Min Lee

Factors Affecting Improvement in Engineering Properties of Residual Soil through Microbial-Induced Calcite Precipitation

AbstractStudies of soil improvement by microbial-induced calcite precipitation (MICP) have focused primarily on fine sand. This paper explores the viability of the MICP technique for improving the engineering properties of a typical tropical residual soil. A species of Bacillus, B. megaterium, was used to trigger calcite precipitation. Four variables were considered in this study: the concentration of B. megaterium, the concentration of the cementation reagent, the treatment duration, and the flow pressure of the cementation reagent. The results show that the improvement in the engineering properties of the MICP-treated residual soils is comparable to those of treated fine sands. The preferable treatment conditions for the soil studied are B. megaterium concentration of 1×108 cfu/mL, cementation reagent concentration of 0.5 M, flow pressure of 1.1 bar of the cementation reagent, and treatment duration of 48 h. Using this combination of parameters, the obtained shear strength increase and hydraulic conduct...

Extreme rainfall characteristics for surface slope stability in the Malaysian Peninsular

This paper discusses the results of an investigation on the influence of rainfall intensity and duration on the suction distribution within a soil mass. A series of numerical analyses were conducted on an infinite slope model to simulate the responses of the slope consisting of typical soil types to various rainfall intensities and durations from selected locations in the Malaysian Peninsular. The study showed that the critical duration was governed by three major factors: the saturated permeability of the soil, the geographical location, and the depth of the slip plane. The critical rainfall duration for highly permeable soil was 1 day, while 30 days of antecedent rainfall were required for the stability analysis of a slope made of soil with low saturated permeability. The critical duration of antecedent rainfall in soils with intermediate saturated permeability was found to vary with the rainfall pattern. A chart is proposed to determine the critical duration, critical intensity and critical suction for each type of soil.

Hulu Kelang, Malaysia regional mapping of rainfall-induced landslides using TRIGRS model

Rainfall-induced slope failure is one of the most destructive natural disasters that occur frequently in natural or engineered residual soil slopes. Rainfall-induced slope failures often occur as a shallow slope failure, with slip surfaces orientated parallel to the slope surface, especially in Hulu Kelang areas where a residual soil profile has formed over a bedrock interface. The possibility of using the transient rainfall infiltration and grid-based regional slope stability analysis method (TRIGRS) is applied to unstable slopes and three rainfall threshold chart conditions that result in landslides in the study area. We compare the intensity–duration of 3-day rainfall threshold charts (I–D)3, cumulative 30-day rainfall–number of rainy day (API30–N), and cumulative 3-day rainfall–30-day antecedent precipitation index threshold chart (E3–API30) conditions capable of producing slope instability in the study area predicted by TRIGRS, with empirical rainfall I–D thresholds for possible landslide occurrence in the northeast part of Kuala Lumpur. The results showed that TRIGRS is capable of reproducing the frequency of the size of the patches of terrain predicted as unstable by the model, which match the frequency size statistics of landslides in the study area, and the rainfall threshold based on the E3–API30 threshold chart could give a better prediction to a landslide than other conditions in Hulu Kelang area. Our results are a step towards understanding the mechanisms that give rise to landslide regional modeling.

Implication of subsurface flow on rainfall-induced landslide: a case study

Post-failure field investigation, instrumentation, monitoring, and numerical simulation were performed to give insights into the failure mechanism of a 13-h-delayed rainfall-induced landslide. A conceptual hydrological model was postulated based on the findings obtained from the investigation works. The results showed that subsurface flow was recharged by intense and prolonged rainfall through outcrops of fissured bedrock. The recharged water was mounded in the moderately weathered granite layer and caused an increase in hydraulic head. The groundwater seeped gradually upward into the overlying fill layer even after the rain has ceased, and eventually triggered the landslide when the water table was raised to a critical state. As most of the existing hydrologic-slope stability models were developed on the basis of soil-impermeable bedrock model, this could result in great discrepancies between the simulated results and the real hydrological responses of the slope. The findings from the present study highlighted the importance of considering subsurface flow and hydro-geological features in assessing the mechanism of rainfall-induced landslide.

