季冻区框锚支护边坡变位多场耦合分析

Multi-field coupling analysis of slope displacement with frame-anchor supporting in seasonal frozen zone

为了探究冻融荷载作用下框锚支护边坡的温度、水分、应力场以及锚杆内力的变化,基于传统水热力耦合方程,建立了考虑排水与补水条件的水热力耦合方程。通过COMSOL软件PDE和固体力学模块接口实现温度、水分及应力场的耦合求解,从而建立框锚支护边坡的多场耦合计算模型,较好地反映了冻融过程中各物理量变化规律。进一步结合室外试验,对比分析冻融期内土体温度、位移、未冻水以及锚杆内力等的监测值与计算值,结果表明:冻结期内,未冻水含量沿地表向下由小到大分布,地表温度变化对土体温度最大影响深度约为2.5 m,导致在融化期出现了2条与地表接近平行的融化带,致使未冻水含量由地表向下由大到小再由小到大分布。由应力分布云图得知,支护前在冻结期边坡没有剪应力集中发展趋势,处于稳定状态;在融化期,土体融沉导致在坡顶和坡地面出现明显的剪应力集中,边坡处于不稳定状态;支护后剪应力集中现象消散,表明支护效果良好。在整个冻融期内,锚杆轴力在冻结期增量最大,在融化期轴力大幅度下降但仍比初始时大,说明坡体发生了永久变形,冻胀变形对锚杆内力影响不容忽视,类似土质气候地区边坡工程中需给予重视。

In order to explore the temperature,moisture,stress field and internal force of the anchor rod under the action of freeze-thaw load,a new hydro-thermal-mechanical coupling equation is established based on the traditional hydro-thermal-mechanical coupling equation and considering the conditions of drainage and water replenishment.Through the COMSOL software PDE and the solid mechanics module interface,the coupled solution of temperature,moisture and stress fields is realized.The established slope multi-field coupling calculation model can well reflect the changing laws of various physical quantities during the freezing and thawing process.Combined with outdoor tests,the monitoring and calculation values of soil temperature,displacement,unfrozen water,and internal force of anchor rods during the freezing and thawing period are compared and analyzed.The result shows that during the freezing period,the unfrozen water content is dis-tributed from small to large along the surface.The maximum impact depth of surface temperature changes on soil temperature is about 2.5 m.During the thawing period,there are two thawing zones that are nearly parallel to the ground surface,which cause the unfrozen water content to be distributed from the ground surface downwards from large to small and then from small to large.From the stress distribution cloud diagram,it is known that before the support,the slope has no trend of concentrated development of shear stress during the freezing period and is in a stable state.During the melting period,the melting of the soil causes obvious shear stress concentration on the top of slope and the foot of slope,and the slope is in an unstable state.After the support,the concentration of shear stress dissipates,indicating that the support effect is good.During the entire freezing and thawing period,the axial force of the anchor rod increases the most during the freezing period.During the melting period,the axial force drops sharply but is still larger than the initial time,indicating that the slope is permanently deformed.The influence of frost heave deformation on the internal force of the anchor rod cannot be ignored,and the attention should be paid to slope engineering in the areas with similar soil climate.