大直径埋地钢管管顶土压力及其设计模型研究

Soil pressures at top of large-diameter buried steel pipes and their design model

以往埋地钢管的管顶土压力研究结果多基于小直径管道,对大直径管道并不完全适用。建立了埋地钢管有限元计算模型,分析了不同管径、径厚比和埋深下的管顶土压力,并与传统设计模型进行比较,探讨了相关参数对土压力的影响。提出了一种新型的土压力设计模型--盆式模型,采用“直线+抛物线”形式描述土压力分布,根据管径和埋深情况采用“Marston+胸腔”荷载计算土压力数值,并深入研究了盆式模型对大直径埋地钢管的适用性。结果表明:对于大直径埋地钢管,管顶土压力分布的基本形式为“倒盆形”,径厚比及埋深均会显著影响土压力,但径厚比大于200后,土压力变化很小;管径小时,土压力大体呈抛物线分布。增加回填土变形模量和泊松比、沟槽接触面粗糙程度,减小沟槽宽度,均可降低土压力,但影响有限。高埋深时,棱柱荷载过大;低埋深时,Marston荷载偏小,这两种模型的计算精度及适应性较差;盆式模型与有限元分析的计算结果吻合度较好,计算精度高,适应性强,可为大直径埋地钢管的结构设计及规范制定提供借鉴和参考。

The previous research results of soil pressures at the top of buried steel pipes are mostly based on the small-diameter pipes,which are not fully suitable for large-diameter pipes.Here a numerical investigation is conducted on the soil pressures from the aspects of pipe diameter,diameter-thickness ratio and cover depth,and it is furtherly compared with the traditional design models.The influence parameters on the soil pressure are discussed.A new design model for soil pressures,basin model,is proposed.Wherein,the distribution of the soil pressures is described as"straight line+parabola",and the load calculation adopts the"Marston+pleura"according to the pipe diameter and cover depth.Furthermore,the applicability of the basin model is studied.The results show that the basic form of the soil pressures is the"inverted basin"distribution for large-diameter pipes,while the soil pressures are a parabolic distribution for small-diameter pipes.The diameter-thickness ratio and cover depth have significant influences on the soil pressures,but the soil pressures change very little after the diameter-thickness ratio is greater than 200.The increase of the elastic modulus and Poisson's ratio of backfill and roughness of trench interface,and the decrease of trench width can slightly reduce the soil pressures.The prism and Marston load are too large at high cover depth and small at low cover depth,respectively,which have poor accuracy and adaptability.The basin model is in good agreement with the finite element results,with high calculation accuracy and strong adaptability.It can provide a reference for the structural design of large-diameter buried steel pipes.