2024-10-22_Heart_Butte_Dam_Industry_Day_Presentation_1.pdf

Heart Butte Dam Safety of Dams Modification

Industry Day Schedule

Heart Butte Dam Safety of Dams Modification

Industry Day Project Overview

October 22nd, 2024

Seepage Observations at Heart Butte Dam

• In January 2013, during a routine inspection, fine, gray-colored sand deposits were observed inside the outlet works conduit. Subsequent investigations determined that sand was being transported by seepage through a contraction joint at conduit station 9+62.

• In May 2014, a small amount of fine, grey-colored sand was observed exiting ground surface with seepage flow in the relic river channel area.

• In May 2018, when drilling through the outlet works conduit floor into the foundation sandstone, pressurized seepage flow with uncemented sandstone particles was encountered.

Multiple seepage observations indicated seepage paths exist in the foundation sandstone, and the process of backward erosion piping may have already initiated. The design team believed that the mitigation of the backward erosion concern should focus on two primary seepage paths.

Seepage Path A Backward Erosion Piping Below the Base of Outlet Works Conduit in the Uncemented Sandstone Foundation

The sandstone foundation is predominantly uncemented. The uncemented portion of the sandstone is fine grained and cohesionless with low resistance to backward erosion piping.

Seepage Path B Backward Erosion Piping Below the Dam Embankment through the Uncemented Sandstone Foundation Exiting at Relic River Channel Area.

The Design Concept to Mitigate the Backward Erosion Piping

The concept of the final design takes advantage of two traditional approaches to address backward erosion piping concerns.

1) Construct filter and drainage system and seepage berm to filter the seepage flow and collect and properly discharge the seepage water.

2) Install jet grouting treatment zone and cut off wall to divert the seepage flow and extend the seepage path to reduce the seepage gradients at its exit point.

The Design Concept to Mitigate the Backward Erosion Piping

Six Key Design Components

• Earthworks/Geotechnical Design

• Construction Dewatering Design

• Jet Grouting Treatment Zone and Cut Off Wall Design

• Structural Conduit Repair Design

• Conduit Joint Repair Design

• Foundation Void Filling Design

Geology

• Regional Geology

• Missouri Plateau of the northern Great Plains Physiographic Province

• Site Geology

• Dam foundation includes Alluvium (Qal) and Bullion Creek Formation (Tb)

• Alluvium (Qal)

• Valley section of embankment is founded on alluvium

• Variable compositions and thickness - clay and silt to sand and gravel

• Bullion Creek Formation (Tb)

• Interbedded sandstone, siltstone, and shale

• Spillway and outlet works conduit and chute founded on Tb

• Relatively flat-lying bedrock

Bullion Creek Formation (Tb)

• Sandstone is very poorly cemented, silty, and fine grained

• Some discontinuous lenses of cemented, moderately hard sandstone

• Very friable and easily broken down by finger pressure

• Continuous clay shale bed at ~El. 1980 across site

Typical poorly cemented sandstone (Tb)

Typical clay shale (Tb)

Tb - Sandstone

Outcrop ~1,000 feet downstream of dam

Embankment Fill

• Zone 1

• Silty sands and sandy clays

(SM-SC) and low plasticity clays (CL)

• Zone 2

• Silty sand (SM)

Typical Zone 1

Typical Zone 2

Geologic Profiles A-A’

B-B’

F-F’

G-G’

• A-A’: Profile along Dam CL

• B-B’: Profile along mid-D/S slope

• F-F’: Profile along D/S toe

• G-G’: Profile along Spillway/OW

A-A’: Profile along Dam CL

B-B’: Profile along mid-D/S slope

F-F’: Profile along D/S toe

G-G’: Profile along Spillway/OW

Borrow Material

• Stockpiled material from required excavations

• Borrow area east of the dam

• Alluvium and uncemented sandstone

SM derived from uncemented sandstone

(SP-SM)g - Alluvium

Design Components

• Contractor Use and Borrow Areas

• Geotechnical Work Items

• Jet Grout Cutoff Wall

• Foundation Void Filling

• Structural Conduit Repair

• Alternative Concept for Foundation Treatment Below Conduit

• Conduit Joint Repair

• Dewatering

Contractor Use and Borrow Areas

Possible Jet Grout Plant Locations

• Contractor Question #6: Feasibility of the following locations to set up a jet grout plant?

