Need for Prior Geotechnical Engineering Studies for Foundation Design: Cases of Collapsed Buildings in Port Harcourt and Environs, Nigeria

Cases of collapsed buildings have been on the increase in the city of Port Harcourt and environs in Rivers State, in particular and other major cities in Nigeria in recent times. A critical evaluation of the modes of failures indicates that absence of and / or inadequate subsurface geotechnical investigations have been responsible for these building foundation failures. Case histories of four major building foundation failures within the municipality of Port Harcourt and environs in the southern Niger Delta sub-region of Nigeria in recent times are presented and discussed in this paper. The first case history involves a five-storey building that collapsed because it was constructed across a river channel that had sand and gravels as major subsurface materials beneath the building site. As a result of excessive increase in groundwater table during the rainy season and the attendant excessive pore water pressures build-up that led to a rapid loss of the bearing strength of the subsurface materials, it collapsed in the form of a “punching failure”. The second case was a bearing capacity failure due to rapid construction that did not leave enough time for the dissipation of pore water pressures to allow the foundation soils gain shear strength. It collapsed soon after construction was completed. The third case failed as a result of lack of sufficient time to allow for curing of the block materials used for the building. This was a case of structural failure. The fourth case failed as a result of a complete lack of soil investigations that prevented a detailed foundation design for the residential buildings near the banks of a creek at Opobo town, a suburban settlement along a tidal creek. The paper presents and discusses in details the geology, hydrogeology and modes of failures of these four structures and draws attention to the need to carry out detailed subsurface investigations and abide within the building codes (if any)

Geotechnical Application for the Design and Estimation of Amata-Lekwesi, Nigeria Open Mine

The need for a proper understanding of the subsurface geology of a place and the depositional pattern of what is to be mined is very important in establishing its mining trend especially if such deposits are not exposed at the surface. Eleven borings were made in the quarry pit and around the surrounding berm to depths of 25 meters at a sampling interval of 1.0m into the intrusive rock bodies using Slanzi rotary diamond coring rig. The depth range of the boreholes varies from 15.0 meters to 25.0 meters. Rock/Soil samples obtained from borings were subjected to both visual field examination and laboratory tests/analyses to guide in designing a mine system that is based on the geology, trending pattern and geotechnical properties of the rocks. The intrusive was observed to trend in the east-west orientation. However, north-south trends were also observed at certain sections of the mine/quarry. The values of the plunges of the intrusive were observed to be between 2o and 6o at the northern southern segments. The average thickness of the intrusive bodies varies from 11.20m for the surrounding bench area to 20.00m in the pit. This observed thickness of rock mass covers an area of approximately 81,750 m2, made up of 29,500 m2 for the floor of the quarry and 52,250 m2 for the surrounding bench. The area of the surrounding berm and the pit floor area are  52,250 m2 and 29,500m2 respectively. A total reserve tonnage of 3,874,000 was obtained. Keywords: Geotechnical, Mining design, intrusive body, Slanzi rotary diamond coring rig, Quarry, Trend, Plung

Correlation of Mechanical Properties of Some Rocks in South-Eastern Nigeria

Abstract- The mechanical properties of five different rock types from south-eastern Nigeria were determined through uniaxial compressive strength (UCS) test, point load strength test, impact strength index test and natural density test. The results were correlated by using correlation coefficient and regression analyses. The equation of the best-fit line, and the correlation coefficient were determined for each regression. Among the four rock properties correlated in terms of drillability (penetration rate) of percussive or rotary drilling rig, the uniaxial compressive strength, the impact strength index and natural density are found to be the dominant properties affecting penetration rate of rotary drills. Index Terms- uniaxial compressive strength, impact strength index, natural density, point load, correlation coefficient R I

Soil Physico-Chemical Charateristics and Metalic Corrosion in Parts of The Niger Delta

Soil physico-chemical parameters such as pH, organic matter, chloride and sulphate contents were investigated to assess their effect on buried metallic pipes for a proposed gas processing plant facility at Ovade-Ogharefe, Delta State, Nigeria. Ten sampling points along the pipeline route were investigated. Thus, a total of 10 borings each to a depth of 10.0m were drilled along the pipeline route using the Shell-and-Auger Percussion Rig to collect subsurface soil samples for laboratory analyses for physico-chemical characteristics. Soil pH was determined in-situ electronically using the glass electrode method with a standard calibrated pH meter. On the average, the soil is sandy clayey in nature and the results of the parameters tested are as follows: pH (5.2-7.5), chloride (8.9-85.4ppm), sulphate (126.3-266.5ppm) and organic matter content (0.41-0.42%). The low pH values of 4.2, 5.2, 5.3 and 5.5 as well as the high sulphate contents above permissible limit respectively at locations BH7, BH8, BH9 and BH10 implies that the soil is acidic and deleterious to buried metallic pipes which isnbsp characteristic of clayey soils. It is recommended that the metallic pipes along the pipeline route be buried within the depth of 2.0 to 3.0m because that is the zone or layer of high pH, low chloride and low sulphate contents. However, the impressed current cathodic protection method is therefore recommended to minimize corrosion impact on the proposed gas pipeline