Date:May 2016

Vistas at Providence Park: Compaction Grouting

Lancaster, PA

The Vistas at Providence Park project consisted of an approximate 32,000 sf, multi-story structure with below-grade garages founded on shallow spread footings and continuous wall footings.  A subsurface exploration disclosed a decomposed limestone (saprolite) layer of varying thickness from 1 to 63 ft underlain by limestone bedrock.  Given the thickness and generally low relative densities of the saprolite layer and the known local Karst geology, a compaction grouting program was recommended to improve the existing soil conditions for support of the proposed structure as well mitigate future sinkhole development.

During the bidding process, CGS worked with the Developer and Geotechnical Engineer to further develop an effective and economical grouting program without sacrificing any ground improvement/sinkhole mitigation benefits.  CGS was awarded the project based on value engineering input, competitive unit rates, expertise and efficiency in grouting, and a valued relationship with CCS Building Group that extends 16 years.

The proposed grouting program consisted of 1 to 3 primary grout injection locations per column location and a single primary grout location 12 to 15 ft on-center along continuous wall foundations.  Based on the foundation configuration, a total of 145 primary grout injection locations were proposed for the grouting program.  Injection locations were to be pre-drilled into competent bedrock and then injected with a 2 inch minus slump grout from the bottom of the drilled hole up to the proposed bottom of footing elevation.  Based on the available project data, CGS was able to estimate drilling and grouting quantities as well as a grouting program duration.

CGS mobilized on-time to complete the grouting program during January and February, when soil/site work is extremely difficult if not impossible.  When completed, the final grouting program consisted of 173 total grout injection locations, 9,140 lf of drilling, and 525 cy of grout injection.  Despite a 20% increase in the scope of work and adverse winter conditions, the program was completed on-time for foundation construction and under the estimated budget.