistivity that changes greatly between soil and bedrock layers can be used to detect the soil-bedrock interface. For large-scale investigations, it is sometimes difficult to estimate the location of the soil-bedrock interface because electrical resistivity varies greatly in the colluvial layers and electrical resistivity is sensitive to electrode arrays and the complexity of the colluvial environment. Because CPT is economical and convenient for a large-scale slope environment, we therefore suggest that the combination of ERT and CPT is an effective way to detect the soil-bedrock interface in a colluvial environment.