Spatiotemporal Deformation of Existing Pipeline Due to New Shield Tunnelling Parallel Beneath Considering Construction Process

In this paper, we study the effects of the shield tunnel construction on the deformation of an existing pipeline parallel to and above the new shield tunnel. We propose an analytical solution to predict the spatiotemporal deformation of the existing pipeline and consider different force patterns of the shield tunnelling, i.e., ground volume loss, support pressure, frictional force, and torsional force. The proposed method is validated by the monitoring data of Subway Line 3 of Nanchang and provides a reasonable estimation of the pipeline’s deformation. The parametric analyses are performed to study the influences on the pipeline’s deformation. The main advantage of our paper is that the spatiotemporal characteristics of the existing pipeline’s deformation are analysed, providing longitudinal deformation curve (LDC), deformation development curve (DDC), and grouting reinforcement curve (GRC). Compared with the perpendicular undercrossing project, both LDC and DDC have the same profiles and maximum values and move forward as a whole with the shield tunnel advance. Thus, the spatiotemporal deformation of the overall pipeline can be extrapolated from the deformation of two known points on the pipeline. The spatiotemporal characteristic curves combined with LDC, DDC, and GRC can suggest feasible, effective, and economical construction and grouting schemes to control the pipeline’s deformation after the deformation control standards have been determined.

A simplified approach to reliability evaluation of deep rock tunnel deformation using First-Order Reliability Method and Monte Carlo simulations

abstract: The Monte Carlo simulation (MCS) and First-Order Reliability Method (FORM) provide a reliability analysis in axisymmetric deep tunnels driven in elastoplastic rocks. The Convergence-Confinement method (CV-CF) and Mohr-Coulomb (M-C) criterion are used to model the mechanical interaction between the shotcrete lining and ground through deterministic parameters and random variables. Numerical models synchronize tunnel analytical models and reliability methods, whereas the limit state functions control the failure probability in both ground plastic zone and shotcrete lining. The results showed that a low dispersion of random variables affects the plastic zone's reliability analysis in unsupported tunnels. Moreover, the support pressure generates a significant reduction in the plastic zone's failure, whereas the increase of shotcrete thickness results in great reduction of the lining collapse probability.

Mechanism of Coal Burst and Prevention Practice in Deep Asymmetric Isolated Coal Pillar: A Case Study from YaoQiao Coal Mine

Coal pillar bursts continue to be a severe dynamic hazard. Understanding its mechanism is of paramount importance and crucial in preventing and controlling its occurrence. The extreme roadway deformations from the asymmetric isolated coal pillars in the central mining district of YaoQiao Coal Mine have responded with frequent intense tremors, with risky isolated coal pillar bursts. The theoretical analysis, numerical simulation, and field measurements were done to research the impact of spatial overburden structure and stress distribution characteristics on the isolated coal pillar area, aiming to reveal the mechanism of coal pillar burst leading to the practice of prevention and control in the asymmetric isolated coal pillar area. The study shows that the overburden structure of the asymmetric is an asymmetric “T” structure in the strike-profile, and the stress in the coal pillar is mostly asymmetric “saddle-shaped” distribution, with the peak stress in the east side of the coal pillar, and the coal pillar is a “high stress serrated isolated coal pillar.” Numerical simulation results showed that the support pressure in the isolated coal pillar area on the strike profile was asymmetrically “saddle-shaped” distribution. The peak vertical stress in the coal pillar area continued to rise and gradually shifted to the mining district's deep part. As a result, the response of the roadway sides to the dynamic load disturbance was more pronounced. They developed a coal burst prevention and control program of deep-hole blasting in the roof of asymmetrical isolated coal pillar roof and unloading pressure from coal seam borehole. Monitored data confirmed that the stress concentration was influential in the roadway’s surrounding rock in the asymmetric isolated coal pillar area, circumventing coal pillar burst accidents. The research outcomes reference the prevention and control of coal bursts at isolated working faces of coal pillars under similar conditions.

The Research on Stability of Surrounding Rock in Gob-side Entry Driving in Deep and Thick Seam

The gob-side entry driving is driving in low pressure area, which bears less support pressure and is easy to maintain, so it is widely used. Taking the gob-side entry driving in thick coal seam of Dongtan Coal Mine as an example, the reasonable size of pillar and the section of roadway are numerically simulated by combining numerical with measurement, and the roadway support is designed. According to the distribution of lateral stress in working face, eight pillars of different sizes are designed. By simulating and comparing the stress distribution of surrounding rock and the development range and shape of plastic zone in different positions, the pillar size of gob-side entry driving is optimized to be 4.5m. According to the results of optimization of roadway section, the section of straight wall semi-circular arch roadway is adopted. According to the analysis, the roadway is supported by bolt + steel mesh + anchor cable. By observing the stability of roadway, it provides experience for the stability study of roadway the gob-side entry driving with small pillar in thick seam.

