Packer Injection Grouting for the Long-Term – An Engineering Perspective

Abstract

Packing injection grouting, or also known as testing and sealing of pipe joints, has often been the victim of a poor reputation. A number of utility owners have had bad experiences in attempting to stop or impede the infiltration of clean water into their sewer lines by grouting the pipe joints and laterals. The goal of any sewer rehabilitation is to ensure the proper longevity of the work. Failures that occur within months or even a couple of years after completion of the rehabilitation work are not an acceptable option. Grouting, in theory, has been a cost-effective method of sealing pipe joints and can be a very viable technology for structurally-sound pipes. Grouting has been unsuccessfully attempted in the past by numerous municipalities. However, past failures of grouting are generally attributable to technical issues, some of which are largely unknown by even the contractors who perform the grouting work. Grouting failure is caused by a number of issues. One of the primary causes of failure is related to the control of the grout mixture rather than actual grout injection procedure. One of the critical issues is gel time – the time it takes for the grout to catalyze from liquid form to gelatinous form. Gel times are often set to ensure that the grout moves through the open pipe joint and into the surrounding soil before hardening, thus forming a soil-grout matrix around the pipe joint and sealing it from future groundwater infiltration. However, gel times can vary dramatically with changes in temperature. For typical grout used in sewer pipe joint sealing, manufacturers state that gel times can be doubled (or halved) for every 10°F change in temperature. Operators, engineers, and inspectors who are unaware of this nuance may think that a pipe joint has been successfully sealed because it passes a subsequent air test, but in reality the surrounding soil has very little grout and the joint has been simply “veneered”. This cause of failure and others failures will be discussed in this paper. Some of the other topics will include: E The critical details of the grout mixture and grouting techniques E Highlighting the types of grout available for sewer pipe joint sealing E Specifying the correct gel time based on pipe size, pumping rates, and project goals E Methods to ensure gel times meet the contract documents E Discussing the additives that can be used to increase grout strength and performance in sewer pipe joint sealing applications E Using step-grouting as a technique to pack large voids or soils E Recommended contract requirements to help ensure successful grouting jobs. E Importance of observing the work by a qualified Resident Project Representative