Influence of excavation damaged zone on the dynamic response of circular cavity subjected to transient stress wave

Rearfoot strike (RFS) in children running produces impact forces that give rise to a transient stress wave traveling through the body. It could contribute to the development of injuries. The purpose of this study was to determine RFS prevalence during childhood while running at a self-selected velocity in a prospective longitudinal cohort study. A total of 175 children (68 girls), aged 6 to 14 years, participated in this study. The sample was divided into three age groups (age in 2016): 6-8 years, 9-11 years, and 12-14 years which were analysed three years later (2019). 2D video-based was used to record the RFS Taking into account all samples, in the jogging trial the prevalence of RFS (an average of both feet) was 86.9% in 2016 and 94.7% three years later; in the running trial the prevalence was 82.6 and 94.4%, respectively. In all samples a significant increase of RFS prevalence was found in both the jogging and running trials for both feet over three years (jogging, left foot, p=.011, right foot, p=.023; running, left foot, p=.001, right foot, p<.001). In girls, there were no significant differences in any conditions. In boys, a significant increase of RFS prevalence was found after three years in both feet (p<.01) in the running trial. This study shows that RFS prevalence in children increases with age and the results may be used to characterize typical running development in children population.

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The Method of Determining Excavation Damaged Zone by Acoustic Test and the Application in Engineering Cases

Advances in Civil Engineering ◽

10.1155/2021/5533828 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Qian-Cheng Sun ◽

Hao-Sen Guo ◽

Zhi-Hua Xu ◽

Yue Liu ◽

Xiao Xu

Keyword(s):

Rock Mass ◽

Damage Evolution ◽

Hard Rock ◽

Damage Zone ◽

Jointed Rock ◽

Jointed Rock Mass ◽

Surrounding Rock ◽

Excavation Damaged Zone ◽

Damaged Zone ◽

Columnar Jointed Rock Mass

It is very important to accurately determine the depth of excavation damaged zone for underground engineering excavation and surrounding rock stability evaluation, and it can be measured by acoustic test, but there is no quantitative method for analysis of the results, and it relies heavily on the experience of engineers, which leads to the low reliability of the results and also limits the application of the acoustic method. According to substantial field test data and the feedback of surrounding rock support parameters, the boundary method is proposed to determine the depth of excavation damaged zone in surrounding rock based on the relation between the ultrasonic velocity of measured point and the background wave velocity of rock mass. When the method is applied to the columnar jointed rock mass of Baihetan and the deep-buried hard rock of Jinping, the excavation damaged zone was well judged. The results in the Baihetan project show that the proposed method of determining excavation damage zone by the acoustic test can well demonstrate the anisotropy characteristics of the columnar jointed rock mass, and the damage evolution characteristics of jointed rock mass at the same position can also be obtained accurately. Moreover, the method also can accurately reveal the damage evolution process of the deep-buried hard rock under the condition of high ground stress, which proved the applicability of this method in jointed or nonjointed rock masses.

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