考虑蠕变特性及井壁影响的多冷媒非均质冻结壁理论解

Theoretical solution of multi-refrigerant heterogeneous frozen wall considering creep characteristics and shaft lining influence

  • 摘要: 为应对复杂多变的地层环境,人工冻结法施工中的低温冷媒逐渐从单一种类发展成为多种冷媒联合使用,冻土蠕变特性及井壁施工过程是影响该类非均质冻结壁稳定性的重要因素。为探究考虑蠕变特性及井壁施工影响的多冷媒非均质冻结壁应力及形变特征,以盐水−二氧化碳联合冻结所形成的冻结壁为研究对象,选取距离冻结壁主面1/4管间距处的温度特征截面等效代替冻结壁的温度分布,并采用3段一次函数曲线构建冻结壁的温度场模型。基于黏弹性理论和Newton Cotes数值积分方法,建立考虑蠕变特性的非均质冻结壁、井壁及外围土体共同作用的力学计算模型,推导得出多冷媒非均质冻结壁在不同掘进深度下各区间(Ⅰ、Ⅱ、Ⅲ)的应力、应变和位移的解析解,以及作用于冻结壁和外层井壁上的外荷载和冻结压力的表达式。结果表明:井壁浇筑后的36 h内,非均质与均质冻结壁的位移、应变由内到外均呈非线性衰减趋势;冻结壁的内外缘位移随着蠕变时间的增加先增加后减小,而冻结壁的外荷载先减小后增加;外层井壁与冻结壁之间的冻结压力随着蠕变时间的增加呈非线性增加,而非均质冻结壁的冻结压力始终小于均质冻结壁。以掘进深度600 m为例,考虑冻结壁非均质特性后,在蠕变时间1~36 h,冻结壁的内外缘位移分别减小了1.819~4.723 cm和0.650~1.687 cm,而冻结壁所承受的外荷载提高了0.285%~0.772%;进一步考虑井壁作用后,冻结壁的内外缘位移分别减小了1.967 ~32.274 cm和0.702~11.527 cm,而冻结壁所承受的外荷载提高了0.309%~5.246%。研究成果可为复杂地层条件下多冷媒联合冻结施工的设计提供理论依据。

     

    Abstract: To cope with the complex and changeable stratum environment, the low-temperature refrigerant in the artificial freezing method construction has gradually developed from a single type to the combined use of multiple refrigerants. The creep characteristics of frozen soil and the shaft lining construction process are important factors affecting the stability of this type of heterogeneous frozen wall. To explore the stress and deformation characteristics of multi-refrigerant heterogeneous frozen wall considering creep characteristics and the influence of shaft lining construction, the frozen wall formed by the combined freezing of brine and carbon dioxide was taken as the research object. The temperature characteristic cross-section at 1/4 of the pipe spacing away from the main surface of the frozen wall was selected to equivalatively replace the temperature distribution of the frozen wall, and a temperature field model of the frozen wall was constructed using a three-segment linear function curve. Based on viscoelastic theory and Newton Cotes numerical integration method, a mechanical calculation model for the interaction of heterogeneous frozen wall, shaft lining and peripheral soil with creep characteristics is established, and the analytical solutions of stress, strain and displacement of heterogeneous frozen wall with multiple refrigerants under different tunneling depths (Ⅰ, Ⅱ, Ⅲ) are derived. And the expressions of the external load and freezing pressure acting on the frozen wall and the outer shaft lining. The calculation results show that within 36 hours after the shaft lining pouring, the displacements and strains of both heterogeneous and homogeneous frozen walls show a nonlinear attenuation trend from the inside out. The displacements of the inner and outer edges of the frozen wall first increase and then decrease with the increase of creep time, while the external load of the frozen wall first decreases and then increases. The freezing pressure between the outer shaft lining and the frozen wall increases nonlinearly with the increase of creep time, while the freezing pressure of the heterogeneous frozen wall is always less than that of the homogeneous frozen wall. Taking the tunneling depth of 600 m as an example, considering the heterogeneous characteristics of the frozen wall, the displacements of the inner and outer edges of the frozen wall decreased by 1.819−4.723 cm and 0.650−1.687 cm respectively during the creep time from 1 h to 36 h, while the external load of the frozen wall increased by 0.285%−0.772%. After further considering the shaft lining effect, the displacements of the inner and outer edges of the frozen wall decreased by 1.967−32.274 cm and 0.702−11.527 cm respectively, while the external load borne by the frozen wall increased by 0.309%−5.246%. The research results of this study can provide a theoretical basis for the design of multi-refrigerant combined freezing construction under complex stratum conditions.

     

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