Web Based Real Time Monitoring System Along North-South Expressway, Malaysia

Transcription

1 Web Based Real Time Monitoring System Along North-South Expressway, Malaysia Low Tian Huat Mohd Asbi & Associates, Malaysia; Faisal Ali Department of Civil Engineering, Faculty of Engineering, National Defense University of Malaysia; Abdul Rahim Osman Mohd Asbi & Associates, Malaysia; Norisam Abdul Rahman Projek Lebuhraya Utara Selatan Berhad, Malaysia; ABSTRACT Landslides, mudslides, debris/mud flows are threats that endangering the safety of road users and highway assets especially when they traverse hilly and mountainous terrain. The North-South Expressway which was opened in 1994 is not spared of such threat; several landslides have been reported along the expressway despite the structured maintenance regime which was already in place. The majority of landslides along the expressway are caused by prolonged and intense rainfall, high ground water table and unfavorable geological discontinuities. To avert danger to motorists using the expressway as well as enhancing the maintenance regime, the owner of The North-South Expressway, PLUS, initiated a web based real time monitoring system (RTMS) on rain gauges along the North South Expressway in 2006 as part of the remote monitoring regime. Subsequently four years later, ground water monitoring system using piezometer was proposed to be included in the real time monitoring system. Several slopes have been selected to serve as a pilot study to identify critical rainfall and ground water level thresholds for early warning against slope instability. This paper highlights the web based RTMS and the study methodology in identifying these thresholds. KEYWORDS: Web based, real time monitoring system, landslide, threshold rainfall

2 Vol. 17 [2012], Bund. E 624 INTRODUCTION As rainfall is one of the major factors affecting slope stability in the tropics (Othman, 1989; Low, 2001; Ali et al, 2005; Huat et al, 2006; Huat et al, 2008), the study on the rainfall pattern along the North-South Expressway (NSE) is useful in relating slope failure events with antecedent rainfall. This will help the owner of the expressway (PLUS) in managing slopes in terms of their respective risks and maintenance required to achieve required stability conditions. This is the starting point for early warning system to be adopted for high risks slopes along North-South Expressways (NSE). Real Time Monitoring System (RTMS) of PLUS is an online slope monitoring system which enables users to view the data collected in real time. Data collected is automatically sent to the Server at PLUS Headquaters using General Packet Radio Services (GPRS) connection provided by telecommunication service provider (e.g. Celcom/Maxis/DiGi). The pilot project which involved installation of 6 units of rain-gauges commenced in late 2006 and completed in early First expansion of the system in 2008 involved installation of additional 64 units of rain gauges. Figure 1 shows the exact location of the rain-gauges installed along the NSE. The objectives of the implementation of RTMS along the expressway are as follows: To assist in the maintenance regime of the expressways via transmitting actual information of the particular assets in real time to the respective units / departments for a timely and necessary action required. To establish thresholds for any predicted potential failures for selected slopes in relation to rainfall or any potential triggering factors that might affect slope stability. To monitor the condition of assets in real time and alert the respective units once thresholds are triggered

3 Vol. 17 [2012], Bund. E 625 Figure 1: Location of the rain gauges installed along the NSE. GENERAL CONCEPT OF THE REAL TIME MONITORING SYSTEM (RTMS) RTMS enables users to collect, view and analyze the data collected in real time. Data collected are automatically sent to the Server to be stored into Database. General Packet Radio Services (GPRS) provided by local telecommunication companies such as Celcom, Maxis and DiGi enable the data from site equipments to be sent to the Server even during unfavorable weather conditions. The schematic view of RTMS is shown in Figure

4 Vol. 17 [2012], Bund. E 626 Figure 2: The schematic view of RTMS. Figure 3 shows typical installation of RTMS for a rain-gauge consisting of: Solar panel and solar regulator to charge backup battery. Backup battery to supply power to data logger. Lightning arrester to protect against thunder strike from damaging the site equipment. Perimeter fencing with concrete base - as a safety measure to protect site equipments from vandalism and animal. Tipping bucket rain-gauge - to collect rainfall data. RTMS site equipment: o Data logger collect, process and store data from monitoring instruments into memory card. o GSM/GPRS modem responsible for data to be sent from data logger to Server using GPRS

