The Challenge

During the site assessment, the EWB team quickly recognized a major obstacle that needed to be met in the first phase of construction.

More than 50 large boulders, ranging up to 6 feet in size, blocked the most suitable route for the new street.  The composition of the boulders was identified as predominantly andesite, which has a hardness rating comparable to granite. 

Moreover, the terrain in the vicinity of the proposed street, together with space constraints and lack of vehicle access, ruled out the use of large equipment or heavy air compressors to break or move the boulders.  Removal would need to be accomplished by manual labor, meaning the boulders had to be reduced to pieces that could be lifted and moved by hand.

Further complicating matters, the route for the street is in close proximity to the homes in the Las Pilitas neighborhood.  For the comfort and safety of the families, the EWB team agreed that conventional blasting was not an option, due to safety concerns.

In addition, the volunteer team hoped to develop a low-tech method for boulder demolition and removal that the residents of Las Pilitas could continue to perform independently after the EWB team completed their one week return trip to San Pedro Puxtla.

The Solution

The EWB team turned to Ohio Power Tool in Columbus for advice on how to achieve the rock demolition.  When EWB decided to use plug and feathers to safely break the boulders into manageable pieces, Ohio Power Tool recommended the Bosch 11241EVS 1-9/16-inch SDS-Max Combination Hammer Drill to best meet the challenge of drilling the necessary 5/8-inch diameter holes in the rock.  At only 16 pounds, the Bosch 11241EVS rotary hammer drill delivers 6.2 ft. lbs. of impact force, enough for drilling 5-inch deep holes into the hard rock in less than a minute.  The vibration-dampening handle reduces vibration up to 40%, making drilling for extensive periods more comfortable for the user.

A product demonstration was held in Columbus in March 2009, giving the project team an opportunity not only to see the Bosch hammer drill in action but also to become familiar with the techniques they would need to accomplish the demolition on-site in El Salvador.  Two boulders, each approximately 2-1/2 feet in diameter, were utilized in the test – one a hard granite, the second a dense sandstone.  Six 5/8-inch diameter holes were drilled in each hole across a plane where the rock was to be split.  The 5-inch-deep holes, spaced at 6 inches on center, were each drilled in less than a minute.  After drilling, a plug and feather set was placed in each hole and struck with a mini-sledge hammer in sequence until the rock split.  The plug and feather sets place a tensile force on the rock and are capable of splitting extremely hard rock up to 6 feet in diameter.

Following the success of the product demonstration, Ohio Power Tool provided the EWB team with two Bosch 11241EVS drills at a reduced cost for use at the El Salvador project site.  In addition, Ohio Power Tool donated twelve 5/8-inchdiameter drill bits.  Two drills were to be utilized simultaneously at the project site to increase the speed and efficiency of the boulder demolition.  It was estimated that over 1,500 holes would need to be drilled in order to complete the demolition.

“We were very optimistic about the success of the boulder demolition in the Las Pilitas community,” said Amanda Engle, project manager for the Las Pilitas roadway project.  “The Bosch hammer drills are comfortable, easy to handle and have more than enough power to perform the drilling operations quickly and easily.  Due to the success of our demolition tests stateside, we were confident the method would be well received by the community members performing the labor.”

The Result

The Central Ohio Professionals chapter returned to San Pedro Puxtla in April 2009 for one week to work side-by-side with the local residents to demolish the rocks.  After only a couple of demonstrations with the plug-and-feather technique, the residents were working on their own to break the rocks.  Two workers operated the two Bosch 11241EVS 1-9/16-inch SDS-Max Combination Hammer Drills, while the remainder of the labor force placed plug and feather sets and split the rocks.  With extension cords, the drills could be used in tight spaces that were not accessible with heavy equipment.

 As predicted, each hole took less than a minute to drill, and a team of 5 men completed the required rock demolition in only 10 working days.  The Bosch hammer drills performed flawlessly, even when run continuously for hours at a time.  The manageable weight and shock-absorbing handle ensured that the workers could work 8-hour shifts without experiencing significant muscle fatigue.

“We are very glad that EWB supplied us with these drills and helped us acquire new skills that will empower us to improve our community,” said local project supervisor and Las Pilitas resident, Don Jose Angel.

The project could not have been completed without the advice and assistance of Ohio Power Tool and Bosch equipment.  The equipment donated by Ohio Power Supply and Bosch saved the EWB team nearly a thousand dollars in equipment purchase or rental.

The next phase of construction, tentatively planned to begin in November, will include the strategic placement of retaining walls, fill material and drainage structures to support and define the future road bed. 

“After many years of being separated from San Pedro Puxtla, the residents of the Las Pilitas neighborhood are closer to realizing a dream, thanks to combining their own hard work with the donations from Ohio Power Tool,” said Engle. “We were pleasantly surprised to see the boulder demolition accomplished with no blasting, no dust and no danger to the neighborhood children or others residents.”

About Engineers Without Borders

The activities of EWB-USA range from the construction of sustainable systems that developing communities can own and operate without external assistance, to empowering such communities by enhancing local, technical, managerial, and entrepreneurial skills.  These projects are initiated by, and completed with, contributions from the host community working with our project teams.

Central Ohio Professionals chapter of EWB-USA was established in 2007 in partnership with student chapters at The Ohio State University and Ohio University.  In addition to the San Pedro Puxtla project, the Central Ohio Professionals chapter is also in the initial phase of a project to provide potable water sources for the people of Batoula, Cameroon.  For more information, visit www.ewb-usa.org and www.ewbcoh.org.

About Ohio Power Tool

Ohio Power Tool is located in Columbus, Ohio, (1042 Dublin Rd by Grandview Ave) and provides sales, service and rental of power tools and equipment around the world.  They are a factory authorized service center for all major brands, specializing in air, electric and hydraulic equipment.  The company has grown steadily because of the unique customer service they can provide in determining the right tool for any application.  Contact Ohio Power Tool at 800-242-4424 or visit them on the web at www.ohiopowertool.com.