Engineers Without Borders Bridge Site Assessment in Bolivia

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Clement Gilbert
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1 Engineers Without Borders Bridge Site Assessment in Bolivia Focus on Engineering Data Patrick Ye, Matt Ball, Ben Gagne, Russell Glorioso, Thomas Grothe

2 Background The idea of building a bridge in Bolivia began with Dr. Christine Beaule, my freshman year Writing 20 professor. She mentioned that the village near her research site, Condor Chinoka, desperately needed a bridge to cross the village-dividing river during the rainy season. As a member of the Engineers Without Borders chapter at Duke, I suggested that we go to Condor Chinoka and perform a site assessment to determine whether we could build a bridge and help their community. During the site assessment, we hoped to find out what material and labor resources are available locally, research the impact of this bridge on the community, and collect engineering data for designing the bridge. Thus, in May 2008, a team of five engineering students and Dr. Beaule traveled to Bolivia and successfully returned with data. Figure 1: The travel team. From left to right: Thomas Grothe (Pratt 10), Stephanie Chang (Pratt 11), Tom Hadzor (Pratt 09), Ga-Young Joung (Pratt 11), Dr. Christine Beaule, Matt Ball (Pratt 10), Patrick Ye (Pratt 10). Tom was unable to come with us to Bolivia.

My specific focus as a member of the travel team was to collect engineering data. Our team surveyed five river crossings: one each in Iruma, Jachuma, and Condor Chinoka, and two in Obrajes.

3 My specific focus as a member of the travel team was to collect engineering data. Our team surveyed five river crossings: one each in Iruma, Jachuma, and Condor Chinoka, and two in Obrajes. With the help of Matt Ball and Thomas Grothe, we used a theodolite to survey river cross-sections and banks. With these numbers we can calculate the cross sectional area of the riverbed and figure out the best place to build a bridge. Also, we utilized a dynamic cone penetrometer to measure the soil bearing capacity. This data will help determine whether the soil can support a bridge. Methodology: Surveying For each river crossing, we performed three cross-sections: one near the road, one up to 50 feet upstream and one up to 50 feet downstream. We used nylon string and rocks to mark where we wanted to take riverbed data points. The string ensured that the points were collinear and perpendicular with the flow direction, and the rocks were placed at significant points of the riverbed shape. Along with points in the riverbed, two permanent benchmarks were taken for each river crossing. One person held the measuring rod at each rock, and one person read measurements by looking through the theodolite. Sometimes, another person assisted with the recording of the measurements onto paper. After taking Figure the 2: three Rocks cross-sections, on nylon string we measured used to mark surveying data points. Photo credit: various points along the riverbanks to obtain the general Patrick shape Yeof the river near the crossing.

4 Figure 3: Surveying in action. Thomas is holding the rod, and Patrick is reading the rod through the theodolite. Ga-Young is recording the numbers on paper. Photo credit: Stephanie Chang

5 Methodology: Cone Penetrometer We used a dynamic cone penetrometer lent to us by Trigon Engineering, a geotechnical engineering firm in the Triangle area. First, we dug holes about six inches in depth to remove the top layer of accumulated sand and dirt and six inches in diameter. The cone penetrometer is placed in the center of the hole, and the distance the instrument sinks into the ground just from its weight is recorded. Then, the doughnut-shaped hammer is raised and dropped until the cone penetrometer sinks to six inches, and the number of blows to reach this depth is recorded. This is repeated for twelve inches and eighteen inches until a hundred blows is reached. About five holes were dug in the river and one to two on the riverbank, unless it is clear that the soil is impossible to drill through because of rock. Figure 4: Diagram of the dynamic cone penetrometer that we used. Source: George F. Sowers and Charles S. Hedges, "Dynamic Cone for Shallow In-Situ Penetration Testing," Vane Shear and Cone Penetration Resistance Testing of In-Situ Soils, ASTM STP 399, Am. Soc. Testing Mats., 1966, p. 29.

6 Figure 5: Thomas using the cone penetrometer in Iruma. Photo credit: Patrick Ye Data: Surveying Using Matlab, Matt plotted cross-sections of the riverbed as well as a bird s-eye view of the cross-sections and the riverbanks.

