昆明泥炭土直剪蠕变特性及长期强度试验研究

Experimental study on direct shear creep characteristics and long-term strength of peaty soil in Kunming

昆明泥炭土的蠕变特性影响着该地区各类建(构)筑物的长期稳定性和结构安全。采用改进的应力控制式直剪仪,以分级加载方式开展一系列的直剪蠕变试验,研究不同固结压力下剪应变随剪应力与时间的变化规律,以及长期强度与短期强度间的关系。结果表明:昆明泥炭土具有显著的非线性蠕变特性,当剪应力较低时,直剪蠕变曲线表现为衰减稳定蠕变;随着剪应力增大,蠕变曲线会同时出现衰减稳定蠕变和非稳定等速蠕变;当剪应力较大时,则会呈现出加速蠕变现象,并快速发生破坏。在施加水平剪应力的瞬间,泥炭土即产生较大的剪切应变,且瞬时应变随着剪应力的增加而加大,而瞬时应变占总应变的比例逐渐降低,表明泥炭土在高剪应力水平下,蠕变现象加剧。与短期强度相比,泥炭土长期强度的黏聚力和内摩擦角均有一定程度的下降。当固结压力为50~400kPa时,长期强度约为短期强度的57%~70%。

Creep characteristics of peaty soil in Kunming affect the long-term stability and structure safety.By the improved stress-controlled direct shear apparatus,a series of direct shear creep tests are carried out with the multi-stage loading method.The variation of shear stress and strain with time and the relationship between long-term and short-term strength are studied under different consolidation pressures.The results show that the peaty soil in Kunming has obvious nonlinear creep characteristics.When the shear stress is low,the direct shear creep curve of peaty soil shows decay creep.With the increase of shear stress,both decay creep and unstable equal velocity creep appear in the creep curve.When the shear stress is high,peaty soil exhibits acceleration creep phenomenon,and is destroyed quickly.The large shear strain occurs at the moment of applying horizontal shear stress,the instantaneous strain increases with the increase of shear stress,while the proportion of instantaneous strain to total strain decreases gradually,which indicates that the creep deformation is aggravated under high shear stress.Compared with short-term strength,the cohesion and friction angle of long-term strength is smaller for peaty soil,and the long-term strength is about 57%~70%of the short-term strength when the consolidation pressure is 50-400 kPa.