비연속 절리의 전단 거동에 관한 기초 연구

학위논문(박사)--서울대학교 대학원 :공과대학 에너지시스템공학부,2020. 2. Jae Joon Song.The mechanical behavior of intact rock between adjacent joints (rock bridge) as well as the geometrical and mechanical properties of joints is highly influential with regard to the shear strength of the weakness planes. Usually, several non-persistent coplanar/en-echelon joints interact in a rock mass which is under pressure and eventually form a combined shear plane where failure takes place. Therefore, comprehensive knowledge of the shear mechanism of both joints and rock bridges is required to assess the shear strength of a probable failure path. To investigate the shear behavior of weakness planes a novel procedure was proposed to prepare casted specimens embedding non-persistent (disc-shaped) rough joints using 3D printing and casting technologies. Rock bridge ratio and joint dispersion effects of both single joint and coplanar intermittent joints on the shear strength of the 3D printed and plaster specimens were experimentally examined by conducting several direct shear tests under constant normal load (CNL) condition. The results showed that, regardless of the number of joints on the plane of weakness, the rock bridge ratio has an increasing effect on the shear strength. Digital image correlation (DIC) technique demonstrated that the moment of force exerted due to the boundary condition applied by a direct shear test machine disturbs the uniform distribution of the normal and shear loads on the plane of weakness. Hence, the joint layout on the plane of weakness could be influential to a great extent. DIC analysis also showed that the cracks mainly initiate in tensile mode. Moreover, it was found that the joints embedded in specimens with higher rock bridge ratios have smaller contribution to the shear strength. The influence of the joint roughness on the shear behavior of the rock mass containing a single non-persistent rough joint was studied through an extensive experimental work when other variables, namely nominal normal stress and rock bridge ratio are considered. Three levels for three different variables (joint roughness, rock bridge ratio, and nominal normal stress) were considered, and the effects of these factors on the shear behavior of prepared specimens were tested. The experimental results showed a clear influence of the three variables on the shear strength of the specimens. The rock bridge ratio and the normal stress were found to be relatively more influential than the joint roughness with regard to the shear strength of the specimens. It is proved that the shear strength cannot be traditionally evaluated by simply adding the shear strength of the jointed zone to that of the bridged zone while the zones are under identical normal stress. The results also showed that normal stress applied to the embedded jointed zone of weakness planes is smaller than that to the bridged zone but still considerable and should thus be taken into account during shear strength evaluation. Furthermore, three distinct phases of dilation were detected for specimens containing a non-persistent rough joint. The first phase demonstrates the dilation of the specimens before the failure point. A DIC analysis revealed that the dilation in this phase is partially due to the rotation of the specimens as a result of the inevitable existing gap between the upper and lower specimen holders of the direct shear test machine. In the second phase, dilation due to crack propagation and coalescence is followed by compression due to the closure of the enforced