MICROTUNNELING
Bennett Trenchless Engineers has extensive experience designing microtunneling, open-shield pipejacking, earth pressure balance pipejacking, pilot tube microtunneling, auger boring, and piperamming projects. We have designed projects with pipe diameters from 18” to 96”, and with lengths up to 1,700 feet. Our designs have included many different pipe materials, including reinforced concrete pipe, reinforced concrete cylinder pipe, polymer concrete pipe, clay pipe, centrifugally cast fiberglass reinforced polymer mortar pipe and steel pipe.
Below are descriptions of a few of the projects that Bennett Trenchless Engineers has designed.
 Howe Ave Water Main – Sacramento, California
As a specialty trenchless consultant to Black & Veatch, Bennett Trenchless Engineers provided design and construction management services for the 54-inch diameter water main crossing of the American River near Howe Avenue and the Fairbairn Intake. The project consisted of a single 1,450 ft, 60-inch diameter microtunneled drive, from a concrete caisson jacking shaft on the south side of the river to an auger drilled reception shaft on the north side of the river. The bore passed beneath flood control levees on both sides of the river. Bennett Trenchless prepared a technical memorandum recommending the preferred construction alternative, alignment, and depth, and developed the schedule and cost estimate. Bennett Trenchless also prepared technical specifications and drawing details for the final microtunneled crossing design. In addition, Bennett Trenchless Engineers provided submittal review and on-site construction management services.
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 Beaver Water District Intake Structure – Lowell, Arkansas
As a sub-consultant to MWH, Bennett Trenchless Engineers conducted the feasibility/preliminary design evaluation, geotechnical investigation, prepared Geotechnical Data and Baseline reports, evaluated alternative construction methods, conducted a design workshop, and provided design services for twin intake shafts and eight 60-inch diameter intake tunnels to triple the Beaver Water District’s water supply capacity from 80 MGD to 220 MGD. A ninth microtunnel connected the two intake shafts. The shafts were 30 feet in diameter and 90 feet deep, excavated through very challenging karstic limestone and fissile shale. The eight 60-inch tunnels varied from 90 to 160 feet in length and required underwater retrieval of the MTBM after each bore. The limestone contained numerous solution features and caves, and had unconfined compressive strengths up to 28,000 psi. Bennett Trenchless Engineers also provided full-time construction management/inspection during the shaft excavation and microtunneling.
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 Sacramento River Intake – Sacramento, California
As a sub-consultant to CH2M Hill and MWH, Bennett Trenchless Engineers provided design services, including plans and specifications, for twin, 340 linear foot, 54-inch raw water mains in 72-inch steel casings for crossings of Interstate-5 in Sacramento, California. Bennett Trenchless Engineers provided full-time construction management and inspection for the microtunneled crossings. All microtunneling operations were monitored to assure the quality of the work, as well as to protect the critical section of the Interstate from potential damage.
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