American Railway Engineering and Maintenance of Way Association Letter Ballot

Transcription

1 American Railway Engineering and Maintenance of Way Association Letter Ballot 1. Committee and Subcommittee: Committee 1, Roadway and Ballast, Subcommittee 10, Geosynthetics 2. Letter Ballot Number: Assignment: D Ballot Item: Enhanced Woven Geotextile 5. Rationale: Provide information on an additional geosynthetic material which has not been discussed in previous manual editions.

2 SECTION ENHANCED WOVEN GEOTEXTILE SPECIFICATIONS FOR RAILROAD T RACKBED STABILIZATION APPLICATIONS BACKGROUND (2018) a. Enhanced woven geotextiles are used on subgrade soils to provide the coincident functions of separation, filtration, and stabilization (as defined AASHTO M288-17). Enhanced woven geotextiles have been used when necessary to provide for additional roadbed filtration, planar (lateral) permeability, strength and modulus improvement, and separation of subgrade and sub-ballast or sub-ballast and ballast. Typical conditions where enhanced geotextiles are used include: soft or weak subgrade conditions, fine grained subgrade soils that are sensitive to changes in moisture conditions (i.e. silts and high plasticity clays), and saturated/partially saturated subgrade conditions (or subgrades that may become saturated or partially saturated during the life of the structure). b. Enhanced woven geotextiles and related products have numerous civil engineering applications outside of the track application described herein. Examples are: subgrade stabilization over weak soils, access road stabilization, intermodal or transload facilities, temporary retaining wall construction, erosion control (beneath hard armor systems), and filtration for drains. c. Slit Tape Woven Geotextiles are specifically excluded from these applications due to their low abrasion resistance, permeability, and water flow. Slit tape woven geotextiles are not recommended for use in railway applications APPLICATION LOCATIONS a. An enhanced woven geotextile may be used beneath ballast and/or sub-ballast for mainlines, secondary rail lines, high tonnage unit-train lines, private facility tracks, switches and turnouts, crossings, bridge approaches, retarders, etc., and on new or existing track construction and rehabilitation. b. The enhanced woven geotextile should be placed at the bottom of the sub-ballast directly on the existing or prepared subgrade (see Figure ) or at the sub-ballast/ballast interface (see Figure ). Such placement increases the bearing capacity of the subgrade, reduces the rate of differential track settlement, and minimizes long-term fouling of the subballast from the subgrade, therefore increasing the length of the maintenance cycle. Placement of the geotextile on the subgrade below the ballast is generally favored when the roadbed is founded on a relatively fine-grained soil and/or soft to firm subgrades. c. An engineering analysis of existing or proposed conditions, including subgrade soil classifications, should be performed to determine the type of geotextile used for stabilization REFERENCE DOCUMENTS a. AASHTO Standards b. ASTM Standards M Geosynthetic Specifications for Highway Applications T88 Particle Size analysis of Soils T90 Determining the Plasticity Limit and Index of Soils D123 D276 D4354 D4355 D4439 D4491 D4716 D4751 D4759 D4873 Standard Terminology Relating to Textiles Test Method for Identification of Fibers in Textiles Practice for Sampling of Geosynthetics for Testing Test Method for Deterioration of Geotextiles (Xenon-Arc Type Apparatus) Terminology for Geosynthetics Test Methods for Water Permeability of Geotextiles by Permittivity Test Method for Constant Head Hydraulic Transmissivity (In-Plane) Test Method for Determining Apparent Opening Size of a Geotextile Practice for Determining Specification Conformance of Geosynthetics Guide for Identification, Storage and Handling of Geotextiles