failure plane. Finally, the third phase of dilation complies with the dilation mechanism of a persistent rough joint. Moreover, a camcorder was used to analyze the location and sequence of the initiated cracks. In most cases, the first crack was initiated at the axis of rotation and propagated to the circumference of the embedded joint and the last crack propagated from the other side of the joint circumference, eventually resulting in a rupture. It is important to note that the cracks that initiated and propagated before the final crack did not significantly alter the path of the shear stress-shear displacement curves. The amount of normal load applied to the non-persistent embedded joints (joint normal stress) is one of the key factors for the estimation of joint friction contribution to the shear strength of rock mass containing the joints. Two different experimental approaches are proposed to measure the joint normalstress. The first approach (approach I) retrieves the joint normal stress by examining the normal stress-joint closure relationship of specimens containing non-persistent joints, and the second approach (approach II) utilizes joint crushed area as an indicator. The results of experiments carried out based on the approach I show that the joint normal stress is greater when the size of the embedded joint and the normal stress applied to the specimen containing that joint are greater. An analytical equation is proposed to evaluate the joint normal stress by assuming a uniform normal deformation throughout the rock mass undergoing normal stress, and is validated by the results of approach I experiments. Lastly, the effects of some influential factors, namely normal stress, rock bridge ratio, joint roughness, and material strength, on the shear behavior of the specimens containing a single non-persistent rough joint were experimentally analyzed to reach an empirical model representing the shear strength of the specimens. In order to investigate the pure effects of the main factors and their interactions on the shear strength of the specimens, and also to express the results of the experiments quantitatively, in terms of an empirical model, twenty seven-trial orthogonal array matrix (L27) developed by Taguchi techniques was selected for providing the experimental layout. The shear strength of twenty seven specimens was measured through conducting direct shear test based on the selected experimental layout. Finally, an empirical criterion which can precisely express the relationship between the shear strength of the specimens and the investigated parameters was proposed. 91% of the variability in the shear strength of the specimens can be explained by the proposed model.일반적으로 암반의 연약면은 한 평면상에 존재하는 여러 내포절리(non-persistent joint)가 상호작용하여 형성된다. 암반 연약면의 전단강도는 내포절리의 기하학적 그리고 기계적인 성질과 그 인접한 내포절리 사이에 존재는 무결암(석교; rock bridge)의 기계적인 성질에 의해 결정된다. 따라서, 전단파괴 가능성이 있는 연약면의 전단강도를 평가하기 위해서는 절리와 석교의 전단파괴 메커니즘에 대한 통합적인 이해가 필요하다. 이 연구에서는 연약면의 전단거동을 조사하기 위해 거칠기가 있는 절리를 내포하는 시편을 3D 프린팅 및 주조 기술 이용하여 제작하는 기법을 제안하였다. 일정수직하중(constant normal load; CNL) 조건 하의 직접전단시험을 통해, 석교 비 (rock bridge ratio)와 절리 분산도 (joint dispersion)가 단일 혹은 여러 내포절리를 가진 시편의 전단강도에 미치는 영향을 조사하였다. 그 결과 연약면에 존재하는 내포절리의 개수와 상관 없이 석교 비가 증가하면 시편의 전단강도가 증가한다는 것을 확인하였다. 또한 디지털 이미지 상관법(digital image correlation)을 통해 직접전단시험기의 경계 조건 하에 발생하는 돌림힘이 연약면의 수직응력과 전단응력의 분포를 교란시킨다는 것을 확인하였다. 따라서 교란된 응력 분포에 의해 내포절리의 위치 분포가 연약면에 큰 영향을 미칠 수 있음을 보였다. 더 나아가, 디지털 이미지 상관법을 통해 전단과정에서 발생하는 균열이 대부분 인장균열임을 확인하였다. 그리고 큰 석교 비의 시편에 내포된 절리일수록 전단강도에 더 미미한 영향을 미치는 것으로 나타났다. 