Sedimentary characteristics and engineering geological significance of the middle Pleistocene Hejiang Formation in the eastern suburb platform on the Chengdu Plain, Sichuan

The integration of depositional sequences, grain sizes and gravels has disclosed that the middle Pleistocene Hejiang Formation (Qh₂hj) strata in the eastern suburb platform on the Chengdu Plain, Sichuan are classified into the fluvial deposits, vertically with typical "fluvial binary architectures". The deposits are dominated by the fine-grained deposits, and the basal gravels are made up of pebbles and cobbles with good roundness and orientation. The sedimentary microfacies in the Hejiang Formation comprise the channel, point bar, bankfloodplain microfacies, corresponding to three lithofacies types and four lithofacies associations. The channel gravel lithofacies shows the NW to SE-trending distribution in the Shilingzhen-Honghezhen-Damianzhen zone. The point bar lithofacies is limited to the low relief of the palaeochannel in the eastern part of the Damianzhen-Xihezhen region. The bank-floodplain claystone lithofacies widely occur throughout the study area. On the whole, the abovementioned sedimentary microfacies have different effects on the local engineering construction. The water erosion within the channel gravel beds as the groundwater reservoirs may lead to the instablility of the stratigraphic architentures and thus have the effects on the selection of the engineering stability technology. Due to the limited distribution, the point bar deposits may have the least influence on the local engineering construction. The bankfloodplain clay deposits as the soft beds may reduce the stability of slope and bars.