Emergency Outfall Replacement Project

Project Details

HDD

  • 30-inch HDPE, DR 11
  • 1,050-foot crossing of the Feather River

Geotechnical Conditions

  • Dense sand and stiff silt
  • Dense gravel with high groundwater

Challenges

  • Emergency design and construction
  • Dense gravels
  • Mitigating hydrofracture risk

Project Overview

The Yuba City treated effluent outfall pipeline beneath the Feather River failed suddenly on January 30, 2012. The main channel had migrated and scoured down to the existing 30-inch pipeline. The uncontrolled release of effluent created an urgent situation.

The City assembled a team of City design and O&M staff, consultants, and contractors. Intense working meetings with all the right people in the same room were followed by e-mail and telephone clarifications, to work out the design details. The geotechnical consultant completed the first three borings by February 17. The borings indicated the soils in the upper 50 feet were dense sand and stiff silt, underlain by dense gravels. The bore profile was designed to avoid the dense gravels, while providing sufficient clearance beneath the river channel to avoid exposure from scour and erosion and minimize hydrofracture risk.

The HDD design was completed February 23rd. The Contractor mobilized as the design was prepared. Site grading, surveying, and measures to protect sensitive features were quickly completed. Permitting and regulatory review agencies were extremely cooperative. The HDD Company completed the 1,050-foot pilot bore in two days. Reaming was accomplished in one pass to 54-inches in two days, and pullback of the 30-inch DR 11 HDPE was completed a day later. Total duration of the project from design to construction was 101 days. Keys to the success were the City’s ability to assemble the right team, quickly reach decisions, and the City Council’s trust in its staff.

Platform Holly Power Cable Replacement

Project Details

HDD

  • 10-inch DR9 HDPE electrical conduit
  • 2,250-foot bore from land to ocean

Geotechnical Conditions

  • Silty sand, clay, sandy silt
  • Sandy siltstone (Monterrey Formation)

Challenges

  • Environmentally sensitive coastline
  • Multiple permitting agencies
  • Monitoring for hydrofracture in surf zone
  • Minimizing impacts to underwater exit

Project Overview

The Platform Holly Power Cable Replacement Project was required to replace an approximately three mile long, 46-year old, sub-sea cable that delivered power from the Ellwood Onshore Facility to the Holly oil production platform off the central coast of California, near Goleta. The HDD portion of the project consisted of installing a 10.75-inch OD HDPE pipe in a 2,250-foot bore beginning at the Elwood Onshore Facility and crossing beneath the beach and surf zone to an exit located on the ocean floor. Bennett Trenchless Engineers reviewed the HDD alignment, provided by Venoco and the HDD contractor, performed pipe stress calculations, analyzed hydrofracture risks, assisted with the preparation of an extensive drilling fluid release monitoring and contingency plan, developed design drawings, assisted Venoco in securing approval from the California Coastal Commission and California State Lands, provided training to the environmental monitors, and provided on-site inspection services and coordination with regulators during construction.

Challenges included numerous environmental restrictions, managing hydrofracture risk, monitoring for hydrofracture in the turbulent surf zone and on the ocean floor, high angle joints and fractures in the bedrock with the capacity to absorb large volumes of drilling fluids, and highly variable bedrock which resulted in challenging drilling conditions. The contractor was very proactive in regaining and maintaining circulation when it was lost, but even so a hydrofracture occurred approximately 1,900 feet into the bore. The keys to successfully completing the project were the thorough drilling fluid release monitoring and contingency plan that all regulatory agencies had the opportunity to review and become comfortable with and maintaining open lines of communication throughout design and construction.

