If You Give a Mouse a Cookie

There’s a well-known children’s book titled If You Give a Mouse a Cookie that I had the pleasure of sharing with my children as they were growing up. For those of you who have not had the delight of reading this tale over countless evenings (and years!), it deals with a very resolute rodent intent on improving his lot in life by actualizing the law of cause and effect. For ac- cording to this pre-school primer,“If you give a mouse a cookie, he’ll want a glass of milk.”

What made me think about this timeless tome is that it provides an almost historic synopsis of, and continuing relationship between, the high-density polyethylene (HDPE) pipe industry and the trenchless technology industry.

Although HDPE pipe has its origins in the late 1950s and trenchless installation techniques came around in the 1970s, the two found each other when gas utilities began installing 1- to 2-in. distribution lines using horizontal directional drilling (HDD) in the early 1980s. HDPE’s inher- ent properties, such as flexibility, durability and ductility, provided trenchless contractors a versatile material that accentuated their ability to quickly and economically in- stall gas lines, especially in tight urban settings. So if that was the cookie, what was the glass of milk?

Sections of HDPE pipe are fused together providing a totally leak-free, monolithic pipe string. With the fast installation times available using trenchless techniques, the fusion time started to become an issue. Responding to requests to make longer lengths of pipe, and thus lower the number of joints, the HDPE pipe manufacturers took advantage of the HDPE’s flexibility and began providing large reels of pipe thousands of feet long. Contractors were ecstatic when the need to fuse lengths of pipe was significantly reduced.
In the book, our mouse friend soon finds himself in need of a napkin (cookie crumbs), followed by a mirror (to check for a milk mustache), then scissors (to trim his whiskers after seeing himself in the mirror), a broom (to sweep up the trimmings) and so on.We saw that same scenario played out once the trenchless contractors discovered the versatility of HDPE pipe. No longer satisfied with just installing small diameter gas distribution lines, they wanted to expand into main lines in both gas and water.

Just like the young lad who continually matches the mouse’s progressive requests, the HDPE pipe industry looked for ways to satisfy the burgeoning demand for larger diameters of coiled pipe. Soon, spools of 4-, 6- and 8-in. diameter pipe were being delivered to jobsites, allowing the installers of water and sewer mains to take ad- vantage of this most efficient installation practice. Other equipment manufacturers stepped up to the challenge by building bigger and more robust boring machines and developing tools to help reround pipe that was somewhat flattened when put on the large wheel hubs. Ultimately, not only were contractors happy with this development, but municipalities were as well. No longer were streets having to be torn up and then resurfaced, causing finan- cial and motorist angst.Today, reels nearly 3,000 ft long of 12-in. diameter HDPE pipe can be supplied to the trench-less contractor. By now I’m sure you guessed, just as our young lad found  By Tony Radoszewski out, it didn’t stop there.

Although the ability to wind larger diameters of pipe necessarily finds a limit, the desire to install even larger sizes of pipe continued to grow. Soon civil engineers and contractors wanted to push the limits of trenchless in- stallations and over time the necessary designs and skills were developed to put in 24-in., 36-in. and larger diam- eters. But a new question surfaced: How far can we pull the string of pipe? Once again, the HDPE pipe industry rose to the challenge.

Design of the proper pipe for trenchless installations takes many variables into consideration, including soil types (rocky, gravelly, loose, hardpan, etc.), soil strength, soil stability, soil pressures and other factors, including water tables and groundwater pressure.Added to that is the pullback force and the drill path of the overall installation. To address these issues, the HDPE industry devel- oped ever higher performing resins (such as PE 4710) and appropriate wall thicknesses to be able to manage the various forces bore paths encountered. With an ex- ceptional cold bend radius (25 x outside diameter), HDPE pipe can adapt to challenging site conditions. Countless hours have been dedicated to the development of guide- lines that can be found in the Handbook of Polyethylene Pipe, available online at www.plasticpipe.org. Also, you will find the PPI BoreAid software that can aid in the design process of complex calculations for trenchless applications of PE pipe.

To give you an example of how far our industries have developed, trenchless contractors successfully pulled a 1,400-ft string of 54-in. polyethylene conduit that contained 16-, 20- and 24-in. pipes for an inverted siphon and a 14-in. reclaimed water line. The initial pullback force was 370,000 lbs. And as noted in the October issue of Trenchless Technology, a 44-in. diameter crossing housed a duct bank consisting of seven 10-in. HDPE ducts, five 4-in. grout pipes and one 5-in. grout pipe. This assembly weighed in at 342,000 lbs and was pulled through the heart of downtown Vancouver, British Columbia.

Collaboration among a lot of smart and dedicated people has brought tremendous benefits to our cities and the population at large. Today, trenchless installations of HDPE pipe are commonplace in the gas, water, sewer, communication and electrical utilities, along with other chemical and industrial lines.And with the advent of 98- in. diameter HDPE pipe, I am convinced our abilities to meet demanding circumstances are only limited by our imagination.

So, the next time you “give a mouse a cookie,” don’t be surprised where you may ultimately end up.

Tony Radoszewski is the executive director of the Plastics Pipe Institute Inc., a North American, not-for-profit organization that is the major trade association representing all segments of the plastic piping industry and provides educational sessions, materials and expert testimonials.
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