Investigations of Changjing earth fissures, Jiangyin, Jiangsu, China
- Authors: Wang, Guang-ya , You, Greg , Zhu, Jin-qi , Yu, Jun , Gong, Xu-long , Wu, Jian-qiang
- Date: 2016
- Type: Text , Journal article
- Relation: Environmental Earth Sciences Vol. 75, no. 6 (2016), p. 1-10
- Full Text: false
- Reviewed:
- Description: Fissuring of the earth began at Changjing, Jiangyin City, Jiangsu Province, in 1995. The earth fissure zone consists of a main fissure with a number of secondary fissures on both sides, which range from 20 to 60 m wide. The main fissure is about 500 m long, trends 15° to 30°, and has a scarp 100–200 mm high. Extensive field investigations, including shallow seismic surveys and geological drilling, have been conducted over 20 years. Deposits of a Quaternary paleoriver at 150–160 m depth curve around a bedrock spur which is situated beneath, and lies parallel to, the fissure at about 90 m. A regional trough has formed due to land subsidence over the paleoriver channel, with Changjing at its eastern edge. The fissures resulted from differential subsidence of the Quaternary deposits as a result of extended over-exploitation of groundwater. Groundwater extraction facilitates compaction of the Quaternary aquifers and aquitards from the increase of the effective in situ stresses, which leads to subsidence. Positive relief of the subsurface bedrock defines the location and formation of the earth fissures. On one hand, differential subsidence causes the Quaternary sediments to rotate over the ridge, leading to tensional cracking. On the other hand, temporal differential in subsiding aggravates the vertical shearing or faulting of the fissure, forming a scarp. © 2016, Springer-Verlag Berlin Heidelberg.
Land rebound after banning deep groundwater extraction in Changzhou, China
- Authors: Wang, Guang-ya , Zhu, Jin-qi , You, Greg , Yu, Jun , Gong, Xu-long , Li, Wei , Gou, Fu-gang
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 229, no. (2017), p. 13-20
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- Description: More than 30 years groundwater overdraft had resulted in hydraulic head declined from near the ground surface to 85 m deep in the second confined aquifer (CA2) in Changzhou, and lead to regional land subsidence from 1970's to early 2000's. After banning deep groundwater extraction was banned in 2000, the hydraulic head of CA2 had recovered to 37.6 m in Changzhou by the end of 2013. Based on several stages first and second order leveling results and long term monitoring data from the multi-strata borehole extensometer station (BES), it was revealed that the land subsidence is attributed to the compression of both aquifers and aquitards in the porous aquifer system. The spatial characteristics of subsidence are related not only to hydraulic head pattern in the area, but also to the thickness and compressibility of different soil strata, and distance from the aquifer. Since banning deep groundwater extraction, the ground uplifted 37.22 mm (5.4% of the pre subsidence) at BES, Changzhou due to the hydraulic head recovering. Strata compression and rebound was recorded as: the upper most stratum, and the underlying aquitard of CA2, and the upper CA3 are still in the compression process, the lower CA3 layer and the upper most segment of aquitard of CA2 rebounded about 90% of the pre compression recorded since 1984, and the CA2 and its adjacent overlying aquitard rebounded 3.8%–9.7% of the pre compression. © 2017 Elsevier B.V.
Earth Fissures in Su–Xi–Chang Region, Jiangsu, China
- Authors: Wang, Guang-ya , You, Greg , Zhu, Jin-qi , Yu, Jun , Li, Wei
- Date: 2016
- Type: Text , Journal article , Review
- Relation: Surveys in Geophysics Vol. 37, no. 6 (2016), p. 1095-1116
- Full Text: false
- Reviewed:
- Description: The earth fissures in the Su-Xi-Chang area are caused by differential land subsidence due to long-term excessive groundwater withdrawal and controlled by the bedrock ridge or cliff underlying. There have been more than 15 earth fissures in the area since 1989. The field investigations have lasted for more than 20 years. The earth fissures generally have a main fissure and a number of secondary ones parallel to the main one. The main fissure (crack) has a scarp, is steeply dipping, and can be more than 2000 m long. Geophysical surveys (2D or 3D seismic investigation, controlled source audio frequency magnetotelluric sounding, and electric sounding) combined with geological drilling are effective for the investigation of earth fissures. Geodetic leveling is effective to monitor the ground deformation across the earth fissure, so is the extensometer for the opening of the fissure. The activities of earth fissures are directly related to different stages of land subsidence and controlled by geological abnormalities. Most earth fissures in the area are still active. © 2016, Springer Science+Business Media Dordrecht.