절리 거칠기가 단일 내포절리를 포함한 암반의 전단거동에 미치는 영향을 명목 수직응력 (nominal normal stress)과 석교 비를 고려하여 조사하였다. 3 가지 요인 (절리 거칠기, 명목 수직응력과 석교 비)에 대해 각각 3 가지 수준을 고려하였으며, 각 요인이 시편의 전단거동에 미치는 영향을 광범위한 실험을 통해 조사하였다. 실험 결과, 시편의 전단강도는 3 가지 요인으로부터 명확한 영향을 받았으며 그 중에서 석교 비와 명목 수직응력이 절리 거칠기에 비해 강한 영향을 끼쳤다. 또한 연약면의 전단강도를 단순히 절리면과 주변 무결암의 동일 수직응력 하의 전단강도 합으로 평가할 수 없다는 것을 확인하였다. 내포절리에 적용하는 수직응력이 석교에 적용하는 수직응력에 비해 작지만 연약면의 전단강도를 평가할 때 무시하지 못하는 정도였다. 더 나아가, 거칠기가 있는 내포절리를 포함한 시편의 전단팽창 (shear dilation) 과정을 3 단계로 구분할 수 있었다. 첫 번째 단계는 전단파괴 이전의 팽창을 나타낸다. 디지털 이미지 상관법을 통해 첫 번째 단계에 해당하는 변위의 일부는 직접전단시험기에서 시편을 고정하는 상부와 하부 사이에 존재하는 틈에 의한 시편의 회전에 기인한 것임을 확인하였다. 두 번째 단계에서는 균열 성장에 의한 팽창과 이를 뒤따르는 연약면의 닫힘이 나타난다. 마지막으로 세 번째 단계에서는 완전한 거친 절리 (persistent rough joint)의 전단팽창거동과 일치하는 거동이 나타난다. 전단과정에서 발생하는 균열의 위치와 순서의 경우 전단시험을 동영상 촬영하여 분석하였다. 대부분의 경우에 첫 번째 균열은 시편의 회전축에서 시작하여 내포절리의 가장자리로 성장하였으며 마지막 균열은 내포절리의 반대편 가장자리에서 성장하면서 최종적으로 시편이 파괴에 도달하였다. 이때 마지막 균열 이전에 성장한 균열들은 전단응력-변위곡선의 경로를 크게 바꾸지 못했다. 내포절리에 적용하는 수직응력(절리 수직응력; joint normal stress)은 절리의 마찰이 내포절리가 있는 암반의 전단강도에 미치는 영향을 예측하는데 필요한 주요인자이다. 이 연구에서는 절리 수직응력을 측정하기 위한 실험적 접근법 두 가지를 제안하였다. 첫 번째 접근법은 수직응력-절리 닫힘 관계를 이용하여 절리 수직응력을 측정하며, 두 번째 접근법은 절리의 파쇄 영역을 이용하여 절리 수직응력을 측정한다. 첫번째 접근법을 이용하여 절리 수직응력을 측정한 결과, 절리 수직응력은 내포절리의 크기가 클수록 그리고 시편에 적용된 수직응력이 클수록 큰 것으로 나타났다. 더 나아가 암반의 수직변위가 암반 내에서 균일하다 가정하여 절리 수직응력을 계산하는 이론식을 제안하였으며 실험에서 측정된 절리 수직응력을 통해 검증을 하였다. 마지막으로 수직응력, 석교 비, 절리 거칠기 그리고 재료 강도가 단일 내포절리를 가지는 시편의 전단거동에 미치는 영향을 실험적으로 분석하여 시편의 전단강도를 추정하는 경험식을 도출하였다. 전단강도에 대한 주요인자들의 순수한 영향과 인자 간의 상호작용에 의한 영향을 정량적으로 조사하기 위해, 다구찌 방법 (Taguchi method)의 27-직교 배열 (27-trial orthogonal array matrix; L27)하에서 27 개 시편의 전단강도를 측정하였다. 측정된 전단강도를 바탕으로 전단강도와 조사된 인자들의 관계를 정확히 표현하는 경험식을 도출 및 제안하였다. 제안한 경험식은 시편의 전단강도 변동성의 91%를 설명한다.Chapter 1. Introduction 1 1.1 Motivation 1 1.2 Outline of dissertation 6 1.3 Research contributions 6 Chapter 2. Background and literature review 9 2.1 Analytical background 9 2.2 Experimental studies 13 2.3 Numerical Simulations 16 Chapter 3. Experimental procedure 19 3.1 Equipment and Experimental Settings 19 3.1.1 3D printer 19 3.1.2 Direct shear test machine 20 3.1.3 Loading machine and strain measurement 22 3.1.4 Camcorder 22 3.1.5 3D laser profiler 23 3.2 Materials 24 3.2.1 3D printed specimens 24 3.2.2 Plaster specimens 25 3.3 Specimen Preparation Procedure 27 3.3.1 3D printed specimens 27 3.3.2 Plaster specimens 27 Chapter 4. Shear behavior of artificial rock containing non-persistent open joints/closed rough joint 35 4.1 Shear behavior of artificial rock containing single or multiple coplanar non-persistent open joints 35 4.1.1 Experimental strategy. 35 4.1.2 Influence of the rock bridge ratio. 37 4.1.3 Influence of the joint dispersion 43 4.1.4 Effect of the boundary condition 50 4.1.5 Failure mechanism 52 4.1.6 Dilation mechanism and joint friction mobilization 55 4.2 Shear mechanism of artificial rock containing a single nonpersistent rough joint 61 4.2.1 Experimental strategy 61 4.2.2 Experimental results 63 4.2.3 Shear strength evaluation considering cases I, II, and III. 70 4.2.4 Dilation mechanism 75 4.2.5 Cracking analysis 79 4.3 The highlights of chapter 82 Chapter 5. Empirical model (criterion) for shear strength of rock mass containing a single non-persistent rough joint 85 5.1 Fraction of normal load distributed to non-persistent embedded joints 85 5.1.1 Methodology 85 5.1.2 Results 93 5.2 Empirical model (criterion) 110 5.2.1 Design of experiment (DOE) 110 5.2.2 Experimental design 115 5.2.3 Experimental results 119 5.2.4 Empirical model 121 Chapter 6. Discussions and Conclusions 125 6.1 Discussions and future works 125 6.2 Conclusions 130 References 139 Appendix 147Docto

