1、DAEN-ECE- G Engineer Technical Letter No. 1110-2-286 3535789 0022398 427 11- 36-u0 DEPARTMENT of ME ARMY U. S. Army Corps of Engineers Washington, O. C. 20314 ETL 1110-2-286 25 July 1984 Engi neeri ng and Desi gn USE OF EOTEXTILES* UNDER RIPRAP 1 Purpose. unde-p on the Tennessee-Tombigbee Waterway.
2、2. Applicability. operating activities having civil works responsibil i ties. 3. Reference. CW-02215, Plastic Filter Fabric. 4. Background. Qotextiles have been used extensively throughout the 234- mile Tennessee-Tombigbee Waterway, primarily to replace multi-layered graded filter systems under the
3、riprap. During the past ten years, the Mobile and Nashville Districts have had considerable experience in placing geotextiles under riprap. by the conclusion of the Tennessee-Tombigbee Project. Problems were encountered with clogging, tearing, or puncturing of the geotextile and erosion undermi ni n
4、g the geotexti 1 e. Proper control of both surface and groundwater and close inspection during construction proved to be essential. Thi s ETL provi des i nformation on experiences with geotexti 1 es This ETL applies to all HQUSACE/OCE elements and field Over 4,000,000 square yards of geotextile will
5、 have been placed 5. General. a. The majority of the riprap had a top size of 300-400 pounds with a W50 of 90-100 pounds. types of geotextiles used are listed in Table 1 (see Inclosure i). limited use was made of nonwoven geotextile. by the Nashville District, with woven geotextile used almost exclu
6、sively. design called for the riprap to be placed directly on the geotextile, which resulted in some tearing or puncturing. The type of equipment and the skill of the operator directly influenced the amount of damage. Close inspection during construction and insistence upon a very low drop height of
7、 the stone reduced, but did not totally eliminate damage. It was placed on slopes of lV:2H, 2V:5H, and 1V:3H. The Only b. Over 2,500,000 square yards of geotextile was placed in the Divide Cut The “Geotextiles as used here refers to any permeable textile used in a geotechnical application as an inte
8、gral part of a man-made project. Geotextiles have been called filter cloths, filter geotextiles, civil engineering geotextiles, etc. for impermeable material s. Qomembrane, a related tem, is normally used Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,
9、-,-H 3515789 0022399 363 En 1110-2-286 25 .Jul 84 c. A 6-inch bedding layer was used between the riprap and geotextile by the Mobile District on their portion of the waterway, for the sole purpose Of protecting the textile from tearing or puncturing. crushed rock were used successfully. When availab
10、le on site, natural sand was cheaper than the crushed rock. the sand from under the riprap, resulting in the riprap being deposited directly on the geotextile. When this occurred, and if the slope material directly under the textile was loose or soft enough to allow the riprap to settle, this settli
11、ng tightened the geotextile to the point of puncturing or tearing. The crushed rock bedding did not wash out and continued to protect the geotextile from puncturing or tearing by the riprap. Both natural sand and In some cases rain and surface runoff washed d. lhe monofilament flat yarn geotextile t
12、ended to creep more and was not as durable as the textile consisting of spun yarn in one direction and mono- filament flat yarn in the other. elongate and spread, whereas the characteristics of the nonwoven geotextile tended to prevent a puncture from lengthening. nonwoven geotextiles were tested. b
13、ut not durable; the heavier geotextiles were durable but not cost competi tive. Tears in the woven geotextiles tended to Some small sections of The lighter weights were cost competitive 6. Clogging. silty fine sands. Early contracts specified an equivalent opening size (EOS) ranging from 70-100, pri
14、marily because of these fine sands. be too small as clogging occurred. buildup of several feet behind the geotextile. After changing to an EOS of 30-70, the cl oggi ng was decreased, though not enti rely el imi nated. Many of the slopes that received riprap consisted of fine and The EOS proved to In
15、 some cases, piezometers measured a head 7. Slope Preparation. Specifications generally stated the grading tolerances of slopes to receive geotextile. In addition to meeting the grading tolerances, the slopes needed to be checked for soft spots. Wet, unstable slopes made the proper placement of the
16、textile difficult, while well prepared slopes greatly aided the proper placement of the geotextile. 8. Placement of tkotextile. a. The geotextile was sewn and overlapped as specified in Guide Specification CW-02215. toe, with the downstream edge of the upstream run overlapping the upstream edge of t
17、he downstream run. geotextil e. b. 1977, required the geotextile to be pinned. Districts found that pinning the geotextile tended to make the textile stretch tight as the riprap was placed, making the textile much more susceptible to puncturing or tearing. El imi nati ng the pi nning greatly reduced