• Original river channel area on the left side of the spillway (area currently wet due to spillway releases).

• On top of the right abutment.

• Staging and stockpile area on the left side of the spillway.

Geotechnical Work Items

• Excavation left of the outlet works conduit and spillway stilling basin

• Vertical filter trench excavation into shale bedrock

• Filter trench and filter blanket drainage system

• Seepage berm and mechanically stabilized earth (MSE) wall

• Remediation of stilling basin channel at the end of the concrete spillway chute

• Cofferdam construction (Contractor designed)

Excavation Features

• Left of the outlet works and spillway near downstream toe and within the relic river channel

• Dewatering platform

• Downstream 1.5:1 filter trench

• Working area for excavation of vertical filter trench

Excavation Features

Vertical Filter Trench

• Adjacent to jet grout cutoff wall left of the outlet conduit

• 10-ft wide, 60-ft long, 25-ft deep

• Extends into shale bedrock

• Support excavation using slide rail trench system, or similar

Vertical Filter Trench

Filter Blanket

• Two-stage filter drainage system

• Drain pipes discharge to spillway stilling basin or Heart River

Drainage System

Seepage Berm

• Seepage berm constructed to add weight over the filter and drainage system

• Includes MSE wall to provide vehicular access to the spillway stilling basin and outlet works conduit

Seepage Berm

Stilling Basin Channel Remediation

• Existing riprap channel protection will be removed and new channel protection and filter installed

• Filter sand, riprap bedding, riprap

Stilling Basin Channel Remediation

Cofferdam

• Will be required to keep work areas dry

• Contractor is responsible to design cofferdam

Jet Grout Cutoff Wall

• Jet grout treatment zone constructed within the sandstone foundation and into the shale

• Beneath outlet works conduit

• Flanking both sides of the end of the conduit

• Continuing to the right and downstream of the outlet works

• Terminates just beyond spillway chute

• Divert seepage flow in the sandstone foundation to the left (filtered exit) or right (extensively long seepage path) of the outlet works conduit

• All uncemented or severely weathered sandstone within the jet grout cutoff footprint treated with jet grouting to achieve a minimum UCS of 300 psi

• Weakly cemented sandstone lenses are likely to be encountered during jet grouting operation

• If cementitious grout can’t penetrate the weakly cemented sandstone lenses, it is acceptable to encapsulate the lenses in the jet grout material

• Air not allowed during injection

• Configuration of jet grout column geometry (i.e., column diameter, spacing) will be designed by the Contractor based on a field test section

• Jet grout block below the conduit constructed by jet grouting from within conduit

• Drilling through outlet works conduit will require hydro-demolition and repair of a segment of the conduit

• Contractor Question #1: Is it possible to effectively use jet grouting to create a continuous cutoff wall beneath the outlet works conduit by drilling holes within the outlet works conduit?

• Contractor Question #2: Can a continuous cutoff wall beneath the outlet works conduit be installed without drilling holes through the outlet works conduit?

• Contractor Question #5: Does the proposed CLSM work platform allow sufficient space within conduit to complete jet grouting?

• Contractor Question #7: Can a test section performed outside the conduit verify Contractor’s means and method of installing the jet grouting block from inside the conduit? If the results of test section indicates that some changes of the means and methods are necessary, how quickly can you implement those changes?

• Contractor Question #8: What hole spacing and what size of the hole would you expect to drill inside the conduit to ensure all the uncemented or severely weathered sandstone is treated?

• Contractor Question #9: How would you verify all the uncemented or severely weathered sandstone are treated to achieve an UCS of 300 psi within the footprint of the treatment block?

