Projects

Project Details

Microtunneling

• 4,300′ of 60″ RCCP gravity force main
• 10 drives under I-80, Hwy 50, UPRR, YSRR, Barge Canal

HDD

• 1,780′ of 24″ HDPE siphon under Barge Canal

Geotechnical Conditions

• Very soft to stiff sandy silt and stiff clay
• High groundwater

Challenges

• Densely developed urban neighborhoods
• Caltrans and railroad encroachment permits
• Drainage canal crossings

Project Overview

The West Sacramento Force Main and Barge Canal Project were elements of the larger Lower Northwest Interceptor Program that contained seven twin microtunneled crossings and a twin HDD crossing of the Barge Canal.  As a subconsultant to CH2M Hill, Bennett Trenchless Engineers designed all of the trenchless crossings, including the 1,200-foot trenchless crossing of the Sacramento Barge Canal with twin 60-inch force mains and twin 20-inch force mains. In addition to the Barge Canal, the pipeline also passed beneath several railroad spurs and a flood control levee.  Design concerns included high groundwater, traffic control, settlement constraints, railroad permitting and crossing U.S. Interstate 50.  Bennett Trenchless Engineers performed full design services for this crossing, and six others, including a constructability analysis to determine the preferred trenchless construction method, basis of design report, alignment for the pipelines, cost estimates, schedules, technical specifications, drawing details, settlement calculations and risk evaluation.

Microtunneling was selected for construction of the twin 60-inch LNWI force mains, and horizontal directional drilling was chosen for the construction of the City of West Sacramento twin 20-inch force mains. The design of the two twin bores required minimizing the potential for hydrofracture into the Barge Canal, as well as means to reduce the risk of settlement damage to the rail lines, levee, and canal bottom. Challenges included complex geology and the presence of highly permeable alluvial conditions at the entrance and exit.

Project Details

Microtunneling

• Two-pass 42″ steel casing with 15″ PVC SS carrier pipe
• Two drives totaling 650 feet
• Three shafts, 25- to 32-feet deep

Geotechnical Conditions

• Santiago Formation
• Groundwater at pipe springline

Challenges

• Dense utility corridor
• Constrained work areas
• Caltrans ROW crossing

Project Overview

As a subconsultant to Gannett Fleming, Inc., BTE provided trenchless design services for the microtunnel installation of 650 feet of 42-inch diameter steel casing with second pass installation of 15-inch PVC gravity sanitary sewer over two drives for the City of Vista, CA.  Trenchless methods were selected due to the required depth of the crossings which exceeded 25 feet.  The project was located along a heavily traveled traffic corridor with significant existing overhead and subsurface utilities.  The gravity pipeline was sited within the Santiago Formation sandstone, siltstone, and claystone.  The anticipated rock conditions and critical flat grade necessitated an oversize 42-inch steel casing be installed. Challenges included minimizing impacts to businesses and traffic, constrained work areas, avoiding impacts to utilities, and crossing Caltrans right-of-way.

BTE evaluated geotechnical conditions, evaluated alternative trenchless construction methods, evaluated trenchless alignment alternatives and associated work areas, conducted estimated settlement calculations and proposed mitigation measures, provided technical trenchless specifications, wrote the Geotechnical Baseline Report for the trenchless components, reviewed contractor submittals, and responded to RFIs related to the trenchless work. Construction was completed February, 2020.

Project Details

Microtunneling/Open Shield Pipe Jacking

• 4,930′ of 84″ RCP gravity interceptor EPB Two-Pass Tunneling
• 5,930′ of 84″ RCP gravity interceptor
• 8,010′ of 66″ RCP gravity interceptor

Geotechnical Conditions

• Rapid raveling, poorly graded sand
• High groundwater

Challenges

• Limited work areas
• UPRR crossing
• Drainage canal crossings

Project Overview

As the trenchless subconsultant to CH2M Hill, Bennett Trenchless Engineers provided preliminary and final design services for the trenchless installation of 19,000 feet of 60 to 84-inch gravity interceptor pipe through a congested urban area. In addition to the limited work area, other challenges encountered in the design of the interceptor included high groundwater levels, utility conflicts,  crossing beneath the Union Pacific Railroad and two drainage canals.   The railroad crossings and environmentally sensitive features presented significant permitting challenges.

Bennett Trenchless Engineers led the evaluation of alignment, shaft locations, staging areas and alternative trenchless construction methods as part of the Basis of Design Report. Bennett Trenchless Engineers also reviewed geotechnical information, prepared cost estimates, pipe material recommendations, settlement evaluations, specifications, construction schedules, reviewed design drawings and provided permit assistance.  Bennett Trenchless developed the settlement instrumentation and monitoring plan, including allowable and calculated settlements, and threshold values.  Bennett Trenchless co-authored the Geotechnical Baseline Report.  The construction methods selected for the final design were microtunneling, open-shield pipejacking and two-pass tunneling. Bennett Trenchless also provided on-call inspection services and Engineering Services during Construction, including submittal review and response to RFIs.  The project was successfully completed with no construction claims.