3 D4595 Test Method for Tensile Properties of Geotextiles by Wide-Width Strip SIGNIFICANCE and USE a. Significant performance benefits may be realized when enhanced woven geotextiles are placed at the bottom of the subballast directly on the existing or prepared subgrade or at the sub-ballast/ballast interface (see Figure 1& ). The effects of the stabilization are particularly apparent where the roadbed is placed on soft or medium strength subgrades. b. Potential benefits of the use of enhanced woven geotextiles, due to separation, filtration, and stabilization (functions) within the roadbed section may include one or more of the following: Increased ballast life (life cycle cost savings) due to minimized fouling/migration Reduced roadbed thickness (initial cost savings) Reduced track deflection resulting in less wear and tear of the mechanical components of the rail track Maintenance of good drainage within the roadbed section due to separation of subgrade/subbase Smoother transitions between areas with differing subgrade strengths Reduced ballast/sub-ballast fouling from fine grained subgrade soils migrating into ballast. c. The enhanced woven geotextile mechanisms; tension membrane, lateral confinement and bearing capacity increase, combined with high water flow and soil retention capabilities, form a track bed system that distributes train loads to reduce stresses on the subgrade and minimize the long-term ballast fouling from subgrade particles. Enhanced Woven Geotextile Figure : Enhanced Woven Geotextiles at the sub-ballast/ballast interface Enhanced Woven Geotextile Figure : Enhanced Woven Geotextiles at the bottom of the sub-ballast, directly on the existing or prepared subgrade

4 MATERIAL REQUIREMENTS (2018) a. Yarns used in the manufacture of the geotextile, and the thread used in joining the geotextile by sewing, should consist of long-chain synthetic polymers, composed of at least 95 percent by weight of polyolefins or polyesters. The geotextile should be a woven fabric formed into a stable network such that the yarns retain their dimensional strength relative to each other. Geotextiles outlined in this section are composed entirely of woven continuous monofilament or fibrillated yarns. b. Slit Tape Woven Geotextiles are specifically excluded from these applications due to their low abrasion resistance, permeability and water flow. Slit tape woven geotextiles are not recommended for use in railway applications. c. The geotextile manufacturer should participate in the National Transportation Product Evaluation Program s (NTPEP) GTX-0 Audit program for geotextiles. As outlined in the NTPEP program, all compliant geotextiles should be permanently labeled on the geotextile material. d. The geotextile should meet the property values stipulated in Table e. In case of a disagreement between the test results of a buyer and a seller, the acceptance of the material should be based on the guidelines of ASTM D4749, "Standard Practice for Determining the Specification Conformance of Geosynthetics." Table : Physical Properties for Enhanced Woven Geotextiles used in Track Stabilization Property Test Method Units Minimum Average Roll Value 1 Ultimate Tensile Strength (machine x cross machine direction) ASTM D4595 lbs/ft (kn/m) Flow Rate ASTM D4491 Gal/min/ft 2 (l/min/m 2 ) 4800 x 4800 (70 x 70) 30 (1222) Permittivity ASTM D4491 sec Apparent Opening Size 2 ASTM D4751 US Std Sieve (mm) UV Stability 3 (Retained Strength after 500 hrs of exposure) ASTM D4355/4355M 30 (0.6) MaxARV % 70 The geotextile should be inert to commonly encountered chemicals, hydrocarbons, and mildew. Notes: 1. Unless otherwise indicated, values shown are minimum average roll values (MARVs) determined in accordance with ASTM D Values for Apparent Opening Size represent MAXIMUM Average Roll Values (MaxARV) 3. The geotextile should be resistant to ultraviolet light.