• Contractor Question #10: Would you propose using electrically driven or internal combustion equipment within the outlet works conduit?

Foundation Void Filling below Conduit

• The void filling grouting consists of a total of about 60 grout rows at a spacing of 10 feet, extending from the downstream end of the conduit to the upstream end of the conduit near the spillway inlet

• Each row consists of 3 holes, 2 angled at 25 degrees from vertical and 1 hole drilled vertically from the invert

• Drilling will be performed at each hole location by coring a hole ~2 ft into the conduit, setting a mechanical packer, then coring a hole through the conduit and ~1 ft into the foundation sandstone

Concrete Conduit Repair

• Repair of the outlet works conduit is required due to damage sustained from the jet grouting process

• Loss of reinforcement from drilling through bottom of conduit

• After the jet grouting is completed, temporary shoring will be set up inside the conduit to support the upper half of the conduit section

• A 2-inch saw cut will be made around the perimeter of the repair area to control the extent of the concrete removal

• Reinforcement will be exposed by removing concrete using hydrodemolition

• Concrete must be removed in the area where the jet grouting holes were made plus about 5-feet upstream and downstream to repair the damage to the longitudinal reinforcement

• To repair the damage to the hoop reinforcement, concrete will have to be removed from the bottom half of the conduit section, extending a minimum 5-feet up vertically from the highest jet grout drill hole location

• When exposed, a representative of the government will identify and mark all reinforcement than requires cutting and splicing

• Structural concrete will then be placed with the finish matching the existing concrete flow surface.

• Temporary support removed.

Alternative Concept for Treatment Below Conduit

Alternative Concept for Treatment Below Conduit

• Contractor Question #3: Aside from the two alternative methods outlined in the draft design drawings, can you propose an alternative approach to build a cut off underneath the conduit without drilling through the conduit floor?

• Contractor Question #4: What is the maximum angle to install a jet grout column that can be achieved using a drill rig from the exterior or the interior of the conduit?

Conduit Joint Chemical Grouting

• Chemical grouting to repair the existing joints will be performed at 17 joint pair locations.

• Seal off water from moving into the conduit

• At each joint location, there are two joints each having formed keys.

• At each joint location, there is a ring of injection holes targeting the outside of the joint shear key.

• Drill 1/2-inch diameter holes and chemical grout each joint pair location

• The chemical grout (expansive hydrophobic polyurethane resin) will be injected through the drill holes into the joint.

• Injection begins at the bottom (invert) and progresses upward on each side of the conduit (minimize entrapped air).

• Grouting sequence

• Invert to haunch

• Haunch to spring line

• Spring line to shoulder

• Shoulder to crown

Dewatering Overview

• Unwatering

• Phase 2 Dewatering Wells

• Phase 1 Dewatering Wells

• Outlet Works Prepacked Well Screen Drainage Port

Phase 1 - Dewatering Wells

• Design Goal: Support the installation of the jet grout block and conduit removal/replacement in the dry.

• Design Details:

• 12 wells, 50 feet deep

• Spacing: 10-foot centers

• Drilling Method: Sonic

• Well Diameter: 10-inch diameter

• Completion: 6-inch diameter

• Pump Rate: 10-15 gpm

Phase 2 - Dewatering Wells

• Design Goal: Support dry and stable excavations for the vertical filter trench, filter blanket, stilling basin channel remediation

• Design Details:

• Dewatering Bench El. 2010

• 86 wells, 45 feet deep

• Spacing: 20-foot centers

• Drilling Method: Sonic

• Well Diameter: 10-inch diameter

• Completion: 6-inch diameter

• 9 observation wells

• Pump Rate: 10-15 gpm

Well Design

Unwatering System

• Contractor Designed System

• Key Locations:

• Remove water behind cofferdam

• Inside the excavations

• Shale interface

• May be in the form of:

• Channels/Ditches

• Sumps/Pumps

• Drains/Blankets

• Sediment Control/Discharge Lines

Contractor Designed Cofferdam (for example only)

Outlet Works Prepacked Well Screen Drainage Port

• Support void backfill grouting and chemical grouting

• Requires RWS El. 2030 (dead storage)

• Target Phreatic Surface El. 2000

• Goal: avoid high grouting pressures to overcome hydrostatic pressure

Question for Contractors:

• Contractor Question #11: How close can you jet grout next to a dewatering well without impacting the well performance?

