Map

Bridge Project Team Members:

Amy Curtis – Project Manager, Civil Engineer
Michael Kalisz – Civil Engineer
Jeremy White – Civil Engineer

The beautiful Dominican countryside.


Current river crossing at low river level.

Suspended Bridge Project, International Senior Design, Dominican Republic

CE 4905 Senior Design Summer 2004
Slide Show Scenes of 2004 Projects

Introduction
The bridge project is a result of the international senior design project at Michigan Technological University. Every year, two teams of 12 students and their fearless leader Linda Philips, travel to the Dominican Republic or Bolivia for 2 weeks to work on senior design projects and gain cultural and foreign construction experience. This year the Dominican senior design was broken down into 3 groups. 2 groups designed a spring water distribution system, while the third group designed a suspended bridge for crossing a river when flooded. The bridge group consisted of project leader Amy Curtis, and team members Michael Kalisz, and Jeremy White. Surveying, data collection, and preliminary design took place in the villages of La Vereda and El Cercado, Republica Dominicana. Final design and report preparations took place at Michigan Tech with the aid of its resources and professors.

Problem Statement
Upon arrival in El Cercado, our team was met by MTU Masters International student and Peace Corp volunteer for the area, Lyle Stone. Lyle presented the bridge team with the problem facing the people of La Verada and the surrounding villages. Every spring during the rainy season, a major river to the area becomes heavily flooded and completely impassable for miles around. The high waters prevent the people of La Vereda from going to a large spring, which is one of the few sources clean water in the area, and the people from the neighboring pueblos from crossing the river into town in order to get supplies and have access to a paved road and transportation to medical facilities. This leads people to try and cross a dangerously swollen river in order to get their basic needs met.

Background
The Dominican Republic (La Republica Dominicana) is located south of the United States in the Atlantic Ocean. It shares the Island of Hispaniola with Haiti, occupying the eastern portion of the continent. The country is divided into provinces, much like our states. The site of this project is located in the village of La Vereda and the province of San Juan, which is found at the south central portion of the Haitian border. The largest nearby pueblo, the equivalent to what we call a town, is El Cercado, where the design teams were housed. The northern end of the island of Hispaniola lies on the borders between the North American and Caribbean tectonic plates. This fault zone is quite active today providing earthquakes as recently as a magnitude 4.4 on September 4, 2004. Hispaniola has a high rate of erosion runoff which deposits many alluvium soils in the valleys and along the rivers of the Dominican Republic. The region where La Vereda is located is situated in one of these alluvial plains. Alluviums consist of clays, silts, sands and gravels that are carried along by rivers and deposited along its banks where ever the river flows. With the rivers continually flooding and the severe erosion of the country side, most of the soils left in these valleys are incredibly high in clay content. The area of La Vereda and the surrounding villages are supported mainly by farming. The local economy is poor with a strong dependence on crops for food and family income. Farming is mostly subsistence in the area of La Vereda, but is not sufficient to support a family. Small amounts of surplus are sold at local markets for income. Additional wages are earned through jobs in El Cercado and Los Conucos. Jobs are found in places such as the hardware store, markets, and other farms.

Flood damage to local bridge after a minor flooding.

Mike testing the soil on the river bank.


Jeremy measures the river depth.

Site Analysis
Three different crossing sites were visited and analyzed based on the characteristics of each site. The sites were graded by soil quality, bank stability, accessibility, and river location stability. The most important and highest risk criteria is river location stability. These rivers are small, but become incredibly fast and powerful during flood season. With highly erodible soils, this leads to a lot of meandering rivers that constantly change course. The bridge foundations must be placed such that they will be free from river erosion and have a stable foundation for at least 20 years. Accessibility was a very important characteristic to consider because if the bridge was to far out of the way, the Dominicans would probably not use it at all, and if the path to the bridge was not stable and safe, there would be fewer people willing to venture to the bridge to use it. Finally the soil quality and bank stability are the important factors to help keep the bridge lasting 20 plus years. The soil has to be strong enough to hold the weight of the abutments, and the bank has to be stable enough to prevent large amounts of erosion which could lead to failure of the bridge abutments.