18、 the damage, but the geotextile tended to creep down the slope, conforming to the prepared slope and to the riprap itself. to help hold it in place until the bedding layer was placed was found to he beneficial. lhe textile was placed in runs from top of slope to Equipment was not allowed on unprotec
19、ted uiide specification CW-02215, “Plastic Fil ter Fabric“ , dated November Both the Nashville and Mobile However, temporarily pinning the geotextile These pins were removed as the bedding layer was placed on 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from
20、 IHS-,-,-W 3515789 0022400 905 ETL 1110-2-286 25 Jul 84 the geotextile. geotexti 1 e had fol ded accordion-1 i ke down the sl ope , conformi ng with the sl ope surface. had to be 10-15 percent longer than the slope being covered. creep experienced when the riprap was placed directly on the textile t
21、han when a protective beddi ng layer was used. Upon inspection after placement of the bedding layer, the To compensate for this “fol ding“ the length of instal 1 ed geotextil e There was more c. Placing the upper end of the geotextile in a trench at the top of slope was found to be a good practice t
22、o help control surface runoff. However, if the trench was backfilled before the bedding or riprap was placed, the geotextile was stretched tight and became more susceptible to puncturing and tearing. d. Many geotextiles were sensitive to sunlight, which meant close coordination was required for the
23、entire construction process in order to reduce exposure. 9. Bedding Layer. a. A bedding layer between the riprap and geotextile protected the geotextile during placement of the riprap. Both sand and/or graded crushed rock were used successfully, but the latter provided better protection. a protectiv
24、e bedding layer was used, the rate of stone placement was higher and the damage to the textile less. The preferred placement of the bedding was from the bottom of the slope upward and laterally using light pressure dozers (such as wide-track 0-5) for spreading without damaging the geotextile. Where
25、Sharp turns with even light equipment caused geotextile damage. b. Heavy equipment was not allowed on the riprap without a bedding layer being used as this would have damaged the geotextile. previously placed riprap by backhoes and gradalls al so caused geotextile damage. The extra precautions and r
26、estrictions required when the protective bedding was not used generally slowed the production rate to the extent that the cost of the protective bedding was offset. Rearrangement of the 10. Equipment. Many types of equipment were used to place riprap with varying success in preventi ng damage to the
27、 geotextil e. P1 aci ng riprap directly on the geotextile proved to be extremely sensitive to the equipment and skill of the operator. peel“ worked best in placing the riprap directly on the geotextile. Conventional backhoes did not work very well because the downward pressure of the bucket could no
28、t be controlled. Better results were obtained in placing the riprap with the equipment positioned at the top of the slope because the operator had a better view of the work area. When a protective bedding was pl aced over the geotexti 1 e , very good resul ts were obtai ned with equipment such as sk
29、ip pans and backhoes. On two jobs, satisfactory results were obtained by winching trucks, loaded with riprap, down slopes covered with a crushed stone protective layer; then final spreading of the riprap was done by a backhoe or gradall. For the large “Divide Cut Section,“ over 900,000 tons The mech
30、anical ly-articulated “c1 aw“ or “orange 3 4334 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ETL 1110-2-286 25 Jul 84 of riprap were successfully placed directly on the geotext designed and fabricated riprap placement machine. le with a specially
31、11. failures. The concept of sheet runoff was used in design but this proved to be inapplicable since the runoff tended to create channels in the highly erodible soi 1 s and undermi ne the geotextil e. The geotexti 1 e was either clogged, of too low a permeability, or not in contact with the soil, c
32、ausinq the water to percolate down the slope under the geotextile instead of up through the textile and then down the slope on top of the textile. Any punctures or tears in the textile allowed the trapped water to exit and carry materials with it. Slumps or depressions in the riprap resulted, and in
33、 cases of heavy or prolonged rainfall, a complete washout and failure occurred. Burying the geotextile 2-3 feet deep in a trench at the top of slope after riprap placement helped greatly to control erosion, but it was not a complete solution (Figure i). Modifying berm slopes and stabilizing berms wi
34、th small rock were also tried and met with varied success (Figures 2 & 3). Collector systems for the runoff proved to be the best and most reliable overall solution but were expensive. and pipes were used successfully. Figure 4 shows a typical collector system. See Inclosure 1 for Figures 1 thru 5.
