Applied Research Associates, Inc. Contract or Grant No. TB Sponsoring Agency Name and Address Dimitroplos Supplementary Notes Prepared in cooperation with the U.
Department of Transportation, Federal Highway Administration Abstract This report documents a review of nationwide practices with regard to recommendations for fill heights over high density polyethylene HDPE pipes. Another item of interest to the investigation was typical use of HDPE pipes by various agencies.
All 50 state agencies were contacted for information, of which 47 responded. In addition, a survey questionnaire was developed and sent to selected personnel in five state agencies to gather more in- depth information. Based on this information, recommendations for maximum fill heights and recommended use of HDPE pipes in roadways were developed for consideration by the Arizona Department of Transportation.
Key Words Distribution Statement Security Classification These professionals included: roadway design, hydraulic, standards, geotechnical, and materials engineers. All 50 states were surveyed, of which 47 responded.
In addition, a questionnaire was sent to selected personnel in five states for more in-depth information on the use of HDPE pipes in their states. The most prevalent diameter sizes of pipes used by transportation agencies ranged anywhere from 12 to 48 inches in. Only a few states currently use pipes with diameters of in. Minimum heights of fill are generally in range of 1 to 3 feet ft , with 2 ft being the most prevalent.
Maximum fill heights are somewhat varied, ranging from a few feet to over 50 ft. The most widely used fill heights were 20 ft and 10 ft. In general, the larger diameter pipes have smaller maximum fill heights. The maximum depth of cover is highly influenced by the types of backfill materials used and their compactive effort 2. In all, 5 states of the 47 states interviewed use mandrel testing to detect deflection in the horizontal and vertical direction for smaller size pipes pipes sizes 36 in or smaller.
Generally, maximum deflections are specified at 5 percent. Pipe failure is defined as deflection in excess of 5 to 7. Those same 5 states use video cameras and visual inspections for larger diameter pipes. However, practices for quality control, selection of pipe sizes, installation, selection of backfill materials, and overall criteria for minimum and maximum heights of fill are somewhat varied from one state to another. Several states only allow the use of HDPE pipes as side drains or they limit their use to unpaved and low volume roads.
All pipes both flexible and rigid rely on the properly selected backfill materials for transfer of load into the bedding. Choice backfill materials such as flowfill a mixture of fine aggregate, cement, and fly ash , cement-treated aggregate, or granular backfill material have been used in place of the native soil by DOTs to improve the load carrying capacity of the HDPE pipes, to reduce the likelihood of buckling, and to achieve tolerable deflections.
Properly designed and installed HDPE pipes could provide an attractive alternative to the commonly used reinforced concrete or metal pipes. The positive aspects of using HDPE pipes include ease of installation and hauling, safety, and cost.
Potential drawbacks include buckling and high pipe deflection if improperly used. For locations that require fill heights in excess of 10 ft, more expensive pipes such as reinforced concrete pipes or corrugated metal pipes CMP are used.
The ultimate goal of this project is to develop recommendations for specifications related to allowable HDPE pipe diameters, backfill materials, and fill heights based on surveying existing transportation agency practices and pipe manufacturer recommendations. Develop recommendations on the maximum fill heights and typical usage of HDPE pipes.
In all, 47 of the 50 states contacted for information responded and provided information on their practices for HDPE pipes. The results of the individual phone interviews with states are summarized below. For states contact information refer to Appendix B. Table 5: Structural criteria for smooth interior corrugated polyethylene pipes New York Diameter Minimum.
Table Minimum cover height requirements Hancor, Inc. Calculations assume no hydrostatic pressure and a density of pounds per cubic foot?? Backfill materials and compaction levels not shown in the table may also be acceptable.
Contact Hancor for further detail. For projects where cover exceeds the maximum values listed above, contact Hancor for specific considerations. Alternate backfill materials and compaction levels not shown in the table may also be acceptable. This is a general guideline based on Table 5. Contact manufacturer for further detail.
Class I: Manufactured aggregate, open graded, clean, non-plastic. Class II: Coarse-grained soils, clean, non-plastic. Class III: Coarse-grained soils with fines, very low plasticity. Appendix A presents the questionnaire developed for this purpose. The acquired data was synthesized with respect to HDPE pipe diameter sizes, minimum heights of fill, maximum heights of fill, backfill materials, and construction quality control practices. An analysis of the acquired data on each individual item is presented in the following sections: 2.
