THE USE OF GPS FOR ROAD LEVELING

Abstract

The detailed engineering geometric design for roads depends mainly on the location of the road alignment and elevation ,in other words depends on three dimensional coordinates E,N,h where (E,N) are the horizontal coordinates. The third ordinate (h) is the reduced level from mean sea level to determine the natural ground level to be used to draw the profile of the existing ground surface and the cross-sections to determine cut and fill areas and to calculate the volumes of quantities as a very important stage in road design. In This research another method of determining the levels of natural ground level, before the design in the study stage , and existing levels of pavement layers after design in the stage of construction (value of h) using global positioning system (GPS), the advantage of this method that the positions of points in the centerline can be relocated at any time using GPS which has the capability to stake out the points in three dimensional coordinates(E,N,h) in no time, compared to the ordinary leveling which determine only the hight (h) value and needs another device to fix pegs in the horizontal (E,N) position during the construction of roads. In this study a section of 10 kms is selected from existing Khartoum –Medani road started from Soba toll station. The levels of points had been observed by GPS (real time method) in three different distances and precise levels have calculated each time by ordinary level, all levels had been adjusted to the accuracy 10√k ,Bench marks had been established every 5 km taking the levels values as reference. In the first trail the distance between the control points on which the base GPS is located is 5km and in the second trial the distance is 2.5 km and in the third trail the distance is 1 km. The results of the three GPS measurements had been obtained by 1 km trial, had been found the best values of precision (10√k ) which is appropriate to roads geometric design .During roads construction the fixed pegs will be removed in any time and relocation is needed again using the conventional methods, by using GPS the E,N,h coordinates are saved in the memory of the device and can be retrieved at any time to relocate points, According to the fact that when the distance between control points on which the GPS base (reference station) is changed every one kilometer is reduced more precise levels will be obtained. Using real time GPS to measure the levels in highway and roads projects will reduce time and cost of survey works and detailed engineering design of roads, and the locations of points can be determined easily and accurately every time by GPS. We can conclude that the height precision depends on the base distance ( the least distance is the best precision ), precision is a reference frame dependent.