Pressure Support Versus T-Piece Trial For Weaning From Mechanical Ventilation

Aim: To compare pressure support versus T-piece trial for weaning from mechanical ventilation Methodology: Randomized clinical trial in Surgical ICU, Khyber Teaching hospital Peshawar. 48 patients who had been mechanically ventilated for at least 24 hours and were deemed suitable for weaning took part in the study. SBT with pressure support ventilation of 8cm of H2O was performed on one group of patients for two hours while the other group received a 30-minute SBT with pressure support ventilation. It was successful when extubation process is completed, (being able to go 72 hours without mechanical ventilation after the first SBT). Results: Extubation was successful in 83.3% who received pressure support ventilation and in 75% who employed a T-piece. The patients who required reintubation were 12% with support pressure and 16.7% with T piece ventilation. Mortality rate in support pressure group is 16.7% while 25% in T piece ventilation group. Conclusion: Pressure support ventilation for 30 minutes had a much higher success rate when it came to extubation. For spontaneous breathing trials, a shorter, less taxing ventilation approach should be used rather than the traditional one. Keywords: Extubation, Support pressure, T piece

Evaluation of Input Geological Parameters and Tunnel Strain for Strain-softening Rock Mass Based on GSI

The regression analysis method is being widely adopted to analyse the tunnel strain, most of which ignore the strain-softening effect of the rock mass and also fail to consider the influence of support pressure, initial stress state, and rock mass strength classification in one fitting equation. This study aims to overcome these deficiencies with a regression model used to estimate the tunnel strain. A group of geological strength indexes (GSI) are configured to quantify the input strength parameters and deformation moduli for the rock mass with a quality ranging from poor to excellent. A specific numerical procedure is developed to calculate the tunnel strain around a circular opening, which is validated by comparison with those using existing methods. A nonlinear regression model is then established to analyse the obtained tunnel strain, combining twelve fitting equations to relate the tunnel strain and the factors including the support pressure, the GSI, the initial stress state, and the critical softening parameter. Particularly, three equations are for the estimation of the critical tunnel strain, the critical support pressure, and the tunnel strain under elastic behaviour, respectively; and the other nine equations are for the tunnel strain with different strain-softening behaviours. The relative significance between the GSI, the initial stress and the support pressure on the tunnel strain is assessed.

Research and Control of Underground Pressure Law of Coal Mining Face in Soft Rock Strata Based on Neural Network under the Background of Wireless Network Communication

Our country has a vast territory and rich resources, but it is a country with more coal, less oil, and poor gas. With the increase of our population, the development of society, and the more severe international situation, coal has become more important for our country’s economic development and energy. Security plays an irreplaceable role. Based on the neural network, this paper studies and controls the underground pressure law of the coal mine’s soft rock heading face, aiming at the safe and efficient mining of the first face and providing an experience for the next face. This paper mainly uses BP neural network learning algorithm and support pressure algorithm to measure and study the ground pressure law of coal mine soft rock heading face and establishes the ground pressure online monitoring system, which is used to analyze and summarize the ground pressure abnormal area during the mining of the working face, so as to provide the basis for safe mining of the working face. Through the field measured data, the initial pressure step and periodic pressure step at the upper, middle, and lower parts of the working face, the average working resistance of the support at the working face during pressure, and the dynamic load coefficient of the support are obtained. It is analyzed that the support in the middle of the working face has a large load and the pressure is obvious. The experimental results show that the initial support force of the whole working face is approximately normally distributed, the proportion of the initial support force in the range of 10–30 MPa accounts for more than 85% of the total statistics, and the frequency of the initial support force in the upper, middle, and lower stations at 10–25 MPa is 55%–65%.

Finite Analysis of Support Time for Tunnels in Strain-softening Rock Mass in Consideration of Fictitious Support Pressure

This study considers that the support time is quantitatively determined by the production limit of the displacement reduction factor and the support force under the extrusion conditions of the strain-softening rock mass. Therefore, the two indicators of the downlines under the support time are the displacement reduction factor of the support force and the yield limit. Based on the solution of the fictitious pressure proposed in an existing paper, the finite difference method is adopted to investigate the variations of the support force and displacement reduction factor versus the delayed distance considering different support types, initial stresses, and post-peak behaviours. The results show that on the one hand, the delay distance is suggested within 1 R0 in most tunnel cases; on the other hand, the factors have greater impact on rock-support interactions are rock mass and in-situ stress. Relatively contrast, softening and expansion behavior was not significant enough. Furthermore, it is also very important in composite support systems to assess the proportion of loads shared with the weakest part.

Research on the Rock Pressure Behavior at Close-Distance Island Working Faces under Deep Goaf

In order to realize the safe and efficient mining of the short-distance isolated island working face under the deep goaf area, the 120502 isolated island working face of Liuzhuang Mine was taken as the engineering background. The method of combining numerical simulation and field measurement were used comprehensively to systematically simulate and study the spatial evolution of the stress field, plastic strain field, and fracture field of coal rock during the mining process. The leading support pressure and the vertical displacement of the roof in the overlapping section and noncoinciding section of the isolated working face and the goaf above were measured on site. The results are that the peak value of the advanced support pressure of the overlap section and the nonoverlapping section is 10 m before the coal wall of the working face; the advanced support pressure of the nonoverlapping section is 33.3 MPa, and the vertical displacement of the roof is 300 mm. The advanced support pressure and the vertical displacement of the roof in the noncoincidence section were significantly higher than those in the coincidence section of 18.2 MPa and 210 mm. The results are consistent with those predicted by numerical simulation. This provides theoretical support for the safe mining of the 120502 isolated island working face in Liuzhuang Mine and, at the same time, provides a reference for the study of similar working faces in other domestic mining areas.