跨地裂缝墙体开裂形态分析

应用非线性有限元法对跨地裂缝的墙体开裂形态进行了分析,确定出了具有三维活动性的地裂缝垂直穿越墙基时,墙体出现裂缝的位置、倾向、倾角和后期的发展状况,以及随沉降量与张开量比值变化的规律。结果表明:地裂缝垂直穿越围墙时,墙体上出现的裂缝一般有两种形式:一是位于地裂缝下盘的墙顶竖直裂缝,二是出现在地裂缝正上方墙体底部的斜裂缝;当地裂缝两盘的土体活动以水平拉张为主时,墙体底部出现的斜裂缝以高角度向上扩展,当地裂缝两盘的土体活动以差异沉降为主时,墙体底部出现的斜裂缝则以较缓的角度向上扩展,倾向与地裂缝相反;只要地裂缝的上下盘土体有微小的错动,一般2～3mm时,就会引起墙体的破裂,且墙体裂缝扩展迅速,几个毫米的错动量,就能使墙体裂缝扩展数十厘米,甚至贯通整个墙体;墙体斜裂缝在产生初期较为平直,随着裂缝的迅速扩展,端部稍向下弯曲,倾角减缓,整体呈弧弯状。

ANALYSES OF WALLS CRACKING FORMS OVER GROUND FISSURES

The author in this paper analyzed the cracking forms of walls over ground fissures with non-linear finite element method.The originated position,dip direction,dip angle and later mode of the cracks on walls are accomplished when the walls crossing over ground fissures with three-dimensional activity,and the changing law varying with different ratio of sedimentation and tensor are got.The results show that,there are two types of cracks generating on walls: the vertical cracks on top of walls located in footwall and the skew cracks at the bottom of walls just above ground fissures.The dip direction of the skew cracks is opposite to that of ground fissures.When the activity of ground fissures is mainly the tensor,the skew cracks at the bottom of walling expand upward with high angel;but when the activity is mainly the sedimentation,then the skew cracks expand upward with low angel.The walls could be broken so long as there was minute dislocation,generally 2～3 mm distance,occurred to the ground fissures.And the cracks expand quickly that several millimeters dislocation can make the cracks expand tens of centimeters,even finally breakthrough the walls.At the early developmental stage,the skew cracks are relatively flat,but with the quick expansion of cracks,the dip angles become lower.The later mode of the cracks likes a flexural arc.