Projects

Project Overview

As the trenchless subconsultant to HDR Inc, Bennett Trenchless provided design assistance for the relocation of Solano Irrigation District’s water main crossing of Suisun Creek. The crossing needed to be relocated due to Caltrans’ relocation of the nearby Cordelia Truck Scales on Interstate-80. The 20-inch pipeline was relocated using horizontal directional drilling; the crossing was approximately 350 feet long. Design included selection of the bore profile and alignment, evaluation of hydrofracture and settlement risks, pullback loads and pipe stress calculations, preparation of a Hydrofracture and Surface Spill Contingency Plan, and development of a cost estimate and schedule. Bennett Trenchless also provided submittal review and full-time on-site inspection of the HDD operations.

Challenges on the project included crossing beneath endangered species habitat, high groundwater, high hydrofracture risk, work area restrictions, and protection of nearby utilities. The alignment of the crossing was constrained by the ability to acquire temporary and permanent easement from various private owners on both sides of the crossing.

Project Overview

Bennett Trenchless was the prime consultant to the City of Solvang for preliminary design of the 16-inch diameter, 1,400-foot horizontal directional drilled crossing of the Santa Ynez River. The existing force main had been originally installed in the river bed using open-cut methods. Scour had exposed the pipeline and threatened its survival. A new force main had to be installed parallel to the existing force main, connecting the wastewater treatment plant on the south side of the river, to the pump station on the north side of the river. Preliminary design included review of existing geotechnical information, execution of a supplemental geotechnical investigation, acquisition of environmental permits, calculating pullback loads and pipe stresses, evaluation of hydrofracture and settlement risks, and design of the crossing itself.

Bennett Trenchless teamed with the HDD Company, Inc in a design-build contract to finalize design and construct the pipeline. Horizontal directional drilling was used to install 1,400-feet of 16-inch DR 11 HDPE pipe at a maximum depth of 80 feet below the river bed. Tie-ins on either side of the crossing were designed by Penfield & Smith and constructed by Hanly Construction. Bennett Trenchless provided full-time on-site construction inspection for the horizontal directional drilling portions, as well as the testing and contact grouting. The project was completed within budget and schedule with no claims.

Project Overview

Bennett Trenchless Engineers served as the trenchless subconsultant to O’Dell Engineering on the replacement of the City of Modesto’s 18-inch inverted siphon under the Tuolumne River. The existing siphon was replaced with two new 650-foot, 18-inch fusible PVC pipelines installed by horizontal directional drilling. Bennett Trenchless Engineers provided preliminary and final design services for the trenchless crossing, including hydrofracture and settlement analyses, pipe stress and pullback calculations, technical specifications, trenchless design drawings, and part-time on-site inspection services.

The geotechnical conditions consisted of loose clean to silty sands near the surface, grading to medium dense near the bottom of the bore. High groundwater levels combine with the loose sands near the surface posed a high risk of bore collapse and subsequent settlement of the ground surface and overlying utilities. Conductor casings were specified at the entry points to maintain bore stability and protect the overlying utilities from damage due to settlement or hydrofracture. The bore alignment was designed to minimize risk of hydrofracture into the waterway.

Challenges on this project included sequencing construction to maintain operation of the existing siphon, protecting two existing 60-inch gravity sewers located near the entry point, minimizing impacts to the Dryden Municipal Golf Course on the west side of the crossing, and avoiding conflicts with numerous utilities on the east side of the crossing, near the abandoned Modesto Tallow Company rendering plant.

Project Overview

As a subconsultant to Westech, Bennett Trenchless Engineers provided design assistance and construction inspection services for the Netarts Force Main Replacement Project. The Netarts Oceanside Sanitary District on the Pacific coast near Tillamook, OR had only one sewer force main pipeline that ran along the beach and up a 120-foot high bluff through landslide deposits and was susceptible to ground movements. The District elected to replace the sewer, using HDD to install 1,386 feet of 11-inch inner diameter DR 9 HDPE sewer away from the beach and beneath the landslide deposits.

