Preliminary Study On The Genetic Mechanism Of Ground Fissures Along Kenya’s Neima Railway

In recent years,there have been widespread ground fissure disasters in Kenya,Rift Valley of East Africa,which pose a serious threat to major projects,railways,highways,pipelines,urban construction,industrial parks and the safety of residents in the region.It is necessary to carry out research on the existing and potential ground fissures in this area,to provide a theoretical basis for the prevention and mitigation of ground fissures in future engineering construction,and also to provide some reference for other areas where ground fissure disasters are developed.This paper selects ground fissures along Neima Railway in Kenya as the research object.The technical measures including field investigation,data collection,drilling,trench,physical model tests and numerical simulations were used to study the geological background,development status,distribution characteristics,formation conditions,genetic model,formation and expansion mechanism of ground fissures in this area.The main research results of this paper are as follows:(1)The types of ground fissures in the study area are latent erosion ground fissures.The unique regional tectonic environment and "sandwich" stratigraphic structure provide favorable conditions for the formation and development of ground fissures.(2)The formation conditions of latent erosion ground fissures in the study area mainly include the opening of bedrock fracture,physical properties of soil,soil thickness and hydrodynamic effect.The formation mechanism is put forward as follows: rift extension is the breeding background of ground fissures,fault structure is the main controlling factor for the formation of ground fissures,rainwater infiltration is the expansion factor of ground fissures,and rainstorm is the inducing factor for the formation of ground fissure subsidence zone.(3)The results of physical model tests revealed the deformation and failure process of latent erosion ground fissures under the condition of presupposed bedrock fracture and surface water infiltration.Firstly,with the water infiltrating into the top of the bedrock fracture,a latent soil cave is gradually formed at the bottom under the action of viscous dragging of water flow.Then,with the increase of water content,the increment of soil pressure gradually increases while the shear strength decreases.Finally,when the soil cave reaches the critical collapse thickness,the ground fissure subsidence zone is formed on the ground surface.(4)The numerical simulation results revealed the influence of different crack openings and soil thickness on ground fissure subsidence zone.The surface settlement distance and collapse range increase with the increase of crack opening,and the maximum settlement distance increases exponentially with the increase of crack opening.The surface settlement distance decreases with the increase of soil thickness,but the influence of soil thickness on the surface collapse range is not significant.