Liberty Park is a mixed-use development along I-459 in Vestavia Hills, Alabama with the Miss Liberty statue greeting visitors as they enter.
Beginning in the early 1900s through the 1950s, this property was extensively undermined with room and pillar coal mining operations. A network of abandoned mines was created including two seams that were mined resulting in two levels of underground mines with some of the mines extending below the Cahaba River.
While it was known that the property had underground coal mines, the extensive nature of the relatively shallow depth of the underground mines had yet to be determined.
BHATE Geosciences was retained after the property was purchased by Torchmark to determine the extent of the mines and prepare a development plan with a mine subsidence risk assessment. Our initial evaluation included a review of historical mining maps and a field survey of the mine shaft openings and surface subsidence features. Deep mine probes were conducted with underground examination using borehole cameras to evaluate the condition of the mine void existing supports.
The evaluations were used to develop cost-effective mine remediation plans and this information was used to develop various foundation designs on the property. The structures in the Urban Center at Liberty Park are supported on a variety of foundation systems:
- Boy Scouts of Alabama Headquarters – spread footings after excavation and backfilling of shallow mine voids (less than 40′ deep) and replacement with engineered fill.
- Federal Reserve Bank of Atlanta-Birmingham – the entire mine void in the affected zone was filled by creating barrier walls and flush grouting to prevent potential future issues of unauthorized mine access under the structure.
- Buildings 1000 and 1200 – grout pillars were used for subsidence stabilization for vertical and horizontal movements and for slab on grade support with foundations extended through the mine cavity (depths ranged from 60′ to 90′ below the ground surface) using a 10″ diameter pipe pile through the pillars for a load capacity of 120 tons.
- Buildings 1400 and 1500 – a variable pattern of grout pillars constructed from the ground surface were used depending on the mine depth (from 100′ to 160′).
BHATE was presented with the Associated Builders and Contractors of Alabama “Excellence in Construction Award” in 1994 for our work on Liberty Park. With our extensive knowledge of the site, BHATE was chosen to work on additional projects within Liberty Park including residential developments, the Town Village, the Church at Liberty Park and the Encompass Health headquarters.