不同加载速率下差异性含水率尾砂胶结充填体力学行为及损伤特性研究

Study on Mechanical Behavior and Damage Characteristics of Cemented Tailings Backfill with Different Water Content Under Different Loading Rates

充填体的力学特性是充填配比设计和维护地下采场稳定性的关键指标,而加载速率变化与充填体所处环境(湿度、温度)不同均会对充填力学行为产生影响。本工作对不同含水率(干燥、饱水、自然)充填体开展了变加载速率(0.1 mm/min、0.25 mm/min、0.5 mm/min、1 mm/min、2 mm/min)的单轴抗压强度测试,获得了含水率和加载速率作用下的充填体力学参数和破坏模式,并依据能量守恒定理,研究了不同条件影响下充填体的能量演化规律,建立了基于能量的损伤变量。结果表明:(1)随着加载速率增加,充填体的抗压强度先增加再减小,存在临界加载速率;干燥和饱水对充填体的抗压强度和弹性模量分别具有强化和弱化效应,干燥导致充填体由延性向脆性转变,应力-应变曲线达到峰值应力后快速下降,而饱水虽有利于充填体的延性,但水的弱化作用使其在较小应变下即发生破坏。(2)加载速率由0.1 mm/min增加至2 mm/min,干燥充填体破坏模式由拉剪混合破坏逐渐向以拉伸为主的破坏模式转变,饱水充填体以拉伸破坏为主,而自然充填体整体上表现为拉剪混合破坏。(3)提高加载速率加快了充填体的能量交换,干燥、饱水和自然对充填体能量演化的影响主要体现在应力-应变曲线塑性屈服阶段与破坏阶段,耗散能-应变曲线的斜率由大到小顺序为干燥、饱水、自然。(4)基于能量演化的损伤特征曲线呈现出初始损伤、损伤稳定发展、加速损伤和破坏四个阶段,提高加载速率减小了加速损伤阶段的起始应变,干燥和饱水加剧了充填体损伤发展。该研究可为深入理解开采扰动引起的荷载变化和不同湿度条件下充填体的力学行为和稳定性提供理论依据。

The mechanical properties of backfill are the key indexes for filling ratio design and maintaining the stability of underground stope.The variation of the loading rate and the environment(humidity,temperature)in which backfill is located can affect the mechanical behavior of the backfill.In this work,uniaxial compressive strength tests with variable loading rates(0.1 mm/min,0.25 mm/min,0.5 mm/min,1 mm/min and 2 mm/min)were carried out for backfill with different water content(dry,saturated and nature).The mechanical parameters and failure modes of fillings under state change and loading rate were obtained.According to the energy conservation theorem,the relationship between the energy evolution and stress-strain behavior of backfill under different conditions was studied.On this basis,the damage variable of backfill based on energy was established.The results show that:(i)as the loading rate increased,the compressive strength of backfill first increased and then decreased,and there was a critical loading rate.The dry and saturated had strengthening and weakening effects on the compressive strength and elastic modulus of backfill respectively.The dry led to the transformation of backfill from ductility to brittleness,and the stress-strain curve decreased rapidly after reaching the peak stress.Although the saturated state was conducive to the ductility of backfill,the weakening effect of water makes it destroy under small strain.(ii)When the loading rate increased from 0.1 mm/min to 2 mm/min,the failure mode of the dry backfill gradually changed from tensile shear mixed failure to tensile failure(less shear failure).The saturated filling body is mainly tensile failure,while the nature backfill showed tensile shear mixed failure as a whole.(iii)Increasing the loading rate accelerated the energy exchange of backfill.The effects of drying,saturation and nature on the energy evolution of backfill were mainly reflected in the plastic yield stage and failure stage of the corresponding stress-strain curve.The slope of the energy dissipation strain curve is dry,saturation and nature from large to small.(iv)The damage strain characteristic curve based on energy evolution showed four stages:initial damage,stable damage development,accelerated damage and failure.Increasing the load rate shortens the initial strain in the accelerated damage stage,and the dry and saturated aggravates the damage development of backfill.This study can provide a theoretical basis for further understanding the load change caused by mining disturbance and the mechanical behavior and stability of backfill under different humidity conditions.