Application of 3D printing and micro-CT scan to rock dynamics

2nd International Conference on Rock Dynamics and Applications (RocDyn), May 18-19, 2016, Suzhou, People's Republic of ChinaDepartment of Civil and Environmental Engineerin

The Effects of Metatarsal Pad on Plantar Pressure of the Forefoot in Individuals with Diabetic Peripheral Neuropathy: A Randomized Crossover Study

Introduction: Foot insoles are widely used to reduce excessive pressure exerted on the plantar surface of the foot and prevent diabetic foot ulceration. The objective of this study was to investigate the effects of the metatarsal pad on pressure on the forefoot area. Materials and Methods: This randomized crossover clinical trial was conducted on 18 volunteers (5 women and 13 men) with diabetic peripheral neuropathy. Plantar pressure was recorded while participants walked over a plantar pressure platform in three random conditions of barefoot, with a placebo intervention, and with a metatarsal pad. The processed variables were statistically analyzed using repeated measure one-way ANOVA. Results: The metatarsal pad caused a significant reduction in mean pressure on the forefoot compared to the barefoot and placebo conditions (P < 0.001). The metatarsal pad also significantly reduced the time-pressure integral in the forefoot compared to the barefoot and placebo conditions (P < 0.001). There was no significant difference in the time-pressure integral of the total plantar surface between the three conditions. Conclusion: The metatarsal pad transfers the forefoot load to the midfoot area, thereby, reducing the pressure exerted on the forefoot. This finding implies that using a metatarsal pad can be an effective intervention to prevent diabetic foot ulceration

تأثیر استفاده از کفی‌های طبی در میزان مصرف انرژی افراد دچار صافی کف پا طی راه رفتن

مقدمه: کاهش ارتفاع قوس طولی داخلی پا تحت عنوان صافی کف پا خوانده می‌شود. تحقیقات بسیاری پیرامون اثبات تأثیر صافی کف پا بر ویژگی‌های راه رفتن افراد صورت گرفته است، اما در زمینه تأثیر کف پای صاف بر مصرف انرژی این افراد شواهد اندکی وجود دارد. هدف از مطالعه حاضر، بررسی تأثیر صافی کف پا و درمان ارتزی آن بر تغییرات مصرف انرژی این بیماران بود. مواد و روش‌ها: در این مطالعه دو گروه 25 نفری از افراد سالم و دارای کف پای صاف شرکت کردند. مطالعه از نوع کارآزمایی بالینی بود. نمونه‌های مورد نظر از بین دانشجویان و کارمندان خانم دانشگاه علوم پزشکی اصفهان با میانگین سنی 21 سال انتخاب شدند. ارزیابی هر دو پای افراد هر دو گروه از طریق فوت‌پرینت و به کمک نرم‌افزار Solid work انجام شد. برای اندازه‌گیری میزان مصرف انرژی از متغیر شاخص نرخ فیزیولوژیکی (Physiological cost index یا PCI) استفاده گردید. بررسی این متغیر با کمک سیستم اندازه‌گیری ضربان قلب در حین حرکت، ساخت شرکت پولار صورت گرفت. تفاوت بین PCI هر دو گروه توسطTwo sample t-test  و تأثیر استفاده از ارتز توسط Paired t-test مورد بررسی قرار گرفت. میزان متوسط PCI در افراد سالم 368/0 و در افراد با صافی کف پا 357/0 ارزیابی گردید (0393/0 = P). یافته‌ها: مصرف انرژی افراد دچار صافی کف پا نسبت به افراد سالم تفاوت محسوسی داشت. استفاده از کفی طبی عملکرد افراد دچار صافی کف پا را حین راه رفتن ارتقاء داد (05/0 > P). مقدار مصرف انرژی بر اساس پارامترهای PCI و THB (Total heart rate beat) تفاوت معنی‌داری را حین استفاده از کفی و بدون کفی نشان داد (05/0 > P). نتیجه گیری: راستای نا‌مطلوب مفاصل اندام تحتانی در بیماران دچار صافی کف پا موجب افزایش PCI در افراد این گروه نسبت به افراد سالم می‌شود و استفاده از کفی‌های طبی موجب بهبود راستای پا و در نتیجه کاهش مصرف انرژی در این افراد می‌گردد. کلید واژه‌ها: صافی کف پا، مصرف انرژی، شاخص نرخ فیزیولوژیکی، راه رفتن، کفی طب

