PERMFILE69480 - Laserfiche WebLink

Home Browse Search

April, 2004 S.OPIPE BEDDING Flexible pipe was considered for this project due to the temporary role that the low water crossing would have over the lifetime of the gravel mining operations. The flexible pipe option was also chosen as a least cost option for a temporary structure. The depth of cover for the pipes (dead load), as well as the truck weight (live load), were considerations in the design of the pipe bedding material. Strict adherence to the construction recommendations are important for successful performance of flexible pipe as the pipe gains the majority of it's strength through soil -structure interaction. The pipe must be well bedded at least 6-inches below the invert of the pipe and to a depth 12-inches above the pipe crown. By doing this, the pipe will serve as a form for the soil arch and the soil supports and protects the pipe against vertical loads by arching action of the soil. Dead loads and live loads on the pipe structure were computed on 2 sheets labeled Loads & Supporting Strengths, which are provided in the appendix to this report. Four (4) feet of cover is required above the crown of the pipe to bring the proposed grade to the crossing's finished road surface elevation of 4940. This cover accounts for 520 Ibs/ft2 of vertical soil pressure on the pipe. The live load was computed fora 136,000 Ib. (68 ton) Caterpillar D350E Series II articulated truck. See Appendix D for truck specifications. The heaviest axle load for this vehicle (front axle load = 47,120 Ibs) was divided by 2 to determine a single wheel load. This load was then entered into Holl's Equation for a single wheel load and the Boussinesq Equation for multiple wheel loads. The single wheel load returned the highest vertical pressure on the pipe. The vertical pressure on the pipe due to the live load is 1584.4 Ibs/ft2. Spangler's Modified Iowa Equation was then utilized to determine the percent deflection of an ADS N-12 high density polyethylene pipe (HDPE) under the above loading conditions. A web-based spreadsheet provided by ADS was used to make this calculation using both a 1.0 lag factor and a more conservative 1.5 lag factor. Both calculations returned a value of less than 5% deflection, which is considered to be an acceptable deflection for this pipe. Printouts of the ADS deflection calculations with the appropriate loading inputs are provided in the appendix to this report. The output values for deflection were achieved using the input assumptions shown on the web-based spreadsheet, however if the assumptions are not met using appropriate bedding material with adequate compaction in the field, the pipe will not deflect in the manner reflected by the calculation. It is important that the contractor installing this pipe crossing follow the bedding methods outlined in the General Notes of the Low Water Crossing Detail Sheet. Additional information on the installation of flexible pipe can be found in the ADS Product Note 3.115 re: Installing N-12 Storm, Sanitary Sewer and Culvert Pipe, provided in the appendix to this report. ASTM Standard D 2321 - 89 (Reapproved 1995) Standard Practice for Underground Installation of Thermoplastic Turnpike Pit Low Water Crossing Design Report Page 5 of 6