Microtunneling In St. Louis

By Jeff Griffin, Senior Editor | March 2011, Vol. 66 No. 3

The Metropolitan St. Louis Sewer District (MSD) is in the midst of a multi-million dollar, multi-year capital improvement and replacement program that is expanding and rehabilitating the district’s entire wastewater collection and treatment system. It is the largest, most extensive improvement program in the history of the district.

MSD's boundaries cover 525 square miles and encompass all of the city of St. Louis, MO, and about 80 percent of St. Louis County, serving a population of approximately 1.4 million people. The system has 519,000 single-family residential, multi-family residential, and commercial and industrial accounts.

MSD operates and maintains 9,649 miles of sewers with ages ranging from less than a year old to 150 years old. The MSD has 311 miles of sewers predating 1890, and another 524 miles of sewers predating1930.

At any given time, there are many capital improvement projects under way throughout the MSD service area employing a broad range of construction and rehabilitation technologies.

Of interest to those involved in trenchless methods was a 1,034 linear foot segment of 48-inch steel casing constructed by microtunneling. It was a segment of the Infrastructure Repair Project 087P Caulks Creek Sewer Line “A” (P-750) Phase IV Section B in Chesterfield, MO. The project included approximately 5,771 linear feet of sanitary sewer force main varying in size from 23 to 36 inches in diameter.

Crawford, Murphy & Tilly Inc., St. Louis, was project engineer and the general contractor was Gershenson Construction Co., Eureka, MO. Microtunneling subcontractor was J & J Boring Inc., Winfield, MO.

Conditions
Microtunneling segments for the two tunnels totaled 1,034 linear feet made in two drives under a creek and levee. This trenchless method of construction was required by the levee district to protect the integrity of the levee.

For the first tunnel, surface conditions at the site were a wet and muddy farm field which froze when cold weather came. The second tunnel site was a grassy area adjacent to a shopping center.

The first drive was 434 feet long, said Denny Heisler, P.E., vice president of J & J Boring.

“The access pit was approximately 34 feet deep with the water level in the pit at about 15 feet,” said Heisler. “These conditions required a dewatering system operated 24/7 at both the work pit and come-out pit. Drilling Service Co., Bridgeton, MO, installed the dewatering system.