成都平原东郊台地中更新统合江组沉积特征及工程地质意义

通过地层沉积序列、粒度特征、砾石特征综合分析认为,成都平原东郊台地中更新统合江组为河流相沉积,垂向上具有明显的"河流二元"结构特征,主要以细粒沉积物为主,底部砾石层多为中-粗砾,磨圆较好,具有定向性。该组可细分为河道、边滩、堤岸-河漫3种沉积微相类型,对应发育3种岩相类型。河道砾石岩相沿十陵镇-红河镇-大面镇一带呈北西-南东向展布,边滩砂坝岩相集中发育于大面镇-西河镇东侧古河道凹岸处,堤岸-漫滩粘土岩相广泛分布于研究区内。这3种岩相特性及分布对工程建设的影响存在差异:河道砾石层作为地下水储集层的同时,水溶蚀使其地层结构稳定性被破坏,影响工程稳固技术的选择;边滩砂坝分布较为集中,对区内工程建设影响面最小;堤岸-河漫粘土广泛分布,是一种分布稳定的软弱层,对地下水有一定的封闭效果,同时软弱层的特性使其降低了边坡、坝体的稳定性。

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.