5 Vol. 17 [2012], Bund. E 627 Figure 3: Typical setup of RTMS site equipment Application Components The RTMS application can be divided into 4 main components. They are as follows: Web Based Management System and Data Collector: To view, process, analyze and manage data collected.. Is a web based application enables users (maintenance officers) to access the system via network connection. Threshold Detection Service: To process and analyze data whetherr they exceed preset values. Alert messages will be automatically sent to relevant users (maintenance officers) via and SMS when any threshold value is reached. Flexible Threshold Builder: To create and customized alert equationn (threshold level) for slope. each critical Interactive SMS Service An alternative communication between users and RTMS Server to retrieve information other than access via Web Based Management System

6 Vol. 17 [2012], Bund. E 628 THRESHOLD RAINFALL The analysis of the relationship between the magnitude of rainfall and slope instability provides a rainfall threshold (Loh, 2007). Rainfall threshold value uses rainfall intensities as a landslide warning signal. It is important to identify not just a univocal threshold value for an area but a range of thresholds that can vary according to the local soil moisture condition and the antecedent rainfall amount. The rainfall amount needed to trigger a landslide can vary considerably from slope to slope. Therefore, the determination of rainfall threshold is complicated over any given area due to the lack of homogeneity in the geological, geomorphological, hydrogeological and geotechnical characteristics of the various slopes. Furthermore, the soil moisture is another variable parameter which can undergo various significant changes, depending on the season and the antecedent rainfall amount. The rainfall threshold values can be expressed and determined by analyzing a combination of rainfall intensities and durations. The concept of pluviometric threshold was introduced by Campbell (1975) and successively theorized by Starkel (1976) as a duration-intensity relationship. The rainfall threshold values are useful in predicting slope failures especially for debris flow. With the aim to establish the rainfall thresholds in predicting a slope failure, several rainfall events spread out over a number of years must be identified and analysed. The occurrence of a landslide or slope instability does not happen mainly due to the amount of rainfall on that particular day, but it may be caused by cumulative rainfall events especially for deep seated failure. When the amount of rainfall exceeds the rainfall threshold, thus landslides are predicted to take place. Therefore, the analysis of rainfall data is essential to determine the threshold value. However, the availability of the landslide records within the study area is important to verify the rainfall threshold produced. Currently, the rainfall thresholds adopted for the RTMS along PLUS Expressway is for debris flow and the threshold equations are as follows:- Warning Alert:- (rainfall for 3-day 125mm AND 6-day 175mm) Critical Alert:- (rainfall for, 30min 40mm OR 1-hour 50mm OR 2-hour 60mm) + Warning Alert These existing rainfall thresholds were based on the Genting Sempah Debris Flow event ( Lloyd et al, 2001) Several slopes were selected as case studies to determine the rainfall thresholds. The locations are as follows:- a) Bukit Lanjan Interchange at KM 21.8 on the New Klang Valley Expressway. b) A slope at KM Southbound of PLUS Expressway from Gua Tempurung to Kuala Lumpur, Section C1. c) A slope located at KM Northbound of PLUS Expressway from Ma okil to Kuala Lumpur, Section S

7 Vol. 17 [2012], Bund. E 629 The failure historical records of the adjacent area, subsurface investigation data and rainfall data were studied in detail. Geomorphological mapping was also carried out. The geomorphological mapping includes the evaluation of soil on the following features: slope profile i.e. angle, bench height, berm width, etc., slope surface covers and vegetation; geodynamic features and processes such as: signs of seepage; signs of erosion, rills, gullies, etc.; signs of previous soil/rock failure; surface drainage conditions A series of rainfall parametric study were carried out to determine the effect of rainfall on the stability of this slope. Finite element SEEP/W (2007) software was used to study the rain water infiltration effect on the stability of this slope. Different rainfall intensity and durations were adopted to determine possible thresholds from this parametric study. From the parametric study, the pore water pressure conditions in the slope with respect to rainfall intensity and duration were exported to SLOPE/W (2007) software for stability analysis. Generally, from the parametric study, rainfall intensity does not significantly influence the slope stability of these selected slopes. This is because the rain water infiltration is governed by soil permeability. For residual soil of such location, the permeability is in the order of 1 x 10-7m/s to 1 x 10-8m/s. When rainfall intensity is greater than the soil permeability, the excess rain water will flow down slope as surface runoff. In general, the effect of rainfall for such material is only significant to shallow seated failure or slope surface erosion. Given the relatively shallow gradient of the slope, the rise in ground water table poses greater impact to the slope instability for this cut slope. However, the rise in ground water table depends significantly to the catchment size and the hydro-geology of the slope. To better understand the influence of rainfall, catchment and hydro-geology on the rise in ground water table, detailed topographical and soil investigation are required for better simulation using SEEP/W (2007). To simplify the analysis, ground water parametric study was carried out for these selected slopes. The ground water levels were raised in order to obtain a unity in factor of safety (FOS). The changes of ground water level were assumed to be parallel to the slope profile (see Figure 4). Thresholds for ground water table were established and the thresholds for two selected slopes are shown in Table

