Category Archives: Retaining wall

geotechnical, Retaining wall

MSE Retaining Walls – Components & advantages.

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MSE retaining walls means mechanically stabilised earth or reinforced earth. This is an earth retaining system where compacted granular soil is reinforced with horizontal layers of steel strips or geo-synthetic materials. This compacted earth is held together with thin facing elements made of Precast concrete, shotcrete or weld mesh reinforced panels. They are used extensively for constructing retaining walls, bridge abutments, highway wall systems, dykes, etc. MSE retaining walls cost almost half what a concrete structure would have cost for similar uses.

Components of a MSE retaining wall

a) Reinforcing element

b) Back fill materials

c) Fascia element

Typical section of MSE Retaining wall
TYPICAL SECTION OF MSE RETAINING WALLS

Reinforcement element

The reinforcements are used to reinforce and provides the requisite tensile strength to hold the soil together. Two types of reinforcing elements are used in MSE walls. They are metallic and polymeric reinforcements. Metallic reinforcements (In-extensible) include Galvanised iron ribbed strips (50mm-100mm) or ladder strip arrangements.

GALVANISED IRON RIBBED STRIPS
GALVANISED IRON RIBBED STRIPS AND LADDER STRIPS

Polymeric reinforcement (Extensible reinforcement) could be geo-grids or geo-textiles, which are preferred in corrosive environments. For any vertical and horizontal obstructions, reinforcements are bend at an angle, not more than 15 degrees.

GEOGRIDS
GEOGRIDS

Appropriate connections hooks are embedded behind the fascia walls for the anchorage of geo-grids and metal reinforcements.

Back fill materials

The select back fill materials have to be cohesion-less and have to meet the criteria of gradation, plasticity, organic content, and electrochemical properties, The materials should be free drainage and with minimum fine content. The soil friction angle has to be checked by shear tests. The angle of interface friction between compacted fill and a reinforcing element shall not be less than 30 degrees when measured as per IS 13326 part 1.

FLYASH BACK FILL
FLY ASH BACK FILL

Fly ash can also be used as back fill and shall be as per the standards. The select back fill lift should be placed parallel to the wall and starting approximately three (3) feet from the back of the wall panels. The back fill should be placed in 6″ compacted lifts. Soil materials can also be placed without reinforcement between the stabilised zone and natural surface of the ground called retained back fill.

Facing elements

Facing elements are used to retain the filled materials, prevent local slumping of steeply sloping faces, and to be in line with the structural and design, and aesthetic requirements.
The facings are made of precast reinforced cement concrete, plain concrete hollow blocks forum filled, etc.
The embankment area has to be provided with a suitable drainage system to avoid water logging. (Ref fig) Drainage layers have to be provided on the backside of reinforcement zones for enabling proper drainage of water.
A Drainage layer of around 2-3ft width is provided on the backside of the facing wall using free-draining material to enable proper drainage of water.

WALL DRAINAGE
WALL DRAINAGE

Jointing and filling materials

Rubber or wooden bearing pads are used between horizontal joints of facing elements so that there shall not be any concrete to concrete joints. The interior panel joints are sealed with geotextile filler cloth in the horizontal and vertical directions as shown in fig. This is done to ensure that no interior back fill materials sweep through the joints.

RUBBER PADS AND GEO TEXTILE LAYER
RUBBER PADS AND GEO TEXTILE LAYER

Advantages of MSE walls

Advantages in terms of economy, ease of construction and rapid and speedy construction with minimum disturbances to traffic and other services makes MSE walls one of the most favourites and preferred retaining wall system. A variety of materials and customisation options in terms of design and construction made it one of the most popular earth retaining system. The fascia elements, the back-fill, and the reinforcing system combine to form a gravity retaining structure that relies on the self-weight of the reinforced soil mass. This self-weight resists the lateral pressure from the earth and the service loads, seismic loads, and hydro static pressure.

