With significant new developments occurring in increasingly condensed spaces, construction-induced vibration damage and its causes are a growing concern. Construction in tight spaces often will result in the need for demolition of existing structures, deep excavations for underground parking, and/or pile foundations that require heavy equipment. Consequently, vibrations induced from the use of heavy equipment such as earthmovers, excavators, drill rigs and pile drivers will travel quickly through the surrounding ground and potentially negatively affect nearby existing structures. Twining has the in-house capability to accurately measure the level of vibrations created during construction using the state-of-the-art equipment and software and evaluate the potential effects on surrounding structures. We typically provide these services in three phases: 1) pre-construction survey, 2) field monitoring during construction, and 3) post-construction survey and vibration monitoring report.
Phase 1: Pre-construction Evaluation
The best approach to mitigating damage to surrounding structures due to construction-related vibrations is to prevent any possible damage before it occurs. The objective of the pre-construction evaluation is threefold: 1) perform a pre-construction survey of the existing structures of concern to establish baseline damage that has occurred prior to the start of any construction, 2) establish baseline ground motions caused by vehicular traffic (buses, cars, trucks, trolleys and other non-construction vibration sources) near the structures of concern, and 3) perform an evaluation with the proposed equipment on site to establish acceptable means and methods to accomplish the construction tasks. Vibration levels resulting from a range of specific tasks and equipment, including pile driving activities and equipment, can be compared to threshold vibrations with respect to potential damage to structures of concern. This evaluation will establish the means and methods for use during construction that will enable the contractor to stay within the threshold limits.
Phase 2: Construction Field Monitoring
All aspects of construction from demolition, installation of drilled and driven piles, deep excavation, and the use of all heavy equipment will be monitored through this phase. Using state-of-the-art monitoring equipment and software, Twining can provide continuous monitoring of construction activities. A Twining field engineer can observe vibrations in real time and document specific activities that create those vibrations. This information can be used to immediately inform the contractor of approaching threshold vibrations so that corrective measures can be employed. Also, the vibration measurements will be continuously documented to demonstrate the contractor’s adherence to pre-specified vibration threshold limits. Daily reports can be prepared with graphics that illustrate measured vibrations in an easy-to-read, professional format.
Phase 3: Post-construction Survey and Vibration Monitoring Report
At the completion of construction, a Twining Registered Civil Engineer will perform a
survey of the structures of concern to document any changes to the existing condition of the structures. The post-construction survey will include a narrative of survey scope, a plan showing locations of observations as necessary, and photographs of relevant items in the structures. Twining will prepare a final report with engineering review and approval and graphics that also show the levels of vibrations maintained throughout the construction. The final report includes all monitoring data relative to the specific construction activities observed in the field. This report can be used to demonstrate the contractor’s success with respect to adherence pre-specified vibration limits.