Shotcrete for a Retaining Wall
Retaining walls are rigid structures, typically engineered to retain a cut in excavated ground. The right retaining wall design depends on the criteria of the site, soil composition, the height of the wall and the structural engineer’s approach to solving the problem at hand.
Historically, retaining walls were built with stacked stone. Often mortar was used to bind the stone together, but sometimes they were dry stacked. In California, stone retaining walls are no longer used due to lack of resilience during earthquakes.
Typically modern retaining walls are built with wood, wood and steel or concrete. Wood and steel retaining walls are usually used in areas where the wall is not being designed as a waterproof structure. These types of walls are also referred to as Soldier pile and lagging. The pile can be made of wood or steel. The lagging is the horizontal member that supports the soil, and it can be made of wood boards or precast concrete.
Concrete retaining walls are capable of being designed to be much stronger than wood and steel and are typically composed of a footing and a stem wall. The relationship of the footing and the stem walls can be L or T-shaped. T-shape footing can create an added measure of stability, and many engineers prefer that shape.
Some retaining walls are designed as a flat stem positioned on a grade beam, built on a series of drilled piers. Stems, grade beams and piers are typically integrated by using a series of continuous or spliced bars of reinforcing steel, also called rebar. When placing concrete during retaining wall construction, workers build wooden forms to contain the concrete until the concrete is cured.
An alternative method of placing concrete is the process of spraying high strength concrete against a secure back support and screeding it with various trawls into the desired form. This operation is referred to as Shotcrete or Gunite. This method of concrete placement is also used in swimming pool construction.
Building a retaining wall
Traditionally, the process of building a retaining wall begins with excavating the site to suite the dimensions of the wall. The builder usually excavates an additional 2 feet of space behind the retaining wall for placing a waterproofing membrane, drainage pipe and gravel back fill. The additional excavated space can be larger if the heel of the wall requires it.
Today, with the existence of advanced drainage and waterproofing technologies, gravel back fill is no longer necessary for drainage. Therefore, it is possible to use alternative methods of constructing retaining walls that can save the cost of added excavation, off haul of soil and import of gravel. These methods can be used with L-shaped retaining wall designs that do not require the added excavation for the heel.
The alternative method of building a concrete retaining wall with “L-footing” utilizes advanced drainage mats to replace gravel backfill. Therefore, additional excavation for drain rock is not necessary.
For information on effective drainage systems and waterproofing for retaining walls, please read our blog about drainage and waterproofing systems. If you would like to learn more about retaining wall design for your next project, please contact SteelCore Builders.
About SteelCore Builders
As a division of Trush Construction Company, the SteelCore Builders crew and management have been doing structural concrete and strengthening since 1987. Due to our firm’s extensive engineering expertise and exceptional reputation, we are often retained to undertake very difficult and complex projects. Our continuous research and testing of new building materials and technologies enable us to address unique situations that other firms cannot.