黄土盾构隧道围岩强度指标结构性参数表征与荷载计算

Structural Parameter Expression Method for Loess Strength Index and Soil Pressure Calculation for Loess Shield Tunnels

摘要:

为了考虑黄土地层特征，获取合理的围岩压力以指导黄土盾构隧道结构设计，通过对比盾构隧道与新奥法隧道围岩压力现场测试数据，结合黄土盾构施工实践，验证形变围岩压力计算黄土盾构隧道围岩荷载的合理性；考虑黄土地层的强度参数，通过芬纳公式构建黄土盾构隧道形变围岩压力的计算方法；采用三轴剪切实验，探究原状黄土的应力应变关系以及应力结构性参数的变化规律，构建应力结构性参数下黄土强度指标的计算方法；结合盾构隧道开挖支护下围岩的应力应变变化规律，建立深埋黄土盾构隧道围岩结构性参数场的计算框架，结合结构性参数修正的黄土强度准则，给出深埋黄土盾构隧道围岩压力的计算方法。研究发现，使用形变压力理论计算黄土盾构隧道围岩荷载具有合理性；原状黄土相比重塑黄土有明显的应力峰值及应变软化现象；黄土应力结构性参数与粘聚力存在较好的拟合关系，与内摩擦角相关性低；当仅考虑地层浸水造成黄土结构性演变引起的围岩压力变化时，当含水率由1 %增加到25 %，塑性圈半径由4.6 m增加为5 m，围岩压力由587 kPa增加到622 kPa。

Abstract:

In order to obtain the reasonable surrounding rock pressure with the consideration of the characteristics of loess strata to guide the tunnel structure design， by comparing the field test data of surrounding rock pressure of shield tunnel and the new Austrian tunneling method （NATM） tunnel， and in combination with the construction practice of loess shield tunnel， the rationality of calculating the surrounding rock load of loess shield tunnel by deformation surrounding rock pressure is verified. The calculation method of deformation surrounding rock pressure of deep-buried loess shield tunnel is constructed by introducing the strength parameters of loess stratum through Fenner formula. The stress-strain relationship and stress structural parameters of deep buried undisturbed loess are studied by triaxial shear tests， and the calculation method of loess strength index under stress structural parameters is then constructed. The calculation framework of structural parameter field of surrounding rock of deep-buried loess shield tunnel is established in combination with the stress-strain variation law of surrounding rock under the excavation and support. The calculation method of surrounding rock pressure for deep-buried loess shield tunnel is finally given based on the loess strength criterion modified by structural parameters. It is found that the undisturbed loess has an obvious stress peak and strain softening compared with the remolded loess. There is a good fitting relationship between loess stress structural parameters and cohesion， while the correlation with internal friction angle is low. Under the circumstances that only the change of surrounding rock pressure caused by the structural evolution from the loess stratum immersion is considered， when the water content increases from 1 % to 25 %， the radius of plastic circle increases from 4.6 m to 5 m， and the surrounding rock pressure increases from 587 kPa to 622 kPa.