Geotechnical evaluation of gully erosion and landslides materials and their impact in Iguosa and its environs, southern Nigeria

Background Detailed field surveys and geotechnical evaluation of soils in Iguosa and its environs, Southern Nigeria, were undertaken to determine the root causes, mechanisms, and impacts of landslides and gully erosion. This was done to suggest appropriate mitigation measures to reclaim the affected land and prevent future occurrences in the study area. Results Field study revealed high elevations, a steep slope, high rainfall and inadequate drainage systems. Also, human activities and socio-cultural activities have contributed to the large lateral extents in depths and widths of the landslides and gullies in the study area. The geotechnical analyses reveal that soil samples from SB1, SB2, SB6 and SB7 lithological units are mainly sandy clay with a coefficient of permeability ranging from 3.5 × 10−4 to 4.2 × 10−4 cm/s, the cohesion ranges from 27 to 28 kƿa and angle of internal resistance ranges from 27° to 30° respectively. The plastic limit ranges from 2 to 4, and liquid limit ranges from 33 to 38, and the plasticity index ranges from 30 to 36. Ajali sand units SB3, SB4, SB8 and SB9, consist of coarse-grained sand with no plasticity. The coefficient of permeability ranges from 2.8 × 10−4 to 3.2 × 10−4 cm/s, the cohesion range from 10 to 18 kƿa, angle of internal resistance 24° to 26°, respectively. The soil samples from SB5 and SB10 lithological units are silty-clay with a coefficient of permeability of 4.6 × 10−4 to 4.8 × 10−4 cm/s. The cohesion of 45 to 46 kƿa, and angle of internal resistance of 37° to 40°, respectively. The plastic limits ranges from 35 to 36, and liquid limit is 76, and the plasticity index ranges from 40 to 41. Conclusion Field survey and geotechnical evaluations of the soils revealed that high elevation, a steep slope and the geotechnical properties of the soils were the initial conditions that initiated landslides and gully developments in the study area. This has also been influenced by rainfall, poor vegetation, inadequate drainage systems, and human activities as well as socio-cultural activities. Over four hundred and thirty-two houses and farmlands and other properties have been damaged and abandoned in the study area. Covering the landslide areas with impermeable layers/materials, diverting surface water away from the landslide areas, enacting laws to prevent the erection of structures on landslide prone-areas, sound drainage systems, the use of biotechnical slope and bioengineering methods, afforestation and re-vegetation were the proposed mitigation measures to tackle this menace in the study area.

Remote Geotechnical Evaluation of Rights of Way of Hydrocarbon Transmission Lines

Due to the health emergency currently affecting the planet, it has been impossible for engineering specialists to carry out direct inspections of the land. During this time, it has been necessary to develop techniques and procedures that allow engineers to obtain information from the land remotely. Here, they are supported by the technology that allows them to record images remotely via drones and communicate so they can perform inspections by auxiliary field personnel, directed at a distance by specialists. To do this, a preliminary flight plan is defined, based on the experience and knowledge of the terrain by the specialist and the visual of the drone is transmitted via the Internet from a PC in the field. Later, which images to record and the sites that require more detail or a direct inspection by the field assistant are defined. Finally, the field assistant transmits the images of the inspection. In this way, the specialist’s training and experience, the operational ease of the drone, and the skill of the field staff are taken advantage of. This article details the procedure for remote inspection, and ways in which it can even be extended to corridor recognition tasks to define the layout of rights of way.

The Importance of Geotechnical Evaluation and Shoreline Evolution in Coastal Vulnerability Index Calculations

The aim of this specific study is to present a new weighted Coastal Vulnerability Index (CVIWF), with an emphasis given to the geotechnical evaluation and shoreline evolution rate measured through high-resolution remote sensing, which seem to be the most interfering variables in CVI calculations. As a pilot area for the application of the new CVIWF, the Gulf of Patras in Western Greece was selected, which is suffering erosion problems due to climate change, the sea level rising and human intervention. The new CVIWF, which was applied in this research, includes the following innovations: (1) the use of geotechnical characterization instead of geological–geomorphological characterization, (2) the use of high-resolution remote sensing data for the detection of shoreline evolution rate and (3) the insertion of a specific weighted geotechnical factor in the CVIWF formula. The results from the application of the unweighted CVI show that percentages of 20.13%, 20.47%, 24.56%, 29.39% and 5.45% of the gulf’s shoreline are under the regime of very low, low, moderate, high and very high vulnerability, respectively. On the other hand, the corresponding results from the application of the weighted CVIWF show a percentage of 14.59%, 25.91%, 20.04, 36.48% and 2.98, respectively.

Geotechnical Evaluation of Gully Erosion and Landslides Materials and their Impact in Iguosa and its Environs, Western Anambra Basin, Nigeria.

Background: Field survey and geotechnical evaluation was done to determine the soil characteristics of the gullies and landslides materials and their impact in Iguosa and its environs, Western Anambra Basin. This was done to explain and evaluate the root problems, causes, mechanism of the continuous gullies and landslides in the study area.Results: The field study reveals that the geomorphological characteristics, weakly developed structures, slope steepness, wrong use of the land and poor vegetation cover coupled with intense and prolonged rainfall contributed to the origin, causes of gullies and landslides in the study area. Geotechnical parameters for soil samples in the study area shows that the mean liquid limit (LL) of 40, mean plastic limit (PL) of 8.30, mean plasticity index (PI) of 21.20, mean coefficient of permeability (K) of 3.65 × 10cm/sec, mean cohesion and mean angles of internal angles between grains of 2.56 kƿa and 23.70 respectively. The low PL, low LL and low PI values of the Ajali sand, low cohesion (poor compaction) and low angle of internal resistance between grains of the soil, high K of Ajali sand coupled with the swelling and shrinking nature of the clay beds beneath the Ajali sand, resulted to easily weathering of the Ajali sands, erosional and continuous landslide activities in these affected areas.Conclusions: The origin, mechanism and impacts of landslide hazards have been investigated in Iguosa and its environs, Western Anambra Basin, Nigeria. Field observation reveals that the geomorphological characteristics, weakly developed structure, high slope instability, wrong use of land, as well as the steepness of the slope and intense and prolonged rainfall contributed to the origin of landslide as well as the gully erosion in the study area. The unconsolidated nature of the soil, less cohesion, high permeability, and weak plasticity of the soil that occurs under and above the clay lithologic units (gliding planes) contributed to landslide and gully erosion. Possible prospective implications of the gully erosion and landslides in the study areas are land degradation, destruction of houses and other properties, farm lands and roads. The following suggestions have been made to solve these problems by covering the landslide areas with impermeable layers/materials, diverting surface water away from the landslide areas, enacting laws to prevent erection of structures on landslide prone areas, the use of biotechnical slope techniques and bioengineering methods. The application of these recommended methods will go a long way in solving the problem of landslide hazards in the study area.