Landslide is one of disasters which commonly run at hilly area. Damages caused by this disaster can cause great lost. Not only infrastructure but also environmental and life, both animal and human.
The causes and characteristics of landslide are very difficult to trace due the cover of various geologic deposits and ground water system. The slide can be identified by interpretation of aero photography, remote sensing (such as infra red and satellite) and spot research. To identify the slide happened, it is very important to determine the type and cause, thus reparation and prevention can be effectively carried out.
Early signs of land movement which can potentially cause slide are lowering of road, ballooning and cracks on road body, fracture on drainage ditch in the hillside, damage on road safety’s hedge. Lowering on bridge’s oprit, inclination of bridge’s tip towards girder’s end of the bridge indicating land movement towards the bridge, inclination of trees, electric- or telephone-installation, pipeline’s fracture, geometric change of buildings in hilly area (the inclination of retaining wall, interior wall, etc).
Landslide usually happens because of various causes, but it is rarely caused by only one cause. The causes are as follow:1.Load increasing on slope area (new buildings, water filters down into soil pores or stagnate on land surface, plants blown by the wind, etc).
2.Excavation or land cutting on hillside.
3.Excavation which exacerbate the inclination of slope.
4.Rapid drawdown on dam, river, etc.
5.Increase of lateral pressure by water (water filling the fracture will push soil towards lateral direction).
6.Decrease on sliding-resistance of land forming slope due to increase on water content, increase of pore’s water pressure, permeation pressure by underground’s water slick, soil on hillside contains clay which easy to swell-shrink, etc.
7.Land vibration or earthquake.
In order to solve landslide, there are repair and/or stiffening needed to stabilize hillside. Methods can be applied for hillside’s repairs are:
1.Change geometric slope.
2.Control drainage and seepage.
3.Make structure for stabilization.
4.Breaking and removing.
5.Protection of slope’s surface.
Repair on slope’s stability by changing slope geometric is taken through digging on certain parts of slope; it is intended to reduce mover forces that cause slope’s movement. These methods are taken through inclination on the hillside and making traps/bench. Make the hillside to be more incline maybe is a relatively cheap method for slope’s repair, but it is depend on free space available. For stack located in the steeper slope, it is maybe more difficult to be taken. Traps/bench digging is appropriate for steep slope. Trap structure can decrease erosion and hold the decline of debris materials (composed of granular materials) on minor slide.
Several methods of surface drainage are surface ditch, redirecting surface water, covering line, fracture and gap, planting trees, re-straighten hillside to avoid puddle, hardening slope surface. Underground’s drainage methods are horizontal drainage, drainage layer, cutter drainage, vertical drainage’s well.Building construction for slope stabilization is purposed to increase forces that hold up slide. Building structure for stabilization includes berm structure, slide ditch, retaining wall, masts or caison.
Breaking or removing method is taken by removing poor material with better/appropriate material, thus can increase forces that hold slope movement.
Purpose of protection on slope surface is to avoid infiltration by rain water, thus slope can be protected from dry or partly dry condition. This method includes shotcrete or chunam plaster and combination pf stone or riprap.
(sources : lecture materials mpsp/hary christadi h.,soundwaves.usgs.gov/2008/01, www.geonet.org.nz,kshitija.files.wordpress.com)
