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FILTERS & STONE. Filters can be very complex, this is a quick overview.

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Presentation on theme: "FILTERS & STONE. Filters can be very complex, this is a quick overview."— Presentation transcript:


2 Filters can be very complex, this is a quick overview

3 7 year old riprap without filter fabric allows for natural plant colonization. Spring River, AR

4 Filter fabric could prove problematic with over-launching of stone (shown), filter interferes with root architecture, plus roots can “run” on filter & open up overlaps Arkansas

5 Thoughts on Filters A filter has at least three tasks: prevent loss of underlying fine bank materials due to piping, extrusion, or erosion; allow water to drain from the bank thus preventing the buildup of excessive hydrostatic pressure; and to prevent bank stabilization materials from sinking into the underlying substrate. A trained soil scientist, geologist, and/or geotechnical engineer is needed to perform an analysis of the stability and erodability of bank materials and determine what, or if any filter is required.

6 Different Types of Filters Self-filtering stone - Designed with a specific gradation that has a component that acts as a granular filter. Typically 10% to 15% of the gradation is either less than 4 inches in diameter, or less than one pound in weight, depending on how the stone is specified. When placed on-site the smaller stones fall through the interstices and cover the substrate, essentially acting as a granular filter. Granular filters - Progressively larger diameter layers of (possibly) sands, gravels, and/or rock. Geotextile filters: Non-Woven - has a thickness, similar in appearance to felt, dull finish, fibers can be seen but don't form a pattern. Geotextile filters: Woven - slick and shiny, has a discernable weave (a pattern similar to a cotton shirt), designed with a specific size of opening to allow the passage of water, but not the underlying bank material. When looking through a section of used filter light should be visible. If no light can be seen the filter has been "blinded", in other words the filter has been clogged by the bank material. It can also be blinded by deposition from the stream side. Is a filter needed?? - gravels, cobbles, bedrock & some clays usually do not require a filter. Always consult with a learned geotechnical expert!!!


8 Large stone with no filter Big stones alone will not work well for bank protection, the stream water will flow between the gaps in stones (interstices) & erode the underlying soil. In-situ soil

9 ZIGZAG RIVER - PORTLAND OR.-BRIDGE PROTECTION-DERRICK 6-8-2011 Looking DS @ large stone as bridge abutment protection. Huge voids will allow water to flow through & under stone protection.


11 Geotextile filter – can be woven or non-woven Geotextile filter provides a barrier between stream forces & in-situ bed & bank materials, it should allow groundwater passage, & provide a foundation for protection materials. Water can still flow through the stone which is a big problem. In-situ soil Filter material keyed in near top of bank

12 Unchoked voids between large stones allowed water to infiltrate & run on the filter fabric resulting in undercutting of the filter @ the DS end & total failure as shown California

13 Concept behind Self-Filtering Stone In-situ soil This stone gradation has a component that acts as a granular filter. When placed on-site, the smaller stones fall through the interstices & cover the substrate, essentially acting as a quasi- granular filter.

14 Concept behind a granular filter Layers of progressively larger granular material are designed to encapsulate & trap the immediate layer below. Groundwater should be able to flow thru all layers. In-situ soil Granular filter Ground- water flow out of saturated bank

15 Big stone protection Big stone is not the answer & does not work by itself. Look at all the gaps that water can flow through. Big stone has to be well-graded, or at least choked. In-situ soil Big stone bank protection Granular filter

16 Big stone protection with choke stone Big stone that is well-graded will self-adjust (self-heal), The smaller stones (or choke, shown in blue here) will block flow from going through the stone bank protection. In-situ soil Granular filter

17 Self-Adjusting, Self-Filtering Stone Depending on size, angularity, & gradation, stone can be neither, either, or both!! Self-Adjusting Stone: Stone must be well-graded (from coarse to fine) so that it has the ability to "launch", or self-adjust into, and armor, scour holes formed on the streamward side, and/or stream end, of a river training structure. Charlie Elliott says a good rule of thumb in Mississippi sand-bed streams {CAUTION: this might not apply equally well to every stream in the world} is that one ton of rock per linear ft will armor approximately three ft of scour Self-Filtering Stone A soil analysis should always be performed to determine stability and erodability of bank materials and whether a filter material, (either granular or synthetic) is required. A self-filtering stone that has worked well on the Mississippi River, and numerous other rivers and smaller streams (acting as a granular filter to prevent loss of underlying bank material) has 10% to 15% of the gradation either less that 4 inches in diameter, or less than one pound in weight, depending on how the stone is specified.

18 A non-woven filter not in intimate contact with the underlying substrate

19 Woven Geotextile Filter Fabric A steep slope, combined with riprap on a slick surface, can lead to problems! Ohio River

20 Woven filter, not blinded, sunshine visible through weave. Woven filters can sometimes be blinded from either the river or bank side

21 Stone

22 An ugly pile of rock!! Median of I-220, Jackson MS. Self filtering, in fact too many fines, but steep angle of repose shows that stone will not self-adjust. This is due to the lack of medium-sized stone (stone is not well graded).

23 Analyze gradation, amount of “fines”, look at pile side slopes (flatter is better). Climb the pile, if it moves that is the stone you need. This is well graded stone, note flat angle of pile

24 Blocky rock will not adjust, but can be used in interesting ways, including end-to end compression, or in a stacked configuration. Medina Quarry, TX.

