Description 506.01 This work consists of the construction of riprap per these specifications and in conformity with the lines and grades shown on the plans or established. Materials 506.02 Riprap shall consist of hard, dense, durable stone, angular in shape and resistant to weathering. Rounded stone or boulders shall not be used as riprap material. The stone shall have a specific gravity of at least 2.5. Each piece shall have its greatest dimension not greater than three times its least dimension. Material used for riprap may be approved by the Engineer if, by visual inspection, the rock is determined to be sound and durable. The Engineer may require the Contractor to furnish laboratory results if, in the Engineer's opinion, the material is marginal or unacceptable. At the request of the Engineer, the Contractor shall furnish laboratory test results indicating that the material meets the requirements for abrasion resistance or compressive strength as indicated in Table 506-1. Table 506-1 Riprap Material Test Requirements Specification Test Description Test Method Requirement Abrasion Resistance by Los Angeles ASTM C535 50% Loss, max. Machine Unconfined Compressive AASHTO T 24 2500 psi, min. Strength of Drilled Core Specimen Riprap shall conform to the gradation requirements given in Table 506-2. 506-1 506.02 Table 506-2 Riprap Gradation Requirements Percent of Stone Typical Typical Material Size Stone Stone Pay Item Smaller Than d50* Dimensions^ Weight+ Typical (Inches) (Inches) (Pounds) Stone# 70-100 12 85
50-70 9 35
Riprap 6
35-50 6 10
2-10 2 0.4
70-100 15 160
50-70 12 85
Riprap 9
35-50 9 35
2-10 3 1.3
70-100 21 440 Riprap 12 50-70 18 275
35-50 12 85
2-10 4 3
100 30 1280
50-70 24 650
Riprap 18
35-50 18 275
2-10 6 10
100 42 3500
50-70 33 1700
Riprap 24
35-50 24 650
2-10 9 35
Table 506-2 Notes: *d50 = nominal stone size #based on typical rock mass ^equivalent spherical diameter +based on a specific gravity = 2.5 Nominal stone size and total thickness of the riprap shall be as shown on the plans. Control of gradation will be by visual inspection. The Contractor shall provide two samples of rock at least 5 tons each, meeting the gradation specified. One sample shall be provided at the construction site and may be a part of the finished riprap covering. The other sample shall be provided at the quarry. These samples will be used as a reference for judging the gradation of the riprap supplied. When it is determined necessary, conformance of the gradation will be verified by dumping and checking the gradation of two random truckloads of stone. Mechanical equipment, a sorting site, and labor needed to assist in checking gradation shall be provided at the Contractor’s expense. 506-2 506.03 Construction Requirements 506.03 Stones with typical stone dimensions that are equal to d50 and larger shall be placed at the top surface with faces and shapes matched to minimize voids and form as smooth a surface as practical. Dumping and backhoe placement alone is not sufficient to ensure a properly interlocked system. The material may be machine-placed and then arranged as necessary by use of an excavator with a multi-prong grappling device or by hand to interlock and form a substantial bond. Excavation for toe or cut-off walls shall be made to the neat lines of the wall. Allowance will not be made for work outside the neat lines. Method of Measurement 506.04 Riprap of the sizes specified in the Contract will be measured by the ton or by the cubic yard. Cubic yards will be by the method of average end areas based on dimensions shown on the plans or ordered. Basis of Payment 506.05 The accepted quantities of riprap will be paid for at the contract unit price per cubic yard or per ton. Payment will be made under: Pay Item Pay Unit Riprap (___inch) Cubic Yard or Ton Structure excavation will be measured and paid for per Section 206. Riprap (Gabions) and Slope Mattress Description 506.06 This work consists of the construction of riprap in wire mesh gabions and in wire mesh slope mattresses per these specifications and in conformity with the lines and grades shown on the plans or established. Materials 506.07 The wire, wire mesh, cages, anchor stakes and riprap shall conform to subsection 712.09. Construction Requirements 506.08 Gabions and Slope Mattresses. Gabions and slope mattresses shall be placed to conform to the plan details. Riprap material shall be placed in close contact in the unit so that maximum fill is obtained. The units may be filled by machine with sufficient hand work to accomplish requirements of this specification. 506-3 506.09 Where the length of the unit exceeds its horizontal width, the gabion is to be equally divided by diaphragms, of the same mesh and gauge as the body, into cells whose length does not exceed the horizontal width. The unit shall be furnished with the necessary diaphragms secured in proper position on the base section in such a manner that no additional tying at this juncture will be necessary.
a.Gabions. All perimeter edges of gabions are to be securely selvedged or bound so that the joints formed by tying the selvedges have approximately the same strength as the body of the mesh. The gabion bed shall be excavated to the width, line, and grade as staked by the Engineer. The gabions shall be founded on this bed and laid to the lines and dimensions required. Excavation for toe or cut-off walls shall be made to the neat lines of the wall. All gabion units shall be tied together each to its neighbor along all contacting edges in order to form a continuous connecting structure.
b.Slope Mattresses. Slope mattresses shall be filled with angular or fractured stone. Rounded boulders will not be permitted. Before the mattress units are filled, the longitudinal and lateral edge surfaces of adjoining units shall be tightly connected by means of wire ties placed every 4 inches or by a spiral tie having a complete loop every 4 inches. The lid edges of each unit shall be connected in a similar manner to adjacent units. The slope mattress shall be anchored as shown on the plans. The Contractor shall determine whether the holes for the soil anchor stakes are to be drilled or whether the stakes may be driven. Care shall be taken to avoid drilling holes to a greater depth than is necessary to place the top of the finished stake slightly above the top of the finished mattress. The Contractor will be allowed to assemble, partially fill, and tie together mattress-units on the subgrade provided they can be placed on the slope without abrading the zinc coating on the wire mattress or permanently distorting the shape of the mattress in transporting and installing the units on the slope. All prefabrication procedures shall be subject to approval. Method of Measurement 506.09 The quantity to be measured under this item will be the number of cubic yards of riprap required to fill the gabions and slope mattresses per the dimensions shown on the plans or ordered. Basis of Payment 506.10 The accepted quantity measured as provided above will be paid for at the contract unit price per cubic yard for “Riprap (Gabions)” or “Slope Mattress” as the case may be. Payment will be made under: Pay Item Pay Unit Riprap (Gabions) Cubic Yard Slope Mattress Cubic Yard Structure excavation and structure backfill will be measured and paid for per Section 206. 506-4 507.01
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Source: 2025 Standard Specifications for Road and Bridge Construction, 2025 Edition. Pages 483–486 of 967. View official source ↗