for Highway Construction Page 390 of 71 5 SECTION 512 – GABION STRUCTURE
512.01 Description.
Construct gabion structure consisting of rock -filled wire gabion baskets. Gabion structure can be a concept design or a plan detailed design.
A.Concept Design. Submit a detailed design of the gabion structure based on the information provided in the concept design. Submit a design in accordance with the latest version, at the time of design, of the AASHTO LRFD Bridge Design Specifications that is signed and s ealed by an Idaho licensed professional engineer. Construct as specified in the design.
512.02 Materials.
Provide gabion materials as specified in 715. Provide riprap/erosion control geotextile as specified in 718.06. Provide granular borrow as specified in 205.02.B.
512.03 Construction Requirements.
A.Preparation of Foundation. Excavate the foundation materials for gabion structure to the lines and grades as specified. Where soft, yielding material is encountered, remove the material below the structure fo undation to a depth of at least 2 feet or as directed. Ensure the width of the excavation is at least 1 foot greater than the bottom width of the gabion structure. Backfill the excavated area below the structure bottom with granular borrow and compact in layers not to exceed 6 inches in uncompacted depth to form a uniform and stable foundation. Repair slipouts caused by the Contractor’s operations to the Engineer’s satisfaction and at no additional cost to the Department.
B.Assembly, Erection, and Filling Gabion Baskets . Submit a detailed, step- by-step construction procedure prepared by the gabion structure manufacturer for approval 15 calendar days before the construction begins. Do not start the gabion structure construction until the submitted procedure is approved in writing.
C.Backfilling the Gabion Structure . Backfill the area behind the gabion structure with granular borrow . Spread riprap/erosion control geotextile uniformly at the bottom and over the back of the gabion structure, if required. Overlap joining edges of the geotextile at least 1 foot and anchor in position with approved anchoring devices. Place the backfill material so the geotex tile does not tear, puncture, or shift. Place the granular borrow backfill material in layers and compact until a uniform density of at least 95 percent of the maximum density is attained as determined by AASHTO T 99 Method C. Do not exceed 1 foot thickness before compaction. Decrease this lift thickness, if necessary, to obtain the specified density. for Highway Construction Page 391 of 71 5 512.04 Method of Measurement. The Engineer will measure acceptably completed work by the square foot of wall surface area from the bottom to the top of the gabion baskets .
512.05 Basis of Payment .
The Department will pay for accepted quantities at the contract unit price as follows: Pay Item Pay Unit Gabion Structure .................................................................................... SF Structural excavation, gab ion basket backfill, geotextile, backfill behind gabion baskets , and compacting backfill are incidental . 513-518 for Highway Construction Page 392 of 715 SECTIONS 513 -518 - RESERVED for Highway Construction Page 393 of 71 5 SECTION 5 19 – DRILLED -IN CONCRETED PILES
519.01 Description.
Provide and install steel piles into pre- drilled holes filled with concrete.
519.02 Materials.
1.Piles . Steel piles as shown in the bridge plans.
2.Concrete. Class 40A self -consolidating per 502.01.A.
519.03 Construction Requirements.
Provide a work plan at least three weeks before drilling begins. The work plan must include the following as a minimum:
1.A description of planned drilling methods,
2.Materials and methods to maintain a stable drill hole,
3.Methods for bracing the piles to maintain their position within the specified tolerances,
4.Methods to place concrete around pile bases ,
5.Methods to fill and stabilize the annular space around the piles above the concrete backfill. Do not begin drilling operations until the work plan is approved. After drilling, clean the sidewall in bedrock and bottom of the drilled holes to the Engineer’s satisfaction before installing piles . No more than 1” of loose material is allowed in the drilled hole bottom bef ore placing concrete . This may require the placement of temporary casings, or additional cleaning with compressed air or other cleaning tools and/or methods before installing piles and concrete . Install piles at the drilled hole centers within 0.25” per foot of pile length from the vertical, or batter shown. Ensure the pile position at cutoff is within 2” of the plan location. Ensure the pile orientation is within 15 degrees of that shown. Use braces to keep the piles in the required position before and after placing concrete . Place concrete no later than 72 hours after pile installation. Place concrete from the bottom of the rock socket with a tremie pipe or a concrete pump. Make sure the concrete filling the rock socket excavation flows around the piles and completely fills the rock socket excavation. Maintain piles in the required position as specified above and braced until the concrete has set. Design and construct corrective measures if the pile location or alignment specified above is not met, and if the Engineer determines that corrective measures are necessary. The Department will not pay for the expense, including schedule delays, associated with the corrective measures. Fill the soil portions of the drilled hole with coarse aggregate for concrete to the top of the drilled holes, as specified in Section 520. Remove casing from the hole as the concrete and aggregate is placed, maintaining the concrete and aggregate top above the casing bottom.
Source: Idaho Standard Specifications for Highway Construction, 2023 Edition. Pages 426–428 of 768.