Slope modelling applied for slope movement at Kalibawang irrigation channel, Km 15.9 Yogyakarta, Indonesia

TU, Nguyen Dinh, Promotor Prof.Dr. Kabul Basah Suryolelono, Dip.,HE.,DEA

2007 | Disertasi | S3 Teknik Geologi

Kalibawang Irrigation Channel has been found to be threatened by landslide risk in every rainy season. Among many types of slope movement ever found, slope creeping is the most devastating hazard to the infrastructures and the private properties. In the case of slope at Km 15.9 which is located in Mejing village of Kulon Progo Regency, Yogyakarta Special Province, the continuously slow slope movement is suspected to induce additional stress on the bridge and the channel bridge downhill to deform in every rainy season. To help solve that problem, this research is conducted, under the AUN/SEED-Net program supported by JICA, to understand the mechanism of creeping as well as to choose the most appropriative modeling applied for slope movement prediction with special consideration given to the local climate and geology. Field investigation, laboratory testing, and field performance monitoring are utilized to investigate the site characteristics and to monitor the spatial and temporal slope behaviors. Numerical analysis, consisting of modeling of slope hydrological process and slope stability analysis, (the Distinct Element Methods of Particle Flow Code 2D, the limit equilibrium methods of GeoSlope/W) are used to enhance or add to the engineering judgment on that process. Results show that the movement of colluvial slope is very complex. It has been found that some movements have occurred not only at the contact between the colluvial deposit and the base of mudstone, but also at the zone above ground water table. The movements at the contact between colluvial deposit and mudstone may have been induced by pore-water pressure in response to the fluctuations in ground water level (increasing or losing pore-water pressure) or perhaps caused by the capillary rise or suction loss in response to the wetting of soil by rain infiltration. Meanwhile, creeping occurred dominantly at the contact between the mudstone layer and tuffaceous medium sandstone as well as tuffaceous fine sandstone, although the tuffaceous fine sandstone had a high SPT value. It has been observed that the slope movement depends on both rainfall and the stage of rainfall. Moreover, all of the recorded movements are noticed to be not only relatively parallel to the slope dip direction but also followed different trends. It has also been noted that the groundwater table achieved its maximum level with the same value as the accumulated 5 rain days (275-285mm) and 7 rain days (300-310mm). Hence, these values can be used to infer the time when the GWT level is at its maximum and the movement will be most intense. Meanwhile, the results of PFC model are in close agreement with the monitoring results. Therefore, it can be said that the PFC model is the appropriate model which could be applied for slope movement of this area as well as of other areas with the same condition. Keywords: slope movement, creeping zone, colluvial deposits, strain-gauges, stress, rainfall, PFC model

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Kata Kunci : Hidrologi Slope,Irigasi,Model Slope