Gully Cavity Identification Through Electrical Resistivity Tomography

Abstract

ABSTRACT. Chaotic urban expansion often leads to hazardous environmental consequences. The absense of rainwater outflow management, coupled with low cohesion in some terrains is a geotechnical threat for the population since it may lead to gully formation...Keywords: piping, geophysics, electrical resistivity, electrical resistivity tomography. RESUMO. A expansão urbana desordenada pode gerar graves consequências ao ambiente. A falta de planejamento no escoamento de águas pluviais, aliado à baixa coesão de alguns terrenos pode proporcionar o surgimento de voçorocas,Palavras-chave: piping, geofísica, resistividade elétrica, tomografia elétrica.

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

“…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. It also validates the weak zones identified on the ERT model as yellow color and interpreted as sand and gravel with a resistivity value of 3,000 Ωm that suggests a permeable loose unconsolidated coarse grain material with a small amount of fine-grained particles (Shelton, 2005) that may be susceptible to soil liquefaction and piping (Carrazza et al, 2016). The particle-size distribution reveals two major types of soils which are coarse sand and sandy loam based on Wentworth (1922) classification.…”

“…Drainage path is a region where failure is initiated in slope because the water flowing through this path can initiate soil internal erosion referred to as soil pipe. Internal erosion such as piping has been responsible for most landslides occurring in the world as reported by several researchers (Carrazza et al, 2016;Okeke and Wang, 2016;Bernatek-Jakiel and Poesen, 2018). Resistivity values > 5,000 Ωm were interpreted as basement rock without cracks or openings.…”

“…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.…”

Tracing shallow lateral preferential pathways of fluid movement using electrical geophysics

“…Previous studies have implemented combinations of geophysical techniques including ERI and FEM for identification of near-surface features; these include an investigation on detecting cavities by Carrazza and Helene (2016) as well as another study into cave systems associated to urban hazards conducted by Lazzari et al (2010). Carrazza and Helene (2016) conducted a near surface geophysical investigation implementing ERI for the detection of cavities.…”

“…Carrazza and Helene (2016) conducted a near surface geophysical investigation implementing ERI for the detection of cavities. It was hypothesized that the piping phenomenon of soils generated these air-filled cavities related to material failure.…”