SECTION_31_23_13_-_Subgrade_Preparation_R1_0003.pdf

BUREAU OF INDIAN AFFAIRS OGLALA DAM SPILLWAY AND OUTLET WORKS

OGLALA DAM SPILLWAY AND OUTLET WORKS SECTION 31 23 13

JUNE 2023 SUBGRADE PREPARATION

FOR BID REV 1 PAGE 1 OF 6

SECTION 31 23 13

SUBGRADE PREPARATION

GENERAL

1.01 SCOPE OF WORK

A. This Section specifies the requirements for the following general items of Work:

Preparing the finished excavated surface for placement of conventional concrete, roller compacted concrete, embankment fill, or other structures.

Protecting the subgrade until placement of overlying concrete or fill.

1.02 DEFINITIONS

A. The geotechnical and geologic conditions for all excavations defined herein and as shown on the Drawings are based on interpretation of conditions observed in borings, field mapping, and other historic data. It is CONTRACTOR’s responsibility to become familiar with the data presented in the Design Documents. CONTRACTOR shall make their own interpretation of these geotechnical data and shall assume full responsibility for their interpretation. The estimated extent of each excavation is shown in the Drawings. Actual required excavation may be deeper or shallower than that indicated on Drawings based on observed subsurface conditions.

B. Dental Concrete: Concrete placed in areas of bedrock overhang or to prepare rock foundations for roller compacted concrete, conventional concrete, or embankment fill.

C. Prepared Foundation: Finished excavated surface, after subgrade preparation, upon which a structure will be placed. Approximate structure foundation elevations are shown on the Drawings; actual elevations will be determined by the BIA Representative based on the material encountered.

D. Slush Grout: Sanded Portland cement grout used to fill open fractures exposed in the bedrock surface after loose materials have been removed.

E. Subgrade: Ground surface after completion of required clearing, grubbing, stripping, and excavation prior to subgrade preparation, placement of overlying concrete or other structure.

F. Temporary Cover: Native material left in place over final foundation subgrade to protect subgrade from damage by wetting, drying, freezing, erosion, and physical disturbance by construction equipment traffic and personnel until the time of final subgrade excavation and preparation.

BUREAU OF INDIAN AFFAIRS SECTION 31 23 13

JUNE 2023 SUBGRADE PREPARATION

FOR BID REV 1 PAGE 2 OF 6

1.03 QUALITY CONTROL

A. The BIA Representative will conduct visual inspection of the excavated surface before placement of fill or concrete. Provide 24-hour notice to the BIA Representative when final excavation is to be completed for a particular area so that they can make arrangements for visual inspection.

B. Notify the BIA Representative immediately when excavation has reached the designated subgrade elevation.

C. Notify the BIA Representative immediately when soft, loose, or wet subgrade zones are detected.

1.04 SEQUENCING AND SCHEDULING

A. Perform foundation preparation only when subgrade is unfrozen and free of ice, snow, and standing water.

B. Perform foundation preparation only during daylight hours.

PRODUCTS

2.01 BACKFILL AND DENTAL CONCRETE

A. Conform to the requirements of Section 03 30 00 – Cast-In-Place Concrete.

2.02 SLUSH GROUT

A. Slush grout will be used to treat cracks observed at the bedrock or weathered bedrock surface after removal of weathered bedrock and/or overburden materials, as applicable based on the Drawings, at the embankments, embankment cut-off trenches, and service spillway.

B. Cement for slush grout shall conform to the requirements specified in Section 03 30 00 – Cast-in-Place Concreteto ASTM C150, Type I/II. Use only cement furnished in sacks for slush grout. Make available a sufficient quantity of cement at the site to ensure that slush grout operations will not be delayed by shortage of materials. Use cement in the same sequence that it is received at the site of the Work.

C. Sand for Slush Grout: Clean, washed silica sand containing no deleterious material and conforming to the following gradation limits in accordance with ASTM C117 and

ASTM C136.

US Standard Sieve Size

Permissible Range Passing (in percent by weight)

#60 90 - 100 #200 0 – 2

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D. Prepare slush grout by mixing one part Portland cement to three parts sand, by weight, with just sufficient water for fluid consistency. The BIA Representative may require adjustment of slush grout mix proportions or sand gradation as necessitated by foundation conditions in any particular area. In some locations, the BIA Representative may direct that slush grout to be made with cement and water, without sand.

2.03 AIR JET

A. Air Jet: An air jet used for foundation preparation and shall consist of a 1-1/2-inch-diameter nozzle with a supply hose connected to a suitable source of compressed air. The compressed air shall have a pressure between 90 and 120 psi and shall be controlled and measured at the nozzle.

EXECUTION

3.01 GENERAL

A. Claystone bedrock shall be protected from slaking as described in Paragraph 3.02 PROTECTION OF SLAKING OF CLAYSTONE BEDROCK of Section 31 23 16 – Excavation.

B. Remove existing dam structure and foundation rock to the limits shown on the Drawings.

C. Shape excavation to produce a uniform and regular profile with no abrupt changes in slope, sharp projections, steps, overhangs, or benches except as shown on the Drawings or as approved by the BIA Representative.

D. Preserve the foundation below and beyond the lines of excavation in the soundest possible condition. Repair any damage from CONTRACTOR’s operations, including fracturing of material beyond the required excavation lines, as approved by the COR or the BIA Representative.