Bio-Mediated Soil Improvement under Various Concentrations of Cementation Reagent

Bio-mediated soil improvement is a relatively young technology in geotechnical engineering. The practical applications of the technique are still exposed to some uncertainties. This paper investigated the effect of the concentration of the cementation reagent on the performance of bio-mediated soil improvement. The shear strength, calcite content, pH, and ammonium content of the bio-mediated soil were measured under three concentrations of a cementation reagent, i.e. 0.25 M, 0.5 M, and 1 M. The results showed that the calcite precipitation and shear strength improved with the increased concentration of the cementation reagent up to 0.5 M. However, the improvement was retarded at higher concentration (i.e. 1.0 M). This is likely due to the inhibitory effect and halophilic characteristic of the bacteria used for the biocementation

Regional modeling of rainfall-induced landslides using TRIGRS model by incorporating plant cover effects: case study in Hulu Kelang, Malaysia

The objective of this paper is to develop a spatial temporal regional modeling of local rainfall patterns effect on the plant cover slopes in Hulu Kelang area. Rainfall interception, tree root cohesion, and tree surcharge were considered as main plant cover effects on the slope stability. In this regard, an improved version of the Transient Rainfall Infiltration and Grid-based Regional Slope stability model (TRIGRS) was performed using Microsoft Excel® and GIS framework system for coupled hydrological–mechanical modeling of rainfall-induced landslide by incorporating plant cover effects. The infiltration process of the improved model was integrated with the precipitation distribution method and rainfall interception approach while the slope stability analysis of TRIGRS model was replaced with the improved analysis with consideration of root cohesion and tree surcharge. In the following, the spatial temporal analysis of slope failures was performed using the monthly average rainfall during two different monsoon seasons of 2008 and 2009 for triggering shallow slope failure in Hulu Kelang area. The corresponding changes in pressure head and consequent water table depth were calculated during two monsoon seasons. Subsequently, factor of safety is computed using local rainfall patterns, along with root coefficient and tree surcharge in the study area. The results showed the plant-covered slopes are inducing an overestimation of the slope failure susceptibility using existing TRIGRS model, while the improved model resulted that less landslide susceptible areas were more representative of the actual stability conditions of the slopes at the study area.

Development of Data Acquisition System for Consolidated Undrained Triaxial Test

Consolidated Undrained (CU) triaxial test is a common laboratory test used in practice for determining effective and total shear strength parameters of soil. This paper reported works carried out to develop a data acquisition system for a self-assembled triaxial machine. The developed system was capable of acquiring signals from the installed sensors (i.e. pressure transducer, load cell, LVDT), interpreting and presenting the data in real-time graphs. In addition, the study highlighted the advantages of performing double vacuuming method to saturate the soil specimen. The saturation can be obtained quicker and at a significantly lower cell pressure compared to the conventional stepwise increment of back pressure and cell pressure method.

Discussion of “Critical Hydraulic Gradients of Internal Erosion under Complex Stress States” by D. S. Chang and L. M. Zhang

Wei Chao Li; Yan FengWen; Hong Cai; Min Chen Xue; Ding Song Xie; and Lee Min Lee Senior Engineer, State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, Beijing 100048, China; Senior Engineer, Dept. of Geotechnical Engineering, China Institute of Water Resources and Hydropower Research, Beijing 100048, China (corresponding author). E-mail: liwc@iwhr.com Professor, State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, Beijing 100048, China; Professor, Dept. of Geotechnical Engineering, China Institute of Water Resources and Hydropower Research, Beijing 100048, China. Professor, State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, Beijing 100048, China; Professor, Dept. of Geotechnical Engineering, China Institute of Water Resources and Hydropower Research, Beijing 100048, China. Engineer, State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, Beijing 100048, China; Engineer, Dept. of Geotechnical Engineering, China Institute of Water Resources and Hydropower Research, Beijing 100048, China. Senior Engineer, State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, Beijing 100048, China; Senior Engineer, Dept. of Geotechnical Engineering, China Institute of Water Resources and Hydropower Research, Beijing 100048, China. Associate Professor, Dept. of Civil Engineering, Faculty of Engineering and Science, Univ. Tunku Abdul Rahman, 53300 Kuala Lumpur, Malaysia.