FHWA FP-24Public Domain

Section 251 — Riprap

Division 250 — Earth Retaining Systems and Slopes|PDF pages 165–168

Description

251.01This work consists of providing and placing riprap. Riprap gradation is designated according to Subsection 251.07.

Material

251.02Conform to the following Subsections:

Geotextile

Neat hydraulic cement grout Rock for riprap 714.01 701.04(a) (2) 705.02

Construction Requirements

251.03General. Excavate and backfill according to Section 209. Dress the slope to produce a smooth surface. Place geotextil e according to Section 207, as required.

251.04Placed Riprap. Place riprap on a prepared surface. Place riprap to its full thickness in one operation. Do not place riprap material by methods that cause segregation or damage to the prepared surface. Place or rearrange individual rocks by mechanical or hand methods to obtain a dense uniform blanket with a reasonably smooth surface.

251.05Keyed Riprap. Key riprap on a prepared surface and set i nto place by impact pressure. Place rock for keyed riprap according to Subsection 251.04. Set the riprap into place by exerting impact pressure with a hydraulic -powered bucket or an approximate 5000-pound flat -faced mass. Repeat impacts until the rock is firmly seated and forms a reasonably uniform surface without reducing the effective sizes of the rocks. Do not use impact pressure on riprap below the water surface.

251.06Grouted Riprap. Place or key riprap on a prepared surface with the voids filled with grout. Place rock for grouted riprap according to Subsection 251.04. Place rock for keyed grouted riprap according to Subsection 251.05. Thoroughly moisten the rocks and wash excess fines from the riprap or to the underside of the riprap. Do not place grout unless the air temperature is at or above 35 °F within the near-surface voids of the riprap. Prevent segreg ation during grout placement . Start placing grout at the lowest elevation of the riprap. Fill voids without unseating the rocks. Do not exceed 5 -foot thickness for each layer of grouted riprap. Allow 3 days curing time before adding the next layer of ripra p and grout. Provide weep holes through the grouted riprap as required. Keep the grouted riprap moist for 3 days after the work is completed and protect it from freezing for at least 7 days after grouting.

251.07Riprap Gradation.

(a)Wolman c ount. For source approval, test individual riprap size by Wolman Count according to FLH T 521.

(b)Size method. During production, test individual riprap using the size method, by confirming that the largest rock has an intermediate dimension greater than the upper limit of the D85 size range shown in Table 705-1.

251.08Acceptance. See Table 251-1 for sampling, testing, and acceptance requirements. Material for grout will be evaluated under Subsections 106.02 and 106.03. Rock for riprap will be eva luated under Subsections 106.02 and 106.04. Placing grout will be evaluated under Subsection 106.02. Riprap construction will be evaluated under Subsections 106.02 and 106.04. Excavation and backfill will be evaluated under Section 209. Geotextile will be evaluated under Section 207.

Measurement

251.09Measure the Section 251 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring riprap by the cubic yard, measure in place.

Payment

251.10The accepted quantities will be paid at the contract price per unit of measurement for the Section 251 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Table 251-1 Sampling, Testing, and Acceptance Requirements

Material or

Product

(Subsection) Type of

Acceptance

(Subsection) Characteristic Category Test Methods

Specifications Sampling

Frequency Point of

Sampling Split

Sample Reporting

Time Remarks

Source

Rock for

riprap (705.02 ) Measured & tested for conformance (106.04 & 105) Apparent specific gravity & absorption – AASHTO T 85 1 per material type Source of material Yes Before using in work –

Soundness

using sodium sulfate – AASHTO T 104 " " " " – LA abrasion – AASHTO T 96 " " " " – Gradation(1) – FLH T 521 " " No " –

Production

Rock for

riprap (705.02 ) Process control (153.03) Gradation – FLH T 521 1 per 100 yd3 per Class Stockpile or source(2) No Before using in work –

Measured &

tested for conformance (106.02 &

106.04) Size method(1) – Subsection

251.07(b) 1 per 100 yd3 per Class On site stockpile or in-place(3) No 24 hours –

(1)Notify CO at least 7 days before performing test.

(2)To be measured before delivery to project.

(3)Point of sampling to be approved.

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