The minimum diameter sizes ranged from 8 to 24 in. Pipes with diameters 54 to 60 in are used by few states, and are currently being considered by some states since AASHTO has recently approved their use. Generally, larger diameter sizes have higher minimum covers. The Hancor, Inc. Drainage Handbook 1 sets the minimum heights of fill cover for pipes 4 to 48 in to 1 ft and for pipes 54 and 60 in diameter to 2 ft.
PPI sets the minimum heights of fill to 1 ft for pipes that have 4 to 48 in diameters and 1. Some states specify higher minimum fill heights for HDPE pipes during construction 1 to 2 ft more especially for larger diameter pipes.
The maximum depth of cover is highly influenced by the types of backfill materials used and their compactive effort. Hawaii DOT has established comprehensive criteria for the fill heights based on the type of backfill materials and compactive effort. Table 14 and Figure 1 represent the ranges of allowable maximum fill heights by the states that were interviewed.
Over 20 percent of the 47 states 11 states interviewed have no specified maximum fill heights. Hancor, Inc. Excluding the 11 states with no specifications, nearly 74 percent 23 of the states interviewed allow maximum heights over 10 ft, 54 percent 17 over 15 ft, 45 percent 14 at or above 20 ft, and 19 percent 6 at or above 30 ft. For more details on state and industry practices on maximum fill heights, refer to Chapter 2, Section 2. Nationwide state-of-the-practice with regard to maximum pipe fill heights 2.
Mandrel testing is used by 5 of the 47 states interviewed to detect deflection in the horizontal and vertical direction for smaller size pipes 36 in or smaller. Maximum allowable deflections are specified at 5 percent.
Pipe failure is defined as deflection in excess of 5 - 7. Video cameras and visual inspections are conducted for larger diameter pipes. The goal was to acquire more in-depth information on the use of HDPE pipes in their respective states, and confirm the already provided information.
These states have been using HDPE pipes of various diameters from the early s to the early s. Backfill materials used including the criteria for maximum and minimum fill heights are primarily based on nationally available documents such as AASHTO specifications and ASTM standards and can be accessed using the Web.
Both visual and mandrel testing is used to inspect the integrity of the pipes during and after construction. The anecdotal reports on the overall performance of these pipes ranged from marginal to very satisfactory. Newer pipes seem to have better quality. These professionals included: roadway design, hydraulic, standard, geotechnical and materials engineers. So although a number of alternative treatment systems including these gravelless methods are capable of working in a smaller total square foot area than a conventional drain field, depending on what the local authorities require in spacing, more area may be required than the minimum.
For example, many states require that space be set aside to allow for future absorption line replacement in between the planned lines.
Gravelless distribution systems shall be installed in conformance with the manufacturer's instructions because of the proprietary design of some products. The essential difference between a gravelless wastewater treatment system and a conventional perforated-pipe and gravel-trench drainfield is the use of a special product to distribute and release effluent sketches above and the absence of gravel in the trench where the distribution system is buried.
The special gravelless products used are designed to avoid soil-clogging right at their surface or they would have a short life. This concern is addressed by use of special materials such as geotextiles which resist soil clogging, and by a design that provides an adequate total area in square feet for soil contact.
Each product manufacturer should be expected to provide an installation manual for the product that you are going to use. The list below is generic and incomplete as site specific and product specific details can't be provided here. Consultants or suppliers in this field can be listed at our alternative septic designers page at no charge by contacting me.
While polyethylene wrapped or peforated-plastic-wrapped plastic pipe is discussed in older no-rock septic system design manuals, the use of poly-wrapped pipe for gravel-less septic effluent disposal has, in our OPINION, been eclipsed by the use of geotextile-wrapped pipe instead.
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Apologies for the delay. Just ask us! Search the InspectApedia website. Comment Form is loading comments Robillard and Kelli S. Jantrania, Mark A. Anish Jantrania, Ph. Outstanding technical reference especially on alternative septic system design alternatives.
Written for designers and engineers, this book is not at all easy going for homeowners but is a text I recommend for professionals--DF. This comprehensive guide filled with case studies can prevent that. Master plumber R.
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