In modern urban environments, heavy construction often must be conducted immediately adjacent to neighboring properties and structures. Often the neighboring buildings are occupied and must remain open to business or residency during the full course of construction. This can be problematic if the new construction involves high levels of noise or vibration (i.e., pile-driving or heavy traffic loads), deep excavation, or dewatering.
Vibration damage occurs when construction activity, such as pile driving or soil compaction, produces waves in the ground that travel outward from the source to adjacent properties. Construction typically produces traveling ground deformations known as Raleigh waves. While these waves decrease in intensity (attenuate) with distance from the source, depending on soil type or the fragility of the adjacent property, the waves may still be sufficiently strong to cause discomfort, if not damage.
There are two fundamental mechanisms for vibration damage—1) distortion from intertial loads, and 2) settlement of the soils supporting the foundation. If the soil settlement is not uniform, distortion and damage can occur. Such differential settlement can also be due to deep excavations adjacent to existing foundations, or to changes in groundwater levels due to dewatering to keep the construction site dry. To reduce the risk of vibration damage, contractors are often required to maintain vibration levels below damage thresholds established by building departments or technical standards. Underpinning of adjacent foundations is often done to prevent damage from excavations or dewatering.
Because few structures begin free of distress, it is often difficult to differentiate between preexisting damage and new damage caused by adjacent construction. To help differentiate, preconstruction surveys of adjacent properties are often done to map the cracking and foundation elevations prior to the beginning of construction. It is often possible to resolve construction damage from other sources by comparing post-construction and pre-construction photographs and elevation surveys.
Our services include:
- Pre- and post-construction surveys to document the preconstruction conditions and differentiate construction damage from preexisting distress
- Consulting with owners of adjacent properties to help protect their facilities and reduce the risk of construction-related damage or business downtime
- Analysis of post-construction damage observations to determine the nature and extent of damage, whether the damage can be attributed to construction activities, and the most appropriate repairs and measures to prevent further damage