NUMERICAL INVESTIGATION OF THE INFLUENCE OF ROCKFALL ON CIVIL STRUCTURES IN SELECTED SOUTHWESTERN STATES, NIGERIA

Abstract

Influence of rock fall on civil structures within Southwestern Nigeria was investigated. In this study, seven highly susceptible rockfall locations near civil structures were selected, Dips 7.0 and RocFall 8.0 (RocScience software) was used for kinematic and numerical simulation model to investigate the influence of rockfall. Based on the field investigation, the study areas are characterized by hanging rocks and jointed rocks marking the areasprone to rockfalls. Rock properties of rocksunder investigation ranged from 46.0 – 50.4 and 134.10 MPa - 153.96 MPa. The kinematic analysis results indicated that the outcrop in the fifth location will not experience any form of instability failure, since the analysis showed no state of criticality on any of the discontinuities. The analysis for other locations clearly indicated that the outcrops present in the first, second, third, fourth, sixth and seventh locations have minimal level of criticality to experience either planar or wedge sliding failure. The analysis of the seventh location further revealed that the first joint set for toppling failure has criticality of the discontinuities equals the percentage critical point at which failure will occur and has a higher likelihood of toppling failure occurrence. Rockfall movement trajectory and bounce height were modeled with their corresponding translational velocity and kinetic energy for predicting the influence of rockfall. Location 6 has the maximum bouncing height of 26.3 m and location 4 has the minimum bouncing height of 1.9 m as compared to other locations. The results of the rock fall simulation model established that the study areas are at risk of rock falls influence capable of causing mortality and damage to civil structures, as summarized in Table 4.2 the total kinetic energy of falls observed ranged from low (< 30 kJ) to medium intensity hazard level zones (30 - 300 kJ). In conclusion the research was able to establish the degree of damage of rock fall on civil structure base on rock fall hazard intensity classification. It is recommended that further research should be done in all parts of the country to establish rock fall hazard map for Nigeria. The residents of these study areas should be cautious of rockfall occurrence and adequate barriers are required to prevent rock fall vulnerability/consequence.