隧道水平冻结施工期地表融沉的历时预测模型

A duration prediction model of surface thawing settlement in construction period of tunnel with horizontal freezing method

隧道冻结工程中所形成的人工冻结壁为临时支护结构,隧道衬砌结构施工后,冻结壁要进入解冻期,由于冻结壁解冻过程中的地层融沉现象对隧道周边环境影响较大,因此,应建立合理的方法对地表融沉量进行预测,以便于实际施工中采取相应的融沉控制措施。为此,考虑冻结壁的自然解冻过程,基于随机介质理论,建立了隧道水平冻结施工期地表融沉的历时预测模型。并提出冻结壁自然解冻条件下瞬态温度场由平板解冻理论近似求解,基于平板解冻理论和一维情况下已融土层的稳定融沉量计算公式,确定了预测模型中解冻锋面半径和融缩区域内半径这2个关键参数的取值方法。将所建立的预测模型应用于隧道全断面水平冻结工程中,得到了地表融沉随解冻时间的变化规律。研究结果表明,地表融沉在解冻初期增长速度较快,而在解冻后期增长速度减缓,地表历时融沉量与崔托维奇通过试验得出的天然冻土历时融沉量变化规律相一致。

Artificially frozen wall is a temporary support structure in tunnel freezing engineering;and frozen wall will gradually thaw after construction of the tunnel lining. In the process of frozen wall thawing, thawing settlement of ground can produce serious influence on the surrounding environment. So a reasonable method must be established for predicting surface thawing settlement. On this basis, suitable thawing settlement prevention measures can be determined in the actual construction. For this reason, considering the thawing process of frozen wall, using stochastic medium theory, a duration prediction model of surface thawing settlement in the period of tunnel construction with horizontal freezing method is presented. Temperature field under natural thawing conditions can be approximately analyzed by flat-panel thawing theory;based on flat-panel thawing theory and thawing settlement content calculation formula in one-dimensional case, value methods of thaw front radius and thaw compression region inner radius are determined in the duration prediction model. The prediction method is applied to circular tunnel full section horizontal freezing engineering, surface thawing settlement variations with thawing time are presented. The results show that surface thawing settlement grows faster in the early stages of thawing, and grows slower in the later stages of thawing. Surface thawing settlement variations with thawing time is presented, which is consistent with thawing settlement characteristics of natural permafrost researched through test method byЦЫТОВНИЧ.