Project Details

Open Shield Pipe Jacking

• 48″ steel casing for 16″ gravity sewer
• 325′ drive beneath Interstate 30

HDD

• HDPE siphons (12″ and 18″)
• Two 740′ bores beneath Trinity River

Geotechnical Conditions

• Lean clay and clayey sand
• Limestone bedrock

Challenges

• Flat grade (0.20%) for IH-30 crossing
• Mixed face soil conditions

Project Overview

As a trenchless subconsultant to Kimley-Horn, Bennett Trenchless Engineers provided design assistance for two trenchless crossings for utility relocations associated with the Trinity River Vision Project.  The Part 7 – Gateway Site E Project involved the relocation and replacement of 2,200 feet of existing sanitary sewer, including major crossings of the existing Trinity River and Interstate Highway 30 (IH-30).  The project used a mixed-bag of trenchless construction methods including HDD, open-shield pipejacking, and auger boring.  BTE selected HDD for construction of the twin, inverted siphon crossings of the Trinity River, and open-shield pipejacking for the gravity sewer crossing of IH-30.  Challenges on the project were varied and included mixed conditions of soils overlying limestone bedrock; work area and site access constraints; and coordination with USACE regarding environmental risk mitigation for hydrofracture.

Project Details

Open Shield Pipe Jacking

• 72″ steel casing
• 30″ DIP for raw water
• 215′ crossing of I-80

Geotechnical Conditions

• Embankment fill consisting of sand, gravel, and weathered rock pieces

Challenges

• I-80 built on 50′ of embankment fill over old road or railroad
• Steep terrain
• Constrained work sites
• Difficult access to east side of crossing

Project Overview

As the trenchless subconsultant to Brown and Caldwell, Bennett Trenchless provided full design assistance, permit assistance, and trenchless submittal and RFI review for a trenchless crossing to replace an existing raw water pipeline. The existing pipeline was predominantly riveted steel pipe and open-channel conveyance that was installed in the early 1900s.  During preliminary design, Bennett Trenchless evaluated several potential crossing locations, including an alternative for a trenchless crossing of the nearby UPRR tracks.

The final selected crossing location presented several challenges. It did not cross the UPRR tracks, but in this location  I-80 was built on approximately 50 feet of embankment fill over an old road or railroad.  The embankment fill had a high potential for unknown materials to be present, which posed significant potential risk for most trenchless methods.  Two alternative trenchless designs were presented to PCWA: an open-shield pipejacking crossing in the fill and a deep microtunnel crossing below the fill in the native rock.  The open-shield pipejacking alternative was selected, in part due to the challenges associated with access to the east side of the crossing and therefore in constructing a deep shaft.  The trenchless component of the project was successfully completed in 2017.

Project Details

Microtunneling

• 60″ ID RCP storm water
• 1,300′ drive beneath city streets
• Very deep alignment

Geotechnical Conditions

• Stiff clay
• Medium dense sand

Challenges

• Very shallow jacking shaft – lack of thrust
• Protection of numerous utilities
• Densely developed urban neighborhood

Project Overview

As the trenchless subconsultant to Carollo Engineers, Bennett Trenchless provided full design services for the trenchless components of the separation of the combined sewer from Miller Park to the Pershing Detention Pond in Omaha, NE.  Trenchless construction methods were chosen due to the very deep gravity stormwater pipeline alignment  and to minimize disruption to the surrounding neighborhood.  Microtunneling was chosen to minimize settlement risk and because the groundwater level was above the  crown of the pipe.  The microtunnel drive was approximately 1,300 feet of 60-inch ID unlined RCP, with the downstream end exiting through a very steep bluff into the  Pershing Detention pond. 

Challenges on the project included protection of existing utilities and limited work area at both ends of the microtunnel drive, resulting in locating the jacking shaft within the detention pond where the soils were very weak.  The lack of sufficient thrust capacity from the soil resulted in the contractor constructing a very robust thrust block using ten 80-foot tiebacks and ten 40-foot H-beams.  The project was completed within budget and schedule with no claims.

Project Details

Microtunneling

• 30″ steel gas transmission main
• 350′ crossing of I-880
• I-880 ~20 feet below surrounding ground

Auger Bore

• 30″ ID steel gas transmission main
• 130′ crossing of UPRR
• Two sets of active tracks

Geotechnical Conditions

• Low aquifer with artesian pressures
• Fat clay

Challenges

• Very deep watertight shafts required
• Highly constrained work areas

Project Overview

As a trenchless subconsultant to PG&E and Golder, Bennett Trenchless Engineers provided full design assistance and full-time construction inspection services for two trenchless crossings to relocate PG&E’s gas transmission main.  During preliminary design, Bennett Trenchless conducted a feasibility analysis to evaluate the use of HDD as an alternative trenchless construction method. However, due to site constraints and limited pipe layout area, it was decided that pipejacking methods from a deep jacking shaft would be required.  Microtunneling was used for the 350-foot I-880 crossing and auger boring was used for the 130-foot railroad crossing.  