  • They can be designed to take extremely heavy loads like bridge abutment footings, crane loads, service loads, etc
  • MSE walls can resist seismic and dynamic forces and transfers the bearing pressure to a wide area.
  • Faster construction than conventional retaining walls.
  • Less site preparation is required and can be constructed in confined areas where other retaining walls are impossible to construct.
  • There is no supports, finishes and curing time.
  • The granular back filling enables free drainage of water through the exposed panel joints and reduces hydro static pressure.
  • The fascia walls are lightweight and are precast and conveyed to the site and lifted using simple lifting equipment. These walls can be made to any height and can resist unequal settlements
  • They can be customised to any geometry and the construction process is very simple. They do not need any heavy types of machinery and specialised workers.
  • The fascia can be customised for designs and logos and gives superior and elegant finished and aligned walls.
  • Any obstructions inside the back filled areas can be managed by adjusting the angle of the reinforcing elements.
  • They possess a very good service life in extreme loading and complex applications.

Disadvantages of MSE retaining walls.

  • MSE retaining walls require granular material in huge quantities. Areas where there is a scarcity of granular material the construction cost increase and make the structure uneconomical.
  • The corrosion or reinforcement and deterioration of geo-grids on exposed to sunlight has to be addressed. The reinforced component must be designed to withstand erosion and corrosion processes which can highly deteriorate the mechanical behaviour of the composite structure.
  • Proper drainage system should be provided.
  • The wall must obtain a minimum width in order to acquire adequate stability

Also read

INSTALLATION METHOD OF MSE RETAINING WALLS

geotechnical, Retaining wall

Soil Nailing – Installation,advantages and applications

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Soil nailing is a slope protection technique for supporting unstable natural slopes and over steeping of existing slopes. Soil nails are reinforcing passive elements drilled and grouted sub-horizontally in the ground. They are used to support excavations in soil, or soft and weathered rock and slope protection works.

Soil nail walls are used as permanent earth-retaining structures in highway projects. They can also be constructed as temporary structures in roadway work when used as shoring of deep excavations.

Components of soil nail and its function

Components mainly constitutes installing passive reinforcement without any post tensioning in existing ground know as nails. Soil nails are later grouted if they are installed in drilled holes. Soil nails using solid bar drilling system or hollow bars (sacrificial hollow bar system which drills and grouts simultaneously ) need not need any grouting. Let us go in detail each and every component of soil nailing system.

Typical cross section of soil nail

a) Tendons

They are the ground reinforcing elements and are equivalent to steel bars. Tendons can take care of tensile stress developed during the lateral movement and deformation of retained soil and also the external loads in the service stage such as surcharge loads and traffic loads.

There are two methods of fixing soil nails or reinforcement bars.
a) Holes are drilled and pressure grouted with fully threaded bars embedded inside.
b) Using sacrificial drill bits where drilling and grouting will be done simultaneously and the sacrificial drill bit is converted to rebar.

b) Grout

Normal OPC cement mixed with water is used for grouting. The function of grout are

a) Transfers shear stress between the ground and tendons and

b) Corrosion protection for rebars.

c) Installation of facing 

Soil nail construction is done from top to bottom. Every nail is installed with anchor plates or bearing plates.
First, a single row of soil nails is installed after excavating the surface. Excavate further and install the second layer of soil nails as per design. After completing a reasonable height at which soil can free stand ( 1-2mtr) for at least 2 -3 days the next phase of the shotcreting process will start.

soil nailing

d) First face shotcrete on soil surface

A geotextile drain matting is placed over the soil and is followed by welded wire mesh as shown in the figure. Rebar stiffeners are sometimes provided to strengthen the shotcrete against punch shear forces. On completion of the first phase of shotcreting bearing plates with bevelled washers are installed over the shotcrete surface.

e) Second phase of reinforced concrete

If required as per design the first layer is covered with a second phase of reinforced concrete layer as shown in the figure. This concrete covers the nail head.

Applications of soil nails

Soil nails are one of the most economical and feasible tops to bottom constructed retaining walls system. They are technically feasible, fast, and reliable slope protection and earth retaining system. Soil nails offer a perfect cost-effective system for temporary retaining walls for deep excavations..

  • High way cut excavation of hilly areas
  • Road widening under an existing bridge end.
  • Repair and reconstruction of existing retaining structures.
  • Temporary or permanent deep excavations in urban areas.

Feasibility of soil nail

Before confirming the soil nail system please ensure the following parameters at the site.

