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2015SpringShotcreteEMag

Goin’ Underground Sewer Rehabilitation Using Shotcrete By Randle Emmrich Fshotcrete. Most of these sewer systems are sewer as a back-form). If the sewer is structurallylining can be constructed (in essence, a new concretepipe is built inside the existing one using the oldor more than 70 years, century-old brick, clay,and tile sewers have been rehabilitated with found in the United States’ major cities where the sound but is experiencing water leaks, soil infil­ infrastructure was put into place by hand between tration, or loose clay/bricks/tiles, a 3 in. (75 mm) 80 and 100 years ago. It is impressive to view the thick polypropylene fiber­reinforced shotcrete craftsmanship that went into the construction of lining is sufficient, along with a grouting program these miles of pipe. It is just as impressive to wit- to fill any voids outside of the sewer. A shotcrete ness how well they have held up over time. lining can add 50 years of new life to a sewer. Unfortunately, most of these systems are reaching Most of these old systems are large in diameter or exceeding their life expectancy and are in need (ranging from 4 to 21 ft 1.2 to 6.4 m) and can of rehabilitation or repair. Enter shotcrete. be horseshoe, elliptical, or round in shape. Usually All of these sewer systems, whether they are the flow in the sewer never reaches full capacity; sanitary, storm, or combined, are located under therefore, a 3 to 6 in. (75 to 150 mm) lining does roadways, buildings, and other structures—not not impact the sewer’s capability of handling peak exactly convenient or cost-effective for tearing flows. In addition, the hydraulic capacity can be up and rebuilding. Thankfully, these structures do increased due to smoothing of the lining using not need to be closed, dug up, or altered for a shotcrete. Shotcrete is especially beneficial in that shotcrete liner to be installed. In fact, most of the it is versatile and can be placed over abnormalities time the public is unaware that work is being and around tight turns in the system, unlike other performed underneath them. rehabilitation liners. In addition, manholes do not Shotcrete equipment can be set to the side of need to be enlarged or altered as long as a person the road near the manhole used for accessing the is able to gain access to the sewer line. Other pipe. Water in the pipe can be diverted, bypassed, rehabilitation liners can require 4 ft (1.2 m) dia- or handled within the sewer line. If the sewer is meter manholes to place the new liner. in structural disrepair, reinforcing steel can be Coastal Gunite Construction Company installed and a 4 to 6 in. (100 to 150 mm) shotcrete completed the rehabilitation of a large-diameter, Fig. 2: Installed galvanized welded wire reinforcement Fig. 1: Existing 100-year-old brick combined sewer (2 x 2 in. 50 x 50 mm, 12 gauge) 40 Shotcrete • Spring 2015


2015SpringShotcreteEMag
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