Modelling the effect of heterogeneities on suction distribution behaviour in tropical residual soil

The formation of tropical residual soils introduces heterogeneities in soil mantle. While the hydraulic conductivity of Grade VI soil is controlled only by the variation at the material scale i.e. grain size, void ratio, and mineralogy, the hydraulic conductivity of Grade V soil is also influenced by the presence of heterogeneity features at the field scale. One of the important features of heterogeneity is relict discontinuities which affects the saturated hydraulic conductivity, ksat. This study focuses on the effect of the heterogeneities on the mechanism of rainfall infiltration and the resulting suction distribution within residual soil mass when subjected to different rainfall patterns. Three approaches were employed in this research i.e. field observation, laboratory experiment, and numerical modelling. Field observation was carried out at an instrumented site for a period of one year to monitor soil response, in term of suction distribution, when subjected to actual rainfall. Forty two (42) series of laboratory infiltration tests were performed on homogeneous and two-layered soils with relict discontinuities subjected to various rainfall intensities to study the effect of different rainfall patterns on suction distribution. The field response was then simulated numerically based on the mechanism found in the laboratory tests to obtain the most appropriate approach in modelling the heterogeneities within soil mass. The field observation shows rainfall patterns play an important role in the propagation of wetting front and suction variation in the soil slope. There was an upper limit of the soil suction in the residual soil slope, even during prolonged dry period which approximately identical to minimum suction, ?min corresponding to the residual water content, ?r in the soil water characteristic curve, SWCC of the soils. The laboratory study also shows that heterogeneities cause the ksat of the soil to vary from one to five orders of magnitude. The flow mechanisms in the residual soils are controlled by the ratio of rainfall intensity to saturated hydraulic conductivity of the soil, q/ksat, the suction potential at the interface between two layers, and the physical flowing conduit within the heterogeneous soil mass resulting in disparate suction distribution profile. Continuum model is capable of modelling the effect of heterogeneities in Grade V material on the mechanism of rainfall infiltration and suction distribution in tropical residual soil. In this method, the relict discontinuities in Grade V soil were simulated by subdividing the layer into multiple isolated zones with an identical SWCC but with different average ksat. The study indicated that the presence of thin Grade VI layer and the relict discontinuities in Grade V layer should be considered in the analysis of suction distributions in residual soil slope subjected to rainfall infiltration

Laboratory investigation of drainage cell as transport layer in residual soils

The results of laboratory investigation of transport layer using drainage cell system are presented in this paper. The drainage cell was sandwiched between grade V and grade VI residual soil in a two-dimensional laboratory slope model. Coarse particles of gravel were compacted inside the holes of the drainage cell to facilitate capillary break development and modify hydraulic properties between the soil layers. The grades V and VI residual soils were compacted in the slope model to their dry densities. The whole set up was subjected to three rainfall patterns of 1.0586 x 10-5 m/s, 1.2014 x 10-6 m/s and 3.7337 x 10-7 m/s for 2 hour, 24 hour and 7 day, respectively. These rainfall intensities were applied through a rainfall simulator which is part of the laboratory set up. The results show that inclusion of drainage cell in between the two soil layers impedes percolation of the infiltrating water into the lower grade V residual soil layer and facilitates lateral movement of the infiltrating water along the grade VI and transport layer interface towards the toe of the slope model. Similarly, it provides a definite direction through which the infiltrating water can further flow and diverted laterally in case it percolates the drainage cell due to prolonged rainfall pattern

Susceptibility assessment of shallow landslides in Hulu Kelang area, Kuala Lumpur, Malaysia using analytical hierarchy process and frequency ratio

Hulu Kelang is known as one of the most landslide susceptible areas in Malaysia. From 1990 to 2011, a total of 28 landslide events had been reported in this area. This paper compares two models as Analytical Hierarchy Process (AHP) and probability–frequency ratio (FR) methods for recognizing landslide susceptibility regions in the Hulu Kelang area. Eleven landslide influencing factors were considered to form the probability–FR and AHP matrix, i.e. lithology-weathering, land cover, curvature, slope inclination, slope aspect, drainage density, elevation, distance to lake and stream, distance to road and trenches, the Stream Power Index and the Topographic Wetness Index. The accuracy of the maps produced from the two models were verified using a receiver operating characteristics. The verification results indicated that the probability–FR model based on probabilistic analysis of spatial distribution of historical landslide events was capable of producing a more reliable landslide susceptibility map in this study area compared to AHP model. About 89 % of the landslide locations have been predicted accurately by using the FR map

Monitoring of Deformation Behaviour of Unsaturated Soil Slope using Distributed Optical Fibre Sensor

