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Rejoice-CS 95060611356 M, alhis Dallas. Texas 75229-3157 ~214) 556-2204. FAX ~214i 556-1753 CSI INC. RECEIVED June 6, t995 -.. Mr. Gary Sieb, City Planner' """ ...... City of Coppell -.. '"x -- , · 420 Southfork '\ r.e ~ -~ .... ~4. .... /.' Lewisville, Texas 75057 'i ~ ~ .~,.- / Attention: Mr. Mike Tompkins/ r..~.,,~ ~ ~ .,, Subject: Alternate Pavement Design RecOmmendations ":- PROPOSED NEW CHL'RCH '\:" Sandy Lake Road, West of McArthur Road ,. Coppell, Texas ATEC Project No. 25-07-92-06154 A}-" Dear Tomp -kins: As you requested during a telephone conversation on Tuesday, June 6, 1995, ATEC Associates, Inc. (ATEC) has prepared this letter providing alternate pavement recommendations for use on the above referenced project. These recommendations should be used in conjunction with the recommendations provided in our original geotechnical report. Within Section 4.3 of the report, ATEC recommended that the upper 6 inches of clayey subgrade soil be lime or cement stabilized. The purpose of the stabilization was not to reduce potential vertical rise movements (PVR) beneath the pavements, but instead to improve the bearing value of the pavement subgrade soils. Most importantly, mixing lime or cement with the clayey soils would provide uniform soil conditions on which to construct the pavements. The Portland Concrete Association (PCA) has often stated that the key contributor to long term performance of rigid concrete pavements is having uniform subgrade conditions. In this fashion, the rigid pavement cannot distinguish between subgrade areas which are hard versus soft or dry versus wet. By adding lime or cement to the clayey subgrade soils, the lime or cement physically changes the clay so their is a breakdown of the clay particle attraction to each other. With pulverization equipment, the clay soil is easily broken down into uniform particle si~ed material, and when compacted at the correct moisture content, a uniform subgrade condition is achieved. A secondary benefit of the lime or cement stabilization is that a good working surface is achieved to traffic construction equipment over which is generally not affected by rain and will drain quickly with proper sloping. Ame,icaq Testing and Engineering Corporation Comsu!t.~g Environmental. Geo*.ec,hn,c3! 'an ~ '~ffic¢-s mt, 1&;.:,r U.S. Cities/Since 1958 Materials E:~ginee. :- ATEC understands that a value engineering study of the project was performed in order to find ways to reduce construction costs. The stabilization of the clayey subgrade soils was identified as a process which could be eliminated. ATEC notes that over the last 6-8 months, numerous clients have requested ATEC to evaluate eliminating stabilization of the clayey subgrade soils. We believe this high frequency of request to be related to the high volume of construction activity in the DFW Metroplex. Lime producers (and other product suppliers) have raised prices significantly to take advantage of the high demand. If the owner decides to eliminate stabilization of the subgrade soils, then their is an increased risk that the long term performance of the concrete pavement will be diminished. The following recommendations must be followed regardless of the increased risk. (1) In an attempt to create uniformity of the subgrade conditions, once rough subgrade elevations have been reached, the exposed surface of the clayey subgrade soils should be scarified to a depth of at least 6 inches, wetted to a moisture content of -1 to +4 percentage points of the soils' optimum moisture, and compacted to at least 95% but not exceeding 100 percent of the standard Proctor (ASTM D-698 Method A) density. Scarification and breaking down of the clay soil would be best achieved with pulverization equipment. However, a dozer equipped with conventional ripping teeth might alternately be used. (2) The compacted material should be kept moist until the paving is in place. This could be accomplished by lightly spraying the subgrade twice daily. -.'"x (3) Due to the increased risk associated with not being able to achieve uniformity of "" subgrade conditions by elimination of the stabilization, it is recommended to add I inch of concrete to the City of Coppell requirements for pavement sections. The following ..,. reinforced concrete pavement sections should be used. Light to Heavy Traffic (automobiles, occasional light trucks, parking areas, fire lanes) 6.0 in. Reinforced concrete ......... 6.0 in. Scarified and compacted subgrade ................. All concrete used on site should exhibit the following properties: (4) With elimination of the stabilization, it is essential that an aggressive maintenance program to keep joints and cracks sealed to prevent moisture infiltration be performed to help extend the pavement life. 2 Once again, we appreciate the opportunity to be of service to you on this project. If you should have any questions about information in this letter, please call us at (214) 556-2204. Sincerely, ATEC ASSOCIATES, IN~.~.~ OI~ l,:~'~l-, AssoCiate Vice Presid~t~): · . . Manager, OME DPZ:ch cc: (3) CSI; Inc.