Experimental Study on Shear Mechanism of Rock-Like Material Containing a Single Non-Persistent Rough Joint

The geometrical and mechanical properties of non-persistent joints as well as the mechanical behavior of intact rock (rock bridges) are significantly effective in the shear strength of weakness planes containing non-persistent joints. Therefore, comprehensive knowledge of the shear mechanism of both joints and rock bridges is required to assess the shear strength of the planes. In this study, the shear behavior of specimens containing a single non-persistent rough joint is investigated. A novel procedure was used to prepare cast specimens embedding a non-persistent (disc-shaped) rough joint using 3D printing and casting technology, and the shear strength of the specimens was examined through an extensive direct shear testing program under constant normal load (CNL) condition. Three levels for three different variables of the joint roughness, rock bridge ratio, and normal stress were considered, and the effects of these factors on the shear behavior of prepared samples were tested. The experimental results show a clear influence of the three variables on the shear strength of the specimens. The results show that the normal stress applied to the jointed zone of weakness planes is considerable, and thus joint friction contribution should be taken into account during shear strength evaluation. Furthermore, the dilation mechanism of the specimens before and after failure was investigated through a digital image correlation analysis. Finally, a camcorder was used to analyze the location and sequence of the initiated cracks

Evaluating the short term effects of kinesiology taping and stretching of gastrocnemius on postural control: A randomized clinical trial

Introduction: The ability to maintain balance is essential for both remaining in the standing position and preventing falls. Physical therapy techniques such as kinesiology taping (KT) and stretching are considered to be effective measures in ameliorating balance issues. However, there is no available study comparing the effects of these two methods on postural control. Thus, the current study aims to investigate and compare the efficacy of interventions accomplished through these methods on young and elderly subjects. Method: In a single-blind randomized clinical trial, 40 young subjects (60 years) were randomly assigned to two groups of KT and stretching. In the first group, inhibitory tape was applied to the gastrocnemius muscle. In the second group, 60 s of stretch was repeated 4 times. The static balance was evaluated before and after the interventions using the single-leg standing (SLS) test along with measurements of the velocity and displacement of the center of pressure by the force plate. Results: Based on the Mann-Whitney test, there were no significant differences between the tape and stretching techniques in the study variables of either group of participants, before and after the interventions (p > 0.05). However, the results of the Wilcoxon test showed a significant increase in single-leg stance time in the stretching group in the elderly subjects (p = 0.03). MANOVA results demonstrated significant group and time effects only in the SLS parameter (p < 0.05). Conclusion: Stretching the gastrocnemius seems to be more efficacious than KT for improving balance problems in older adults. Level of evidence: II. © 2019 Elsevier Lt

Research Paper: Evaluation of the Effects of Two Types of Foot Rockers on the Temporal-Spatial Gait Parameters in Diabetic Patients