7 Iruma

8 Jachuma

9 Condor Chinoka

10 Obrajes 1

11 Obrajes 2

12 Data: Cone Penetrometer Abbreviations: SD starting depth, N# number of blows to go # inches in depth, TD total depth, TG Thomas Grothe, MB Matt Ball, NA not applicable, rd - road Iruma # Location User SD Sink N6 N12 N18 TD Description and Notes 1 River, middle TG Dry soil, pebbly. 2 River, middle TG Very soft, firmer/clammier 3 Bank TG NA 19.5 Very hard sandy max depth 9 4 River, middle MB Moist soil 5 River, middle MB Same as Iruma 4 6 River, middle MB Same as Iruma 4 7 River, middle MB Sandier soil than Iruma River, middle MB In line with 2 nd cross-section Jachuma # Location User SD Sink N6 N12 N18 TD Description and Notes 1 River, middle TG Sandy, muddy for last 7 2 River, middle TG Same as Jachuma 1 3 Closer bank TG Same as Jachuma 1 4 Close to bank TG Rocker, 13.5 mud 5 Bank near rd TG NA NA 14.5 Compact, max depth Oppos. Bank TG NA 45 Rocky, dry, max depth 16 Condor Chinoka # Location User SD Sink N6 N12 N18 TD Description and Notes 1 River near rd TG NA NA 16.5 Sandy/pebbly, max depth River near #1 TG NA NA NA 8.5 Layers of rock, max depth 2 Obrajes 1 (Hot Springs River) # Location User SD Sink N6 N12 N18 TD Description and Notes 1 River, middle MB NA 19.5 Wet, pebbly, max depth River, middle MB NA 22 Same as #1, max depth 16 3 River, middle MB Same as # 1, groundwater 3 4 Bank MB Er Dry, sandy bank, repeated #5 5 Bank MB Same as #1-4 6 Riverbed MB NA 22 Moist, max depth 16 7 Riverbed MB NA NA 17 Same as #1-6, max depth 11

13 Obrajes 2 (Río Iruma) # Location User SD Sink N6 N12 N18 TD Description and Notes 1 Bank by road TG NA NA 6.3 Packed sand, max depth Bank by road TG NA 21 Sandstone, max depth 14 Sites notes: The riverbed here consists entirely of sheet rock drilling is futile. Instead, the depth of the mud covering said sheet rock was measured all over the crossing area. Analysis The next step towards building the bridge is the analysis of the data for designing the bridge. Engineers Without Borders analyzed the data back at Duke to determine the spans and depths of the crossings as well as the toughness of the soil near the crossing. These values will be used to help determine which crossing site is best for building the bridge. Analysis: Surveying Table 1: Spans and depths of each crossing. Calculated by Ben Gagne (Pratt 11) Crossing Name Span (ft) Maximum Depth (ft) Average Depth (ft) Condor Chinoka Iruma Jachuma Obrajes I Obrajes II

14 Analysis: Cone Penetromter Graphs of cone penetrometer results. Made by Russell Glorioso (Pratt 12) Blows/In Avg Blows/In Avg River near rd River near #1 Figure 6: Condor Chinoka. The soil became impossible to penetrate after a depth of 16.5 inches Blows/In to 6 Blows/In to 12 Blows/In to 18 Blows/In Avg 0.0 River, River, middle middle Bank River, middle River, middle River, middle River, middle River, middle Figure 7: Iruma. The soil is soft and sandy in the river but is harder on the bank.

15 Blows/In to 6 Blows/In to 12 Blows/In to 18 Blows/In Avg 0.0 River, middle River, middle Closer bank Close to bank Bank near rd Oppos. Bank Figure 8: Jachuma. Similar results as Iruma Blows/In to 6 Blows/In to 12 Blows/In to 18 Blows/In Avg River, middle River, middle River, middle Bank Bank Riverbed Riverbed Figure 9: Obrajes I. Similar results to Iruma and Jachuma, although the bank is less sturdy.

16 Bank by road Bank by road Blows/In to 6 Blows/In to 12 Blows/In to 18 Blows/In Avg Figure 10: Obrajes II. The soil is composed of sheet rock, and drilling was futile. Conclusion When we were applying for the Mellon Undergraduate Award, we thought we would find nine villages, and that, barring any major circumstances, Condor Chinoka would be the most likely place to build the bridge. Once we arrived in the Obrajes valley, we quickly realized we were mistaken. First, we found only four communities, not nine. There wasn t one single valley but two. And each community needed at least one bridge. The project adapted to this different-than-expected situation by changing its scope. For engineering, we decided to measure at least one river crossing in every community. As a result, we have collected plenty of data, but now we have to the responsibility of choosing which site would be best suited for a bridge. We will have to consider not just the engineering logistics but also where the bridge can have the most impact for all the communities. Looking back, this site assessment was quite an adventure. Practically nobody spoke English; my Spanish language skills came in very handy. Being able to actually go out into the

17 field and take engineering data was an enjoyable hands-on application of what I ve learned in my classes. I hope that, someday, we will be able to return to Bolivia and build a bridge. Acknowledgements I would like to thank the Center for Latin American and Caribbean Studies for awarding me a travel grant and thus enabling me to complete this study and have a great learning experience. Also, Dr. Christine Beaule was an invaluable mentor who helped us adjust to Bolivia, meet community members, and get us established to do our research. Dr. David Schaad, associate professor of civil and environmental engineering, helped us tremendously with understanding the engineering aspects of the site assessment. Thank you to my fellow site assessment travel teammates for making the site assessment trip enjoyable. Ben Gagne and Russell Glorioso, new members to the EWB Bolivia team, performed almost all of the engineering data analysis in the report. Also thanks to Trigon Engineering for lending us the cone penetrometer.

Field Instruction. This instruction applies to Horizon Power employees and contractors involved in Horizon Power s underground projects.

Field Instruction. This instruction applies to Horizon Power employees and contractors involved in Horizon Power s underground projects. 5.23 Soil Compaction Testing Requirements Purpose This instruction has been developed to support projects where the reinstatement and compaction of soil is required following an excavation. The purpose