*2.2. Engineering Geological Conditions*

The upper part of the stratum from Hongguzhong Avenue Station to Yangming Park Station is mainly artificial fill <Q4al>, Quaternary Holocene shock layer <Q4al>, Pleistocene alluvial <Q3al>, and the underlying bedrock is mainly the third Xinyu Group (Ex) argillaceous siltstone, etc. According to lithology and engineering geological characteristics, the site stratum can be divided into miscellaneous fill <1-1>, plain fill <1-2>, silty clay <2-1>, silt <2-2>, fine sand <2-3>, medium sand <2-4>, coarse sand <2-5>, gravel sand <2-6>, round gravel <2-7>, silty clay layer <3-1>, fine sand <3-3>, fine sand layer <3-4>, coarse sand <3-5>, gravel sand layer <3-6>, round gravel layer <3-7>, pebble <3-8>, argillaceous siltstone layer <5-1>, glutenite <5-2>, and mudstone <5-3>. In the section between Hongguzhong Avenue Station and Yangming Park Station, shield tunnels mostly pass through the Quaternary overburdened soil layer, the surrounding rock types are VI to IV which mainly consists of weathered argillaceous siltstone, as shown in Table 1.