  • Soil should be able to free stand at a height of around 1-2 mtr unsupported for a minimum of two days.
  • All soil nails within a cross-section will be above the water table.
  • If the soil nails are not located above the groundwater table, the groundwater should not negatively affect the face of the excavation, the bond between the ground and the soil nail itself.
  • They can be used for almost all types of soils including stiff/sandy/hard clay, dense sand and gravel areas, evenly weathered rocks.
  • Avoid using soil nails in dry, poorly graded cohesion-less soils, soils with a high groundwater table, soils with cobbles and boulders, soft to very soft fine-grained soils, highly corrosive soils, weathered rock with unfavourable weakness planes, etc.

Advantages of soil nails over other retaining systems

  • Soils nails require very little workspace comparing with any other retaining systems.
  • The operations are mostly light and silent and there is no disturbance to the traffic and people residing nearby.
  • Soil nails do not need any foundation or any structural whaler beams at the bottom like cantilever and anchored retaining walls.
  • With the soil nailing method, we can reduce the duration of work, and fewer materials are consumed in this process.
  • They are so flexible and easily customizable and nail location can be easily adjusted on encountering any obstructions.
  • Small equipment is used for soil nailing works.
  • They can accommodate differential settlements and deflection of soil nails are usually within tolerable limits.
  • They are cost-effective than any other retaining wall system because shotcrete of minimal thickness is used than heavy structural walls in the case of other retaining wall systems.
geotechnical, Retaining wall

Anchored retaining walls/Tie back system-Advantages

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Anchored retaining wall system is a structural element installed through the rock or soil to transfer the tensile forces developed in the structure to the ground. Anchored retaining walls are often slimmer than all their counterparts like gravity walls and cantilever retaining walls.

  1. Anchored retaining wall or Tie back system – Installation method.
  2. Fixing of anchors in a tie-back system
  3. Advantages of anchored retaining walls
  4. Youtube video – 15 Types of Retaining wall systems

Anchored retaining wall or Tie back system – Installation method.

Anchored retaining wall is also known as a tie-back system. They are used in combination with cantilever retaining walls, piled retaining walls, sheet piles, tangent walls, etc. The Tie-back system enhances the stability of the structure and plays an important role in equipping the walls to handle additional loads.

The anchored walls are installed when the load acting on the structure is high. In this case, the design of cantilever retaining walls / piled retaining walls/ sheet piles etc seems uneconomical. Moreover, it is difficult to accommodate the foundation and structures due to space constraints. For enhancing the load-carrying capacity and economising the structure additional anchors are embedded in the earth to be stabilised. These anchors in combination with the main structure negotiate the loads.

Related posts from vincivilworld

Also Read : Soil Nailing – Installation, Advantages and applications.

Fixing of anchors in a tie-back system

One end of the tieback is anchored to the wall and another end is driven to the soil/rock. Sometimes stable concrete structures are driven into the ground to get a good anchorage. Tiebacks and drilled through the wall to the soil at an angle of around 15-45 degrees.

After drilling the holes ties or struts are provided inside the drilled holes and pressure grouted to give greater stability. In the case of piled retaining walls, the tie-back system is drilled through whaler beams installed between the piles as shown in the figure. Steel rods are placed inside the drilled holes and grouted under high pressure. This creates a bulb-like anchor at the rods’ end, preventing the tie-backs from pulling out the load.

Anchored retaining wall/Tie back system
Waler system used for anchoring

These walls can be very tall and support high loads and are ideal for smaller areas that need earth retention.

Some times instead of rods, helical anchors are also driven to in place and the capacities are decided by the torque required for tightening the anchors.

Anchored retaining wall - Typical section of helical anchors
Helical anchors

The main purpose of the tieback system is to develop a strong soil mass to resist external failure modes. The moment of soil and wall has to be restricted to get better serviceability.

Advantages of anchored retaining walls

  • Mostly used for slope protection and retaining earthworks of deep excavations.
  • Thin walls or very light structures can be designed in combination with anchored walls.
  • Anchored walls are one of the most economical systems of earth retention.
  • Combination with sheet piles, cantilever retaining walls, piled retaining walls etc are very useful for deep excavations to provide a safe working area.

For more details about the retaining walls watch the below video.

Youtube video – 15 Types of Retaining wall systems

Types of retaining walls
geotechnical, Retaining wall

Crib retaining walls, Bin retaining walls & Gabion Walls

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Retaining walls are rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. The soil got a natural angle of repose and when it exceeds the range a retaining wall structure has to be provided.

They are vertical or near vertical structures constructed to hold soil between two terrains when the slope exceeds the natural one. The slope can be vertical or steep or much above the range of angle of repose.

