Public wastewater line installation joins private for development of a new residential project in Georgetown. Lewis Contractors, Inc is in the process of installing approximately 23,000 feet (4.35 miles) of mostly 36-inch Hobas pipe along the South Fork of the San Gabriel River west of Interstate 35.
The line installation through this Hill Country terrain ranges from 12 feet to 40 feet in depth, but for most of the distance the line is approximately 30 feet in depth, according to Ronnie Lewis, owner of Lewis Contractors, Inc.
Lewis Contractors, Inc. specializes in underground utility and sitework construction in the Austin area. Lewis Contractors has completed projects ranging from subdivisions to large-diameter water and sewer line projects and almost every type of civil construction. The last 30 years have brought substantial growth not only to the Austin area, but also to the business. Lewis Contractors, Inc. has grown from about 20 employees in 1977 to over 150 today with an annual revenue that has grown to over$25 million.
The initial section of this wastewater line was a $2.1-million contract with the city of Georgetown that Lewis' crew completed during the latter months of 2007. That was a lift station on the north bank of the South Fork of the San Gabriel River just west of Interstate 35 with 2,500 feet of 42-inch interceptor line. The city's wastewater line is positioned along the centerline of the river for the most part because of the narrow channel and the river banks being vertical, according to Georgetown Public Works project manager Michael Hallmark. "The line crossed the river at a skew twice, then runs parallel with the river."
"We diverted the water to one side while we dug," said Lewis. "When we were through, we diverted it back to the other side." This second diversion allows vehicle access to the work train farther upstream.
The approximately $15.7-million project consists of furnishing and installing 17,591 lineal feet of 36-inch and 4,885 lineal feet of 30-inch Hobas gravity sewer, sewer manholes, bores, trench safety, and other miscellaneous items. The line will serve a new residential development, Water Oaks at San Gabriel, under construction for Laredo WO, Ltd.
Lewis' crew started the private phase of the line in January 2008. They expect to be completed with the entire line by October 2008.
Anyone familiar with the rock strata of this region knows that installing 4.35 miles of underground line at mostly 30-foot depths in only 9 months is an extremely aggressive schedule. Ronnie Lewis opened his bag of tricks to open this four miles of rocky earth.
Joe McDaniel Construction, a utility contractor, first clears the trees and brush with a Hydro-Ax mounted on a front end loader, so that the trenching and pipe-laying train can follow behind.
"We're doing the initial excavation using two Caterpillar 637 push-pull scrapers assisted by a Caterpillar D9 to clear all the overburden and then trenching a channel with excavators. Most of the job is 15 to 20 feet of dirt, then 15 to 20 feet of rock below that."
A pair of EX 1200 Hitachi excavators outfitted with 72-inch-wide Leading Edge Multi-Ripper buckets trenches a channel down to the rock layer.
Leading Edge Attachments, Inc. president, Lee Horton, P.E., of Jefferson, Massachusetts, describes the reason for the Multi-Ripper Bucket's power. "The staggered ripper teeth fracture the substrate in sequential order. No two ripper teeth align with each other, resulting in the maximum breakout force being applied sequentially to each tooth. The distance from the excavator stick pivot to the tooth tips is also shorter than the standard bucket for the machine. The shorter distance actually multiplies the tooth tip force."
Lewis kept the ownership of his Leading Edge Attachments a secret for a couple of years. They were his "secret weapon" for low-cost trenching productivity. "There are enough people who know I have these now that I'll admit to using them."
"There are some areas where we can get all the way through the rock with the Leading Edge buckets, other areas where the top five feet may be hard and we'll have to use the [Atlas Copco HB 7000] hoe ram." The Atlas Copco HB 7000 hydraulic breaker comes into play when workers reach the strata of blue limestone at about 20 feet throughout the range of the project.
When introduced at ConExpo in 2005, the HB 7000 was the world's largest hydraulic breaker attachment. Weighing in at 7 tons, the HB 7000 is ideal for demolition, trenching and foundation work as well as primary and secondary rock breaking in quarrying and mining.
The breaker's 119-gpm hydraulic flow at 2,610 psi of pressure allows the HB 7000 to deliver an impact frequency of 280 bpm to 450 bpm (blows/min). Atlas Copco in Round Rock installed the extra-heavy-duty wet kit from Rocky Mountain Hydro Tech in Colorado.
"You have to have the plumbing to operate the hammer," explained Tom Ling, representative for Atlas Copco. "Typically on the end of the excavator stick, there are only enough hydraulic lines to run the hydraulic cylinders for the stick and bucket and the boom."
The 36-inch diameter HOBAS centrifugally cast glass fiber-reinforced plastics pipe is lowered into the trench with a Caterpillar 385B excavator. The bedding gravel is placed via a John Deere excavator hoisting a remote-controlled gravel bucket built in the Lewis Contractors shop.
The wastewater line will cross the river seven times in the length of this project. In all, the project requires 17 bores amounting to approximately 2,700 feet. The boring subcontractor, Bryant and Frey, is boring the river crossings with an auger for environmental and safety reasons, with the water being the basis for both.
"In consideration for the water, the crew is using an auger instead of microtunneling as a safety measure so that there is no chance for a cave-in to trap a man in the tunnel with electrical equipment," said Lewis.
John Birchfield with Bryant and Frey said, "The other reason is that microtunneling discharges a lot of spoils and bentonite that are difficult to contain for an area as environmentally sensitive as Travis and Williamson counties in the Hill Country." The crew is using a horizontal boring machine built by Leo Barbaro and outfitted with a Robins roller head.
Although the 4.35-mile long project is being privately funded, the city of Georgetown inspectors must oversee the project. Once it is completed, the city will own the wastewater line.