NG , SOON MIN (2016) Development of Evaluation System for Groundwater Level in Relation to Slope Stability Forecasting. PhD thesis, Universiti Sains Malaysia.
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Abstract
Penyelidikan ini bertumpu kepada pembangunan sistem penilaian paras air bumi bagi ramalan kestabilan cerun berdasarkan kajian kes bertempat di cerun Presint 9, Putrajaya, Malaysia. Sistem ini melibatkan pembangunan model konseptual subpermukaan, pembangunan model untuk penilaian turun naik paras air bumi dan penilaian kestabilan dan penyiasatan perilaku tanah tak tepu yang merangkumi tekanan liang udara. Pencirian subpermukaan untuk kawasan kajian telah dijalankan dengan menggunakan integrasi lubang gerudi, kajian pembiasan seismik dan kaedah keberintangan elektrik. Model subpermukaan tiga dimensi (3D) yang terdiri daripada stratigrafi, halaju seismik dan keberintangan elektrik berjaya mengenal pasti zon kegagalan cerun berpotensi tinggi yang juga merangkumi kawasan kegagalan cerun lampau. Zon kegagalan yang terdiri daripada tanah kelodak dikenal pasti mempunyai ciri-ciri kandungan air yang tinggi dengan julat keberintangan elektrik dari 10Ωm ke 300Ωm dan julat halaju gelombang P (vp) yang sederhana dari 500m/s ke 1000m/s. Ini diikuti dengan pembangunan model tangki pelbagai dan analisis berangka untuk menentukan perubahan air bumi dan taburan tekanan liang air di dalam cerun. Model tangki pelbagai berjaya menghasilkan ralat punca kuasa dua (RMSE) bernilai 0.156 dan 0.169 untuk model kalibrasi yang menggunakan data tahun 2011 dan model ramalan yang menggunakan data tahun 2012. Faktor keselamatan (FOS) cerun sepanjang tahun 2012 menunjukkan perubahan berdasarkan turun naik paras air bumi yang dianalisis menggunakan kaedah keseimbangan had (LEM) dan kaedah unsur terhingga (FEM). Disamping itu, FOS untuk model cerun yang menggunakan paras air bumi model tangki pelbagai memperoleh ralat sebanyak 1% berbanding dengan model cerun yang menggunakan paras air bumi ukuran di tapak. Keputusan kajian membuktikan bahawa sistem penilaian yang dibangunkan ini boleh diterapkan sebagai satu sistem penilaian untuk ramalan kestabilan cerun. Selain itu, komponen tekanan liang udara yang sering diabaikan dalam perilaku tanah tak tepu semasa penyusupan air hujan juga disiasat menggunakan simulasi berangka dan permodelan fizikal kolum tanah satu dimensi (1D). Keputusan kajian menunjukkan bahawa pembangunan tekanan liang udara adalah dipengaruhi oleh jenis tanah, keamatan hujan dan kandungan air permulaan. Keputusan simulasi berangka dan eksperimen makmal menunjukkan bahawa sampel tanah dari tapak dengan keamatan hujan sebanyak 26751.6mm/hr dan kandungan air permulaan sebanyak 21% menghasilkan tekanan liang udara yang maksimum. Saiz zarah yang halus serta intensiti hujan dan kandungan air permulaan yang tinggi akan menyebabkan penyusupan air hujan tidak dapat menggantikan liang udara dengan lancar maka mengakibatkan tekanan liang udara meningkat. ________________________________________________________________________________________________________________________ The aim of this study focused on developing a new evaluation system of groundwater level for slope stability forecasting by conducting a case study at a cut slope in Precinct 9, Putrajaya, Malaysia. This system involved the development of subsurface conceptual model, development of groundwater table fluctuation model, stability assessment and investigation of unsaturated soil behaviour which incorporates the response of pore air pressure. Subsurface characterization of the study area was carried out by using the integration of borehole drilling, electrical resistivity survey and seismic refraction survey. Three dimensional (3D) models of stratigraphy, electrical resistivity and seismic velocity were proven to be effective in identifying the potential failure zone that coincides with the past slope failure zone. The potential failure zone that consist of silt soil was identified to have high water content with electrical resistivity ranges from 10Ωm to 300Ωm and intermediate P-waves velocity (vp) of 500m/s to 1000m/s. Subsequently, the multi tank model and numerical analysis was developed to determine the groundwater table fluctuations and pore water pressure distributions of the slope. The multi tank model was able to produce a root mean square error (RMSE) of 0.156 and 0.169 for the calibration model using year 2011 data and prediction model using year 2012 data respectively. The factor of safety (FOS) of the slope throughout the year 2012 varies according to the fluctuations of groundwater table analyzed by using both limit equilibrium method (LEM) and finite element method (FEM). Furthermore, the FOS for the slope model assigned with multi tank model groundwater table produced approximately 1% error compared to the slope model assigned with the observed groundwater table. Therefore, this outcome proven that the developed evaluation system can be utilized as an assessment tool for slope stability forecasting. In addition, the component of pore air pressure which is often neglected in unsaturated soil behaviour during rainfall infiltration was also investigated through one dimensional (1D) soil column numerical simulation and physical modelling. It was found that the development of pore air pressure can be influenced by soil type, rainfall intensity, and initial water content. Both results of numerical simulation and laboratory experiment show that the soil sample from site with rainfall intensity of 26751.6mm/hr and initial water content of 21% produced the maximum pore air pressure. Finer particle size with higher rainfall intensity and initial water content lead to the development of confined pore air as the rainwater cannot replace the pore air smoothly subsequently resulting in pore air pressure build up.
| Item Type: | Thesis (PhD) |
|---|---|
| Additional Information: | Full text is available at http://irplus.eng.usm.my:8080/ir_plus/institutionalPublicationPublicView.action?institutionalItemId=2804 |
| Subjects: | T Technology T Technology > TA Engineering (General). Civil engineering (General) > TA1-2040 Engineering (General). Civil engineering (General) |
| Divisions: | Kampus Kejuruteraan (Engineering Campus) > Pusat Pengajian Kejuruteraan Awam (School of Civil Engineering) > Thesis |
| Depositing User: | Mr Mohd Jasnizam Mohd Salleh |
| Date Deposited: | 12 Jul 2018 04:29 |
| Last Modified: | 15 Aug 2018 04:03 |
| URI: | http://eprints.usm.my/id/eprint/40996 |
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