Also read : Retaining walls – All Types, Materials, features and uses

In this article we are mentioning about some special type of retaining walls

Gravity retaining walls are made of stone, bricks, concrete or any other heavy material.  Gravity walls are made with or without mortar They are designed to counter the earth pressure by their self weight. Following are the special types of gravity retaining walls.

a) Crib retaining wall

b) Bin retaining wall

c) Gabion retaining wall

Crib Retaining walls

Crib retaining wall or crib lock retaining wall is one of the oldest types of retaining wall. They consist of cribs or cells made of timber, concrete, and plastic/fibres. The cribs or interlock areas are filled with free-draining materials or earth back-fill, eliminating the hydro-static pressure and enabling a free escape of water.

Most common materials used for crib wall construction is 

  • Timber crib retaining walls
  • Precast crib retaining walls

Timber crib retaining walls

Timber crib walls use timber to form the cells of the crib. The cells are filled with free-draining stone materials for maintaining the mass of the wall. Water drainage can happen freely through the cribs. The timber sections are interlocked to make the walls.
They can also be planted with trees to create a natural appearance. These types of walls are ok up to a height of 5-6 mtrs and mostly used for landscape walls etc.

Timber crib retaining walls
Timber crib retaining walls

Precast concrete crib retaining walls

This system consists of a precast concrete header and stretcher units. They are erected to form precast crib retaining walls.
Precast concrete cribs are the cheapest form of earth-retaining systems and are used for landscaping structures, plant terraces, and other works with heights around 10- 20 mtr with proper professional design.
They do not require any skilled labour to do the erection. Trees or shrubs are planted to give natural and excellent looks. Crib walls are erected for small curves and are considered a very flexible material.

Precast Concrete Crib retaining walls
Precast Concrete Crib retaining walls

Bin retaining walls

Steel bin walls are made from corrugated steel sheets and are usually bolted together and then filled with crushed rock or other free-draining material. They are mostly used for bank erosion protection, holding encroaching slopes, breakwaters, etc. They can resist unforeseen ground movements that may cause failure to other types of retaining walls.

Gabion Retaining walls

Gabion retaining wall systems are one of the oldest forms of gravity wall. Gabion walls are manufactured by factory fabricating a galvanised hexagonal wire mesh of varying diameters into box cages. These box cages are site filled with locally available stones and fully closed and laid in a pattern as per design. They are used in areas where the foundation conditions are not favourable for adopting any other retaining structures. The concept of a gabion wall is to increase the shear capacity of rock by providing the box cages. They can accommodate substantial ground movements without failures. Gabion boxes are free-draining structures that can reduce hydro-static pressure drastically.

Gabion Retaining walls
Gabion Retaining walls

The main advantage of these types of systems is that they do not need an exclusive foundation structure. Gabion walls are installed directly over the surface in specified patterns according to design requirements.
The mesh is PVC protected or coated with special coatings to protect from rusting in areas subjected to continuous water flow.
These walls provided a Good visual appeal of the product and the satisfying rock finish look.
Gabion walls are erected mainly for soil stabilisation behind the wall. They can also act as a cover wall. The gabion boxes are stacked in layers with a proper design. They are a very economical alternative for concrete retaining walls and rock anchors for soil stabilisation works and slope protection works.

Also read : MSE retaining walls or Mechanically stabilised Earth walls

geotechnical, Retaining wall

Types of Retaining walls – All types,materials,features and uses.

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Retaining walls are rigid structures used for supporting soil laterally and retained at different levels on the two sides.
They are vertical or near-vertical structures constructed to hold soil between two terrains when the slope exceeds the natural angle of repose. The slope can be vertical or steep or much above the range of angle of repose.

Design criteria of retaining wall

The main criteria behind the design of the retaining wall are to counter the downward slope movement of back filled soil by gravity. The lateral pressure developed behind the wall depends on the angle of internal friction & cohesive strength of retained materials. The lateral pressure can also be liquid (hydro-static pressure), and pressure from any type of back-fill material like sand, granular material, fly ash, etc. A proper drainage system is to be provided to reduce the hydro-static pressure.

There are several types of retaining wall depends on the nature and type of soil and situations they are to be used.

