What Makes a Retaining Wall Safe?

Retaining walls are not glamorous, but it can make or break a building or project. But what makes a retaining wall safe is the skill and experience of the engineers who assess, design, and oversee the construction.

Whether it’s a landscape feature that is required for grading of a site or a major construction component that is integral to or to protect a building or other structure, prudence dictates that a thorough investigation is conducted of the subsoil conditions, specifically soil testing in Montgomery County, PA and the tri-state area.

Subsurface Investigation Prior to Design

When assessing the location of a retaining wall, both the architect and engineer must consider the practical aspects of its position, size, and footprint to ensure that it can perform the task it’s designed for.

An assessment of the soil conditions, both behind and in front of the retaining wall, is a necessary part of the subsurface investigation. Soils are subject to various tests to assess their shear strength to determine their ability to withstand the forces associated with the retaining wall structure. Retaining walls fulfill a range of functions and based on these functions together with the soil conditions, a decision is made regarding the type of wall, its dimensions, the use of reinforcement, as well as groundwater and drainage considerations.

Retaining walls can be temporary or permanent.  Temporary walls are typically soil nail/rock anchors with shotcrete or soldier piles and lagging.  Permanent walls can be basement walls, segmental block retaining walls for site grading, or reinforced masonry walls. This is where a reputable company like Earth Engineering Inc. can assist you with conducting retaining wall design & consulting in Philadelphia and the surrounding region.

The Various Forces That a Retaining Wall Must Withstand

A wall design engineer will have a pretty good idea of what type of wall they will design, based on their assessment of the building site and their experience in designing similar structures.

If they have any concerns regarding the ability of the subsurface conditions to support the size of the retaining wall, a geotechnical report is necessary to assess the subsurface conditions. They’ll look at the presence of groundwater as well as the stability of the global stability of the retaining wall system.

Once the engineer has sufficient information for their design, they’ll model it using specialized design software which will help them to assess the sliding friction, vertical & shear forces, and moments that will act on the wall.

Of particular interest is the overturning moment that determines the point at which the retaining wall might fail if the lateral forces push the wall over. A margin of safety is built into these calculations to account for any mistakes that may creep into the equation such as variability in soil properties, a result of human error during the construction phase, or variations in construction materials.

The Professional Team and Main Contractor

No matter how carefully an engineer may complete a design, it comes down to the contractor to ensure that the structure is built according to the design and specifications. It is for this reason it is important that the selection the contractor who will complete the retaining wall and other structures is experienced and familiar with the type of wall system, local building conditions, and material suppliers.

Often, the professional team worked together on previous projects and can assess the suitability of contractors. Merely basing decisions on the price quoted in tender documents is often not the best course of action.

Inspections and Testing

Once a design has been finalized, the earthworks will commence. The engineer will inspect the work at critical times to ensure that to the best of their knowledge, the retaining wall, footings, and drainage are all built according to the design criteria, with the correct strength materials.

The engineer and architect then rely on the contractor to inform them of changing conditions on-site that might require a change of design or an alternative solution to overcome any problems.

Are You in Need of Specialist Geotechnical Advice?

Contact Earth Engineering Inc. for expert geotechnical advice, technical services, and foundation testing and consulting in Philadelphia, NJ, and the surrounding region.