Last Updated on August 13, 2022 by Admin
When the ground on slopes becomes unstable, landslides happen. The unstable terrain, which might include dirt, rocks, mud, and any other debris left in its wake, collapses and runs down the side of a hill or mountain. A landslide can do a lot of harm if it happens close to populated areas. They have the speed to demolish entire villages. Roads, bridges, and other infrastructure can be demolished or damaged by the debris, which also damages or flattens buildings.
Fast relief and rescue efforts are necessary owing to the nature of such disasters in order to reach trapped survivors, but this can be delayed since landslides block simple access to the impacted area. Satellites make important assessments of the region, evaluating the damage and pinpointing potential hiding places for survivors. Heavy rainfall and flooding, seismic activity, erosive action from the oceans and rivers, and changes in vegetation that alter the composition of the soil can all contribute to the destabilization of the ground.
What is Landslide and its stabilization?
The movement of a mass of rock, rubble, earth, or soil downslope is referred to as a landslide, sometimes known as a landslip (soil being a mixture of earth and debris). Landslides happen when the shear strength (resistance to shearing) of the materials that make up a slope is exceeded by gravitational and other types of shear pressures.
Several factors can cause shear stresses to accumulate within a slope. These include loading the slope, such as by an inflow of water, a rise in the groundwater table, or the deposition of material on the slope’s surface. Over steepening of the slope’s base, such as via natural erosion or excavation. Landslides can also be triggered by short-term stresses like those brought on by earthquakes and thunderstorms.
Additionally, actions that reduce a slope’s material’s shear strength might cause landslides to occur. Shear strength is primarily influenced by two variables: cohesive strength, which is the strength of the link between the particles, and frictional strength, which is the resistance to motion between the interacting constituent particles of the slope material. Sand grains and other coarse particles have high frictional strength but low cohesive strength, whereas clays, which are made up of small particles, have the opposite property.
The spatial arrangement of a slope-forming material’s component particles, also known as the sediment fabric, has an impact on the material’s shear strength. If they are manually disturbed or submerged in water, some materials with a loose, open sediment fabric will start to lose strength.
Increased water content, whether from natural processes or human activity, typically weakens clays through the dissolution of interparticle cements, the hydration of clay minerals, and the removal of interparticle (capillary) tension while weakening sandy materials through the reduction of interparticle friction.
Types of Landslides
According on the type of movement (slides, flows, spreads, topples, or falls) and the type of material, landslides can be categorized (rock, debris, or earth). Within a single landslide, more than one movement type can occasionally occur, and because the temporal and spatial interactions between these movements are frequently complex, analyzing them frequently necessitates careful interpretation of both landforms and geological sections, or cores.
Falls are abrupt movements of soil, rock, and other materials that break free from cliffs and slopes. Falls landslides happen as a function of gravity, earthquakes, and mechanical deterioration.
This type of mass movement occurs when the sliding material separates from the stable substance beneath. Rotational and transitional slides are the two types of slides that can occur during this form of landslide. Slumps are another name for rotational slides because of how they move. A planer or two-dimensional surface of rupture is what transitional slides are made of. They entail mass landslide movement that follows a surface that is roughly planar and has reduced rotation or a backward inclination. Slides happen when the slope’s toe is undercut. They move slowly while maintaining the material’s uniformity.
When the topple collapses, landslides called topples happen. The forward spinning and movement of enormous volumes of rock, rubble, and soil from a slope is referred to as a “topple failure.” This kind of slope failure occurs around an axis that is either close to or at the base of the rock block. A debris cone formed below the slope mostly as a result of a toppling landslide. A Talus cone is the name given to this mass of debris.
They are frequently referred to as “lateral spreads” and occur on flat surfaces as a result of lateral extension and tensile fractures.
Earth flows, debris avalanches, debris flows, mudflows, and creep are the five subtypes of this kind of landslide, and they can be seasonal, continuous, or progressive. Depending on the type of geological material, such as soil, debris, and bedrock, flows are further divided into subcategories. Rock falls and debris flows are the two types of landslides that occur most frequently.
Main causes of Landslides
Although landslides are thought of as naturally occurring catastrophes, they have recently increased due to changes in the environment brought on by humans. Although there are many different reasons why landslides happen, they all share two things in common: they are caused by the failure of the soil and rock components that make up the hill slope and they are gravitationally propelled.