An in depth site analysis was done for two of the three sites. The third site was rejected outright due to it’s high chance for river relocation which would probably undermine any attempts to build a bridge in that location. The first site presented an excellent view of the soil layering in the area. There was a 6’ vertical cut in the bank of the river that showed alternating layers of rock and soil. Soil testing was performed on the bank using a pocket penetrometer, and Torvane shear tester. Soil was tested at varying depths and on both sides of the bank. Profiles of the site were drawn up and a rough flow calculation at the site was taken using a 2 ½ gallon plastic bag. The bag was submerged empty, and airless, then the bag was opened and timed until it was full. This was performed to give a rough estimate of flow through the river channel.

This site was ultimately rejected due to being placed only a few feet upstream from a 90 degree bend in the river and very bad accessibility. It was not known how much the path of the river would change in the coming years, but since it was so close to an open corner, it was decided that the risk was too much. And to top things off, the path to the site was through a rice field which meant the trail was just a bunch of mud and fertilizer with frequent irrigation ditch crossings that made travel difficult without any loads. It would have been an unpleasant trip for the women carrying upwards of 7 gallons of water along the trail. So the second site was ultimately chosen.

The stream depth at low flow conditions was measured at 15” along the main channel where the bridge crossing was proposed. This showed us where the center of the river was, and where we needed the most base clearance for any trees or debris floating down river during a flood.
The river crossing was measured to be 70 ft from bank to bank using a measuring tape. One of the biggest design issues is the fact that the opposing river banks are differ in height from 15ft above water level to 5 ft. This meant either a tower would need to be created to even the heights out or an angled bridge would need to be constructed. Either choice would prove to be a challenge to design and build.

The first step after choosing the optimum site was to survey the proposed site and create a bridge profile based on the current stream height and river bank elevations. Surveying in the Dominican Republic was a little primitive by today's standards, but was more then effective enough to provide an accurate layout of the site. The survey crew consisted of a three person team, an Abney level and a 100’ tape measure. The person with the tape measure walks out a distance until the shooter with the Abney level was able to sight in on a feature of the other persons face. This height of the facial feature and Abney level from ground were recorded. For our survey, it was the base of the measurers nose and upper lip. The vertical angle to the measurers facial feature and distance from the shooter to measurer were recorded. A straight line along the bridge centerline was eyed and shot using this method both backwards and forwards. By combining the heights, angle of sight, and distance measured, an accurate horizontal and vertical profile was established.

Site 2 Surveying: Mike Shoots to Jeremy with the Abney level, while Amy records.

The second site visited was located along a well traveled and dry dirt path, which solved our accessibility problems. The site was offset about 800 ft. from the main road through La Verada, which added to the convenience of the location. The soils were tested again, and the results ended up a little higher then site one which helped us further decide on this site. The location of the abutments would be approximately 150 ft downstream of a slight bend in the river path, which concerned us at first. A more detailed look at the river path showed that both sides of the river were heavily vegetated and though there were some signs of erosion, it was apparent that the river had been on this present path without much meandering for quite some time. The bridge site was located near the beginning of a nearly ¼ mile long straight stretch of the river. The river banks were both overgrown with trees up to 15” in diameter that grew straight up with no major bends in the trunk suggesting that the banks hadn’t been eroded away beneath the trees and that the trees started growing in the same spot as they now occupy on the bank. This satisfied our bank stability criteria by proving that the bank hadn’t moved more then a few inches in at least 10 years.

