Slope Stabilization Techniques: Methods and Applications
Acting on Geometry
1. Remove the unstable mass: This involves removing material from the upper slope to reduce the forces tending to cause movement.
2. Slope reshaping (Descabezamiento): This involves the removal of material from the upper slope to reduce the driving forces.
3. Toe berms or breakwaters: This involves the placement of a land mass or pier at the foot of the unstable slope to increase the normal stresses at the bottom of the slide surface, which increases its strength.
4. Berms: This corrective action is usually decided upon before the construction of the slope, in the design phase, unlike the previous measures. Berms not only produce stabilization benefits but also facilitate the construction process of the slope.
Drainage Correction
This type of correction aims to reduce the pore pressures acting on the potential or existing sliding surface, increasing its strength.
1. Surface Drainage: These systems prevent surface water from reaching areas close to the slope and raising the water table. They also prevent the erosive effects of runoff from the face of the slope.
2. Deep Drainage: These systems consist of holes that penetrate the ground and collect the water contained within, bringing it to the surface and lowering the water table. Different structures are used for this purpose:
- Horizontal drains
- Vertical wells
- Drainage galleries
- Filled drainage ditches
Correction Using Bearing Components
These measures seek to stop or fix the slip with resistant structures that oppose the movement.
Anchors: These are metal armatures housed in holes drilled from the slope and cemented. These elements work in tension and contribute to slope stability in two ways:
- They provide a counterforce to the movement.
- They increase the normal stresses on the rupture surface, causing an increase in slip resistance.
The anchorage length is usually between 10 and 100 meters, and the drilling diameter is between 75 and 125 millimeters. Anchors can be classified in terms of their service life:
- Provisional Anchors: They work long enough for other resistance elements to take over.
- Permanent Anchors: They are installed for permanent action.
They can also be classified according to how they work:
- Passive Anchors: They are not pre-tensioned. They begin to act when ground movement occurs.
- Active Anchors: The armature is pre-tensioned to reach its load, compressing the ground.
- Mixed Anchors: The armature is pre-tensioned with a load lower than the permissible load so that the full load is achieved with the start of ground motion.
Walls
Walls are used to stabilize landslides by introducing a containment element at the foot. They may have disadvantages, such as the need to dig into the foot of the slope. They may not be able to prevent possible landslides above or below them. Walls can be classified into three groups:
- A. Retaining Walls: These are built by separating the natural ground and filling it later.
- B. Cantilever Walls: These are excavated and constructed to contain unstable ground.
- C. Facing Walls: Their mission is to protect the soil from erosion and stabilize it.
Types of Walls
- Gravity Walls: These are the oldest type. They are passive elements in which the dead weight is the fundamental stabilizing action.
- Lightened L-Walls: They act as a vertical screen and an offset cantilever beam, balancing the thrust of the terrain with the stabilizing moment of the soil on the heel.
- Walls Lightened with Buttresses: Buttresses are structures used to save weight or increase the wall’s resistance.
- Crib Walls: These consist of a sturdy fabric-shaped cage filled with compacted granular soil.
- Gabion Walls: Gabions are rectangular prism-shaped elements consisting of a granular fill of non-degradable rock fragments retained by a metal wire mesh.
- Stone Walls (Dry Stone Walls): Stone walls are structures built with blocks or boulders of rock placed on top of each other manually or by tipping.
- Tire Walls: These are walls constructed using tires.
Piles
Pile walls consist of alignments of these elements. Their use on slopes is twofold:
- As support for stabilizing excavated slopes.
- As a landslide containment measure.
Diaphragm Walls
Diaphragm walls are concrete walls buried on-site. They work similarly to pile walls, but the former are continuous structures.
Barriers
The objective of these structures is to stop the advance of blocks by interception and braking. They fall into two main groups:
- Static Barriers: These are placed at the base or on the surface of the slope. They usually consist of metal posts embedded in the ground or laid down with resistant metal mesh.
- Dynamic Barriers: These are capable of absorbing the impact energy of the blocks through elastic and plastic deformation. They consist of interwoven steel wire mesh supported by cemented steel posts anchored to the slope and joined together by wire.
Tunnels and Galleries
These protect roads and railways from rock detachments. They are constructed of concrete, and a layer of granular material is placed on their roof to cushion the impact of the blocks and prevent bouncing.
Surface Correction
These are measures applied to the surface of the embankment to prevent or reduce erosion and weathering, eliminate problems caused by falling rocks on rocky slopes, and increase the safety of the slope against small surface failures.
- Rockfall netting
- Guided metal meshes
Slope Revegetation
This involves maintaining a vegetative cover on the slope, which helps prevent surface erosion, drains the superficial part of it (water uptake by plants), and increases the shear strength of the soil in the area they occupy.
Shotcrete
This consists of a layer of concrete sprayed onto the surface of rock slopes. This prevents the weathering of the rock and provides some resistance on the outer edges of the discontinuities that arise in the slope, increasing the resistance of the sliding block.