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83 CLSM part of the National Geotechnical Experimentation Site, the types of soils and clays at the sites have been well documented. For this project, test pits on both sites were excavated using a backhoe-mounted auger to collect and analyze the soil and clay. The clay site is underlain by four distinct layers. The sur- face layer is mottled red and gray clay. This clay layer is very (a) uniform in thickness down to about 1.83 m below the surface. The plastic and liquid limits of the clay were 20.9 and 53.7 per- SOIL cent, respectively. The hydraulic conductivity coefficient was 4.99 × 10-3 m/year. The surface layer at the sand site is mot- tled red and tan silty sand. The percentage of fine particles was 17.4 percent, and the hydraulic conductivity coefficient was 5 × 10-2 m/year. Metal pipes were placed in six trenches on each site using CLSM three different trench conditions. The trenches were 12.19 m (b) long, 0.76 m deep, and 0.46 m wide. Figure 4.22 shows the three trench conditions used in the test: · Condition I: Metallic pipes are completely embedded in CLSM (Figure 4.22(a)). · Condition II: Metallic pipes are placed on a CLSM bedding SOIL and backfilled with soil from the site (Figure 4.22(b)). (c) · Condition III: Metallic pipes are completely embedded in soil (Figure 4.22(c)). Figure 4.22. Three trench conditions used for the field test. Commercially available ductile iron pipes and corrugated steel culverts were delivered to the site. Both types of pipe were the site, which aims to replicate field conditions that lead to cut into 0.76 m long pieces. The ductile iron pipes had an corrosion and to accelerate the rate of deterioration. asphalt coating that was removed by sandblasting after soaking in lacquer thinner. Copper wires (2.32 mm diameter) were attached to each ductile iron and culvert sample to be used for Site Layout and Construction corrosion observations later. After drilling and tapping the Two sites, a clay site and a sand site, were selected to observe ductile iron pipe pieces, screws and washers were used to attach the corrosion performance of embedded ductile iron pipes the wires as shown in Figure 4.23(a). Exposed wires and screws and galvanized corrugated steel culverts. Because the sites are were coated with epoxy to prevent corrosion. Grounding clips (a) (b) Figure 4.23. Wiring of ductile iron pipes and corrugated steel culverts.
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84 were used to attach wires to corrugated steel culvert pieces. After the wires were connected, the exposed sections of the wires and clips were coated with enamel. Epoxy was applied after the enamel was cured as shown in Figure 4.23(b). Twelve of the cut ductile iron pipe samples and twelve of the cut corrugated culvert samples were painted with epoxy inside and outside leaving only a 0.15 m diameter circular area ex- posed. Counter electrodes for polarization studies were 0.15 × 0.15 m nickel-chromium wire mesh. Copper wires (2.32 mm diameter) with alligator clips were attached and soldered to the meshes. The alligator clips, the solder area, and exposed wires were coated with epoxy. These 24 pieces of pipes with limited exposure areas together with the counter electrodes can be used later for long-term corrosion rate measurements. Figure 4.24 shows three of the samples prepared for polarization testing. The six trenches were excavated on each site in a 6 × 30.5 m rectangular area using a backhoe with a 0.46 m wide bucket. After the bottoms of the trenches were cleared, pipes were placed with 0.6 m space between them. Four ductile iron pipe samples and four corrugated steel culvert samples, including one of each with limited exposure areas, were placed in each trench. The pipe pieces were placed on steel chairs to allow free flow of CLSM mixture underneath the pipes. Each piece of pipe was also secured using four stakes, driven 1 foot into the ground to prevent lateral and vertical movement. Figure 4.25 Figure 4.25. Clay site trench with pipes. shows a trench in the clay site with pipes. The pipes prepared for polarization testing were placed at the two ends of the trenches. These pipes were placed with the cement, and 135 kg/m3 fly ash. The watercementitious ma- exposed areas facing sideways so that when the trenches were terial ratio was 0.8. The CLSM was delivered in ready-mixed backfilled they would be exposed to a CLSM and soil environ- concrete trucks and was placed into the trenches using a chute ment. Counter electrodes were placed adjacent to the exposed as shown in Figure 4.26. areas. The average time to fill the condition I (completely filled After the placement of the pipes, trenches were backfilled with CLSM) trenches was 8 minutes. The truck was placed at with a CLSM mixture provided by a local concrete supplier. one end at the trench and the trench was completely filled from The CLSM mixture contained 1483 kg/m3 sand, 34 kg/m3 this point (Figure 4.26(a)). The average time to fill the condi- tion II (CLSM bedding and soil backfill) trenches was 11 min- utes, and the truck had to be moved three times to ensure uniform thickness of bedding layer. Condition II and III trenches were filled with native soil after the setting of the CLSM backfill. The soil was placed into the trenches in layers with a backhoe and compacted with an average of three passes of a jumping jack compactor. The average time to compact an approximately 0.25 m thick by 12 m long layer of soil was approximately 5 minutes. This speed equals approximately 30 minutes for sample sized trenches filled with CLSM (3 to 4 times longer). The wires connected to the pipe pieces in each trench ran along the bottom of the trenches and were collected in PVC boxes at the surface of each trench. The wires entered into the boxes through an inverted U-shaped conduit to prevent rain- Figure 4.24. Metal pipes with 0.15 m diameter water from entering into the boxes. A smaller box was placed exposed surface and a counter electrode. inside each PVC box and wires were soldered to female con-