35、Surface Water. Failure to properly handle surface water resulted in many Various combinations of ditches, paved channels, 12. Groundwater. Groundwater seeping out of cut slopes also presented prob1 ems. Coup1 ed wi th the hi ghly erodi bl e and horizontal ly 1 ami nated soi 1 s , the groundwater see
36、page eroded the slopes badly and created soft unstable areas. Extensive slope preparation was required to correct the erosion problem. Interceptor trench drains parallel to the waterway center-1 ine were required to stabilize the slopes before the geotextile and riprap could be placed. These drains
37、were installed as determined in the field, with as many as six lines of drains needed on a single slope. Figure 5 is a typical section of these drains. , 13. Mobi 1 e Di strict, 205 -690-2685 and Ben Couch, Nashville District, 615-251-5693. Points of Contract. For more detailed information contact R
38、ay Gustin, FOR THE COMMANDER: 1 Incl as WILLIAM N. McCORMICK, JR. Chief , Engi neeri ng Di vi si on Di rectorate of Engineering and Construction 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I I -_ _.-_- 3535789 0022402 788 En 1110-2-286 25 Jui 8
39、4 TABLE 1 Geotextiles Used On The Tennessee - Tombigbee Waterway Manufacturer Product Name EOS Di strict Advance Construction Special ties Adva-Fil t 70-100 ORN, SAM Amoco Geotextiles Co. Propex M-1195 70 ORN Bradl ey Materi al s Co. EPR 323 70-100 ORN, SAM - Bradl ey Materi al s Co Carthage Mil 1 s
40、 Carthage Mi 11 s Laurel P1 astics Laurel P1 astics Dupont Monsanto Inclosure 1 Filter Weave 30-70 ORN, SAM Tenn-Tom Poly-Fil ter X 70 ORN, SAM Poly-Fi 1 ter GB 40 SAM ORN, SAM Type 1 Erosion 70-100 Control Cloth Type 2 Erosion Control Cloth TYPar Bi dim 1- 1 40 SAM NIA ORN N/A ORN Provided by IHSNo
41、t for ResaleNo reproduction or networking permitted without license from IHS-,-,-EXL 1110-2-286 25 Jul 84 I a, Q O uj s Cu I I U E .- M 3535789 0022403 bL4 M x- r o C C W I! w I o 1-2 5 r U a C 5 o a a O ui Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS
42、-,-,-m 3515789 0022404 550 m 4 we * 8? Stabi ETL 111-2-286 25 Jul 84 18? Riprap 2% Slope. P zed Turf FIGURE 3. Stabilized Berm with Riprap Extended and No Entrenched Geotextile. Slope Varies a. Berm Section . FIGURE 4. Typical Surface Water Collector System. 1-3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-35L57B9 0022405 497 ETL 1110-2-286 25 Jul 84 5 FIGURE 5. Typical Lateral Drains for Groundwater Seepage Control. 1-4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
