Riprap Installation Construction Inspection for Field Office Activities

Riprap Installation Construction Inspection for Field Office Activities Will use Riprap Gradation and Riprap Subgrade Problems from Class Problem Section USDA is an equal opportunity provider and employer.

Objectives Ø Understand importance of rock quality Ø Define D 50, Dmax and Dmin Ø Understand importance of subgrade Ø Visualize good placement vs. bad

Specifications Ø Construction Specification 61 - Rock Riprap Ø Construction Specification 62 - Grouted Rock Riprap Ø Material Specification 523 - Rock For Riprap

Riprap definition Stone materials, generally less than two tons in weight, specially selected and graded, and when properly placed prevents erosion caused by minor wave action, or erosive currents and thereby preserves the shape of a surface, slope, or the underlying structure.

Materials Rock

Rock Approval Ø Specifications 61 and 62 require the contractor to designate the material source prior to delivery to the site Ø When possible the inspector should visit the source to avoid rejecting on site Ø Geologist can help determine rock quality (if requested)

Why is good rock quality important? Ø Rock size always shrinks with time Ø The design is based on certain rock weights/sizes

Rock Inspection Ø Rock size/weight decreases (does not grow) § From loading § Dumping § Placing § Weathering

Rock, Field Checking Ø At quarry § Rock quality § Rock size § Rock name for acceptable pile Ø Measure out a sample size (2 ton? ) if quarry will allow it § Quarry equipment may be needed to move rocks § Visual reference for operator loading at quarry

Rock Inspection at Quarry Ø Rock quality § Drop rock on another § Foot protection § Hit with hammer § Eye protection § Look for seams

Rock Inspection at Quarry Ø Rock size/shape § Angular not rounded § Gradation/Weight calculations

Gradation Check rock size(s)

GRADATION Rock that is too small may become displaced. Planned limits Rock that is poorly graded may not protect the subgrade as intended. flow Rock that is too large will cause quantity overruns. Exposed subgrade

What is D 50? Ø D = rock diameter (inches) Ø 50 = 50% of rock is lighter § By weight not volume Ø Example gradation § D 100 = 24” (usually between 2 D 50 to 2. 5 D 50) § D 50=10” § Dmin=5” (about 0. 5 D 50)

Poorly graded

Poorly graded

Well graded

Will half the rocks in a properly graded truck load be D 50 size? No, rock gradation is by weight not by the number of rocks.

Sample gradation Ø The following specification will apply to the slope rock: § 5 % (by weight) shall be equal to or less than 150 lbs. § 95 % shall be between 300 and 3, 000 lbs. and wellgraded. § maximum weight of 4, 000 lbs

Measure rock sizes

Field estimate of rock weights (assuming rock is cube shape) Ø Measure 3 sides of a typical rock Ø Multiply the sides Ø Multiply answer by 165

Multiply volume times weight Ø 3 ft x 2 ft rock = 18*165 = approximately 3000 lbs

Weight adjustment if rock is not cubical Ø if rocks are more rounded than square reduce this by as much as 75% Ø OR

MNTC (double perimeter) method assumes rock is spherical shape Ø W (lb) = (P 1+P 2)3/3 P 1 = perimeter of major axis (ft) Ø P 2 = perimeter of minor axis (ft) Ø AND Ø d (in) = 2. 41 W 1/3 Ø Ø d = rock diameter (in)

Examples Ø P 1 = 2. 3 ft Ø P 2 = 3. 3 ft Ø W = (2. 3+3. 3)3/3 = 58 lb Ø AND Ø d = 2. 41(58)1/3 = 9. 3 in

Graph located at back of section Use graph to answer Riprap Size problem

Riprap Gradation Problem: Use Friendly Farmer GSS specs and graph From Friendly Farmer GSS specifications, 80 D 50 = ______lb D 90 = _____lb, Assume this is Dmax 200 D 10 = _____lb, Assume this is Dmin 10

Riprap Size Problem: Use Friendly Farmer GSS specs and graph From Friendly Farmer GSS specifications, D 50 = 80 lbs Dmax = 200 lbs Dmin = 10 lbs From graph 14” 1. Probable diameter of Dmax is ____ 8. 4’ 2. Sum of perimeters is ____ 5” 3. Probable diameter of Dmin is ____ 4. Sum of perimeters is _____ 3. 1’

Class Exercise: Weigh each riprap sample using: 1. The sum of perimeter method 2. The three dimension method.

Class Exercise Results: Sample #1–Actual weight is 31. 5 lbs Sample #2–Actual weight is 44. 2 lbs

On-Site Installation Process Ø Sediment & Erosion Controls Ø Staking Ø Sub-grade Preparation Ø Filter Bedding, or Geotextile Ø Placement

Erosion and Sediment Control Ø Planned controls in place Ø Functioning as planned Ø Do not work in standing water Ø Never work in flowing water (unless the locations are specifically identified on the permit)

Concrete barrier diversion Diversion channel

Inspect sediment controls

Staking/Layout Survey rod Record station number, H, and D on lathe near hub. H Set hubs away from the immediate work area. D

Subgrade Ø Toe excavation alignment Ø Toe excavation elevation Ø Check for proper slope on bank, cut and fill Ø Watch type of soil excavated Ø Removal of water

POOR SUBGRADE PREPARATION

Subgrade Note alignment Toe rock excavation

Subgrade Ø POINT OF NO RETURN § Do it right the first time § Plan ahead § Check elevations and dimensions ØClass Problem Time!!!

Bedding vs. Filter Ø Bedding is a structural base Ø Filter is for preventing or delaying movement of fines

Bedding vs. Filter Ø Bedding and filter may be required together Ø Can be soil or geo-textile or both

Bedding vs. Filter Ø Bedding and filter installed smooth Ø Must be stable Ø Compaction only if called for by Designer

Geotextile placement Good or Bad placement?

Bedding soil Ø Check source of material Ø Inspect gradation and quality Ø Prepared bedding must be inspected before rock is placed § To ensure proper thickness

Sandy-gravel bedding

Onsite gravel soil bedding

Rock, Field Checking Ø Rock delivery tickets show that rock is from previously agreed-upon source Ø Rock, on truck, and as dumped looks like rock from source Visual Inspection Measurements Ø Amount of fines are acceptable

Placement

Placement

Placement Ø Assure rocks are touching (no voids, no soil showing) Ø A thumb attachment is very useful for this work

SECTION VIEW of PROPER vs. IMPROPER PLACEMENT Large rocks evenly distributed, small rocks fill voids between large rocks IMPROPER PLACEMENT Large rocks distributed unevenly with pockets of small rock in between

PLAN VIEW OF PROPER PLACEMENT Large rocks touch small rocks filling voids between. Should not see much ground when looking down.

AVOID DOUBLE DECKING Double decking usually occurs when hand placed. Small rocks are placed on top of the rock fill to bring it up to the specified grade. Looks good, works bad.

Poorly placed

Poor placement

Better placement

Better placement

Close-up good placement

Placement Ø Watch thickness Ø Watch Slopes

Measure average thickness Measure here

Checking Slope

Questions?