1 st International Conference

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1 Bridge Slope Stability Probabilistic using Applied Deformation Analysis 1 st International Conference Geoscience for Energy, Mineral Resources, and Environment applieds 2014 Agus Wiramsya Oscar 1,2 1 PT. Sekawan Anugerah Sejahtera / PT. Komunitas Bangun 2 Ph.D Student Faculty of Geology, UniversitasPadjadjaran (Unpad), Jl. Raya Bandung Sumedang KM-21, Jatinangor-45363, Sumedang, Indonesia oscar.agus@yahoo.co.id Abstract Hauling road and bridge have a major role in a mining production process at X Coal Mine, Batulicin. Therefore, in order to maintain appropriate mining production inbatulicin, bridge condition monitoring is a priority. This study is using deformation analysis, one of the applied geodetic methods, which its focus is on object displacement. In this study, the measurement is done by using GPS because of its accuracy and efficiency. After all of the observation points are observed, the data is downloaded into a computer to be calculated. Deformation analysis is by a using GPS survey is very effective in order to determine object displacement. T- student test can ensure the validation of the result which taken from the survey. The analysis shows that vector displacement that occurred at the observation points are mainly 1 dm. The displacement can be used to determine the durability of the bridge. Also, the analysis shows that average displacement velocity, which taken from the six observation points, is 1 cm per week. Keyword: Geodetic, Deformation Analysis, Bridge, GPS Survey, T-student Test Introduction Hauling road has a major role in a mining production process, especially at X Coal Mine, Batulicin. In Batulicin, land transportation such as truck is used in order to move coal from the mining pit to port. As well as the road condition, which has 52 km long, the bridge condition is also a factor that should be considered. Moreover, the bridge constructed by wooden material which age is more than 10 years. In order to maintain appropriate mining production in Batulicin, bridge condition monitoring is a priority. Site Condition As noted by our survey team, total amount of bridges along the hauling road from pitto port are 93 units, varied in size. In this study, the bridges that located at KM51 and KM39 are chosen as study object because of several reasons, i.e.: both of the bridges are considered as the biggest and the longest bridge among other bridges, the wooden material that construct both of the bridges is very old, and both of the bridges are heavily eroded. Page 1

2 Fig Location The bridges at KM51 and KM39 are very vital to land transportation from mining pit to port, and now are considered very susceptible to failure. Furthermore, an efficient and effective bridge condition monitoring has to be done. So, in this study, condition monitoring is mainly focused at bridges that located at KM51 and KM39. Fig Field photo, shows the bridge which located at KM51 Page 2

3 Fig Field photo, shows the bridge which located at KM39 Method Deformation Analysis Deformation analysis is one of the applied geodetic methods which its focus is on object displacement. The measured object displacement can be in varied from a high scale into a smaller scale, based on the size of the object. The most important thing in this method is to ensure that the displacement is caused only by a change in coordinate that solely represent the object displacement. In the other word, the deformation analysis has to ensure that the coordinate change, as a parameter of the study, is not occurred by an error in measurement, i.e.: faulty instrument and human error. Because of that legitimate measurement and instrument which can eliminate error are needed. There is a lot of way that could be applied in order to measure the deformation, e.g.: by using a waterpass to measure height and length differences, by using theodolite to measure angle and length, or by using global positioning system (GPS). In this study, the measurement is done by using GPS because of its accuracy and efficiency. The GPS that used in this study is Sokkia ISX2700 which has dual frequency feature and also can provide a real-time kinematic operation. By using the GPS, the measurement is based on static survey at a benchmark near the bridge and brief static survey at spots around the bridge. The Static survey takes more than an hour while the brief static survey only takes 15 to 30 minutes. Data are taken from the measurement which has less error. Then, the data is verified in order to ensure that the data only represent the object displacement Page 3

4 using statistical method, T-student. In order to achieve a reliable result, the statistical method is done by 99% confidence level. Bridge Condition Monitoring by using GPS Survey The measurement is started by placing a primary benchmark near the measured bridge. The primary benchmark is bounded to a zero order reference spot (BM00) which is Arutmin Batulicin office at Gua Sugung. The BM00 is taken from static GPS which operates for 3 days and 2 nights, and bounded to other 20 reference spots that spread around the world. Fig The BM00 photo taken at the office in Gua Sugung The primary benchmark is measured more than one hour. The length of baselines taken from the primary benchmark for each bridge is different. The baselines that used for KM51 have 3 km long, while the baselines for KM39 have 9 km each. By using the standard operation procedure that stated by NOVATEL, according the time taken for measurement for each length parameter, we can ensure that the primary benchmark has already taken a sufficient time in its measurement. However, in order to increase the accuracy, ambiguity solving phase is required and done by using L5. After the primary benchmark is acquired, the next step is to pinpoint the observation points of deformation which located above the bridge. The chosen observation points have to fulfill these requirements, i.e.: easy to be observed, have a consistent stance, and easy to be planted by the device. In this study, we have six observation points which located at KM51 and five observation points which located at KM39. All of the observation points are located along the side of the Page 4

