盾构施工扰动对天津结构性黏土动力特性影响的试验研究

Experimental Study on Influences of Shield Construction Disturbance on Dynamic Characteristics of Tianjin Structured Clays

盾构隧道施工扰动会改变周围土体的应力、应变状态,破坏土的结构性,从而影响隧道后期的地震响应.通过共振柱试验和动单剪试验,分析了施工扰动对天津结构性黏土动剪切模量和阻尼比的影响.试验结果表明:施工扰动程度越大,平均应力归一化动剪切模量的初始值越小(应力释放程度较大的D4试样的平均应力归一化动剪切模量初始值为无应力释放的D1试样的74%),在相同剪应变下的归一化动剪切模量越小,动剪切模量的衰减速率越快,在相同剪应变下的阻尼比越大;土的结构性越弱,初始动剪切模量越小(无水泥掺量的B1试样的初始动剪切模量为4%水泥掺量的B4试样的59%),在相同剪应变下的动剪切模量越小,动剪切模量衰减速率越快,在相同剪应变下的阻尼比越大.盾构隧道施工扰动对结构性黏土动力特性的影响机理为:施工扰动会使结构性黏土的结构破损、结构性减弱,从而导致其归一化动剪切模量减小,动剪切模量衰减速率增大,阻尼比增大.因此,在进行盾构隧道抗震设计时应考虑前期施工扰动引起的结构性黏土的结构破损对动剪切模量的影响.

The construction disturbance of a shield tunnel will change the stress and strain states of its surrounding soils and destroy the structure of soils,thus affecting the tunnel’s subsequent seismic response.In this paper,the influences of construction disturbance on the dynamic shear modulus and damping ratio of Tianjin structured clays were analyzed by carrying out resonance column and dynamic simple shear tests.Results show that a larger degree of construction disturbance resulted in a smaller initial value of the dynamic shear modulus normalized by mean stress(e.g.,the initial value of normalized dynamic shear modulus by mean stress for specimen D4 which had a larger stress release degree was 74%of that for specimen D1 which had no stress release),a smaller normalized dynamic shear modulus under the same shear strain,a faster attenuation rate of dynamic shear modulus,and a larger damping ratio under the same shear strain.In comparison,a weaker soil structure led to a smaller initial dynamic shear modulus(e.g.,the initial dynamic shear modulus for specimen B1 which had no cement admixture was 59%of that for specimen B4 which had a cement admixture of 4%),a smaller dynamic shear modulus under the same shear strain,a faster attenuation rate of dynamic shear modulus,and a larger damping ratio under the same shear strain.The mechanism of influences of construction disturbance of shield tunnel on the dynamic characteristics of structured clays is that the construction disturbance causes the structural degradation of structured clays and weakens their struc-tures,which will lead to a decrease in normalized dynamic shear modulus,an increase in the attenuation rate of dy-namic shear modulus,and an increase in the damping ratio. Therefore,the influences of structural degradation of structured clays caused by construction disturbance at an early stage on the dynamic shear modulus should be consid-ered in the seismic design of shield tunnels.