Unloading Effect of the Shear Resistance of Rock Joints

To investigate the stress path dependent of rock joints, a comparative experimental study was conducted using cement mortar replicas of artificially split rock joints. In total, 32 replicas were casted and divided into four groups by joint roughness coefficient (JRC). The effects of morphologic characteristics, normal stress levels and stress paths on the shear strength of joints were investigated through tangential loading tests and normal unloading tests. The comparative analysis on the test results indicated that the shear resistance has a distinct unloading effect. The variation trend of shear/normal stress ratio against the normal stress and JRC of the two test conditions were identical. However, under low normal-stress condition, the stress ratio of the joints under normal unloading stress is the higher one; while under higher normal stress, the relationship becomes converse. Compared to that of the tangential loading condition, shear/normal stress ratio of the unloading stress path reduces rapidly as the increasing of normal stress, and the influence of the morphology is masked under lower normal stress. The comparative study revealed a previously unknown unloading effect on the mechanical behavior of rock joints and will aid the estimation of the rock joints’ stability in a complex stress environment.

The Effect of Depth of Anaesthesia on the Severity of Mitral Insufficiency by Transesophageal Echocardiography

Background The assessment of mitral regurgitation (MR) is complex and complicated by the dynamic nature of this valvular abnormality. Intraoperative transesophageal echocardiography (TEE) is a well-established tool that is used to assess the mitral regurgitation (MR) before and after mitral valve reconstruction. Objectives This study conducted in the National Heart Institute in Cairo aimed at assessing the effect of depth of anaesthesia guided by bispectral index on the severity of mitral insufficiency as measured by transesophageal echocardiography. Patients and Methods This study was conducted in the National Heart Institute in Cairo. The study was conducted for a period of about six months after the approval from Ethical committee. Informed oral consent for every patient was obtained. Prospective observational cross-sectional study with a random sample of 20 patients at National Heart Institute. A sample size of at least 15 data pairs achieves 80% power to reject the null hypothesis of zero effect size when the population effect size is 0.80 and the significance level (alpha) is 0.05 using a two-sided paired ttest. Adult patients undergoing elective cardiac surgery in National Heart Institute. Results The MR severity decreased at a deeper anaesthesia at low BIS than at a shallower anaesthesia at high BIS in patients with organic MR. Eight patients out of twenty patients (40% with organic MR) showed a + 1 grade of improvement in MR grade, by semi-quantitively measuring maximal JA and VC width. Improvement in mitral regurge severity thought to be secondary to unloading effect of general anaesthesia on left ventricle causing a decrease in afterload, preload, and left ventricular dimensions. This study demonstrated that, a comparison between deep anaesthesia and shallow anaesthesia using BIS showed there is a significant reduction in multiple parameters of MR severity assessment secondary to unloading effect of general anaesthesia on left ventricle caused by a decrease in both afterload and preload. Conclusion This reduction in MR severity appeared to be significant enough to modify intraoperative decisions regarding valve surgery by underestimation of valve severity. Thus, strong consideration should be given to thorough preoperative assessment of MR severity, rather than relying on intraoperative findings.

Influence of the location of unloading piles in backfill on the stress-strain state of the bolverk

This article is devoted to the reconstruction and strengthening of structures of the bolverk type. The paper describes the calculation of the active ground pressure on the berth wall of the bolverk type when the latter is reinforced by unloading piles in the backfill of the wall. The aim of the work is to assess the change in the degree of impact of active ground pressure when changing the distance from the unloading piles to the mooring wall. This author calculated, which are identified and shown with the help of nomograms and graphs based on active earth pressure from the main characteristics of the soil, spacing of discharge piles, the angle of internal friction, the distance from the unloading of the piles to the wall; the options considered overlapping discharge zones without overlap; the resulting coefficients reduce the load under various conditions of construction. The proposed calculation allows us to estimate the unloading effect of the use of piles in the backfill of existing berth walls of the bolverk type.

