CIGMAT Report: Update From This Unique, Industry-Specific Ongoing Research Program

By C. Vipulanadan, PhD, P.E., professor of Civil Engineering, director of CIGMAT and the Texas Hurricane Center for THC-IT | September 2010 Vol. 65 No. 9
1) Macro-cells 2) Macro-holes in the Macro-cell walls 3) Macro-cell walls. Fig. 1: Microstructure of a polyurethane grout.

Grout tests for leak control
CIGMAT has not only tested various materials for civil infrastructure and offshore pipeline applications but has developed several test protocols for testing grouting and coating materials and wastewater pipeline joints for leaks under various loading conditions.

A critical issue facing the nation today involves the increased pollution found in the waterways, shorelines, rivers, bays and streams. The EPA estimates that 70 to 80 percent of this increase comes from the inflow and infiltration (I/I) of the home laterals [EPA 2000 Web site]. Several types of grout materials have been used in controlling I/I problems in wastewater systems and storm systems [Vipulanandan, 1996c]. These materials have been commonly used for leak control in below grade wet wells or holding tanks, manholes, sewer and storm lines, cracked retaining walls and other underground structures [Karol, 1990, Vipulanandan, 1996a, Vipulanandan, 2000]. CGMAT researchers investigate the grout behavior based on their microstructure using the scanning electron microscope. Figure 1 shows the microstructure of a polyurethane grout where the cell structure and the distribution and size of pores are investigated.

(1) Macro-cells (2) Macro-holes in the Macro-cell walls (3) Macro-cell walls

Fig. 1: Microstructure of a typical polyurethane grout used for rehabilitation.

Many owners are discovering that if I/I problems are not adequately controlled it will lead to frequent overflows and undue burden on the treatment facilities. The primary goal of grouting these facilities is to return the structure to its original working conditions by the oldest trenchless technology method – in situ grouting. Using grouting to control leaks in wastewater facilities and other leaking structures is one method currently being adopted. CIGMAT researchers are investigating the fundamentals of grouting leaking joints using 2D and 3D physical and numerical models [Ozgurel et al. 2005]. In Figure 2, a 2D physical model is used to investigate grouting of a leaking joint under various soil and in situ stress conditions. A typical grouted soil bulb with very low permeability that is formed around the leaking joint after grouting is shown in Figure 3. This model study also was used to quantify the advancement of the grout front based on the pumping parameters.

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Fig. 2: 2D model test for infiltration and grouting study.

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Fig. 3: Grouted soil bulb at the leaking joint.

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