Researching Grout Mix Performance in the Presence of Low Velocity Crossflow Using Large Scale Laboratory Testing for Logan Martin Dam

ABSTRACT ONLY - Alabama Power Hydro partnered with Alden Research Labs in Holden, Massachusetts to design and construct a large-scale grout test chamber to test the effectiveness of various High-Mobility and Low-Mobility grout mixes used in past grouting projects at Logan Martin Dam. Over the past year, the test chamber and process have been modified to incorporate a low velocity (~2 ft/min) water crossflow though the chamber to further challenge grout mix performance. The test chamber used is 10 feet long, 3 feet wide and 3 feet high. The chamber is equipped with discharge ports on the sides, top, and end to allow water and subsequently grout to be displaced from the chamber as new grout is injected. Throughout the test, the grout injection and crossflow water flow rates, discharge flow rates from each port, internal chamber temperatures and pressures, and discharge fluid specific gravity are monitored in real time to evaluate grout dispersion through the chamber. The recent crossflow test protocol integrates water injection into the test chamber through a 6'• dimeter porous conduit centrally located along the length of the test chamber with perpendicular grout injection though the side of the test chamber. The crossflow conduit is surrounded by rock media that simulates the Karst geology typical to Logan Martin. To accurately simulate the crossflow phenomenon, flow through the chamber is only allowed to initially discharge through the end port of the test chamber which establishes a primary flow conduit. As grout accumulates and begins to close the primary flow conduit, the chamber pressure increases, similar to field conditions. As the pressure increases, flow redistributes into secondary, more restrictive conduits. To model secondary conduits, all other chamber discharge ports are outfitted with pressure regulated pinch valves that are set to a target open pressure, such that flow cannot discharge until the primary conduit begins to grout. During a test, a grout mix is considered successful if both primary and secondary flow conduits are grouted shut. Testing completed to date has shown that traditional neat cement grout mixes can effectively redirect and ultimately grout off low velocity crossflow water. Additional testing is scheduled for 2022 to evaluate other grout mix designed to determine the most effective mix design for a crossflow situation.