Upas Street Pipeline Replacement Project

Project Details

HDD

  • 30-inch HDPE, DR 9 water line
  • 42-inch HDPE, DR 13.5 casing
  • 1,700-foot crossing of CA Hwy 163

Geotechnical Conditions

  • Dense to very dense silty sand

Challenges

  • Crossing of 75-foot deep ravine
  • Restricted work areas at entry/exit
  • Minimizing impacts to park/residents
  • Caltrans permitting

Project Overview

Bennett Trenchless Engineers served as the trenchless subconsultant to Infrastructure Engineering Consultants (IEC) for the trenchless crossing of CA State Highway 163 for the Upas Street Pipeline Replacement Project. At the location of the crossing, Highway 163 runs within a ravine between the two ends of the project area. The trenchless portion of the project consisted of replacing approximately 1,700 feet of 30-inch cast iron water main with a new 24-inch inside diameter water line, inside a 36-inch HDPE casing per Caltrans permit requirements.

Bennett Trenchless provided preliminary and final design services for the trenchless component of the project. During preliminary design, based on the evaluation of the available work areas, required depth of cover beneath Highway 163, and depth to tie-ins, horizontal directional drilling was selected as the preferred construction method. Final design included pullback load and pipe stress analyses, settlement, and hydrofracture risk evaluations, specifications, drawing edits, construction cost estimate, and schedule.  A Surface Spill and Hydrofracture Contingency Plan was also prepared to assist with permitting and manage risks.

Challenges on the project included very restricted work areas on both the entry and exit sides. The HDD rig was located with Balboa Park, and the City prioritized minimizing impacts to the Park and its users. The pipe layout side was located within a densely developed residential and business community. The long area needed for pipe string fabrication and layout was carefully selected and managed to minimize impacts to traffic patterns in the neighborhood. The large ground surface elevation difference from Highway 163 to entry and exit also complicated the design geometry and influenced the pipe material selection.

Facilities Modifications – Suisun Creek Crossing

Project Details

HDD

  • 20-inch DR 11 HDPE
  • 350 feet of water main
  • Suisun Creek crossing

Geotechnical Conditions

  • Very stiff clay
  • High groundwater

Challenges

  • Confined work areas
  • Existing utilities
  • Managing hydrofracture risk

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.

Santa Ynez River Sewer Force Main Design-Build Replacement Project

Project Details

HDD

  • 16-inch HDPE sewer force main
  • 1.400-foot crossing of Santa Ynez River

Geotechnical Conditions

  • High plasticity hard clay, shale, and silt
  • High groundwater

Challenges

  • Design-Build contract
  • Restricted work areas
  • Managing hydrofracture risk
  • Permit issues

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.

Pullback of FPVCP

Shackelford Sewer Crossing

Project Details

HDD

  • Twin 18-inch inverted siphons
  • DR 25 Fusible PVC
  • Twin 650-foot crossings
  • Tuolumne River crossing

Geotechnical Conditions

  • Loose to medium dense silty sands
  • High groundwater

Challenges

  • Existing large diameter utilities
  • Minimizing impacts to golf course

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.

Netarts Force Main Replacement Project

Project Details

HDD

  • 11-inch, DR 9 HDPE
  • 1,400-foot crossing under bluff

Geotechnical Conditions

  • Extensive gravel and cobbles
  • High groundwater

Challenges

  • Minimizing impacts to beach
  • 120-foot elevation difference between entry and exit

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.

Line 107 – Irvington Station

Project Details

HDD

  • 36-inch steel gas transmission line
  • 1,200-foot crossing under I-880

Geotechnical Conditions

  • Medium dense to dense silty sand
  • Soft to hard lean clay
  • High groundwater

Challenges

  • Tight utility corridor
  • Developed urban neighborhoods
  • I-880 and Alameda County flood control channel crossing

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.

Western Terminus Replacement Project

Project Details

HDD

  • 42-inch HDPE treated effluent
  • 1,200-foot wetland crossing

Geotechnical Conditions

  • Young Bay Mud
  • High groundwater

Challenges

  • Accelerated design timeline
  • Environmental restrictions
  • Minimizing impacts to residents

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.

Line 177A: Hayfork Creek

Project Details

HDD

  • 12-inch steel gas transmission main
  • 850-foot crossing of Hayfork Creek

Geotechnical Conditions

  • Highly weathered and fractured slate bedrock

Challenges

  • Restricted pipe laydown area
  • Managing hydrofracture risk
  • Tight design tolerances and steering issues
  • Tight construction schedule

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.