Planning and design started immediately after all the testing and surveying was completed. Lyle Stone and Father John Cervini of the local catholic church assisted in helping to compile a list of requirements that the bridge would need to meet in order to serve the public interest of the people of La Vereda. The requirements were to allow a bridge wide enough so 2 people could pass side by side, the bridge would need to be stable so as to not sway when people walked upon it and cause them to loose their balance, a way to provide a handrail system that connected to the walkway is a way to prevent anyone from falling into the river below, and if possible, be able to handle the weight of a medium sized cow or burro in case the locals needed the animals to help transport goods or people in need of medical treatment.

Design
Most of the design ideas and procedures came from a book in the MTU Library, entitled “Survey, Design, and Construction of Trail Suspension Bridges for Remote Areas”. Inside this book listed proven methods for calculating cable sag, abutment size and amounts of materials based on bridges that had been built in southern Asia. This book was a most valuable resource along with other textbooks and the help of many MTU professors, such as, Stan Vitton, William Bulleit, George Dewey, Bogue Sandberg, and our beloved senior design professor, Linda Philips.

The design was split up into three parts. Amy Curtis was responsible for calculations of cable sag, effects of temperature on the steel, tension and cable design, and connections design. Mike Kalisz was responsible for the profile drawing of the bridge in AutoCAD, slope protection, walkway plank design, and initial specifications. Jeremy White was responsible for the foundation analysis, anchorage design and gabiones design.
The full design process started upon return to the United States with all three team members located at least 7 hrs apart from each other for the duration of the summer and fall design period. Work was shared and distributed through many e-mails, instant messages and phone calls. The ability of the team to overcome such a large distance obstacle showed our determination to see this project through to hopeful construction in the spring of 2005.

Dominican concrete mixers

Amy and Linda working on cable design.	Father John Cervini, whom without his help, these projects in the Dominican would not be possible.

Along with the calculations for the bridge design itself, many other logistical problems arose. The design needed to be flexible enough to adapt to the changes of the building site one year after the initial survey. The bridge had to be designed to be able to be built in under 14 days. That includes excavation, concrete pouring, plank assembly cable tensioning and anchoring and final assembly.

The main goal of the design was to be as simplistic as possible, yet still be able to meet strength and dimension requirements. Another problem that had to be solved through design was the height difference of the two river banks. With the lower bank being only 5 ft above the river height, it was impossible to have the bridge at an incline and still meet freeboard requirements for clearance underneath the bridge. A creative solution was devised using the Survey, Design, and Construction of Trail Suspension Bridges for Remote Areas book. A wooden tower will be constructed on top of the lower bank’s abutment and will bring the bridge level with the higher bank in order to create enough clearance underneath the bridge. A set of stairs will be built leading up to the tower. The only problem with this design, will be that the animals will probably not be able to be brought across the bridge now as they would have a hard time climbing up and down the stairs. One cost saving measure will be to use boulders from the river as ballast in the abutments. The rock will greatly reduce the amount of concrete needed, thereby saving a lot of money and time. Also, the slopes will be grown with native plants as part of the slope protection, and will hopefully be able to inspire some locals to think more environmentally in order to reduce the severe soil erosion problem in the country.

A bridge is needed in the village of La Vereda over the Rio Valle Juelo. It is necessary to protect the men, women and children from death due to floodwaters that occur during the annual rainy season. This river has proved to be fatal, just as many just like it during the floods of June 2004. The loss of life and supplies can be prevented through the construction of a suspended bridge. The bridge will be constructed of ¾ inch stainless steel wire rope and connections, 2” x 6” x 4’ timber floor planks, a timber tower, concrete and rebar anchorages, native cobble bank protection, and trench slope protection. Material cost of the bridge reaches a total of $3900 before donations. An additional cost of approximately $7,000 is required to fund travel and living expenses for the designers that will be necessary on site for anchorage placement and construction aid. Sources for these funds will include both material and financial donations.

We would like to thank, John Cervini, Linda Philips, Lyle Stone, Matt Niskanen, Dr. Robert Baillod, Dr. Stan Vitton, Dr. William Bulleit, Dr. George Dewey, Dr. Bogue Sandberg, and Loos & Co.

© 2004 Michigan Technological University
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