Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Dams310of injection application. High-range, water-reducing, shrinkage-compensating,plasticizing admixtures may be beneficial.The grout should be tested in accordance with ASTM C 939. The designshould specify mix design, density, viscosity, maximum injection pressure, initialset time, 24-hour and 28-day compressive strength, shrinkage, stability, and“bleed” or fluid loss. A minimum design compressive strength of 4,000 lb/in 2at 28 days is generally acceptable.The grouting contractor must have dependable equipment of a size that willallow the grouting to be done quickly. The contractor must also have backupequipment available and ready at the site. Any grout not used after 20 minutesshould be wasted. Grouts are susceptible to degradation by excessive waterinfiltration before the grout sets. Extensive use of flyash aggravates thisproblem. Therefore, flyash-based lightweight grouts are not recommended.• Sequencing and injection.—The grouting equipment should be capable of mixingand delivering the grout at a rate that will allow the annular space to be entirelyfilled in a continuous operation, unless staged grouting is being used. Thecontractor should monitor the grout pressure. If the existing conduit hasdeflected vertically from a straight alignment, trapped air could result in a voidin the grout.Grout injection can be accomplished by a number of methods, includinggravity and pressure:1. Gravity.—Injection of grout into the annular space starts at the upstreamend of the HDPE slipliner and progresses toward the downstream end, soas to more easily displace water and debris. Suitable injection tubes mustbe inserted at the upstream end. Vent pipes installed at the downstreamend should be 150 percent larger than injection tubes, to minimize thepotential for clogging. Dirty water and excess grout discharged from thedownstream vent tube should be collected and disposed of properly.Grouting should continue until heavy grout exits from the downstreamvent tube.2. Pressure.—HDPE grout pipes (typically 1 to 1½-inch diameter) areextrusion welded to the crown of the slipliner prior to installation. Thedesigner will need to determine the required number and length of eachindividual grout pipe. The number of grout pipes required for a particularsliplining application is a function of the diameter of the pipe and theexpected length of grout travel, once it leaves the end of the grout pipe.A rule of thumb used by Reclamation assumes about 25 to 30 feet of grouttravel from the end of the grout pipe. For example, if a deteriorated outlet