25 Better looking stone, note flat pile, Medina Quarry, TX. We mixed the two piles of stone from the previous picture to come up with a well-graded stone that will self-adjust.

26 Well-graded stone, but few fines, for Skunk River project, Denmark, IA. To effectively use this stone we installed a granular filter of 1 to 3 inch stone, then installed this stone.

27 Key trench for Bendway Weir, Skunk River, Iowa. Granular filter (1 to 3 inch stone) is installed, then overtopped with key stone.

28 A SHORT TALK ABOUT ROCK QUARRIES - distance from project, quality of rock, price, ability to deliver amount of rock needed (14 to 16 tons per truckload for tandem axle trucks is typical) COMPOSITION - granite, limestone, basalt, dolomite, sandstone, etc. HARDNESS - varies from quarry to quarry and sometimes within the quarry SHAPE & SIZE - block shaped rocks will lock together, look at the shape of the pile of rock at the quarry, climb the pile to see how well rocks will roll downhill, measure for size (B-axis) and visually access gradation, compare quarry’s gradation curves to standard gradation curves. GRADATION - well graded (poorly sorted) is best (largest, then smaller, smaller, smallest with the fine component that will work as a granular filter) WEIGHT - varies, for limestone 1.5 tons per cubic yard is good for estimation purposes (115 lbs/cu. ft.) VOLUME ESTIMATES - estimate amount needed, then add 10 to 15 percent SPECIFICATIONS - Can be "made" to custom specifications or to common specs HAUL RATES - Stone weighing over 400 pounds must be transported in steel bodied trucks, or a “bedding layer” of gravel is placed in aluminum bodied trucks. Haul rates are usually multiplied 1.5 or 1.75 times the base haul rate. WEATHERING - look for examples in the quarry &/or local stream or highway projects, check rocks lining the entrance to the quarry

29 Eudora bend, Kansas River, KS. End dumping like this will sort out even a well- graded stone!! Don’t do this!!

30 Differential weathering turning big stone to gravel, Dome Pipeline Crossing, Minnesota River, Mankato, MN

31 Gradation curves courtesy of Vicksburg District, COE





36 "SHOT ROCK" (Also called “quarry run”, or ungraded stone) "Shot" rock, also called "quarry run" stone, is an ungraded stone blasted at the quarry with the only specification being a maximum (top) size or weight. No specific gradation, or amount of "fines" is specified. The amount of usable stone depends on the skill and knowledge of the blasting technician. Advantages: Cheaper, usually close to 1/2 the cost of graded stone. The ungraded characteristics of the stone can result in increased void spaces (interstices), possibly providing within-channel refugia for aquatic species (especially juveniles). Disadvantages: A truckload of rock might be all top size or dust. Inspector's knowledge/experience critical when deciding where, or if, a load of stone should be placed/used. Some material might be wasted. This stone is typically NOT self-adjusting. It might or might not be self- filtering and could vary by the truckload.

37 Hat for scale Gradation can be varied for environmental purposes


39 CONSTRUCTION -NEWTOWN CR. HORSEHEADS, NY- DERRICK 5-2011 CONSTRUCTION-Looking @ a small portion of the 820 tons of well-graded, self-adjusting, self-filtering stone for LPSTP & keys. Jimmie Joe Carl calculated stone size 4 different ways, and came up with a great custom gradation shown here. Stone top size is 500 pounds. Note flat side slopes of pile.

40 CONSTRUCTION -NEWTOWN CR. HORSEHEADS, NY- DERRICK 5-2011 CONSTRUCTION-Close-up of stone pile. This is a self-adjusting (well-graded), self-filtering (10-15% is one pound or less) stone. D10 17 lbs D50 170 lbs D85 340 lbs D100 500 lbs

41 CONSTRUCTION -NEWTOWN CR. HORSEHEADS, NY- DERRICK 5-2011 CONSTRUCTION-Looking across @ 5 to 8 ton boulders to be used for Bendway Weir (BW) construction. These are the largest & will be placed on the DS edge & at the stream end of the BW. These will not adjust at all.

42 CONSTRUCTION COMPLETE-Looking DS @ Bendway Weir # 4. DS edge is angled 70 degrees from bank to redirect flow toward center of stream. Bendway Weir height is 1 ft above base flow water surface. These stones will not adjust. COMPLETE NEWTOWN CR. HORSEHEADS, NY- DERRICK 5-2011


44 Aug 29, 2006 -high water- Looking US, This stone bank was constructed of large stone & all voids tightly choked with smaller stones so the entire section would be hydraulically smooth & not allow ice to jam in this critical area. Photo by Dave Spann

45 6 YEARS LATER-CHAUTAUQUA CR @ SPANN’S- DERRICK–7/9/2012 6 YEARS LATER-Looking US. Volunteer veg has rooted in the choked stone & is providing shade & cover to the stone protection.

46 This PowerPoint presentation was developed & built by Dave Derrick. Any questions or comments, call my personal cell @ 601-218-7717, or email @ Enjoy the information!!

47 WE ARE DOG TIRED, THIS LECTURE IS DONE !! Cleophus Speed Elvis Derrick

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