5 PACKING AND IDENTIFICATION REQUIREMENTS (2017) a. Geotextile labeling, shipment, and storage should follow ASTM D4873 and NTPEP GTX protocols. A tag or other method of identification should be attached to each roll per the NTPEP GTX Audit Plan indicating the following: 1) Manufacturer, Manufacturer Location Code (NTPEP) or Supplier Name 2) Product or style name 3) Roll number 4) Lot or batch number 5) Width of roll 6) Length of roll b. Additionally, a label should be attached to the insides of the core on both ends indicating the labelling details above. c. Each geotextile roll should be wrapped with a material to protect the geotextile from damage due to shipment, sunlight, and contaminants. The protective wrapping should be maintained during periods of shipment and storage. d. During storage, geotextile rolls should be elevated off the ground and adequately covered to protect them from the following: site construction damage, precipitation, extended ultraviolet exposure, chemicals that are strong acids or strong bases, flames including welding sparks, temperatures in excess of 160 F (71 C), and any other environmental condition that may affect the physical properties of the geotextile COMPLIANCE, INSPECTION, AND SAMPLING REQUIREMENTS (2018) a. An accredited GAI-LAP laboratory will be maintained by the producer of the geotextile, at the location of manufacture, to ensure that quality control is in accordance with ASTM D4354 Procedure B. The manufacturer s laboratory will maintain records of its quality control results and provide, upon request of the specifying agent prior to shipment or at any other reasonable time thereafter, a manufacturer s letter of certification. The certification will be based on minimum average roll values, and include: 1. Name of manufacturer 2. Chemical composition 3. Product description 4. Statement of compliance to specified requirements 5. Laboratory test results from the lots corresponding to the rolls shipped 6. Signature of legally authorized official attesting to the information required 7. Purchaser name b. It is recommended that product samples be taken at random, or at an interval specified by the engineer in the field and tested at an independent competent laboratory to indicate compliance with the project specific specifications CONSTRUCTION DETAILS AND METHODS (2018) a. Stabilization applications may include, but not be limited to, installation under track, turnouts, rail and highway crossings, tunnels, and roadways. b. In all applications, the geotextile should be installed in accordance with the plans, specifications or as directed by the Project Engineer.

6 c. In subgrade applications involving new construction, the subgrade areas should be prepared to the proper lines and design grades. d. When undercutting, plowing or sledding operations occur, the installation surface should be prepared as smoothly as possible and a minimum of 12 inches (305 mm) of aggregate should be provided between the geotextile and the bottom of the cross-tie. e. When the proposed roadbed is founded on existing soil, the installation area should be prepared by clearing any unsuitable material or large protrusions. For very soft soils having a CBR < 0.5, it may be beneficial to minimize subgrade disturbance and leave root mats in place, cutting stumps and other projecting vegetation as close and even to the ground surface as possible. For more competent soils having a CBR > 3, it may be prudent to lightly proof roll the subgrade to locate unsuitable materials. f. The geotextile should be unrolled as smoothly as possible on the prepared surface without wrinkles or folds. Construction traffic should not operate directly on the geotextile. g. In all applications, the geotextile may be spliced by overlapping or sewing. Place overlaps at ends of rolls in direction of aggregate placement with previous roll on top. h. Adjacent rolls of geotextile should be overlapped along their sides and ends. Guidelines for the required overlap length required are (in accordance with AASHTO M288): CBR < 1.0 (man walking sinks 2 to 3 in): 3ft overlap, or sewn CBR (pickup truck ruts ½ to 1 in): 2ft overlap CBR > 3.0 (loaded dump truck ruts not more than 3 in): 1ft overlap i. When Enhanced Woven Geotextiles are used at the sub-ballast/ballast interface, where tines are being used to compact aggregate, the geotextile should not be placed within 4 inches of the bottom of the ties. j. The contractor will be allowed to patch small rips or tears in the geotextile when approved by the Engineer and in accordance with the foregoing requirements. Damaged areas will be repaired by placing new geotextile over the area and extending beyond damaged area a minimum of 3 ft on each side of the rip or tear. k. The fill or aggregate should be placed on the geotextile in compacted lifts not less than 6 inches (150 mm) thick. In cases of track undercutting, a lift of ballast 6 inches (150 mm) thick should be placed on the geotextile, the track raised and additional ballast added before any ballast tamping operations begin. When used with other geosynthetics, lifts less than 6 inches may be acceptable in accordance with Manufacturer recommendations MEASUREMENT AND PAYMENT (2018) a. Geotextile may be measured for payment by the square yard (square meter). b. Geotextile may be paid by the square yard (square meter) shipped, unless otherwise prescribed by the purchase contract.