Sliplining helps avoid water service problem
The responsibility for water, waste-water and reuse entry for San Antonio belongs to the San Antonio Water System Department, which has an on-going program of reviewing, maintaining and upgrading the city’s aging systems. As part of that program, the department identified a particularly critical 40-year-old, 48-inch concrete sanitary sewer that had reached its design-life expectancy and was begining to corrode.
Because the line was still basically intact, sliplining made sense because of the lower dollar and social costs. With sliplining, only one entry pit is necessary; therefore, only a small portion of the road will need restoration when the project is completed. Working within the host pipe means little or no likelihood of damage to adjoining utilities. Moreover, utilities will not have to be relocated.
Sliplining can be accomplished at a fraction of the time required for direct burial and at significantly lower cost. Additionally, bypass pumping is not required in live sewage so there is no service interruption.
Residents are not disturbed, and businesses do not suffer lost revenue because of the inconvenience caused by construction activity.
Furthermore, because the department is familiar with trenchless technology and has experience working with other sliplining jobs, it wrote the specs for the project, saving money that would have been spent on outside consulting fees.
E-Z Bel Construction, San Antonio performed the work, selecting 42-inch Lamson Vylon PVC closed-profile slipliner pipe in 15-foot laying lengths.
Initially, a 10-by-20-foot pit was excavated but lengthened slightly to give more flexibility in maneuvering the pipe. The top portion of the concrete pipe was cut away at the springline to create the entry area for the slipliner process.
A simple system of cables and pulleys was attached to a two-ton crane, which was used to assemble the joints and push the slipliner in place. The average time required to make a joint between lengths was three minutes. The pipe was pushed 2,600 feet in one direction and 800 feet in the other.
Although some sliplining was done in the evening, with sewage at the two-thirds level, the bulk of the work was accomplished in the morning with the sewage level at about one-third of the pipe.
A high-pressure, hydrojet system cleaned sections of the 48-inch host pipe before the PVC was inserted and joined. Air bags were used to hold the pipe in place for proper alignment during joining. Bulkheads were installed at manholes and junction boxes at either end of the 48-inch conduit and the annular space between the liner and the host pipe were grouted.