Rehab Of A 100-Year Old Brick Storm Sewer

U-TECH
By Datta Shirodkar, Boyer Inc. and Michael Spero, P.E., Danby LLC | July 2010 Vol. 65 No. 7

From good to bad to worse
On the first day of the grouting operation, the grout flash set, which was never a problem on previous jobs. Initially, it was thought that there was some problem with the pump, but the next day rocks, pebbles and clumps of set-up cement were discovered in the mix. The mix is supposed to contain only cement and fly ash; no aggregates. A screen was installed at the transfer hose from the mixing to holding tank and started catching rocks, pebbles and cement clumps which were causing the hose to clog up.

Once this problem was solved, random batches of the grout started flash setting. On two separate occasions, five batches had to be pumped out and wasted into a wooden box because of flash setting in the holding tank in five to 10 minutes. The supplier was again informed about this problem.

While grouting the third lift of the first section, the liner buckled. It was determined that the grout in the first and second lifts had not set, even after 36 and 12 hours respectively. This allowed the liquid grout in the upper lift to migrate downward where it exerted an excessive hydrostatic force on the lower sections of liner causing buckling. Because of the inadequacy of the grout and the buckled liner, Boyer decided to remove the liner and grout installed for the first 300 feet. Testing of the defective grout showed that it did not meet required strength requirements. New liner was reinstalled for that section. Removing the liner and grout was a tedious process that entailed cutting out the liner and then removing the hardened grout in pieces using a jack hammer.

The primary issue with the cement/fly ash blend was the inconsistency of material and apparent deficiencies in the QA/QC at the supplier’s plant. After switching suppliers for the cement/fly ash blend, no further problem with grout quality were experienced.

Conclusions
This project had many challenges, both expected and unanticipated. Between the grout problems, removal and replacement of liner and grout and 18 rain days, the job took twice as long to complete than was planned. Unfortunately from the standpoint of cost, this was not a profitable job. However, the contactor, Boyer Inc. was professional and did the right thing and corrected any shortcomings at their own expense even though the problems were caused by circumstances beyond their control.