The ground conditions presented unique challenges on this project.  The preferred alignment elevation was located between two aquifers.  The local flood control district was concerned about cross-contamination between the two aquifer layers, specifically arising from shaft construction.  Shaft construction methods were specified that minimized the risk of cross contamination.   Significant work area constraints combined with numerous existing utilities made selection of shaft location challenging.  The trenchless components of the project were successfully completed in 2017.

Project Details

Microtunneling

• 1,410′ of 54″ RCCP water main
• Caisson jacking shaft
• Auger drilled reception shaft

Geotechnical Conditions

• Hard sandy silt
• Gravel, cobbles, and boulders

Challenges

• Difficult geotech required deep shafts
• Long drive required IJSs
• Crossing flood control levees
• Coordination with Cal State Univ. at Sac.

Project Overview

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 1,410-foot, 54-inch diameter microtunneled drive, from a 28-diameter, 79-foot deep concrete caisson jacking shaft to a 20-foot ID , 74-foot deep auger drilled reception shaft.  The geotechnical conditions were predominantly hard sandy silt overlain by a 20-foot thick layer of gravel with cobbles and boulders and high groundwater.  The deep alignment was chosen to avoid complications with tunneling in the gravel with cobbles and boulders, and to position the pipe below anticipated future scour elevations associated with a 100-year flood event.   

Bennett Trenchless prepared a technical memorandum recommending microtunneling as the preferred construction alternative, recommending alignment and depth, and developed a planning level cost estimate. Design also included selection of the crossing alignment to minimize impacts to the existing water treatment plant on the south end of the crossing and to California State University – Sacramento on the north end of the crossing. Shaft locations were selected to avoid adverse impacts to the stability and performance of the flood control levees on both sides of the American River. Bennett Trenchless conducted settlement and jacking force calculations, and prepared technical specifications and drawing details for the microtunneled crossing design. BTE also provided submittal review and specialty, full-time, on-site construction management services.

Project Details

Microtunneling, Open Shield Pipe Jacking, Hand Mining

• 96″ steel casing for 78″ FRP sewer
• 88 & 106″ steel liner plate for 60″ & 78″ FRP sewer
• 23 drives totaling over 11,000 feet

Geotechnical Conditions

• Very stiff to hard clay
• Gravelly clay
• Soft claystone/marlstone

Challenges

• Large diameter casing/tunnel
• Fast raveling to flowing conditions
• Constrained work areas with congested overhead utility corridor
• Coordination with SAMMC property
• UPRR and TxDOT encroachment permits
• Creek crossings

Project Overview

As a subconsultant to Kimley-Horn, Bennett Trenchless Engineers provided trenchless design services for over 11,000 feet of trenchless casing installations for the San Antonio Water System through the San Antonio Military Medical Center base.  Microtunneling was specified for much of the trenchless installation due to gravelly conditions below the water table that can be prone to flowing behavior.  A significant challenge was working within the existing narrow right-of-way which was constrained by parallel overhead utility lines which complicated use of large equipment to excavate the launch and reception shafts.  Unstable soil conditions also posed a significant challenge and required the use of microtunneling to stabilize the face and control groundwater inflows into the large diameter tunnels.

Project Details

Microtunneling

• Total of 3,100′ of 36″ and 54″ RCCP
• Raw and treated water
• 7 drives under levees and UPRR

Geotechnical Conditions

• Very soft to soft organic silt
• Medium dense sand, high groundwater

Challenges

• Managing risk of damage to levees
• Flood control district coordination
• UPRR settlement concerns
• Watertight construction methods

Project Overview

Bennett Trenchless Engineers, as the trenchless subconsultant to CDM, provided trenchless design of seven trenchless crossings for raw and treated water pipelines, including multiple UPRR and levee crossings, for this large water supply project.  BTE was responsible for leading the trenchless design effort, evaluating alternative trenchless construction methods and alignment options, preparing trenchless cost estimates and schedules, performing supporting calculations for all trenchless work, providing shaft locations and tunnel profiles, as well as preparing the technical specifications for the trenchless construction. 

Microtunneling was selected as the trenchless installation method for most of the crossings due to saturated ground conditions.  The total footage of trenchless construction was over 3,100 feet, and the individual drive lengths ranged from 150 to 1,000 feet.  Tunnel diameters varied from 48” to 84” to house 36” to 54” water pipelines.  The two longest crossings (each > 900’) were required to pass beneath large, levee-supported canals (Bishop Cut and Honker Cut) associated with the San Joaquin River Delta.  The designs for these trenchless crossings required specialized design evaluations and mitigation measures, such as fully watertight shoring, subsurface settlement monitoring, and shaft collars rising up the 100-year flood elevation.  BTE and CDM coordinated extensively with the local reclamation districts to ensure the safety and stability of the levees during construction.