5 bridge and planted to the wooden material which constructs the bridge, marked by nails in order to measure at exactly the same place. Fig Field photo, shows the GPS observation point Fig Field photo, shows the GPS observation point After all of the primary benchmark and its observation points are available, all of the observation points are measured by using brief static measurement which only takes 15 to 30 minutes long. The measurement is done without the tripod, because of that the GPS receiver is placed to a stick which held by hand during the Page 5

6 measurement. The cause is that the tripod cannot be placed at the observation point which mainly located at the side of the bridge. In order to minimize systematic error that caused by the observed data that not taken at a center of the point during the measurement, a nivo assist is equipped to the stick. Because of the length which taken from primary benchmark to observation is very close, not more than 200 m, the brief static measurement is very sufficient to provide data which its accuracy in millimeter scale. Moreover, all of the observation points are bounded by using radial baseline system. Fig Field photo, shows the brief static GPS observation point Fig Field photo, shows the brief static GPS observation point Page 6

7 After all of the observation points are observed, the data is downloaded into a computer to be calculated. The data calculation phase is done by using software, Spectrum 3.7. The calculation is solved by baseline radial system without network alignment. In order to ensure that all the result does not have any measurement error, and only represent vector displacement, T-student test is taken. If the T value is higher than t, then the result then can be accepted. In the other word, vector displacement was occurred at the observation point. In this study, all of the observation point is measured in 7 days interval, at four times measurement phase. The observation is done at 16 July 2008, 21 July 2008, 28 July 2008, and 4 August By using the same interval, not only the data of vector displacement can be taken, but also the velocity of the displacement. Result and Discussion As mentioned before, we know that the measurement was taken in 7 days interval, at each measurement phase. Due to efficiency, in this discussion we only present one sample at KM21 at two phases, 16 July 2008 and 21 July 2008, herewith the result of the measurement; as a note, STD is the standard deviation in meter scale and D is the difference between the first phase (16 July 2008) and the second phase (21 July 2008). Table First Phase (16 July 2008) Table Second Phase (21 July 2008) Page 7

8 Table The difference between the STD in first phase and second phase Table T-Student test result for the displacement Table Covariance displacement velocity variance Page 8

9 Table and are the result taken from observation point which located at KM51 in the first and second phase. All of the differences between the first and second phase, as well as the STD are presented at Table The vector displacement tested with T-student test is presented at Table From the test, we can ensure that the observation point taken at both phases have a vector displacement. Also from the test we also determine the vector direction, but we do not show it in this study due to efficiency. Moreover, velocity can determine the velocity of the displacement. As a note, if the result from three phases included in this section, then we could discuss the vector displacement and its velocity. In the deformation analysis using GPS, especially in the bridge monitoring, we were facing some issues. First, the available unit is limited, and not enough to fulfill the required amount to do periodical measurement. This affecting the analysis result, especially the displacement velocity. Second, the structural strength of the bridge is set aside. Due of that, we cooperated with civil engineering department in order to achieve a proper result which taken from the deformation analysis. Conclusion Deformation analysis is by a using GPS survey is very effective in order to determine object displacement. T-student test can ensure the validation of the result which taken from the survey. The analysis shows that vector displacement that occurred at the observation points are mainly 1 dm. However we do not discuss the direction of the vector due to efficiency. The displacement can be used to determine the durability of the bridge. Also, the analysis shows that average displacement velocity, which taken from the six observation points, is 1 cm per week. Acknowledgements Firstly thanks to 1st International Conference Geoscience for Energy, Mineral Resources, and Environment Applieds 2014 committe to accepted this paper and publish. And also thanks to Mr. Jose Antonio Esparrago Reyes, Mr. Dennes HL to allowing and supporting the authors colleted the data. References [1] Devore, L., Jay, Probability and Statistic for Engineering and Sciences, eighth edition [2] Abidin, H.Z., Penentuan Posisi GPS dan Aplikasinya, [3] Abidin H.Z., Andreas H., Gamal M., Surono, dan Hendrasto M., (2004b) : Studying Landslide Displacement in Megamendung (Indonesia) Using GPS Survey Method, Jurnal, Proc ITB Eng. Science. Vol 36B, No.2.pp [4] Hoek E., 1987, (edisi 1), 2000 (edisi 2), 2007 (edisi 3), Practical Rock Engineering [5] Lollino, Georgio, 2014, Engineering Geology for Society and Territory Volume Page 9

10 2 Land Slides Processes, Springer. [6] Srbulov, Milutin, 2014, Practical Guide To Geo-Engineering, Springer Apendix [1] Fig Field photo, shows the static GPS observation point [2] Fig Field photo, shows the bridge which located at KM39 [3] Fig Field photo, shows the GPS observation point [4] Fig Field photo, shows the GPS observation point [5] Fig Field photo, shows the static GPS observation point [6] Fig Field photo, shows the static GPS observation point Page 10