  • Gravity retaining wall
  • Cantilever retaining walls
  • Counter-fort retaining wall
  • Buttressed retaining wall
  • Sheet pile retaining wall
  • Bored pile retaining wall
  • Anchored retaining wall

There are a lot of innovative and alternated methods used for retaining walls

Also read : Innovative alternatives for retaining walls.

Gravity Retaining walls

Brick gravity wall & Stone gravity wall
Brick gravity wall & Stone gravity wall

Gravity retaining walls are executed with stone, bricks, concrete, or any other heavy material. They are done with or without mortar and are designed to counter back-fill soil pressure by their self-weight.
Dry retaining walls do not require rigid footing but have to be designed to counter sliding, overturning, and bearing loads acting on the structure.
These types of retaining walls are mainly adopted in landscape areas and also in locations with height is around 2-3 meters.

Gravity retaining wall
Gravity retaining wall

Gravity retaining walls are used for larger heights using composite gravity walls. Composite gravity walls include precast crib walls or timber walls filled with granular materials, Gabion walls, Geowalls, etc.
The gravity wall when provided with a small amount of reinforcement is known as semi gravity retaining wall. The load transfer mechanism remains the same as that of gravity retaining walls.

Gabion Walls
Gabion Walls

Cantilever retaining walls

Cantilever retaining walls are the most common retaining wall type. They are reinforced concrete structures wherein the lateral earth pressure is countered by the cumulative action of total structural members.
Cantilever retaining walls consist of a stem, a base slab which is divided into toe slab and heel slab as shown in the figure.

Cantilever retaining walls
Cantilever retaining walls


The vertical stem wall is extended to the back fill side or heel side and is called a heel slab and the slab on the other side is a toe slab as shown in the figure.
The stem wall, toe slab, and heel slab act as cantilevers fixed injunction and spanning to other ends. The back filling of soil over the heel slabs imposes additional stability against lateral pressure and stabilises the wall against overturning and sliding.

The loads induced on various components

a) Heal slab and toe slab = Upward soil pressure from the bottom and tends to bend upward. Rebar is placed in a tension zone.
b) stem= Lateral earth pressure tends to bend in the opposite direction of back-fill.
These types of walls are economical and can be used for heights around 5-7 mtr. They are much lighter than gravity walls and require comparatively small foundations. These types of walls can be constructed as to cast in situ and precast and prestressed concrete depending on the site requirements.

Prestressed retaining wall & Retaining wall
Prestressed retaining wall & Retaining wall

Counter-fort retaining walls

Counter-fort retaining wall is a cantilever retaining wall used when the height is around 7 mtr or more. For economising the structure, vertical bracing called counter-forts are provided on the back fill side. These counter-forts connect the heel slab and stem as shown in the figure. The stem and heel slabs between counter-fort act as continuous slabs and negotiate the high bending movements. The counter-forts function as tension stiffness and reduce the bending and shear stresses. These types of retaining walls are used for heights ranging from around 8-12 mtr.

Counter-fort Retaining walls
Counter-fort Retaining walls

Buttressed retaining walls

Buttress retaining walls have the vertical bracing located on the front side of the retaining wall in place of the back-fill side like that of counter-fort retaining walls. The structural action of the stem remains the same as the counter-fort walls.

Sheet piled retaining walls

Sheet pile walls are erected using steel sheets into a slope to be protected or for excavations up to a required depth. Sheet pile retaining wall economical till a height of 6m and cannot negotiate huge loads. Sheet pile acts as a temporary wall that is driven into the excavation area for protecting the area from collapsing. They provide high resistance to driving stresses. They can also be reused and are considered the most economical retaining solutions. They can be bolted and driven easily and do not deform on driving. The problem with sheet piles is the noise it creates while driving.

Sheet pile
Sheet pile

Piled retaining walls

Piled retaining walls
Piled retaining walls

These types of retaining walls consist of a sequence of bored piles. The bored piled retaining walls are often accompanied by erection earth anchors, shot-creating the pile gaps, and provision of additional supports depending on the site conditions and designs. Bored pile retaining walls are used in areas where sheet pile tends to create a lot of noise and disturbs the areas.
These types of piles are used for temporary and permanent works. They can hold huge lateral pressure and are used for holding earth for high depth excavations without disturbing the nearby structures. Bored pile retaining walls are classified into contiguous pile walls, tangent pile walls & secant pile walls according to the sequence of piling works.

Also Read : ANCHORED RETAINING WALL