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Soon Min Ng,Mohd Ashraf Mohamad Ismail,Ismail Abustan 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.6
A massive slope failure occurred on the 22nd March 2007 after 3 days of continuous rainfall at Precinct 9, Putrajaya, Malaysia. Back analysis carried out identified that the main cause of failure is due to the existing high groundwater level within the cut slope. It is also observed that the continuous discharge from the horizontal drains yield approximately 100 ml/s even during dry season. Thus, it is suspected that the main contribution to the high groundwater level is due to the leakage from the large water tank constructed on the crest of the slope. Electrical resistivity survey was adopted to facilitate the investigation for the source of high groundwater level within the slope. A 3-dimensional resistivity model was developed using the Inverse Distance Weighting (IDW) interpolation method. The 3D resistivity model shows that the high water content zone is not caused by the leakage of water tank but is originated from an unknown source at the south-east side of the slope.
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Mohd Ashraf Mohamad Ismail,Soon Min Ng,Ismail Abustan 대한토목학회 2017 KSCE Journal of Civil Engineering Vol.21 No.6
Horizontal drains are commonly used in stabilizing slopes. This paper presents a case study of slope failure in Precinct 9, Putrajaya, Malaysia which buried 23 cars and caused the evacuation of 1000 people from their apartments. Recorded data showed that it had been raining heavily with a total cumulative rainfall of 210 mm two days prior to the slope failure occurrence. Post failure investigations suggested that the slope failure is caused by the rise in groundwater level that increased the pore water pressure thus reducing the shear strength. Therefore, horizontal drains were proposed as a remedial measure to enable the lowering of groundwater level to a safe level. Parametric study was carried out to determine the suitable length and ideal location of horizontal drains installation. Geophysical electrical resistivity survey was carried out to determine the ideal location for installing the horizontal drains. The Finite Element seepage analysis and Limit Equilibrium method were used to examine the effect of horizontal drains on slope stability during rainfall. The minimum length required for the horizontal drains is 22.5 m and the best location for installation is at the toe below the lowest berm of the slope. Field monitoring results from piezometers and measurements of discharge rate verified that the installation of horizontal drains are able to lower the groundwater level effectively.
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Aqil Azman,Fei Chong Ng,Mohd. Hafiz Zawawi,Aizat Abas,Mohd. Remy Rozainy M. A. Z.,Ismail Abustan,Mohd. Nordin Adlan,Wei Loon Tam 대한토목학회 2020 KSCE Journal of Civil Engineering Vol.24 No.2
Three-dimensional stepped spillway problems are simulated numerically using smoothed particle hydrodynamics (SPH) to visualize the flow of water along the steps and its flow dynamics. In particular, two distinct scaled-down stepped spillway models were studied with each having barrier heights of 10 mm and 25 mm, respectively. The impact of varying the height of the barrier in the design of the stepped spillway is studied in terms of it flow pattern, flow dynamics, aeration efficiency and oxygenation performances. State-of-the-art particle image velocimetry (PIV) experiment was carried out to affirm the validity of SPH findings and it turns out that both the water flow patterns attained in the SPH and PIV are quantitatively comparable. Further quantitative analysis revealed that the flow velocities in both methodologies are in great consensus. Conclusively, this has demonstrated that the capability and reliability of SPH to precisely approximate the water using finite set of particles to model the flow along the stepped spillway. Both stepped spillway configurations show nappe flow regime as the water descends down the steps. Nonetheless, vigorous hydraulic jump phenomena that is associates with the formation of turbulence and vortices is prominently observed in the configuration with larger barrier height. Decisive SPH data obtained concluded that as the barrier height increases from 10 mm to 25 mm, the water flows down the steps faster at lower pressure value and the overall aeration efficiency is improved from 1.1% to 1.2%. The usage of the higher barrier would promote the occurrence of substantial air entrainment during water swirling that will increase the power dissipation in flow. Subsequently, this while lower the power drawn to achieve the desired aeration effect. Ultimately, this study has justified the critical influence of barrier height dimension on the stepped spillway flow behavior and aeration performance.
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