8 Vol. 17 [2012], Bund. E 630 Table 1: Recommended threshold for ground water table. Case Study Gua Tempurung Triggering factor Ground Water Recommended RTMS Instrument Piezometer Recommended Thresholds Warning Alert: 12m below ground level (b.g.l) Critical Alert: 10m b.g.l Ma okil Ground Water Piezometer Warning Alert: 60m b.g.l Critical Alert: 50m b.g.l h The changes of ground water level were assumed to be parallel to the slope h Figure 4: Ground Water level Assumption in Parametric Study The RTMS is not limited to monitor rainfall only. It is expandable and can be integrated with other instruments such as piezometers, inclinometers/lateral displacement tubes, extensometers, tiltmeters and etc. The next expansion involves; Flood level monitoring for selected flood prone areas along NSE. Installation of Strain gauge Piezometers at 6 selected slopes to monitor ground water level. Integration between RTMS and GIS application

9 Vol. 17 [2012], Bund. E 631 CONCLUSION Seventy rain gauges have been installed along the north south expressway. A web based real time monitoring system was developed for these rain gauges. Rainfall threshold for debris flow and shallow slides has been established based on debris flow failure events in Malaysia. In which the threshold will be fine tuned from time to time. For deep seated slides, real time ground water table monitoring was found to be more relevant. REFERENCES 1. Ali, F. H., Huat, B.B.K and Low T.H. (2005) Infiltration characteristics of granitic residual soil of various weathering grades, Amer. Jour. of Environmental Sciences, 1(1), Campbell, R.H. (1975) Soil slips, debris flow and rainstorms in Santa Monica Mountains and vicinity, South California, U.S. Geological Survey Professional Paper 851, 51 p. 3. Huat, B.B.K., Ali, F.H, and Low, T. (2006) Water infiltration characteristics of unsaturated soil slope and its effect on suction and stability, The International Journal of Geotechnical and Geological Engineering, 24, Huat, B.B.K., Ali, F.H., David H. B., Singh, H. and Omar, H. (2008) Landslides in Malaysia: Occurrences, Assessment, Analyses and Remediation, University Putra Malaysia Press ISBN Low, T.H. (2001) Rain water infiltration on slopes M. Eng. Sc. thesis, University of Malaya, Malaysia, unpublished. 6. Loh, W. L. (2007) Parametric study on rainfall thresholds for slope instability B. Eng. Thesis University of Malaya, unpublished 7. Lloyd, D., Othman, M.A. and Anderson, M.G. (2001) Predicting Landslides: Assessment of an automated rainfall based landslide warning system 14th South East Asian Geotechnical Conference, Hong Kong 8. Othman, M.A. (1989) Highway cut slope instability problems in West Malaysia, Ph.D thesis, University of Bristol, United Kingdom, unpublished 9. Seepage Modeling With SEEP/ W (2007), (An Engineering Methodology) GEO- SLOPE International Ltd. Second Edition. 10. Stability Modeling With SLOPE/ W (2007), (An Engineering Methodology) GEO- SLOPE International Ltd. Second Edition

10 Vol. 17 [2012], Bund. E Starkel, L. (1976) - The role of extreme (catastrophic) meteorological events in contemporary evolution of slopes. In: Derbyshire E. (eds.), Geomorphology and Climate, , Wiley 2012 ejge