Natural Causes of Landslides
Following are the natural causes of Landslides
Soil stability may be greatly impacted by long-term climatic changes. A general decrease in precipitation results in a lower water table, a lighter total soil mass, less material solution, and less intense freeze-thaw action. The amount of ground water would rise rapidly if there was a significant increase in precipitation or ground saturation. Landslides can happen when water is totally soaked into sloped regions. The soils begin to run off if there is no mechanical root support.
For a very long time, earthquakes have caused landslides all across the world. The dirt that covers tectonic plates moves whenever those plates do. Numerous times when earthquakes occur in locations with steep slopes, the soil slips, causing landslides. Ashen debris flows triggered by earthquakes may also result in significant soil movement.
Weathering is the process through which rocks naturally deteriorate and become porous, landslide-prone materials. Water, air, plants, and microbes all have chemical reactions that result in weathering. Landslides are caused when the rocks become too weak and begin to slide away.
Latent and lateral slope support are destroyed by erosion brought on by periodic running water such as streams, rivers, wind, currents, ice, and waves, making landslides more likely to occur.
Landslides can be brought on by volcanic eruptions. In the event of a rainy eruption, the dirt will begin to slide downward and cause a landslide. A classic example of a volcano that causes the majority of landslides worldwide is the stratovolcano.
- Forest fires
Forest fires cause flooding and soil erosion, which can result in landslides.
Gravitational force and steeper slopes can cause a large-scale landslide.
Human causes of landslides
Landslides are frequently caused by human activity in addition to natural reasons.
Landslides are greatly exacerbated by mining activities that use blasting techniques. The explosives’ vibrations have the potential to damage the soil in other regions prone to landslides. A landslide could happen at any time because of the weakened soil.
- Clear cutting
Clear cutting is a method of collecting timber that involves removing all old trees from the region. This method is risky since it completely destroys the local mechanical root system.
Effects of Landslides
Landslides can cause a variety of other problems, some of which are listed below, that can disrupt the social and economic environment:
- Contribute to economic deterioration
It is known that landslides cause property to be destroyed. The economy of the region or the entire country could be negatively impacted by a big landslide. The impacted area of a landslide typically goes through rehabilitation. It will cost a lot of money to complete this renovation.
- Infrastructure collapse
Property damage from a landslide can be severe due to the force flow of mud, debris, and rocks. A single landslide has the power to completely destroy infrastructure, including buildings, communication networks, and transportation routes and recreational locations.
- Loss of life (Fatality)
Landslides pose a larger threat to communities that are situated at the base of hills and mountains. Huge rocks, hefty debris, and heavy soil are all carried along by a significant landslide. This particular type of landslide has the potential to instantly kill many individuals.
- Affects how attractive a landscape is
Rugged, unattractive landscapes are left behind by the erosion caused by landslides. The area that the community uses for social or agricultural reasons may be covered by the downhill pile of soil, rock, and debris.
- Effects on river ecosystems
The natural flow of rivers can be obstructed by dirt, debris, and rock that slides downhill. Fish and other river ecosystems might perish when the normal flow of water is impeded. Communities that rely on river water for irrigation and domestic needs will suffer if the water flow is halted.
Landslide mitigation and prevention
In most parts of the world, especially in some areas that have seen tremendous population and economic growth, landslides constitute a recurring threat to human life and livelihood. Hazards are primarily reduced through preventative measures, such as restricting or even removing populations from areas where landslides have historically occurred, banning certain land uses where slope stability is in question, and putting in early warning systems based on the monitoring of ground conditions like strain in rocks and soils, slope displacement, and groundwater levels.
There are also a number of direct methods for preventing landslides, such as altering slope geometry, rerouting surface and underwater drainage, installing piles and retaining walls, grouting rock joints and fissures, diverting debris pathways, and installing structures like piles and retaining walls. Cost, landslide magnitude and frequency, and the extent of vulnerable human settlements are constraints on such direct procedures.
Methods to prevent and remedial measures for landslides
Landslide issues are solved using a variety of techniques. Of course, the best course of action is to stay away from landslide-prone areas entirely. An engineering geologist or a geotechnical engineer should be consulted before buying land, renovating an existing structure, or constructing a new one to assess the likelihood of landslides and other geology-related issues.
The following are some typical corrective techniques applied when landslide-prone slopes cannot be avoided. No one technique or set of techniques can be guaranteed to fully stabilize a rolling hillside.
- Improving surface and subsurface drainage: Since water is a major cause of landslides, a slope that is prone to landslides can become more stable by improving surface and subsurface drainage at the site. By directing water through a lined drainage ditch or sewage pipe to the bottom of the slope, surface water should be redirected away from the area that is prone to landslides. In order to prevent a landslide from occurring close to the location, the water must be diverted. On the landslide-prone slope, surface water shouldn’t be permitted to collect.
