Advances in Measuring Grouting Pressures Using an Instrumented Packer

Many of today’s grouting projects, specifically those related to earthen dams and levees, require careful control with regards to the grout injection pressure used. Embankments and fracture zones in the rock must be protected against hydraulic fracturing during drilling, water pressure testing and grouting operations. The best way to effectively manage injection pressures during all phases of construction is to measure the pressure being exerted in the ground at the point of injection in real-time. Development of down-the-hole tooling that can measure pressures above and at the injection zone has given rise to the prospect of precisely monitoring and thereby facilitating the determination of the actual effective pressure acting upon the ground. Furthermore, the reaction of the surrounding strata can be precisely measured and analyzed. During the exploratory drilling and grouting program at the U.S. Army Corps of Engineers (USACE) Rough River Dam, an instrumented packer assembly, with injection pressure and column pressure sensors, was used for all facets of work including barrier bag inflation, casing installation, water testing, and rock grouting. Along with the instrumented packer, a calibrated gauge at the collar of the hole was used and all data recorded. This paper will compare two methods of calculating effective grouting pressures applied to the surrounding overburden and rock. The first method is the current industry standard of measuring the pressure at the collar of the hole and calculating the resulting effective pressure after taking into account the various dynamic line and head losses. The second method measures effective pressure at the point of injection using an instrumented packer. This second method, first presented, has now been applied to other grouting activities successfully executed during the Exploratory Drilling and Grouting program at the Rough River Dam. A number of benefits have been observed when using the instrumented packer on this grouting project. One of these benefits is the precise grouting of annular space and detection of grout loss during casing grout operations. Another advantage to using this device is the detection of packer by-pass during water pressure testing and grouting operations. It has also been observed that false refusals for thicker mix designs are non-existent using an instrumented packer while this phenomenon has been found to exist with traditional grouting methods. Finally, the pressure applied to barrier bags can be precisely monitored and controlled using an instrumented packer to ensure the bags are not over-pressurized during inflation.