Effectiveness of Geoelectrical Resistivity Surveys for the Detection of a Debris Flow Causative Water Conducting Zone at KM 9, Gap-Fraser’s Hill Road (FT 148), Fraser’s Hill, Pahang, Malaysia

Abstract

This study reports the findings of resistivity surveys which were conducted at the initiation area of debris flow at KM 9, Fraser’s Hill Gap road (FT148). The study involves three slope parallel survey lines and two lines perpendicular to the slope face. The parallel lines are FH01, FH02, and FH03, while the lines FH04 and FH05 are perpendicular. A granite body was detected at the central part of the east line and is nearest to the ground surface along FH02. The existence of low resistivity zones within the granite body is interpreted as highly fractured, water conducting zones. These zones are continuous as they have been detected in both the east-west as well as the north-south lines. The residual soil layer is relatively thin at zones where weathered granite dominates the slope face of the failure mass. The weak layer is relatively thick with an estimated thickness of 80 m and water flow occurs at the base of it. The high water flow recorded from the horizontal drains further supports the possible existence of these highly fractured, water conducting zones located within the granite. The shallow fractured granite is virtually “floating” above the water saturated zone and therefore is considered unstable.

Analysis of Geotechnical-Assisted 2-D Electrical Resistivity Tomography Monitoring of Slope Instability in Residual Soil of Weathered Granitic Basement

“…The inverted ERT models were interpreted on the scale of resistivity values that were classified into zones as shown in Table 6. The table shows both weathered and unweathered basement and its spatial distribution of resistivity values into saturated zones with resistivity values ranging from 1 to 600 Ωm, weak zones with resistivity values ranging from 600 to 3,000 Ωm, and basement rock of resistivity value > 5,000 Ωm (Palacky, 1987;Reynolds, 1997;Ghazali et al, 2013).…”

“…These properties are similar to cohesive materials of high proportion of fine-grained particles because electrical resistivity has the advantage of detecting clay content (cohesive soil) as a very low-resistivity zones (Suzuki et al, 2000), which are usually unstable weak zones of failure. Saturated zones ( Figures 9A,B) occurring in the 0-5 m depth will slide downslope when fully saturated during prolong heavy rainfall because the soil water will cause the soil to lose its cohesion which will induce movement (Carrazza et al, 2016;Ghazali et al, 2013). However, the lowest percentage of 11.4% was also obtained for soil sample collected at 41 m in Figure 9F with the highest estimated density and hydraulic conductivity obtained as 1,458 kg/m3 and 1.34 × 10 −2 m/s, respectively, with the lowest percentage of 5% silt and clay.…”

Effectiveness of Horizontal Sub-drain to Increase Slope Stability with Vertical Cracks and Weathering Soil in Areas with High Rainfall Intensity

“…McCarter (1984) showed that at low water contents, the resistivity rapidly decreases with increased water content. (Ghazali et al, 2013) stated that high-water content and weak zones can be determined as low resistivity regions by the methods used in this study. The report by (Ghazali et al, 2013) was also conducted to determine the debris ow in the soil using Geoelectrical Resistivity Surveys.…”

Pencirian Geohazad Tanah Runtuh Pendam Lama di Kawasan Bukit Fraser, Pahang

“…Bukit Fraser terletak di batolit granit Banjaran Utama yang didominasi oleh granit biotit (Mohamad Anuri et al 2013). Dua sesar utama, iaitu Sesar Kuala Lumpur dan Sesar Bukit Tinggi, berpotongan dengan rangkaian bukit ini dan terdapat sesar-sesar kecil di dalamnya (Gobbet & Hutchinson 1973).…”