Upper Northwest Interceptor, Section 9

Project Details

HDD

  • 24- and 36-inch VCP and PCP
  • 27,200 feet of gravity sewer
  • 42 shafts and 41 drives

Geotechnical Conditions

  • Medium to very dense sand
  • Stiff to hard silt and clay
  • Perched groundwater

Challenges

  • Congested urban area
  • Tight work areas and traffic control
  • Sequencing constraints

Project Overview

As the trenchless subconsultant to HDR, Bennett Trenchless Engineers provided preliminary and final design services for the trenchless installation of 27,200 feet of 24- and 36-inch gravity interceptor and trunk sewer pipe through a congested urban area. In addition to the tight construction areas, other challenges encountered in the design of the pipeline included high traffic volumes, high groundwater levels, utility conflicts, sequencing constraints, non-disruptive shaft construction methods, and minimizing impacts to residents and businesses.

Bennett Trenchless Engineers led the evaluation of shaft locations, shaft types, staging areas, and trenchless construction methods. Bennett Trenchless Engineers also reviewed geotechnical information, prepared cost estimates, recommended pipe materials, evaluated potential settlements, prepared specifications for trenchless work, developed construction schedules and provided input for design drawings. The construction methods selected for the final design were microtunneling and open-shield pipejacking. Bennett Trenchless Engineers also provided engineering services during construction for this project.

U & S Street In-Line Storage Project

Project Details

Microtunneling

  • 72-inch RCP
  • 550 feet of gravity sewer
  • Interstate 5 crossing

Geotechnical Conditions

  • Soft to very soft soil
  • High groundwater

Challenges

  • Congested urban area
  • Tight work areas and traffic control
  • Nearby critical utilities

Project Overview

As a subconsultant to CH2M Hill, Bennett Trenchless designed a 72-inch diameter by 550-foot microtunneled gravity sewer pipeline crossing of Interstate 5 at U Street in Sacramento, CA. Challenges included soft to very soft soils, severe work area restrictions, multiple critical nearby utilities, and permitting issues.

Bennett Trenchless Engineers conducted preliminary design analysis and calculations, prepared preliminary design report, technical specifications, drawing details, assisted with Caltrans permit, and prepared the Geotechnical Baseline Report. Bennett Trenchless also provided submittal review and full-time on-site inspection services of the trenchless components of the work.

Secret Town Pipeline – Phase II Improvements

Project Details

Microtunneling

  • 54-inch casing for 36-inch ID RCP water
  • 257 feet of microtunneling
  • Crossing of Interstate 80

Geotechnical Conditions

  • Highly fractured rock
  • Moderately weathered
  • No groundwater

Challenges

  • Difficult access to working areas
  • 50-foot elevation difference
  • Difficult ground conditions

Project Overview

As the trenchless subconsultant to Hydroscience, Bennett Trenchless Engineers assisted with the design and inspection of 257 feet of 54-inch casing for a 36-inch ductile iron water carrier pipe. Trenchless construction methods were required to cross beneath Interstate 80. Bennett Trenchless was contracted to design the crossing and to assist with the Caltrans permit application. Microtunneling was selected to install the pipeline to effectively excavate the fractured rock and ensure a stable excavation to minimize settlement risk to the Interstate. The stable soil conditions and lack of groundwater allowed the use of trench boxes for the shafts.

Challenges on the project included coordination with Caltrans, difficult ground conditions, a 50-foot elevation difference between the jacking and reception shafts, tight working areas, and access issues. The project site was very remote and access to both shaft locations was constrained and difficult. In addition, the reception shaft was located within a steep ravine and presented challenges for shaft construction and microtunnel machine retrieval.

Folsom South Canal Connection Project

Project Details

Microtunneling

  • 84-inch ID RCCP raw water
  • 430-foot river crossing
  • First Cutter Soil Mixing shafts constructed in United States

Geotechnical Conditions

  • Soft rock
  • High groundwater

Challenges

  • Very deep watertight shafts required
  • Strict environmental constraints
  • Tunneling through rock

Project Overview

As the trenchless subconsultant to Fugro West, Bennett Trenchless Engineers provided full design assistance and full-time construction inspection services for four trenchless crossings on the 19-mile raw water pipeline project connecting EBMUD’s Folsom South Canal to the Mokelumne Aqueducts. Microtunneling was used for three of the four crossings and open-shield pipejacking was used for the fourth. The crossings ranged from 110 feet to 430 feet in length and 84– to 102-inches in diameter. Trenchless methods were used to cross beneath the Mokelumne River, California Highway 12, a major surface road, and a wetland area.

The most challenging trenchless crossing was the 430-foot microtunneled crossing of the Mokelumne River. Shafts were constructed using a new technology called Cutter-Soil Mixing that allowed the construction of deep, watertight shafts through very difficult soil and rock conditions. A specialized drill rig created interlocking panels of soil-crete to form the shaft walls. This project was the first project completed in the United States using this technology to create shafts for microtunneling. Additional challenges on the crossing included construction of deep shafts, high groundwater, the presence of soft rock at the tunnel elevation, a prohibition on rescue shafts in the river should the machine have gotten stuck, and tight environmental restrictions.

Raw Water Intake Expansion Project

Project Details

Microtunnels

  • Nine 60-inch intake tunnels, 90-160 feet long
  • Twin 30-foot diameter shafts

Geotechnical Conditions

  • Karstic limestone and fissile shale
  • High groundwater, nearby source of recharge

Challenges

  • Underwater MTBM retrieval
  • Shafts constructed by blasting
  • Challenging ground conditions

Project Overview

As a sub-consultant to MWH, Bennett Trenchless Engineers conducted the feasibility/preliminary design evaluation, planned and conducted the 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 water supply capacity from 80 MGD to 220 MGD.

The twin shafts were 30 feet in diameter and 100 feet deep, excavated through very challenging karstic limestone and fissile shale. The eight 60-inch tunnels varied from 90 to 160-feet 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 provided full-time construction management/inspection. The project was completed within budget and schedule, with no claims.

A-Line Relief Interceptor Phase 2A

Project Details

Earth Pressure Balance Pipejacking

  • 96-inch ID RCP gravity sewer
  • 3,000 feet in two drives (Record Length)

Microtunneling

  • 72-inch ID RCP gravity sewer
  • 1,000 feet in two drives

Geotechnical Conditions

  • Soft to stiff fat clay, high groundwater

Challenges

  • Traffic control in urban area
  • Very shallow grade
  • Flight path restrictions
  • Golf Course protection

Project Overview

As the trenchless subconsultant to Carollo Engineers Inc., Bennett Trenchless Engineers provided preliminary and final design services for the trenchless installation of 4,000 feet of 72- and 96-inch gravity sewer through a golf course and a congested urban area. In addition to reducing impacts to residents and businesses, challenges included coordination with the local airport, limited work areas at shaft locations, high groundwater levels, low earth cover, utility conflicts and limiting impacts to a high traffic bike trail.

Bennett Trenchless Engineers led the evaluation of shaft locations, staging areas, and trenchless construction methods. Bennett Trenchless Engineers also reviewed geotechnical information, and prepared cost estimates, pipe material recommendations, settlement evaluations and monitoring plan, specifications, and construction schedules. The construction methods selected for the final design were earth pressure balance pipejacking for the 96-inch pipeline, and microtunneling for the 72-inch pipeline. Bennett Trenchless also provided construction inspection for the trenchless components of this project. The project was completed within budget with no claims.