Retaining Wall DesignRetaining Design & Construction Costs
If you’re looking to level the contours of a sloped section, to have flat areas for patios and lawns, you’ll need to design a retaining wall. Properly designed, retaining walls can also be imaginative additions to your property. Below are some great retaining wall design ideas.
Council approval is often required for the design of retaining walls, when they are over a specified height, next to a boundary, or supporting a driveway or other structures. Make sure to check your local authority’s regulations prior to starting the design of your retaining wall. The design of any retaining wall should also include the design of the drainage system, to prevent hydrostatic pressure building up behind the retaining wall. Poor design and no drainage leads to most retaining wall failures. If soil behind the retaining wall and becomes saturated, a poorly designed wall can not support the saturated soil plus the weight of water.
Gabion retaining walls are a simple low cost gravity wall, that do not require a concrete foundations or deep footing piles. This gabion wall has a attractive night lighting and is a feature of the garden, while providing retaining. The welded mesh wire gabion baskets have a longer life expectancy than timber in ground. Farmers are continually replacing rotten fence posts, when the fence wire is still good. Gabion Retaining Walls
By design gravity retaining walls rely on thier mass or weight to resist the overturning forces of the bacfill behind the wall. The retaining walls mass comes from the gabion rocks which need to be hard, heavy and durable. On larger walls the engineer will specify the size and location of the retaining walls, and will also design the drainage system required behind the wall, which is critical to prevent hydrostatic pressure damaging the retaining wall.
The site geology and soil profiles can be significant factors in the loads that a retaining wall will have to be designed to withstand. The final design and construction of retaining walls can be substantial, the construction needs to be abl;e to hold back tonnes of rock and soil. Some sites have a history of soil creep and other geological factors that will require the services of a qualified geotechinal engineer or geologist.
Poor or inadequate drainage is the cause of nearly all retaining wall failures. The design and maintenance of the drainage system, is critical to the long term structural stability of any retaining wall. Nearly all retaining wall failures occur when the soil is fully saturated and the resulting hydrostatic pressure pushes the wall over.
The profile of the property, directly influences the retaining wall design and calculations by determining the weight of soil the wall has to hold up. Also the site profile determines how the retaining wall is going to resist the loads placed upon it. Vehicle and building surcharges must be allowed for in the final retaining wall design.
Because the gabions are porous, it is virtually impossible for hydrostatic pressure overturn the retaining wall. When you have cheap low cost local rock, gabion walls are very inexpensive. Gabion Retaining Walls
Retaining wall design considers all the forces acting on the wall. Backfill which is referred to as active pressure, hydrostatic pressure is not considered as the drainage system eliminates this from the retaining wall design process. The forces that resist the wall sliding and overturning are the weight of the wall, and the friction force of the retaining wall on its foundation. Gabion Retaining Walls
The retaining wall design considers the four possible failure modes, sliding, overturning, bearing failure at the toe of the retaining wall, and the overall site stability. A qualified geotechnical engineer is able to assess the potential risk of each failure mode and design the retaining wall to suit the site loads and geology.
The retaining wall design calculates the location of the resultant force, from the soil backfill and the weight of the wall, this resultant force needs to act within the middle third of the retaining wall for stability. The active load against the retaining wall, combines with the dead weight of the retaining wall and the resultant force is then checked against the design guidelines.
The design of all retaining walls needs to consider, the soil profile, soil type, (clay, gravel or sand), the final height of the wall and any loadings from driveways and nearby buildings, that will increase the design forces that the wall has to withstand. Site access, the look of the wall, material and labour costs are also factored into the final retaining wall design selected for any project.
Often local authorities require the design work to be done by a registered engineer, before issuing a building consent. The geotech or civil engineers stability calculations, site inspection, design notes and soil analysis are submitted with the consent or permit application.
Home owners, weekend builders, and diy specialists can build most retaining walls depending on size over several weekends. For larger retaining walls you can get a quotes from, local landscapers, small earthworks contractors and specialist retaining wall builders, who have both the machinery and experience to build the larger retaining walls quickly for you.
