Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 12—Renovation of Conduitscross-sectional area of the pipe wall thickness. The pulling load is a function ofmany variables, such as the weight of the slipliner and frictional drag. A varietyof pulling head configurations are possible, depending upon the application.Approved manufacturer pulling head recommendations should be followed.The nose cone pulling head (also known as the banana nose or soft nose) is asimple and cost effective configuration to use where the pulling stress on theHDPE slipliner is less than 700 lb/in 2 . The nose cone pulling head is madefrom a few extra feet of HDPE pipe that has been fused onto the slipliner.Evenly spaced wedges are cut into the leading edge of the pulling head. Acouple of alternatives exist for the nose cone configuration: (1) the wedges arecollapsed towards the center to form a cone and fastened together with bolts.A pulling cable is attached to secondary bolts that extend across the collapsednose (figure 172) and (2) holes are drilled through the wedges and cables ornarrow plates are attached to the wedges. The cables or plates are attached to apull ring (figure 173).If the sliplining application requires higher pulling stresses, the manufacturershould be consulted for specialty pulling head configurations. Fabricatedmechanical pulling heads are available.Blocks of wood or other material (called blocking or bridging) should beattached to the top of the HDPE slipliner, so that the slipliner will not contactthe top of the existing conduit. Once the slipliner insertion (figure 174) begins,it should continue without any stoppage until completion. The pulling methodwill result in some stretching of the HDPE slipliner (1 percent of the totallength). The slipliner will also experience differential temperatures before andFigure 172.—Nose of HDPEslipliner modified for pullinginto an existing conduit.Figure 173.—A nose cone configuration utilizing a pullring.307