E. Keep foundation free of ponded water and deleterious materials.

F. Do not use sections of prepared foundation as haul roads. Protect prepared foundation from traffic.

G. Maintain prepared foundation in finished condition until overlying fill, backfill, or structure is placed.

H. Acceptance: Do not place slush grout, concrete or fill in any excavation until the excavation has been accepted by the COR in writing. In the event the CONTRACTOR places concrete or fill in an excavation prior to receipt of written acceptance, the concrete or fill will be rejected and the CONTRACTOR shall remove such concrete or fill. No payment will be made for any such rejected concrete or fill or for the costs of its removal and disposal.

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3.02 PREPARED FOUNDATIONS ON ROCK

A. The BIA Representative shall be on site during the excavation to final subgrade and bedrock cleaning and preparation. Concrete or approved, compacted embankment fill shall not be placed without approval from the BIA Representative.

B. Rock foundation surfaces shall be cleared of all loose or unsuitable material as determined by the BIA Representative.

C. Blasting is not permitted in the preparation of the foundation.

D. Concrete or embankment shall not be placed until the foundation preparation is completed and the foundation and excavations have been inspected and approved.

E. Protection of Treated Foundation: Take all necessary measures to prevent contamination of the treated foundation surfaces by loose rock, soil, debris or the like before placement of fill or concrete. Such measures include, but are not limited to, directing water away from the surface, avoiding construction traffic on the treated surface, and treating access roads to minimize tracking of debris onto the foundation. Should the cleaned and treated foundation rock surfaces be contaminated by loose rock, soil, debris, or otherwise damaged before or while being covered, remove the damaged work and clean and repair the surface as specified herein at no additional cost.

F. Initial Foundation Cleanup:

Remove all loose, soft rock, shattered materials, pockets of fines, sand, rock rubble, gravel, and objectionable materials including standing or running water from the specified foundation area using methods that will leave surfaces in the best practicable condition.

Clean the excavated rock surface of loose materials and debris using compressed air of sufficient pressure, such that the foundation surface is exposed for inspection and geologic mapping. Clean the rock surface sufficiently to expose all rock fractures. Use care to prevent deterioration of foundation areas due to the methods of cleanup utilized or waste-water runoff. Use hand methods as required to remove material from local depressions. Maintain cleaned surfaces in a cleaned condition.

The BIA Representative will perform geologic mapping of the foundation.

CONTRACTOR will cooperate with the BIA Representative and assist in the geologic inspection, evaluation, and mapping activities. Provide access and surveying support as required by the BIA Representative for geologic mapping and control purposes, including but not limited to providing station and elevation markers throughout the foundation at 50-foot station intervals along the dam axis and providing points at the top of both abutments and at the bottom of the foundation tied to existing horizontal and vertical control.

G. Slush Grout Foundation Treatment

CONTRACTOR shall place slush grout at locations identified by the BIA Representative.

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Prior to placement of slush grout, clean out all seams, shears, and open discontinuities identified by the BIA Representative to depths as indicated on the Drawings or directed using hand excavation, high pressure air, or other acceptable methods.

Remove shattered, decomposed and other unacceptable materials from the shear zones and discontinuities for a horizontal distance not less than 3 feet beyond the limits of the foundation excavation.

If groundwater seepage from fractures, seams, or other subsurface zones is encountered at or above final foundation grade, control seepage as specified in Section 31 23 19 – Dewatering. All such Work shall be considered foundation dewatering.

Prepare grout mixture by mechanical mixer and place within one-half hour after mixing.

Wherever possible, grout shall be poured and hand troweled into cracks and openings until the cracks and openings are completely filled. Wherever the width of the crack permits, the grout shall be rodded into the cracks; alternatively, a pipe shall be set to the bottom of the crack and grout funneled in until the crack is completely filled. Grout shall then be broomed across the top of the cracks and openings to ensure the tightness of the grout filling. For small cracks, the grout mix shall be poured onto the rock surface and forced into the surface cracks and openings by sweeping it briskly with a stiff bristle broom. Confine the grout to the cracks and fractures; remove from the rock surface all grout which cannot be worked into the joints and any spillage and avoid feather-edging.

CONTRACTOR may place slush grout and cure grout prior to placement of dental concrete or place dental concrete immediately over uncured slush grout. Cure surface of slush grout and dental concrete by moist curing as specified in Section 03 30 00 – Cast-in-place Concrete. Moist curing shall start as soon as the grout has taken its final set. Membrane curing is not acceptable for curing. Allow at least 3 days of curing time before placing fill over slush grout or dental concrete.

Place slush grout immediately before placement of RCC. For prepared foundations under the closure embankments, allow slush grout to cure for at least 6 hours prior to placing overlying fill.

H. Dental Concrete Treatment

Fill depressions in the bedrock foundation with dental concrete as directed by the BIA Representative. Dental concrete may require rough face forming. Placement of RCC overly actively setting dental concrete is acceptable provided the dental concrete can support the RCC materials and equipment without uncontrolled displacement or settlement.

I. Final Foundation Cleanup

Completely clean foundation of all remaining loose materials with air jets of sufficient pressure, or with vacuum, to thoroughly clean the foundation to bare rock, without damage to surface.

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Complete the final cleanup after foundation treatment and immediately prior to placement of concrete or any structures. Do not use water for final foundation cleanup unless accepted in advance by the COR.

END OF SECTION