Water Cutoff in Karst Limestone

Location: Niagara Falls, Ontario
Sector: Energy

Case description

An elevator shaft accessing Sir Adam Beck I powerhouse was excavated through karst limestone and shale in the early 1900’s; shaft dimensions are approximately 5 m x 5 m x 60 m deep. Water from the power house forebay intake canal was infiltrating through karst limestone rock formation and entering the brick-lined elevator shaft, creating maintenance problems for elevator equipment and corroding installed structural and electrical components within the shaft.

Solution

A series of large diameter holes were cored through the brick lining to expose the rock walls of the shaft for inspection purposes. It was observed in many locations that loose rock debris had fallen from weak zones and accumulated behind the brick lining.

After reviewing information from adjacent vertical core holes, it was determined that the majority of water infiltration was associated with limestone formations situated near the top of the elevator shaft.

These water-bearing rock formations were isolated from dry rock formations by strategic injection of water-activated polyurethane resin between the brick lining and the shaft rock excavation. Staged drilling and systematic injection of holes at progressively longer lengths displaced infiltrating water away from the shaft wall and gradually reduced active water inflow rates.

Deeper core drilling in conjunction with cement grouting was subsequently used to systematically fill open water flow channels and prevent water from migrating fromthe forebay intake canal towards the elevator shaft.

Water inflow rates as measured at the bottom of the elevator shaft throughout the project were systematically reduced as work was underway and were eventually eliminated. The original water-bearing channels did not propagate or cause water to migrate elsewhere within the elevator shaft.