The Problem

The deterioration of CMP happens over time from the exposure of oxygen and moisture which forms rust. Deterioration can depend primarily on soil conditions and the acidity of the water flow. In some instances, this condition can cause sinkholes to form that allow water to escape during heavy rain and destroy property. Flow line corrosion causes loss of structural integrity. Bottom bedding and support fill is exposed and begins to erode away. As bottom bedding material is lost, flow begins to occur around and beneath the pipe. Side wall bedding and support material is lost leaving voids and loss of structural support. Sink holes start to develop at the surface. Catastrophic failure potential is increased and disaster looms. In such cases, it would be prohibitively expensive and time-consuming to repair the entire pipe and it would also not stabilize and fill the void areas exterior to the pipe.

About Us

Fayetteville, TX (Before)

Fayetteville, TX (After)
The Application Method

Prior to beginning work, all debris, stones, rubble and loose material will be removed from the pipe. Beginning at the outfall, the overlay sheets will be placed in the bottom of the pipe, centered over the corroded flow path, and pressed into place to conform to the arc of the pipe. While held in position, the sections or sheets are fastened with two rows of fasteners every 8” to 12”. Advancing in the counter-flow direction, each subsequent section/sheet is “shingled” over the leading edge of the prior sheet with an overlap of 6”.
Once the needed sheets are installed, multiple injection holes (5/8” dia.) are drilled through the new invert and through the host CMP. The overlay sections/sheets will be blocked and braced sufficiently to prevent movement when the next step of injections begin. High Density Polyurethane (HDP) is injected in multiple locations through the injection holes, allowed to expand, void fill and seal the back side of the repair area. As necessary, polymer is injected at depth through injection tubes placed into the supporting subsoil so as to further strengthen and stabilize the supporting subsoil. Outcropped HDP material is removed with hand tools and disposed of. The repaired area is inspected for completion.

Injection of High Density Polyurethane

Relining invert with Trenchcoat coated galvanized metal plates


Material for filling voids behind the pipe wall, stabilizing the supporting soil, and sealing any points of infiltration will be two-component High Density Polyurethane (HDP).

The material must be hydro-insensitive (capable of reacting and expanding in the presence of water), hydrophobic (capable of driving away water and sealing thru water), and capable of expansion rates of up to 20 times initial volume. Material shall cure to 90% of ultimate compressive strength within 15 minutes of injection. Cured compressive strengths shall be as follows:
  • Density (pcf)—ASTM 1622 3.0 3.5 4.0 6.0
  • Compressive Strength (psi) ASTM 1621 40 50 60 110
Overlay of the corroded bottom flow area shall be standard galvanized steel sheet, meeting requirements of ASTM A653/A653M with minimum zinc coating of 0.90 ounces per square foot.  The sheet metal will have a factory applied coating (Dow Trenchcoat) on both sides.  An alternative method for overlaying the corroded area would be a fiberglass section pre-molded to conform the specific pipe diameter and thickness as specified by the engineer.

Corrosion resistant mechanical fasteners for attaching the sections/sheets to the host CMP shall be self tapping or self anchoring and of sufficient size and strength to properly hold sheets in place.