Adrin Tohari

Prediction of landslide run-out distance based on slope stability analysis and center of mass approach

Mitigation of landslide hazard requires the knowledge of landslide run-out distance. This paper presents the application of slope stability analysis and center of mass approach to predict the run-out distance of a rotational landslide model with different soil types. The Morgenstern-Price method was used to estimate the potential sliding zone and volume of landslide material. The center of mass approach used a simple Coulomb friction model to determine the run-out distance. Results of the slope stability analysis showed that the soil unit weight can influence the depth of sliding zone, and the volume of unstable material. The slope model of silty sand and gravel would have the largest volume of unstable mass. From the Coulomb friction analysis, this slope model has higher run-out distance and velocity than other slope models. Thus, the run-out distance will be influenced by soil type and the dimension of unstable soil mass.

Monitoring and Modelling of Rainfall-Induced Landslide in Volcanic Soil Slope

Reactivated landslides have often posed a significant hazard to human lives and properties in many regions of Indonesia. In order to mitigate the hazard, a better understanding of mechanism leading to the reactivation of landslides is necessary. For this purpose, a long-term monitoring and numerical analysis of an active landslide in a volcanic soil slope in West Java, Indonesia was conducted. Monitoring instruments consisted of jet-fill tensiometers, inclinometers, open stand-pipes, and a tipping-bucket rain-gage. The records of pore-water pressure responses of the soil slope show that a transient perched water table could develop within the shallow soil profile, and the groundwater table could rise significantly in the middle portion of the slope during heavy rainstorms. Meanwhile, the inclinometer records show the existence of a multiple sliding zone at a maximum depth of about 17 m. Based on the monitoring data, a couple analysis of seepage and slope stability was performed to evaluate the effect of rainwater infiltration on long-term stability of the slope. The numerical results indicated that the total rainfall of at least 550 mm, with intensity of more than 80 mm/day was the triggering hydrological condition for reactivation of the landslide.

Introduction: Landslide Modelling: Landslide Mechanics and Simulation Models

Session 2.3 of the WLF4 themes on Landslide Modeling: landslide mechanics and simulation models provides a general overview of the recent developments and research studies pertinent to physical and numerical modeling related to landslides causes, mechanism and remediation techniques. Twenty contributions from ten different countries have been submitted and, after a review process, were accepted for publishing. In this introduction to Session 2.3 of the WLF4, a short summary of each of the accepted papers is presented, divided regarding to their general topics.

Rain-Induced Failure of Railway Embankment at Double Track Lane at Bogor and Its Countermeasure

Open image in new window Slope failure occurred in a 100-m railway embankment between Jakarta and Bogor City during a heavy rainfall period in November 2012, causing disconnection of one railway line and damaged several houses below the railway embankment. Sub-surface investigations and numerical analyses were carried out to evaluate hydrological and geotechnical conditions of the embankment for the purpose of an immediate embankment reconstruction and a long-term stabilization. The geotechnical drilling data show that a soft clayey silt layer, acting as the slip zone, exists at the top of a volcanic rock layer. The groundwater monitoring data show that a shallow groundwater table exists in the upper and the middle parts of the embankment slope. Based on the geotechnical data, the embankment was then reconstructed using woven geotextile reinforcement. However, the numerical analysis indicates the safety factor of the reconstructed embankment was still below the required safety factor under a low train load and a slow train speed. Under a time and space constraints, one line of bored piles of 1 m in diameter was selected to increase the embankment stability. The numerical analysis showed that the bored pile reinforcement was effective to increase the safety factor of the embankment slope to more than 1.3 under a train load of 18 tonnes with a maximum speed of 80 km/h. The inclinometer data also suggest the effectiveness of this bored pile for long-term stabilisation of the new embankment.

Open image in new windowUnderstanding of Landslide Movement at Bumi Waluya Railway Station, Garut, Indonesia

Mitigation of a slow-moving landslide hazard requires a good knowledge of the landslide movements. This paper presents results of geophysical investigation and slope movement monitoring to understand the characteristics of an active landslide above a railway station in Garut, Indonesia. For this purpose, a series of resistivity surveys was then conducted using a dipole-dipole method to map the hydrological condition of the landslide area, and geotechnical monitoring was conducted to characterize the movement. Based on the N–S resistivity profiles, highly saturated zones, indicated by low resistivity values, exist in soil layers at a depth greater than 7.5 m. The saturated zone also develops in the near-surface soil layer in the landslide body. The slope movement monitoring records suggest that the landslide consists of several landslide segments with different rates of movement and deep sliding zone. Based on this current study, the characteristics of landslide movement is very site specific and is mainly associated with localized hydrological conditions. Because the surface water infiltration from the irrigation ditches and rice fields controls the landslide reactivation, a better surface water and sub-surface water management is, therefore, necessary to reduce the landslide risks to the railway infrastructures.

Development of wireless sensor network for landslide monitoring system

A wireless sensor network has been developed to monitor soil movement of some observed areas periodically. The system consists of four nodes and one gateway which installed on a scope area of 0.2 Km2. Each of nodehastwo types of sensor,an inclinometer and an extensometer. An inclinometer sensor is used to measure the tilt of a structure while anextensometer sensor is used to measure the displacement of soil movement. Each of nodeisalso supported by awireless communication device, a solar power supply unit, and a microcontroller unit called sensor module. In this system, there is also gateway module as a main communication system consistinga wireless communication device, power supply unit, and rain gauge to measure the rainfall intensity of the observed area. Each sensor of inclinometer and extensometer isconnected to the sensor module in wiring system but sensor module iscommunicating with gateway in a wireless system. Those four nodes are alsoconnectedeach other in a wireless system collecting the data from inclinometer and extensometer sensors. Module Gateway istransmitting the instruction code to each sensor module one by one and collecting the data from them. Gateway module is an important part to communicate with not only sensor modules but also to the server. This wireless system wasdesigned toreducethe electric consumption powered by 80 WP solar panel and 55Ah battery. This system has been implemented in Pangalengan, Bandung, which has high intensity of rainfall and it can be seen on the website.