Timothy P. Reilly, P.E., ACTAR, Civil Engineer
Sidewalks are an essential part of any urban or suburban landscape, providing safe and convenient walkways for pedestrians to move around the environment. When properly installed, new sidewalks and other pedestrian facilities should generally be flush and free of sudden elevation changes that would present hazards to the public. Over time, however, sidewalk slabs can shift or become uneven, creating tripping hazards that can lead to serious injuries. Considering an elevation change of as little as one quarter of an inch can constitute a tripping hazard, even a minor vertical displacement can cause a hazard to develop. This leads to the question: how do tripping hazards typically develop on a sidewalk which was initially flush?
Sidewalks are usually constructed using large concrete slabs that are installed next to each other with construction joints. However, due to several reasons, these slabs may shift or become uneven over time, creating a tripping hazard. The more individual surface-level sections a walkway uses, the more opportunities for shifting of the individual components. Walkways comprised of bricks, cobblestones, or small pavers are particularly vulnerable to the development of tripping hazards over time.
Soil erosion or settlement is one of the most common reasons why sidewalk slabs shift. As the soil underneath the sidewalk settles, one or more slabs can shift downward leading to an uneven walking surface between adjacent slabs. Soil settlement can occur for several reasons, such as changes in the water table, erosion, or inadequate compaction of the soil during construction. Soil settlement can be more severe in areas with high levels of groundwater, such as in coastal regions or areas with heavy rainfall.
Another cause of shifting sidewalk slabs is tree roots. Trees planted near sidewalks can cause significant damage to the concrete slabs as their roots grow underneath them. Tree roots can push up the sidewalk slabs, causing them to lift or become uneven. This can create tripping hazards for pedestrians walking along the sidewalk.
Freeze-thaw cycles are another factor that can cause shifting sidewalk slabs. In colder climates, water can seep into the cracks between the slabs and freeze. As water freezes, it expands, causing the sidewalk slabs to lift or heave. When the ice melts, the sidewalk slabs can settle back down, but they may not settle evenly. Over time, this cycle can cause the slabs to become uneven and create tripping hazards. Temperature variances and precipitation levels can accelerate the process of shifting the individual concrete slabs that form a sidewalk path.
Heavy loads are another cause of shifting sidewalk slabs. If heavy vehicles or equipment are regularly driven or parked on the sidewalk, it can cause the slabs to shift or crack. Heavy loads can cause the soil beneath the sidewalk to compact, leading to settlement and unevenness. Additionally, poor installation or aging of the sidewalk can cause the slabs to shift or become uneven. If the sidewalk was not installed correctly, the slabs may not have been level to begin with, leading to shifting or unevenness over time. Similarly, as sidewalks age, they may become more prone to shifting and cracking due to wear and tear over time. Poor compaction and installation of subgrade materials can also create more opportunities for shifting of the sidewalk over time.
Tripping hazards on sidewalks can be dangerous and can cause serious injuries. Elderly pedestrians and people with disabilities are particularly vulnerable to tripping hazards on sidewalks. They may have difficulty walking or may be using assistive devices such as canes or walkers that can get caught on the uneven slabs, leading to a fall and injury. In addition to the physical harm, tripping hazards on sidewalks can also lead to legal and financial consequences. Property owners or the agency which owns and maintains the sidewalk may be held liable for any injuries that occur due to a tripping hazard on a sidewalk.
To prevent pedestrian incidents on sidewalks and other walkways, it is important for property owners to address any issues promptly when discovered through an inspection or when a property owner is notified. Some minor surface-level hazards can be remediated simply, but oftentimes subsurface repairs should be made when it is determined that the source of the shift may continue to worsen. The repairs necessary may include lifting and leveling the slabs, filling in any gaps or cracks, addressing tree roots or subsurface voids, and/or replacing the slabs altogether.Civil Engineering | Premise Liability | Sidewalk Shift | Timothy P. Reilly | Trip and Fall