Mohamad Razip bin Selamat

Filtration of Broadly Graded Cohesive Dispersive Base Soils

AbstractDispersive soils are highly susceptible to erosion, particularly when they are used as a base soil for the core of an earth dam. To prevent migration of the core material, the required filter must be designed and properly positioned in the structure. A study was carried out to assess the adequacy of the existing filter design criteria in controlling core materials that are not only dispersive but also broadly graded and are commonly available for use in the construction industry. The criteria of D15f/d85≤5.5 and D15f≤0.28  mm, each with a reasonable factor of safety, were found to be applicable for the broadly graded, highly dispersive soils from Group 1 and Group 2, respectively. The criteria of D15f/d85reduced≤9 for the soils of Group 1, D15f/d85reduced≤7 for the soils of Group 2 with significant clay content, and D15f/d85reduced≤2 for the soils of Group 2 with significant silt content were also found to be acceptable. Thus, the required D15f size of a filter reduces with the increasing dispersi...

A Critical Review on Filter Design Criteria for Dispersive Base Soils

Dispersive soils have become common materials for the construction industry. Highly susceptible to internal erosion and piping, dispersive soils must only be used with specific engineering measure in order to avoid failures that were often catastrophic. In an earth dam, clayey soils are used for the core and sandy materials are used for the filter to retain the eroded core soils and prevent their migration. In the absence of first-rate core material, dispersive soils have been used instead. This paper provides a review of the current knowledge and experiences regarding filtration of core soils, particularly the dispersive ones. The engineering problems associated with the use of dispersive soils are discussed and significant findings from previous studies on protective filters are summarized. It is worthy to note that the current review considers both, the conventional, rather empirical filter design criteria based on particle sizes and the current, quite theoretical state-of-the-art filter design criteria based on constriction sizes, with discussion given on the advantages and disadvantages of both. The information provided by this review should be handy for the study, design, construction, and operation of related geotechnical and geo-environmental projects.

Direct Determination of Groundwater Direction and Velocity Using Colloidal Borescope at Jenderam Hilir, Selangor

The colloidal borescope can be used for measuring groundwater flow directions and velocity. It is an integrated high-resolution flux gate compass with a high-magnification colloid-imaging camera that can measure flow at selected depths within a well. In this study, the colloidal borescope was used to determine flow direction and measure velocity during a pumping test for the riverbank filtration study in Jenderam Hilir, Selangor. During each measurement, the instrument, which monitored the movement of the suspended particles, was inserted into a well at a particular depth (screen well). The relative flow direction was determined by plotting the trajectory and speed of colloidal particles across the screen with AquaLITE Software, which determined the horizontal speed of the particles and flow speed. The groundwater flow pattern was dtermined at four boreholes in the study area, and the groundwater flow velocities were found ranging from 0.72 to 2.45 x (10-4) m/s. The direction of the groundwater flow at boreholes monitoring well 02 (MW02) and monitoring well 19 (MW19) was moved toward borehole pumping well (PW). The groundwater flow at monitoring well 01 (MW01) was moving toward the northwest of the study site which was parallel with the Langat river. The groundwater flow in borehole monitoring well A (MWA) was toward the southern part of the study site and was not affected by the pumping test activities at borehole monitoring well 03 (MW03).

A Study on the Characteristic and Properties of Riverbank Soil Samples as RBF Natural Materials from Sungai Perak, Kota Lama Kiri, Kuala Kangsar, Perak Darul Ridzuan, Malaysia

For a developing country such as Malaysia, riverbank/bed filtration (RBF) technology is still new and only few efforts have been made to understand the RBF mechanism and processes. Soil characteristics play important roles in determining the water quality and the ability of water to be abstracted from the wells during RBF process. A research has been carried out to identify the characteristic of riverbank soil at different layers in the pumping well (PW) borehole at Kota Lama Kiri, Kuala Kangsar, Perak, Malaysia. Soil samples were collected during the development of PW for RBF application. The maximum depth of PW was 8.50 metre. The soil samples were transported to Geotechnical Engineering Laboratory, School of Civil Engineering, Universiti Sains Malaysia and the properties were determined by a series of laboratory test. Soil particle size distribution (PSD) and hydraulic conductivity were obtained from sieve analyses and constant head test with reference to BS 1377: Part 1-9;2:1990. Laboratory results show that the value of Cu (coefficient of uniformity) for the soil samples within the borehole of PW was found to be within the range of 2.00 to 10.00 while the value of Cc (coefficient of gradation) lies in the ranges of 0.06-1.19. The One Way Analyses of Variance test was performed using Minitab statistical packages and the results indicate that the p-value was 0.996, where there was no significance difference between the mean sizes of soil samples within the PW. The hydraulic conductivity, k for PW ranges between 0.10-0.91 cm/s. Soil samples from depth 6.00-7.00 metres has the highest hydraulic conductivity, which is 0.91 cm/s. The overall well production from the pumping test was found 112.10 m3/hr.