青藏高原南缘某机场场区深厚覆盖层工程地质特征

ENGINEERING GEOLOGICAL CHARACTERISTICS OF DEEP OVERBURDEN IN AN AIRPORT FIELD ON SOUTHERN MARGIN OF QINGHAITIBET PLATEAU

青藏高原南缘某拟建机场场区发育第四系深厚覆盖层,对该工程建设具有较大的制约作用。钻孔资料显示,该深厚覆盖层普遍分布于整个场区,厚度均在30 m以上,最大孔深105 m仍未揭穿。纵向上深厚覆盖层由上而下可划分为4层:全新世泥石流堆积层(Q_4~(sef))、全新世冲洪积堆积层(Q_4~(al+pl))、全新世湖相堆积层(Q_4~l)和晚更新世冲洪积堆积层(Q_3~(al+pl))。其中:泥石流主要由角砾和碎石组成,最大厚度约13 m,分布于研究场区西侧;全新世冲洪积层组成物质复杂,以粉细砂和圆砾居多,无明显分层规律,最大厚度约7 m;湖相沉积粉质黏土呈可塑-流塑状,局部夹含砂,最大厚度约43 m;晚更新世冲洪积层以细砂和中粗砂为主,局部夹有卵砾石,厚度大于42 m。分析表明,深层覆盖层成因与晚更新世以来喜马拉雅快速隆升及间冰期气候密切相关,而表层覆盖层与全新世以来青藏高原气候回暖及短期冷暖交替气候密切相关。试验揭示深厚覆盖层物理力学性质差异明显,研究场区存在不均匀沉降、渗漏破坏、边坡稳定性及冻融诱发地基破坏等主要工程地质问题。

The Quaternary deep overburden is developed in a proposed airport site on the southern margin of the Qinghai-Tibet Plateau,and induces a great restriction on the construction of the project.Drilling data shows that the deep overburden is generally distributed in the entire field area with a thickness of more than 30 m,and the maximum hole depth of 105 m has not been exposed.Vertically,the deep overburden can be divided into four layers from top to bottom:Holocene debris flow accumulation layer(Q4sef),Holocene alluvial accumulation layer(Q4al+pl),Holocene lacustrine accumulation layer(Q4l)and Late Pleistocene Alluvial accumulation layer(Q3al+pl).Among them,the debris flow is mainly composed of breccia and gravel,with a maximum thickness of about 13 m,distributed on the west side of the research site;the Holocene alluvial strata is composed of complex materials,mostly silty fine sand and round gravel,without obvious layering rules,with a maximum thickness of about 7 m;the lacustrine sedimentary silty clay is plastic-flow plastic,with sand in some parts,and the maximum thickness is about 43 m;the late Pleistocene alluvial strata are dominated by fine sand and medium-coarse sand,with pebbles and gravels locally,and the thickness is greater than 42 m.The analysis shows that the cause of the deep overburden is closely related to the rapid uplift of the Himalayas since the Late Pleistocene and the interglacial climate,while the surface overburden is closely related to the warming and the short-term alternate climate of cold and warm of the Qinghai-Tibet Plateau climate since the Holocene.The test results reveal that the physical and mechanical properties of the deep overburden are obviously different,and there are major engineering geological problems including uneven settlement,seepage failure,slope stability,and foundation damage induced by freezing and thawing.