分级加载条件下深部灰岩蠕应变特性研究

Creep Strain Characteristics of Deep Limestone under Step Loading

为研究深部灰岩蠕应变特性,采用GDS-VIS三轴流变仪对不同深度试样做分级加载单轴蠕变试验。基于试验结果,计算出灰岩长期强度与瞬时强度之比的均值为0.758,且深度越深比值越小;分析不同深度灰岩在各分级应力水平下轴向蠕应变增量与加载级数的变化规律,并将蠕应变增量进行一次累加,得到轴向蠕应变。结果表明:蠕应变增量随级数的增加呈现先减小后剧增的变化规律,且随深度增加,蠕应变增量达到谷底所对应的应力百分比有明显增大趋势;在分级加载过程中,随级数增加,轴向蠕应变先后呈现减速增加、等速增加和加速增加3个发展阶段;当恒载应力百分比为60%~70%时,蠕应变趋于稳定,当超过该范围后,蠕应变加速增加直至发生蠕变破坏。研究得到的这一应力百分比范围可以为识别深部灰岩是否会发生蠕变破坏提供依据。

In the aim of exploring th e c re ep ch a ra c te r is t ic s of d e e p l im e s to n e ,u n iax ia l with GDS-＂VIS triaxial rheome ter by step loading on sp e cim en s from different d e p th s. Accordthe mean value （0.758） of th e ratio of long-term s trength to in stan tan eo u s strength d e c re a s e s as d ep th in c re a s e s.Furthermore ’ the variation law of axial c re ep strain in c rem en t of limestone in d iffe rent levels was investigated, and th en axial cre ep s train s were o b ta in ed by a c cum u lat in g c re ep strain in c rem e n t. Resultsrevealed that creep strain inc rement d e c re a s ed first an d th en in c re a sed drama tic ally with th e el. As depth increased , th e p e rc en tag e of stress cor responding to th e minimcreased. Moreover ’ with th e in c re a se of loading level ’ th e axial c re ep strain ex p e r ien c ed from decelerated growth ’ cons tant growth an d a c c e le ra ted growth. When th e stress p e rc en tag e ratio of co n s tan t loadwas within the range from 60% to 70% ’ c re ep strain ten d ed to b e s ta b le; whereastrain acceleratedly increased u n t i l c re ep fa i lu re. T h e re fo re, th e ran g e of stress p e rc enence for identifying whether c re ep fa ilu re will h ap p e n or not for d e ep lim e s to n e.