Four borings completed along the alignment encountered clay, silt, sand, gravel, cobbles, wood, and embankment fill, providing serious challenges. A conductor casing was used to bridge and support the near-surface gravels and cobbles along the beach. However, gravels and cobbles were also encountered within the bluff, and random roadway fill was anticipated near the exit. Therefore, an alternative exit was developed if the bore could not be completed through the fill.

Bennett Trenchless Engineers designed the HDD crossing, provided geotechnical evaluations, and provided trenchless specifications and drawings. Bennett Trenchless Engineers also provided full time on-site inspection for the horizontal directional drilling. Design issues included selecting a profile to avoid excessive gravels and cobbles, minimizing disruption while working on the beach during the tourist season, 120-foot elevation changes between entry and exit, random fill materials at the upper end of the alignment, controlling drilling fluid pressures to prevent hydrofracture, steering control in gravels and cobbles, and pipe layout along the highway. The project was successfully completed within budget and schedule with no claims or over runs.

Project Overview

Bennett Trenchless Engineers served as the trenchless consultant to PG&E to upgrade the capacity and relocate a portion of a 36-inch steel gas transmission line under Interstate 880 and an unlined flood control channel. The Interstate 880 crossing was a key element of the Line 107 replacement project and was located in a tight utility corridor in a congested urban area. Bennett Trenchless conducted a trenchless feasibility analysis to determine the most appropriate method for the crossing. HDD, guided boring, open-shield pipejacking and microtunneling were evaluated. After HDD was selected as the recommended method for installation of the 1,200-foot crossing, BTE evaluated potential bore alignments, evaluated settlement and hydrofracture risks, and conducted pipe stress calculations. Bennett Trenchless also provided full-time on-site inspection services and assisted in analysis and approval of the pilot bore alignment prior to reaming and pullback.

Challenges included restricted pipe laydown area requiring the pipe string be laid out in three sections, environmental concerns related to crossing the flood control channel, settlement and hydrofracture concerns crossing beneath Interstate 880, minimizing impacts on nearby residences and businesses, and working below high voltage power lines. The profile was selected to manage settlement and hydrofracture risks to the interstate and canal while maintaining installation pipe stresses within acceptable limits.

Project Overview

As a subconsultant to Brown and Caldwell, Bennett Trenchless Engineers provided trenchless design services for the HDD installation of 1,200 feet of 42-inch HDPE treated effluent pipeline under an environmentally sensitive area in San Lorenzo, CA. Challenges included the large diameter and length of the HDD crossing, and the presence of soft Young Bay Mud soils. The more severe challenges of the project included a significantly accelerated design timeline, work area constraints, numerous environmental restrictions, a very tight construction window, maintaining access to a bike path that ran through the construction zone, minimizing disruption to nearby residents, and managing a high risk of hydrofracture.

In addition, the project had a significantly accelerated design timeline; construction was completed within one year of receiving the Notice to Proceed for design. Bennett Trenchless provided preliminary and final design services, specifications, hydrofracture and settlement risk evaluations, cost and schedule estimates, and submittal review assistance.

Project Overview

Bennett Trenchless Engineers provided design review, full-time on-site construction inspection, and as-built review services for the 850-foot HDD crossing of Hayfork Creek near Red Bluff, CA. PG&E identified a need to replace approximately 1,500 feet of the existing 12-inch Line 177A due to corrosion. Line 177A provides natural gas to the Eureka area as well as the Humboldt Bay Power Plant. It was important, therefore, to replace the line quickly. GTS Inc. was selected as the design engineer for the project. Hayfork Creek was identified as an environmentally sensitive area, requiring full time biological monitoring.

Challenges on the project included crossing beneath an environmentally sensitive creek, drilling through highly weathered and fractured slate bedrock, high hydrofracture risk due to the highly fractured bedrock, wood debris and challenging geotechnical conditions near the ground surface, tight bend radius, restricted pipe laydown area requiring two intermediate welds during pullback, and a tight construction schedule due to the need to coordinate with the Humboldt Bay Power Plant.