The AEP Racine Locks and Dam facility consists of two parallel lock chambers and a dam constructed on the Ohio River in the mid 1960s. The dam itself has a total length of approximately 1,200 feet, with an American Electric Power (AEP)/Federal Energy Regulatory Commission (FERC) hydroelectric generating facility located on the Ohio (right) dam abutment. The project includes two 24,000 KW turbines operating 24 hours per day as run of river conditions permit.
When Sheet Piles Fail
In early 2016, the riverward sheet pile coffer cell comprised a portion of the dam, and the AEP power generating facility experienced a sudden and significant internal failure. The interlocks on several of the riverward sheet piles failed (“bursting” failure). This resulted in substantial loss of coffer cell granular fill material and collapse of the coffer cell concrete cap. Several of the riverside sheet piles moved significantly outward due to the loss of confinement. The adjacent AEP concrete powerhouse facility appeared to have prevented more significant failure by “buttressing” the coffer cell’s failed side.
DLZ Provides Emergency Drilling
Immediately, AEP engaged DLZ to perform an emergency drilling program and evaluate the adjacent (landward) undamaged coffer cell. DLZ conducted the evaluation to determine if the undamaged coffer cell could support the weight of the construction equipment needed to facilitate emergency repairs to the damaged cell. This required placement of a 100-ton crane on top of the undamaged cell. There were concerns that placing such a large load (surcharge) on top of the undamaged cell could cause it to fail similarly as that of the damaged cell. The 2016 field exploration included drilling six borings through the undamaged cell to determine the composition of the cell fill material. Carefully coring through the coffer cell concrete cap was essential. Two standpipe type piezometers were also installed for future monitoring of the phreatic surface within the cell fill.
DLZ performed all engineering analyses for the cell in accordance with the US Army Corps of Engineers (USACE) guidelines. The analyses results and recommendations were provided to the client less than a week after official work authorization. The landward coffer cell was capable of safely supporting the repair equipment as a result of the exploration and analyses. Emergency repairs were made to the damaged coffer cell and dam, preventing a potentially serious dam safety emergency.
Additional Analyses Required for Permanent Dam Repairs
In March 2017, DLZ performed additional analyses of the landward coffer cell on the AEP Racine Locks and Dam. The analyes was completed to determine if it could support even heavier construction equipment required for permanent repairs to the damaged facility. DLZ drilled and tested an additional four land-based borings and five river-based (barge) borings at the site, just upstream of the dam and damaged coffer cell. The drilling and field testing work were performed under an accelerated schedule due to the permanent dam repairs’ emergency nature.
The land-based borings were drilled to depths of up to 160 feet, with pressuremeter testing and packer testing performed in both the soil and rock stratums. Fully-grouted vibrating wire piezometers were installed in the boreholes. The river-based (barge) borings are being advanced through over 50 feet of water. Then, to depths of nearly 140 feet into soil and rock, with pressuremeter testing and packer testing performed in both the soil and rock stratums. All drilling and testing was completed in accordance with strict USACE and FERC guidelines and approval protocols.
Accelerated Schedule Meet
The accelerated nature of the work required DLZ to begin drilling the river-based (barge) borings within approximately two weeks after authorization. Within this time, DLZ:
- obtained a barge and tug for the river-based drilling operations
- coordinated with numerous parties involved (AEP, FERC, USACE, Contractors)
- submitted and received approval of various safety and work plans, and
- applied for and obtained a USACE “Notice of Navigation Interests” for work on the AEP Racine Locks and Dam.