Stability Analysis of TBM Tunnel Undercrossing Existing High-Speed Railway Tunnel: A Case Study from Yangtaishan Tunnel of Shenzhen Metro Line 6

During the construction of the underpass of a new tunnel, the excavation unloading effect disturbs surrounding rock masses and promotes surrounding rock deformation, inevitably changing stress and displacement in the existing tunnel. Taking Yangtaishan tunnel excavation of Shenzhen Metro Line 6 as an engineering example, effects of excavation programs of left and right lines on the deformation characteristics of newly excavated and existing tunnels were evaluated based on Midas numerical model and priority excavation advantages of the left line were determined. The settlement and horizontal deformation characteristics of the existing tunnel were analyzed using the construction monitoring method. Results showed that maximum settlement and horizontal deformation of the existing tunnel were 1.35 and 0.23 mm, respectively. Settlement of invert and inverted top along axis direction was from growth to decline, and then a V-shaped settlement trough was formed with maximum settlement values of 1.36 and 0.97 mm, respectively. Maximum settlement and uplift of the newly built tunnel appeared on the upper and bottom parts of invert, respectively. In the newly built tunnel segments, the top settlement was dominated and deformation was mainly distributed in both side areas. At the top of the existing tunnel segment, convergence settlement was 3.09 mm and settlement rate was slow first which was accelerated, then stabilized, and finally slowed down again which was opposite to the uplift development trend of the bottom of tunnel segment. The top of the existing tunnel segment showed four settlement stages, slow, rapid, stable, and slow settlement stages. Compared with the right line, preferential excavation of the left line had obvious advantages in terms of tunnel stability. The unloading effect of TBM excavation created vault settlement in the existing tunnels where actual settlement values were 1.12 and 1.13 times, which theoretically calculated settlement. The horizontal deformation of the existing tunnel was varied first linearly and then nonlinearly with maximum deformation in the convergence stage of 1.47 mm.

Study on Internal Force of Tunnel Segment by Considering the Influence of Joints

The mechanical performance of segments is an important aspect of the safety of tunnel structures. Study on the internal force of tunnel segment by considering the influence of joints is beneficial for obtaining a better understanding of the influence of various factors on the internal force of the segments. Based on the mechanical characteristics of shield segment joints, in which the displacements and stiffness are discontinuous, a mechanical model of the segment component under the constraints of elastic support was established. The elastic centre method and the principle of superposition were used to quantify the influence of joint displacements on the internal force of the segment component. Combined with a practical engineering application, the internal force of the segment component with joint rotation and dislocation was analysed. The displacements of the segment joints cause an unloading effect of the corresponding internal force of the joints, leading to internal force redistribution of each segment cross section. According to the spline interpolation results of the load test data of the segment joints, the internal force of the segment component under an external load is solved by the iterative method.

Biomechanical and Metabolic Effectiveness of an Industrial Exoskeleton for Overhead Work

Overhead work activities can lead to shoulder pain and serious musculoskeletal disorders (WMSD), such as rotator cuff injury and degeneration. Recently developed exoskeletons show promising results in supporting workers in such activities. In this study, a novel exoskeleton was investigated for two different overhead tasks with twelve participants. To investigate the effects of the device, electromyographic (EMG) signals of different shoulder and adjacent muscles as well as kinematic and metabolic parameters were analyzed with and without the exoskeleton. The mean EMG amplitude of all evaluated muscles was significantly reduced when the exoskeleton was used for the overhead tasks. This was accompanied by a reduction in both heart rate and oxygen rate. The kinematic analysis revealed small changes in the joint positions during the tasks. This study demonstrated the biomechanical and metabolic benefits of an exoskeleton designed to support overhead work activities. The results suggest improved physiological conditions and an unloading effect on the shoulder joint and muscles which are promising indicators that the exoskeleton may be a good solution to reduce shoulder WMSD among workers who carry out overhead tasks on a regular basis.

COMPARISON OF THREE CONTROL STRATEGIES FOR AXIAL BLOOD PUMP

Facing the gradually increased prevalence of heart failure (HF) and the shortage of donated hearts, the blood pump is widely used to prolong the life of end-stage HF patients: however, the pump generates continuous flow under constant rotational speed, declining the arterial pulsatility and causing related complications. Previous studies show that synchronous copulsation might be the best control strategy for restoring pulsatility, but synchronous strategies are needed to monitor the phase of the heartbeat, which will make the controller complex and impair its robustness. Here, we compare constant speed, synchronous copulsation in a model of a cardiovascular system with a blood pump, which shows that copulsation offers more arterial pulsatility, less pump power-consumption, and thus better battery endurance, and constant speed offers a greater ventricular unloading effect. Meanwhile, we design a strategy based on transforming left ventricular pressure, which is easier to implement and has similar effect to synchronous copulsation.