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Creekview II 1B-CS 991110HUFFMAN & HUFFMAN, INC. 243 Ridgeway Circle Lewisville, Tx. 75067 972-434-3640 November 10, 1999 Re: Creek View Office Bldg Denton Tap at Bethel Rd. Dear Mr. Campbell, I would like to thank you for allowing us to use Hancor Polyethylene pipe for the storm drain improvements. Enclosed is the material you requested regarding this pipe. Sincerely, Backfill Recommendations for Sure-Lol¢, Sure-Lold' 10.8, Hi-Q* and HEAVY DUTY PIPE Hancor polyethylene pipe and a well-constructed backfill envelope work together to support soil and traffic loads. Although backfill has special significance ~n applications ~nvolvin9 high loads, it is important to take reasonable precautions during any pipe installation. Correct installation will ensure long-term trouble-free service for all types of pipe systems. The recommendations presented here detail how to obtain a dependable drainage ~nstallation with proper backfill materials, compaction levels, and placement procedures. These recommendations assume that the drainage designer used design criteria available from Hancor (Hancor Drainage Handbook, Structures and Installation sections). The or other designer ShOUld d~scus ~nstallations involving conditions not covered by that document (poor soils, high loads, factors that may affect the performance of the system) with Hancor Area Engineers through the nearest manufacturin¢ location. Step 1- Backfill Material Selection Class I, II, iii, and IVA are acceptable backfill materials. A description of the minimum compaction rates and maximum compaction layer heights are summarized in Table 1, Final selection of backfill material will primarily depend on what is available locally in order to mimm~ze costs. Crushed stone and other Class I materials can be dumped around the p~pe, :a,~ng care to ensure voids are eliminated. Non-cohesive sand. sand/gravel mixes, and other Class II or Iii materials must be compacted to a m~nimum of 85% to 90% standard Proctor density. respectively. Class IVA material is acceptable provided it is compacted at optimum moisture to an appropriate density. Guidance from an individual knowledgeable in the behavior of IVA material may be required, especially in areas involving substantial loads. Native soil should be used as backfill material if it meets the requirements of a soil class shown in Table 1 and is suitable for the Icad conditions. Soil not meeting the requirements in Table 1 may be unacceptable backfill material. In these situations, suitabte material should be imported. Step 2 -- Trench Construction The trench or ditch should be just wide enough to place and compact the backfill around the entire pipe. A general rule is to excavate to a width twice the nominal diameter of the pipe out not more than the nominal diameter plus two feet f0,Cm), For 3arallel pipe installations, allow enough space between the pipes for ~roper compaction, Recommended mimmum spacing dimensions are shown in Figure 1 As with any pipe, groundwater or a seasonai h~gh water [a:,e may make pipe installation difficult. During these conditions, trer'cn de- watering will be necessary to make p~pe installation safer, eas~er. and faster. Table 1 Acceptable Backfill Material and Compaction Requirements Sci[ Classification Minimum Compaction Standard Layer ASTM ASTM AASHTO Deon¢ity Height D2321 02487 ',~43 ~n (mi Description Graded or crushed stone O',ass I - 5 dumped 18 {05m) crushed grave! 56 'h'e-graded sated gra.e,s ~_ ass II GW 57 85% 12 (03m) ano gravel sand mixtures: GP ane gravel/sand mixtures: SP !ittie or no fines S, tv or clayey grave~s Class III GM Gravel 90% 9 (0 15m) ano day mixtures s~,ty or SM Sand c avey sands sand~c!av or SC :<10% fines) I norgamc silts and Iow- Class iVA ML g ave y, sandy or silly clays; some fine sands ;i;~n;e;'io~; r;~du-ce~ t; ;;;o-mmodate compact,on method **~'av require culdance from an ~ndividual knowledgeable h~ the behavior of this UP TO 24qNCH (600mrn) D: M=12in (03m) ',1OR E THAN 24-INCH 1600mm~ D M=I,2D Figure 1 - Parallel Pipe Installation Step 2 - Trench Construction (continued) Trench or ditch bottoms containing bedrock, soft areas such as muck or refuse, or other material unable to provide long-term support to the pipe are unacceptable. Remove rock and other unyielding matedal one foot (0.3m) below grade and six inches (0,15m) on either side of the pipe, Excavate soft areas to a depth of about two feet (O.6m) below grade and three times the width of the pipe. If a firm foundation is exposed, replace the excavated matedal with acceptable backfill matehat and compact as shown in Figure 2. If the soft area remains after excavation or if the native soil can migrate into the backfill, synthetic fabric (geotextile) should be used to separate the native soil from the backfill1 After the fabric has been laid on the native soil, replace the excavated material with acceptable backfill material and compact as shown in Figure 2. Step 3 - Backfill Envelope Construction If the native soil cannot carry load as described in Step 2~ adequate bedding material (refer to Figure 3) should be imported. Compact and I level this area of the backfill as shown in Figure 3. [~,,~ Thc bc, ckfill under the haunches of the pipe supports most oi ihe toad. Place and compact the backfill in layers under the haunches of the pipe to meet the requirements of Table 1. Layer heights less than those in Table 1 may be required for smaller pipes. Pipes laid in parallel installations require the same backfill support. Initial backfill distributes loads evenly over the pipe. Place and compact backfill in layers around the pipe and at least six inches (0.15m) above it. Avoid impacting the pipe directly with the compaction equipment. ACCEPTABLE BACKFILL MATERIAL Figure 2 - Modified Trench Bottoms LEGEND SPRING LINE Final backfill material and compaction should be appropriate for the anticipated loading. For areas receiwng regular traffic, the final backfill should extend a minimum of six inches (0.15m) above the initial backfill for Figure 3 - Backfill Zones a total of one foot {0.3m) minimum cover over the pipe, Minimum cover can sometimes be reduced in areas receiving no or infrequent light traffic. Heavy construction equipment traffic may require additional caution in shallow installations. For equipment between 30 and 60 tons (267-534kN), a minimum of two feet {0.6m) of cover is needed over the pipe. Higher loads require a minimum of three feet (lin) of cover, if the pipe is buried so that sufficient cover ~s provided, no further precautions are required. If not, mater~al should be mounded and compacted over the pipe to provide the minimum cover needed for the load. The mound can be leveled to the required grade following constnJction. NOTE: Values stated in inch-pound units are standard; metric equivalents are shown for informational purposes only. CALIFORNIA Bakersfield 6ALIFORNIA Patterson FLORIDA Kissimmee GEORGIA Cordele iNOIANA Brazil IOWA Oelwein MICHIGAN Chesaning MINNESOTA F~irrno~t 1-800-848-3546, Ext. 453 CALL DIRECTLY FROM YOUR FAX ©1997 Hancor, Inc. NEW YORK Waverly NORTH CAROLINA Mebane OHIO Findlay Main Office OHIO Findiay Plant TEXAS Yoakum VERMONT N. Springfield WASHINGTON Olympia FOR OISTRIBUTOR USE: Hancor, Inc. · 401 Olive Street · Findlay, Ohio 45840 Hancor~, Hi*Q*, LandMax~, and Sure-Lo~ are trademarks of Hancor, Inc.