Generative mechanism analysis of ground fissure in the Nairobi–Malaba Railway area across the East African Rift

Abstract

As the Nairobi–Malaba Railway traverses the East African Rift Valley, it has complex engineering geological conditions due to the development of its geological formations. Since March 2018, four large ground fissures have occurred in the East African Rift Valley area crossed by the Nairobi–Malaba Railway engineering construction, posing a significant threat to the safety of the railway engineering. According to the field investigation, it is initially considered that the ground fissures are caused by the loss of strength of the lower soil layers. In view of the fact that the settlement occurred during the rainy season and no earthquake events were recorded in the local and nearby areas during that period, it is inferred that the ground fissures originated from the subduction of the underlying soil layer by the submerged erosion of groundwater. For this reason, a further field investigation was conducted and a geological trench was directly excavated to the underlying rock for the uneven ground settlement, which revealed that the overlying soil layers are mainly silty clay layers and volcanic ash layers, and there are some deep and long cracks of a certain width on the underlying volcanic rock layer and there is gas flow spilling from the cracks. The field investigation also found the existence of some penetrating holes in the volcanic rock layer and caves beneath the volcanic rock layer. Based on the field investigation and phenomenological analysis, it is concluded that during the rainy season, the alternating action phenomenon of downward seepage of water in the surface soil layer and upward reflux of water beneath the volcanic rock layer happened through the cracks and penetrating holes on the volcanic rock layer, and the alternating effect of groundwater flow causes some silty clay and volcanic ash particles to flow into the caves and cracks beneath the volcanic rock layer, which leads to the generation of ground fissures. In addition, to further confirm the reliability of this interpretation of the generative mechanism of ground fissures, related results of conventional geotechnical tests on the overlying soil were studied, which verified the conclusion obtained.

Keywords

East African Rift Valley / effect of water flow / ground fissure / rock crack / volcanic rock

References

[1] Leonard RJ. An earth fissure in Southern Arizona. J Geol. 1929;37:765-774.

[2] Xu L, Li S, Cao X, et al. Holocene intracontinental deformation of the northern North China plain: evidence of tectonic ground fissures. J Asian Earth Sci. 2016;119(1):49-64.

[3] Jin W, Luo Z, Wu X. Sensitivity analysis of related parameters in simulation of land subsidence and ground fissures caused by groundwater exploitation. Bull Eng Geol Environ. 2016;75(3):1143-1156.

[4] Holzer LT. Ground failure induced by groundwater withdrawal from unconsolidated sediment. Eng Geol. 1984;6:67-105.

[5] Liu H, Deng K, Lei S, Bian Z. Mechanism of formation of sliding ground fissure in loess hilly areas caused by underground mining. Int J Min Sci Technol. 2015;25(4):553-558.

[6] Lu Q, Qiao J, Peng J, et al. A typical Earth fissure resulting from loess collapse on the loess plateau in the Weihe Basin, China. Eng Geol. 2019;259:105189.

[7] Peng J, Xu J, Ma R, Wang F. Characteristics and mechanism of the Longyao ground fissure on North China Plain, China. Eng Geol. 2016;214:136-146.

[8] Liu N, Feng X, Huang Q, et al. Dynamic characteristics of a ground fissure site. Eng Geol. 2019;248:220-229.

[9] Li Y, Yang J, Hu X. Origin of ground fissures in the Shanxi Graben system, Northern China. Eng Geol. 2000;55(4):267-275.

[10] Wang F, Peng J, Meng Z, et al. The origin and impact of the Shizhuang ground fissure, Yingxian area, Datong Basin, China. Eng Geol. 2019;261:105283.

[11] Wang JM. Theory of Ground Fissures Hazards and Its Application. Shaanxi Science and Technology Press;2000. (in Chinese)

[12] Xu J, Peng J, Deng Y, Wang F. Development characteristics and formation analysis of Baixiang earth fissure on North China plain. Bull Eng Geol Environ. 2019;78(5):3085-3094.

[13] Lee CF, Zhang JM, Zhang YX. Evolution and origin of the ground fissures in Xian, China. Eng Geol. 1996;43:45-55.

[14] Li YS. Research on Ground Fissures in Xi’an Region and Active Faults in Weihe Basin. Seismic Press; 1992. (in Chinese)

[15] Peng JB. Active Faults and Geological Hazards in Weihe Basin. Northwest University Press; 1992.

[16] Peng J, Meng L, Lu Q, Deng Y, Meng Z. Development characteristics and mechanisms of the Taigu-Qixian earth fissure group in the Taiyuan basin, China. Environ Earth Sci. 2018;77(11):407.

[17] Howard KWF, Zhou W. Overview of ground fissure research in China. Environ Earth Sci. 2019;78(3):97.

[18] Deng YH, Peng JB, Li L, Mu HD. Correlation analysis between substrate extension and cause of ground fissure in the WRB. J Eng Geol. 2013;1:92-96. (in Chinese)

[19] Qiao J, Peng J, Deng Y, Leng Y, Meng Z. Earth fissures in Qinglong Graben in Yuncheng Basin, China. J Earth Syst Sci. 2018;127(1):10-15.

[20] Wang DW, Liu SD, Zhou ZG. Ground fissure characteristics of great rift valley in Kenya and railway construction countermeasure. Subgrade Eng. 2019;19(4):233-238. (in Chinese)

[21] Hao B, Zhou Z, Li Y, Li X, Jin L. Experimental analysis on mechanical characteristics of foundation soil in rift valley area of Kenya Nairobi-Malaba Railway. Front Earth Sci. 2022;10:909102. 1-15.

[22] Ministry of Water Resources of the People’s Republic of China. GB/T 50123-2019 Standard for Geotechnical Testing Method. China Planning Press; 2019. (in Chinese)

[23] Huang XF, Yang XH. A study progress on in-situ soaking test on collapsible loess. Rock Soil Mech. 2013;34(S2):222-228. (in Chinese)

[24] Shao SJ, Wang LQ, Tao H, et al. Structural index of loess and its relation with granularity, density and humidity. Chin J Geotech Eng. 2014;36(8):1387-1393. (in Chinese)

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2024 The Author(s). Earthquake Engineering and Resilience published by Tianjin University and John Wiley & Sons Australia, Ltd.