Objective Foot ulcer is one of the main challenges of diabetic patients influencing their abilities to stand and walk. Various methods have been suggested to decrease the loads applied to the foot in this group of patients; most methods were not deemed successful and could only be used temporarily. Rocker shoes are recommended for foot ulcer treatment. Based on the available literature, it is still controversial whether or not the forces applied to the foot differ between diabetic and normal subjects. &nbsp;Moreover, it is not well understood which kind of rocker (heel or toe rocker) is more successful in decreasing the applied forces to the foot. Therefore, this study aimed to compare the loads applied on the foot in diabetic subjects and normal subjects and to determine the influence of rockers on the load of foot. The main hypothesis associated with this study was that heel and toe rockers had similar effects on the force applied on the foot in diabetic subjects.&nbsp; Materials & Methods In this interventional, and quasi-experimental study, 20 healthy and 20 diabetic subjects were recruited. The sample size was determined based on the average number of the subjects in the previous similar studies. The diabetic subjects were selected from the patients referred to foot clinics in Rehabilitation School of Isfahan University of Medical Sciences. A qualysis motion analysis system with a Kistler force plate (50&times;60 cm) was used to record the temporal-spatial gait parameters and forces applied on the leg during walking. The subjects were asked to walk with a comfortable speed along a level surface in a gait lab. &nbsp;The parameters such as temporal-spatial gait parameters, peaks of ground reaction forces, and force-time integral were used for analysis. The difference between the mean values of the parameters and between the subjects&rsquo; effects were evaluated by use analysis of variance with repeated measures test. The statistical analysis was done by SPSS17 and with significant level of 0.05. Results There was a significant difference between normal and diabetic foot subjects regarding cadence, stride length, and percentage of stance phase (P 0.06). There was a significant difference between the peak of the forces (anteroposterior [fy1, fy2], medio lateral [fx], and vertical [fz1, fz2, fz3]) applied on the leg in normal and diabetic foot. The type of rocker did not affect the spatiotemporal gait parameters (P < 0.05), while exhibited significant effect on the peak anteroposterior forces applied to the leg (P < 0.04). The mean value of the force-time integral of vertical component of ground reaction force varied based on the side and group (P < 0.04). Conclusion The results of this study showed that the force-time integral of vertical component of the ground reaction force increased significantly in subjects with diabetes, which is the main cause of foot ulcers. Although, heel and toe rockers did not influence the force applied to the foot or the force-time integral, it is recommended to use rocker shoes with wide base of support to increase the dynamic stability while decreasing the foot pressure. The main limitation is that the immediate effect of use of rocker was studies in this study . It is recommended to check the effect of rockers interventions after a certain period of their use

Static Balance in Patients with Vestibular Impairments: A Preliminary Study

Aims. Vestibular system is indicated as one of the most important sensors responsible for static and dynamic postural control. In this study, we evaluated static balance in patients with unilateral vestibular impairments. Materials and Methods. We compared static balance control using Kistler force plate platform between 10 patients with unilateral vestibular impairments and 20 normal counterparts in the same sex ratio and age limits (50±7). We evaluated excursion and velocity of center of pressure (COP) and path length in anteroposterior (AP) and mediolateral (ML) planes with eyes open and with eyes closed. Results. There was no significant difference between COP excursions in ML and AP planes between both groups with eyes open and eyes closed (p value > 0.05). In contrast, the difference between velocity and path length of COP in the mentioned planes was significant between both groups with eyes open and eyes closed (p value < 0.05). Conclusions. The present study showed the static instability and balance of patients with vestibular impairments indicated by the abnormal characteristics of body balance

The Comparison of the Effects of Flexible vs Rigid Ankle-foot orthoses on Balance and Walking Performance in Individuals With Multiple Sclerosis: A Crossover Study

Objectives: Ankle-Foot orthoses are used to minimize the impact of weakness in ankle dorsiflexion muscles. The study on different orthotic types defines the optimal design, which effectively improves the users’ mobility. This study investigated the potential benefits and risks of a Dictus-band (flexible orthotic), compared with a thermoplastic (fixed) ankle-foot orthosis on the mobility of individuals with Multiple Sclerosis (MS). Methods: Fifteen subjects with MS and dorsiflexion ankle weakness volunteered in this randomized crossover study. The study participants received either a Dictus-band or a thermoplastic ankle-foot orthosis worn on the weaker leg, compared to barefoot as the control condition. Postural stability during standing, forward reach test, timed up and go test, and walking speed in the 10-meter walking test were compared between the study conditions. Results: There were no significant differences in the postural stability and forward reach tests between study conditions (P>0.5). When the research participants used a Dictus-band, compared to the fixed ankle-foot orthosis, the time required to complete the timed up and go was significantly reduced [P0.5). No adverse or safety events were sustained in this research.  Discussion: The present study data provided initial evidence for the lack of detrimental effects of using the Dictus-band in subjects with MS and ankle dorsiflexion deficiencies