Yearly Archives: 2014

Impervious Gravel vs. Porous Aggregate Paving Systems

Written by William G. Handlos, P.E. For two decades, I held the position of City Engineer and frequently had to explain to disbelieving homeowners, developers and elected officials – that gravel driveways and parking lots were not porous. I would explain that for purposes of stormwater runoff, such gravel pavements must be treated exactly as we would concrete and asphaltic pavements. They often bristled at the idea that gravel did not percolate water and were upset to find that their gravel driveway, lots and roadways were assumed to shed 100% of rainwater. So it is with more than a dose of irony that I now have found myself in the position of regularly explaining to local and state officials that aggregate pavements are not necessarily impervious. Stakeholders are so accustomed to repeating the impervious gravel mantra…that they forget to notice that porous aggregate is not the same thing as gravel. I think it is best to start with a primer on the vernacular. A “good” gravel (Image 1) should have 40 to 70% stone, well-graded from 1/4” to 2-1/2” diameter; 20 to 50% sand; and 10% +/- fines. It should resist abrasion, shed water and be capable of being compacted. A… Read more »

Porous Pavement Systems in Extreme Weather

Written by William G. Handlos, P.E. Porous Pavements Customers are always coming up with new applications for our GEOBLOCK® Turf Protection System, but the University of Wisconsin-Madison just took it to another level. In early 2014, their Space Science and Engineering Center purchased the GEOBLOCK® pavers to aid in staging their ice coring drills in Greenland and Antarctica. The GEOBLOCK® system was utilized for two specific applications. The first was for a footer under the frame of the drill tent(s). This application allowed the weight of the drill tent building to be distributed across the snow’s surface and provide support. Due to the GEOBLOCK® system’s rigid design and load transfer tabs, the same characteristics that make it a strong, durable turf protection system, also delivered value over snow. In the second application, the GEOBLOCK® units served as a flooring system inside the drill tent. Researchers liked the grid surface as it provided a non-skid surface and easy installation at sub-zero temperatures (-40°F). The rigid design also wasn’t affected by on-site drilling fluids (due to the non-reactive and inert polyethylene construction). Researchers also capitalized on the light-weight design and reusability. The remote location required air-lifting the material and hand construction. The… Read more »

The Market for Lightweight Construction Mats

Written by William G. Handlos, P.E. Lightweight Construction Mats Construction access in soft soils present a common challenge engineers and project managers face while attempting to complete a project on-time and within budget while avoiding scheduling delays and associated costs. These soft soil sites may also be located in remote, difficult to access areas making construction impossible without a good site access system. Popular construction mat systems are made out of a range of materials including timber, laminate, steel and composite mats. They can be effective, but are also costly. They can also put laborers at risk as they require heavy equipment to install. The ideal mat system for access road construction would be designed to have a high utility-to-weight ratio and would deliver an eco-friendly alternative to current technology. A lightweight construction mat system made from high density polyethylene (HDPE), GEOTERRA®, was created by Presto Products in 2003 to meet the needs of major oil and gas companies working in remote areas of the Amazon jungle. Transporting materials to these sites by helicopter precipitated the need for light, yet strong mats for work platforms and roadways. As the first of its kind, the mats capitalize on the sustainable characteristics of… Read more »

The Dangers of Breaking Specs and Bid Shopping

Written by William G. Handlos, P.E. Specifying Engineers and Architects work tirelessly to build plans and specifications that capture the essence of their vision as they work to write the guiding documents for their project. They make decisions about product types, grades, and take great pains to build into their documents citations of certifications and standards to assure only quality materials are allowed on the site. Yet, when challenged to accept “or equal” substitutions, it seems that all the standards of care can sometimes be lost and substandard materials seem to too easily find their way onto the site. The reason for this lapse is often a result of the timing of the hand-off between the design team and the project management team occurring just as the contractor award occurs. Contractors are concerned about leaving too much money on the table (the difference in value between the winning and the second bid). Just moments after the bid opening or notice of award, bid shopping commences. Bid shopping on publicly-funded projects is disallowed by legislation in some localities, but even when formally disallowed, informally it occurs widely. With the economic power of the project award and with the pressure of the potential… Read more »

Highway Stormwater Control: Porous Vegetated Road Shoulders

Written by William G. Handlos, P.E. Highway Stormwater Control: Porous Vegetated Drivable Road Shoulders Gravel road shoulders are not porous. Rainwater sheet flowing off highway pavement passes right across the aggregate shoulder carrying with it sediment and other pollutants that ultimately end up in freshwater creeks and rivers. Aside from pollutant loading, re-grading shoulders is a continuous activity for State and County crews to repair eroded sections after several rain events. Some counties have taken a smart solution approach to this problem and are using geocell cellular confinement systems to reduce maintenance costs and to improve water quality.  Shown below are the cross sections detailing a GEOWEB® geocellular drivable vegetated shoulder solution. The infill to the geocell is made up of 2/3rd clear stone aggregate (void ratio 30 – 40%) and 1/3rd topsoil. The topsoil remains uncompressed within the interstitial spaces between the stone, and the stone is the structural component that carries the load. The topsoil allows for the vegetation roots to grow and feed upon the nutrients and water in the topsoil.  This system percolates runoff from the highway while offering proper load support for vehicles that pull off the side of the road. The GEOWEB® cells confine the… Read more »

Distributors Add Value to Geosynthetics

Written by William G. Handlos, P.E. As a manufacturer of specialty engineered geosynthetics, Presto Geosystems markets and sells through a worldwide network of geosynthetics distributors and representatives.  Why?  What value does a network bring?  The decision to work through distribution is driven by the value that the network brings and is reinforced by the success of this model over thirty years of operating experience. Now and then, the model is challenged.  Contractors sometimes see the distributor as a non-essential layer of cost.  But, take a closer look and see how a well prepared network adds value to both the manufacturer, the contractor and most importantly…..to the project owner. It would be impossible for each geosynthetics manufacturer to maintain a sufficient workforce to cover the US, much less the world market.  Distributors function as a sales and service cooperative – shared by all manufacturers for whom the distributor represents.  Distributors vary in the number of manufacturers they represent.  But, it is not uncommon for the local distributor to carry dozens of products from 6 to 10 manufacturers. Engineers and Architects as well as contractors benefit from local trade shows and educational presentations sponsored by informed product salesmen who are known and trusted… Read more »