Gravel-lined trenches with perforated pipes or pumping water wells can be used to remove ground water from the earth. Less water should be used to lawns and plants, and sewers, water pipes, and swimming pools should all be kept in good condition to avoid leaks. Because they have a low hydraulic conductivity and might be challenging to drain, clayey soils and shales.
- Excavating the head: Removing the dirt and rock near the landslide’s head lowers the pushing pressure, which can cause a landslide to slow down or stop entirely. To stop another landslide from forming upslope, more rock and soil will need to be removed from above the slide. Landslide-prone slopes can be stabilized by reducing the angle of the slope at the top of the hill.
- Buttressing the toe: Fill can be added over the toe and along the slope’s base if the landslide’s toe is at the bottom of the slope. The fill strengthens the opposing forces along the toe area failure surface. As a result, the substance in the skull is prevented from migrating in the direction of the toe. However, if the slope’s toe is higher, adding fill would overburden the rock and soil there, leading to the formation of a landslide that would slide down the slope of the fill.
- Building piles and retaining walls: Pile construction involves driving metal beams into the ground or inserting them into drill holes. A reliable rock layer should be reached by well positioned piles beneath the landslide. Because they are weak and prone to decay, wooden beams and telephone poles shouldn’t be used as piles.
Retaining walls are often built because landslides can leak through the spaces between the piles. By placing lagging (metal, concrete, or wooden beams) horizontally between the piles, retaining walls can be built. Tiebacks and buttressing beams can be added to these walls to increase their strength. Long rods called tiebacks are used to secure the piles and a solid rock layer beneath the ground. In order to keep the piles from falling over or tilting, buttressing beams are positioned at an angle downslope of the piles.
Additionally, retaining walls can be built out of concrete, cinder blocks, rock, railroad ties, or logs, although these materials might not be sturdy enough to withstand landslide movement and might even tumble.
- Removal and replacement: Rock and soil that are prone to slides can be taken out and replaced with stronger materials like silty or sandy soils. Since weathering of shale can result in soils that are prone to landslides, precautions must be taken during the removal and replacement process to stop further weathering of the remaining rock. Never attempt to push landslide debris back up the slope. This will only result in the landslide continuing to move.
- Sustaining vegetation: Trees, grasses, and other vegetation can reduce how much water seeps into the soil, limit the erosion brought on by surface-water flow, and draw water out of the soil. Although vegetation cannot stop or prevent a landslide on its own, clearing vegetation off a slope that is prone to landslides may cause one to begin.
- Rock fall prevention: Errant boulders that have broken free from the rock outcrop are slowed down by concrete catch walls, heavy-duty fences, and ditches at the base of the rock exposure. In rare instances, loose rock blocks are fastened to solid bedrock using long metal rods called rock bolts. These bolts are secured in solid bedrock and have a huge nut screwed onto the exterior of them. The end of the rod that protrudes from the loose block is covered by a metal plate with a central hole that resembles a very large washer before the nut is attached and tightened. Remedial actions need to be inspected and maintained after they are built. Lack of upkeep can lead to fresh landslide movement.
Role of engineering geologist/Geotechnical Engineer in Landslides
Industrial facilities built close to slopes run the danger of developing landslides, which could jeopardize their ability to function normally. The effective completion of the difficult task of predicting slope stability depends on the selection of the design scheme and its parameters.
Geotechnical engineers can discover and fix design flaws by analyzing the causes of landslides, which improves the accuracy of the calculations by allowing them to find and fix design problems. To identify which regions are most vulnerable to landslides, geologists and engineers plot slope steepness and form, bedrock and surface geology, previous landslide locations, soil data, and groundwater levels on maps.
Tools like Light Detection and Ranging (lidar) give precise topographic data that is essential for understanding the limits, movement, and vulnerability of landslides. Once a landslide is suspected, experts can perform focused investigations at high-potential sites to determine whether it will happen and what effects it might have. This information can then be used to inform land-use decisions made by policy makers, planners, emergency management, and the general public.
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The importance of studying landslides may be shown in the yearly economic losses they cause. In order to rebuild the areas damaged by landslides, billions of dollars are spent globally. The majority of countries have established organizations to deal exclusively with landslides as a result of these astounding annual losses.
In order to prevent landslides at the appropriate moment, it is necessary to determine their proper cause. The job of engineering geologists and geotechnical engineers becomes increasingly significant in this situation. They can save a lot of lives if they work in the proper direction and use.