Schedule Schedule revolves around a two-drawdown concept.

TWO MAIN CONSTRUCTION WINDOWS

WITH NO CONDUIT FLOW

Government is considering either a 2 or 3 construction season schedule.

• Construction season = April through November.

• No planned winter construction, however, some outlet works interior work could be completed by closing of the ends and heating the space.

3- Season

• 2027 April to August (first drawdown)

• Jet grout,

• Dewatering,

• 2027 Sept to November

• Interior jet grouting

• Interior void grouting

• 2028 March to May (second drawdown)

• Excavation

• Filter trench dewatering

• 2028 June to October

• Filter trench

• Stilling basin filters

• Joint grouting in conduit

• 2029 March to July

• Filter blanket and berm

3-year schedule

2- Season

• 2027 April to August (drawdown)

• Jet grout,

• Dewatering – outlet works

• More dewatering – filter trench

• Filter trench excavation

• 2027 Sept to November

• Filter trench

• Interior jet grouting

• Interior void grouting

• Stilling basin filters

• 2028 April to November

• Filter blanket and berm

• Joint grouting in conduit (August-)

2-year schedule

Conduit Access

• Concurrent interior work may require access through morning glory spillway

Morning Glory

Access

Downstream

Access

Void grouting and joint grouting Interior Jet Grouting

Contractor Interest

• Project is remote with restricted work periods.

• Three questions related to contractor interest in the work

• Availability to work multiple shifts?

• Contract type?

• Housing Needs

• Other?

• What are your concerns that Government should be thinking about?

Questions?

Procurement

• NAICS Code is 237990 – Other Heavy and Civil Engineering construction

• Size Standard is $45.0 Million

• Current Estimated Magnitude is $35M - $55M

• Seeking approval to issue solicitation for full and open competition

• Contract Type: Firm Fixed Price/TBD

• Anticipated Source Selection Method: Best Value

Special Terms and Conditions

• FAR 52.232-5 Payments under Fixed-Price Construction Contracts (May 2014) Retainage will be held until technical submittals approved or through substantial completion

• Safety Plan to Confirm to Reclamation Safety and Health Standards

• WBR 1452.237-80 Alt III – Security Requirements – Bureau of Reclamation

• DI-137 Release of Claims

• Buy American Act Requirements for Construction Materials

• FAR Clause 52.225-11 and Provision 52.225-12

Heart Butte Dam - Milestones

• Acquisition Milestones

• Sources Sought Announcement – December 2025

• Issue Solicitation – June 2026

• Receive Proposals – July 2026 (60 days)

• FAR 52.228-1 Bid Guarantee: Estimated at approximately 20% of the contract value

• Possible Oral Presentations/Negotiations – August 2026

• Award – November 2026

• Bonds due - 10 days after award of contract

• Standard Form 25 – Performance Bond

• Standard Form 25A - Payment Bond

• NTP- immediately after receipt of bonds

• Construction Milestones

• Submittal Review Process – December 2026 through March 2027

• Mobilization – Spring 2027

• Substantial Completion – TBD/Pending

Heart Butte Dam - Milestones

Thank you for attending the Bureau of Reclamation’s Industry Day.

Please contact Mitchell J. Frost, Contracting Officer, via email (mfrost@usbr.gov) with all future questions/comments about the program or to request the PowerPoint Presentation.

Vendors may submit written questions following the breakout sessions by 5:00 p.m. MDT on November 15, 2024. The Bureau of Reclamation will make reasonable efforts to answer all questions and to provide those answers on SAM.gov in a timely manner.

mailto:mfrost@usbr.gov