The geostress and rock blasting in underground engineering may greatly affect the stress thresholds of surrounding rock.In this study,pre-damage impact tests were first conducted on granite under varying confining pre...The geostress and rock blasting in underground engineering may greatly affect the stress thresholds of surrounding rock.In this study,pre-damage impact tests were first conducted on granite under varying confining pressures(5,10 and 15 MPa)and numbers of impacts(1,5,10 and 15 impacts).Then,uniaxial compression tests were undertaken on the pre-damaged granite to study the evolution of stress thresholds using the crack volume strain method and acoustic emission method.The crack damage stresses determined by the two methods were compared.Additionally,based on the rise time amplitude and average frequency,the evolution law of microcracks inside rock specimens was revealed,and an improved acoustic emission method was proposed.The results indicated that as the number of impacts increased,the crack closure stress,crack damage stress,and peak stress of granite specimens initially rose and then declined,while they continuously increased with the confining pressure.The proportion of shear cracks first declined and then rose with greater number of impacts and decreased with higher confining pressure,and that of tensile cracks showed the opposite trend.The improved acoustic emission method was more accurate in identifying the crack damage stress.展开更多
Four key stress thresholds exist in the compression process of rocks,i.e.,crack closure stress(σ_(cc)),crack initiation stress(σ_(ci)),crack damage stress(σ_(cd))and compressive strength(σ_(c)).The quantitative id...Four key stress thresholds exist in the compression process of rocks,i.e.,crack closure stress(σ_(cc)),crack initiation stress(σ_(ci)),crack damage stress(σ_(cd))and compressive strength(σ_(c)).The quantitative identifications of the first three stress thresholds are of great significance for characterizing the microcrack growth and damage evolution of rocks under compression.In this paper,a new method based on damage constitutive model is proposed to quantitatively measure the stress thresholds of rocks.Firstly,two different damage constitutive models were constructed based on acoustic emission(AE)counts and Weibull distribution function considering the compaction stages of the rock and the bearing capacity of the damage element.Then,the accumulative AE counts method(ACLM),AE count rate method(CRM)and constitutive model method(CMM)were introduced to determine the stress thresholds of rocks.Finally,the stress thresholds of 9 different rocks were identified by ACLM,CRM,and CMM.The results show that the theoretical stress−strain curves obtained from the two damage constitutive models are in good agreement with that of the experimental data,and the differences between the two damage constitutive models mainly come from the evolutionary differences of the damage variables.The results of the stress thresholds identified by the CMM are in good agreement with those identified by the AE methods,i.e.,ACLM and CRM.Therefore,the proposed CMM can be used to determine the stress thresholds of rocks.展开更多
目的 比较韶音后挂式骨导助听器对不同类型听力损失患者的听力干预短期效果,探讨其临床应用前景。方法 55例听力损失患者(年龄18~82岁;传导性听力损失9例,感音神经性听力损失15例,混合性听力损失31例;左右耳0.5、1、2、4 kHz四个频率的...目的 比较韶音后挂式骨导助听器对不同类型听力损失患者的听力干预短期效果,探讨其临床应用前景。方法 55例听力损失患者(年龄18~82岁;传导性听力损失9例,感音神经性听力损失15例,混合性听力损失31例;左右耳0.5、1、2、4 kHz四个频率的骨导纯音听阈均≤60 dB HL)配戴韶音后挂式骨导助听器,分别于配戴助听器前和配戴第14±2 d行声场总体听阈、单音节识别率及安静环境语句识别阈测试,比较配戴助听器前后的结果差异。并于配戴第14±2 d使用IOI-HA问卷对助听器使用效果进行评估。结果 患者配戴后挂式骨导式助听器后声场四个频率平均听阈(39.3±4.9 dB HL)较配戴前(56.5±8.2 dB HL)显著改善,差异有统计学意义(P<0.001)。患者助听前单音节识别率(给声强度:患者助听前双音节言语识别阈减5 dB)为29.8%±11.4%,配戴第14±2 d为72.4%±14.4%,配戴后单音节识别率显著提高,差异有统计学意义(P<0.001)。患者语句识别阈由配戴前的48.6±9.7 dB HL降至34.3±5.6 dB HL,差异有统计学意义(P<0.001)。配戴14±2 d时IOI-HA问卷评估总分平均值为29.0±3.8分。结论 后挂式骨导助听器可显著提高传导性、0.5~4 kHz骨导纯音听阈不超过60 dB HL的混合性及感音神经性听力损失患者的听力及言语识别能力。展开更多
