Article by: Michael Ropret, P.Eng
The Ins and Outs of Retaining Walls
Retaining walls are common elements of modern infrastructure. They can range from low-height landscaping applications in your backyard to large-scale highway grade separations. Retaining walls are utilized to retain soil at steeper than natural angles and accommodate height changes in the built environment. We do not pay much attention to retaining walls when they are functioning as intended; however, we do notice them when they show signs of movement or distress. As with many speciality products, understanding the basics about how these systems are designed and constructed can help in evaluating damages when they occur.
Many types of retaining wall systems have been developed over time. The different types of systems include gravity mass, cantilevered walls, tied back walls, mechanically stabilized earth walls, and, piled walls. The different systems each have their own features and construction methods. Some systems are more flexible than others. Gravity mass walls rely on the weight on the wall components to resist the lateral earth pressure exerted by the retained soil. Cantilevered walls utilize the weight of the retained soil to hold a footing firmly in place while the stem of the wall, which is connected to the foundation, retains the soil. Tied back walls rely on anchors driven into the retained soil to resist the lateral earth pressure. Mechanically stabilized earth walls rely on frictional interaction between the retained soil and soil reinforcement within the soil block. Piled walls utilize vertical elements driven into the ground to a specified depth to retain the soil.
The knowledge of soil properties and engineering design principles is necessary in order to select and design retaining walls. Design issues that can result in service problems include inadequate geotechnical information regarding a site, inadequate depth of the retention element, improper specification of backfill, excessive surcharge and poor management of surface or ground water (i.e. drainage).
The construction of retaining walls can involve cast-in- place concrete work, pile driving and anchor drilling. All retaining walls require excavation during site preparation, construction, and backfilling. Sound foundation preparation is key to achieving a well built and long-lasting retaining wall. The specification and quality control of backfill material is very important to the performance of a retaining wall. Service issues with a retaining wall can frequently be associated with the original construction of the system. Effective drainage management during construction is necessary in order that the final assembly is soundly built and will stand the test of time.
Once in service, retaining walls are often subjected to extreme weather conditions, variable loading conditions, impacts and many other challenging service conditions. Typical issues that arise with retaining walls over time include cracked or deteriorated facing, settlement, loss of backfill, rotational displacement, or even collapse. By their nature, retaining walls are intended to be relatively maintenance-free structures once they are constructed. A civil engineer can provide a quick and accurate evaluation of a retaining wall type, as well as ascertain the extent and cause of damage, when damage does occur.
The civil engineers at Roar Engineering have in-depth knowledge of retaining wall systems. Contact them when you have a claim associated with retaining wall damage and you will get the benefit of 15 years of direct experience with different types of wall systems.