Determination of Benchmarks Stability within Ahmadu Bello University, Zaria, Niger

Abstract

Heights of six geodetic benchmarks over a total distance of 8.6km at the Ahmadu Bello University (ABU), Zaria, Nigeria were recomputed and analysed using least squares adjustment technique. The network computations were tied to two fix primary reference pillars situated outside the campus. The two-tail Chi-square hypothesis test of the aposterior variances of the benchmark heights at 5% and 1% levels of significance were carried out in order to determine the reliability of the computed heights. This is meant to establish whether the observations used truly represent the heights of the Benchmarks in the study area. The results showed that, the estimated variances for fore, back and mean (of fore and back) leveling computations were 3.17mm, 1.77mm and 2.93mm respectively. The tests of these variances showed that the results, obtained from fore and mean leveling computations, do not truly represent the heights of the benchmarks. On the other hand, the back leveling computed variance passed the confidence limits test which tends to infer that the heights obtained significantly represent the heights of the benchmarks. That is, only the back leveling observation truly represent the benchmarks’ heights in the study area. Four out of the six benchmarks investigated for stability within the period of study showed displacement values ranging between 4.14mm and 12.42mm over a period of 17years. This may not be alarming but effort should be made toward the continuous monitoring of the benchmarks.

Key words: Benchmark Stability, Leveling Network, Benchmark Monitori ng and Least Squares Technique