基金Project(2023YFC2907400)by the National Key Research and Development Program of China-2023 Key Special ProjectProject(51974043)supported by the National Natural Science Foundation of China+2 种基金Project(SKLCRKF1908)supported by the Open Fund of the State Key Laboratory of Coal Resources in Western China,Xi’an University of Science and Technology,ChinaProject(2023JJ10072)suupported by the Hunan Provincial Natural Science Foundation for Distinguished Young ScholarsProject(2022RC1173)supported by the Science and Technology Innovation Program of Hunan Province,China。
文摘The geostress and rock blasting in underground engineering may greatly affect the stress thresholds of surrounding rock.In this study,pre-damage impact tests were first conducted on granite under varying confining pressures(5,10 and 15 MPa)and numbers of impacts(1,5,10 and 15 impacts).Then,uniaxial compression tests were undertaken on the pre-damaged granite to study the evolution of stress thresholds using the crack volume strain method and acoustic emission method.The crack damage stresses determined by the two methods were compared.Additionally,based on the rise time amplitude and average frequency,the evolution law of microcracks inside rock specimens was revealed,and an improved acoustic emission method was proposed.The results indicated that as the number of impacts increased,the crack closure stress,crack damage stress,and peak stress of granite specimens initially rose and then declined,while they continuously increased with the confining pressure.The proportion of shear cracks first declined and then rose with greater number of impacts and decreased with higher confining pressure,and that of tensile cracks showed the opposite trend.The improved acoustic emission method was more accurate in identifying the crack damage stress.
基金Projects(2021RC3007,2020RC3090)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProjects(52374150,52174099)supported by the National Natural Science Foundation of China。
文摘Four key stress thresholds exist in the compression process of rocks,i.e.,crack closure stress(σ_(cc)),crack initiation stress(σ_(ci)),crack damage stress(σ_(cd))and compressive strength(σ_(c)).The quantitative identifications of the first three stress thresholds are of great significance for characterizing the microcrack growth and damage evolution of rocks under compression.In this paper,a new method based on damage constitutive model is proposed to quantitatively measure the stress thresholds of rocks.Firstly,two different damage constitutive models were constructed based on acoustic emission(AE)counts and Weibull distribution function considering the compaction stages of the rock and the bearing capacity of the damage element.Then,the accumulative AE counts method(ACLM),AE count rate method(CRM)and constitutive model method(CMM)were introduced to determine the stress thresholds of rocks.Finally,the stress thresholds of 9 different rocks were identified by ACLM,CRM,and CMM.The results show that the theoretical stress−strain curves obtained from the two damage constitutive models are in good agreement with that of the experimental data,and the differences between the two damage constitutive models mainly come from the evolutionary differences of the damage variables.The results of the stress thresholds identified by the CMM are in good agreement with those identified by the AE methods,i.e.,ACLM and CRM.Therefore,the proposed CMM can be used to determine the stress thresholds of rocks.
文摘目的 比较韶音后挂式骨导助听器对不同类型听力损失患者的听力干预短期效果,探讨其临床应用前景。方法 55例听力损失患者(年龄18~82岁;传导性听力损失9例,感音神经性听力损失15例,混合性听力损失31例;左右耳0.5、1、2、4 kHz四个频率的骨导纯音听阈均≤60 dB HL)配戴韶音后挂式骨导助听器,分别于配戴助听器前和配戴第14±2 d行声场总体听阈、单音节识别率及安静环境语句识别阈测试,比较配戴助听器前后的结果差异。并于配戴第14±2 d使用IOI-HA问卷对助听器使用效果进行评估。结果 患者配戴后挂式骨导式助听器后声场四个频率平均听阈(39.3±4.9 dB HL)较配戴前(56.5±8.2 dB HL)显著改善,差异有统计学意义(P<0.001)。患者助听前单音节识别率(给声强度:患者助听前双音节言语识别阈减5 dB)为29.8%±11.4%,配戴第14±2 d为72.4%±14.4%,配戴后单音节识别率显著提高,差异有统计学意义(P<0.001)。患者语句识别阈由配戴前的48.6±9.7 dB HL降至34.3±5.6 dB HL,差异有统计学意义(P<0.001)。配戴14±2 d时IOI-HA问卷评估总分平均值为29.0±3.8分。结论 后挂式骨导助听器可显著提高传导性、0.5~4 kHz骨导纯音听阈不超过60 dB HL的混合性及感音神经性听力损失患者的听力及言语识别能力。
