The North-South Expressway in Malaysia, opened in 1994, was frequently afflicted by several landslides. The majority of landslides along the expressway are caused by prolonged and intense rainfall, high ground water table and unfavorable geological discontinuities. To alert the motorists of 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.

 

1 The setting

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 2007. First expansion of the system in 2008 involved installation of additional 64 units of rain gauges. Figure 7 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.

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2 The modelling

The rainfall thresholds adopted for the RTMS along PLUS Expressway are for debris flows and the thresholds 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:

1. Bukit Lanjan Interchange at KM 21.8 on the New Klang Valley Expressway.

2. A slope at KM 302.2 Southbound of PLUS Expressway from Gua Tempurung to Kuala Lumpur, Section C1.

3. A slope located at KM 127.7 Northbound of PLUS Expressway from Ma’okil to Kuala Lumpur, Section S3.

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. Thresholds for ground water table were established and the thresholds for two selected slopes are shown in Table 1.