A distributed optical fibre sensing system named Brillouin Optical Time Domain Analysis (BOTDA) is used to monitor the strain development of a laboratory soil slope model. The technology is yet to be fully implemented due to uncertainties of attachment method or the best way to set up optical fibre sensors for geo-structure health monitoring.  The aim of study is to evaluate the deformation behaviour subjected to the development of horizontal strains from Brillouin-based optical fibre sensor of a residual soil slope under loading impact using BOTDA technology.  In this study, a soil-embedded strain sensor placement approach was proposed to be installed in the 1g model of soil slope which was achieved via the horizontal planting of a three-layered optical fibre cable in S-curve forming slope. In this paper, however, only pilot tests result is demonstrated for preliminary data interpretation purposes.  From the preliminary laboratory tests, the results show the soil-embedded sensing fibre arrangement has efficiently detected and measured the horizontal strain deformation due to loading. Therefore, it can be concluded that the sensing fibre was well-responded with the soil movement under loading impact

Effectiveness of unsaturated drainage layer in water diversion under different rainfall conditions

The concept of capillary barrier principle is widely applied as lasting solution to rainfall infiltration in unsaturated soil slope. However, the performance of a capillary barrier system normally reduced as rainfall duration gets longer, due excessive rainfall infiltration. Therefore this paper uses numerical modeling approach to highlights the effectiveness of a capillary barrier system with unsaturated drainage layer at interface to improve its performance under three different rainfall conditions. The capillary barrier system was constructed using residual soil obtained within the compound of Universiti Teknologi Malaysia, Johor Bahru campus; with sand and gravel employed as unsaturated drainage layer. The system was subjected to rainfall intensities of 1 hour, 1 day and 7 days obtained from Intensity-Duration-Frequency (IDF) curve of Johor Bahru, Malaysia. The results show that high intensity short duration rainfall has less effect on eliminating soil matric suction completely, however the near surface matric suction was eliminated due to prolonged rainfall infiltration and a capillary barrier system constructed with gravel as unsaturated drainage layer is more effective in diverting the infiltrated water before breakthrough occurs under all the rainfall conditions

Numerical investigation of capillary barrier performance with transport layer

A capillary barrier is a promising alternative measure for controlling rainfall infiltration in unsaturated residual soil slopes. Although, capillary barriers have been successfully applied to avert rainfall infiltration in dry and semi-dry climates, its application in humid climates with high precipitation rate is still unsatisfactory. Therefore, this paper evaluates the performance of modified capillary barrier with transport layer under humid climates. The capillary barrier was simulated with Grade V and Grade VI soil and the transport layer was made with gravel material. The complete slope model was subjected to a 24-hour rainfall intensity of 14.6 mm/hr using saturated/unsaturated seepage analysis software (Seep/W). The results show that the diversion length and breakthrough time were greatly improved in the modified capillary barrier with transport layer than the conventional capillary barrier system. Therefore, the inclusion of transport layer in a residual soil capillary barrier improved its performance

Anti-Corrosive Performance Of Wash Primer Based On Mangrove Tannin.

Aqueous acetone extract from bark of Rhizophora appiculata or locally known as bakau minyak was tested for anti-corrosive properties by incorporating the powdered extract in wash primer formulation

Critical Acceptance Factors towards the Ar-Rahnu Scheme in Malaysia

Of late, there is growing acceptance of ar-rahnu as a viable and competitive mode of financial instrument in the Islamic finance industry. Amid the increasing interest, research efforts have been focused on reviewing and examining ar-rahnu particularly on the acceptance factors of ar-rahnu, but scanty exertion has been given on acceptance factors from the perspective of the customers. Through a thorough review of the literature, this study highlights the important aspects on the customers'acceptance of ar-rahnu in Malaysia

Monitoring of Deformation Behaviour of Unsaturated Soil Slope using Distributed Optical Fibre Sensor

A distributed optical fibre sensing system named Brillouin Optical Time Domain Analysis (BOTDA) is used to monitor the strain development of a laboratory soil slope model. The technology is yet to be fully implemented due to uncertainties of attachment method or the best way to set up optical fibre sensors for geo-structure health monitoring. The aim of study is to evaluate the deformation behaviour subjected to the development of horizontal strains from Brillouin-based optical fibre sensor of a residual soil slope under loading impact using BOTDA technology. In this study, a soil-embedded strain sensor placement approach was proposed to be installed in the 1g model of soil slope which was achieved via the horizontal planting of a three-layered optical fibre cable in S-curve forming slope. In this paper, however, only pilot tests result is demonstrated for preliminary data interpretation purposes. From the preliminary laboratory tests, the results show the soil-embedded sensing fibre arrangement has efficiently detected and measured the horizontal strain deformation due to loading. Therefore, it can be concluded that the sensing fibre was well-responded with the soil movement under loading impact

Pricing practices of Ar-Rahnu providers in Malaysia

Ar-rahnu is a shariah-compliant pawnbroking instrument that has high suitability to serve short-term and immediate financial needs of the lower income people. An important component of ar-rahnu is the safe-keeping/service fee on the collateral items charged by the ar-rahnu providers. This study highlights the pricing practices of selected ar-rahnu providers in Malaysia by comparing the service charges that they imposed as well as the loan margins granted by each of the providers. By doing so, the study aims to provide a critical discussion on the related issues arising from the pricing practices. This study hopes to shed lights on the role of ar-rahnu in providing inclusive financing to the low income group. Findings of this study contribute towards better growth of the ar-rahnu industry in particular, and the Islamic finance industry in general