砂卵石地层土压平衡盾构渣土改良难易分类机制研究

针对砂卵石地层中卵石含量高、粒径大、强度高等特点导致土压平衡盾构掘进施工故障多、渣土改良难度大问题，首先，将砂卵石粒径分为≤2 mm细粒和＞2 mm卵砾石粗粒2部分，建立砂卵石渣土中细粒填充并包裹粗料形成的孔隙的二相体物理模型，推导细粒填充包裹粗粒孔隙的临界细粒质量分数；其次，根据该细粒临界质量分数和室内砂卵石渣土改良试验，将砂卵石渣土分为改良容易型、改良较困难型、改良困难型3类，并分别建议相应的渣土改良措施： 稳定性泡沫剂单掺方式、膨润土泥浆+泡沫剂复合掺入方式、泡沫+膨润土泥浆+聚合物复合掺入方式；最后，结合成都地铁17号线某区间盾构掘进渣土改良指导前、后渣土状态和掘进参数对比，初步验证建立的砂卵石渣土改良难易分类机制的合理性。

Soil Conditioning Classification Mechanism for Earth Pressure Balance Shield Tunneling in Sandy Cobble Strata

The earth pressure balance shield encounters many problems, such as multiple machine malfunction and difficult soil conditioning, due to high pebble content, large particle size, and high strength in sandy cobble strata. To address these problems, the sandy cobbles are first divided into fine and coarse particles with a grain size of less than 2 mm and greater than 2 mm, respectively. A two phase physical model is established with porosities formed by coarse gravel residue filling and wrapping by fine particles, and the critical fine particle content is deduced. The sandy cobbles are divided into three types, i.e., very difficult to condition, difficult to condition, and easy to condition, according to the critical content ratio and sandy cobble strata conditioning laboratory testing. Furthermore, the corresponding conditioning measures are given as follows: single mixing mode of stable foam agent, compound blending mixing mode of foam+bentonite slurry, and compound blending mixing mode of foam+bentonite slurry+polymer. Finally, the recommended measures are applied in a shielded section of the Chengdu metro line 17. Moreover, the soil states and shield tunneling parameters before and after soil conditioning indicate the rationality of the sandy cobble strata conditioning and the established classification mechanism.