China has witnessed an unprecedented expansion in tunnel and underground engineering over the past decades.However,the persistent occurrence of collapse-related accidents continues to challenge construction safety and emergency management systems.In scenarios where rapid disaster response directly determines survival windows,improving the operational reliability of large-diameter rescue drilling systems becomes critically important.Against this backdrop,this paper investigated the mechanical response of drilling tools and the disturbance behavior of surrounding rock during penetration through complex collapsed masses.Particular emphasis was placed on identifying key factors governing drilling stability and risk evolution under heterogeneous geological conditions.To realistically reproduce the internal structure of soil-rock mixed collapse bodies,a numerical simulation framework was developed.Rock blocks were randomly generated and spatially distributed based on Monte Carlo principles,while irregular three-dimensional block morphologies were constructed to capture geometric randomness and surface roughness.This approach was a more faithful representation of both the spatial distribution and morphological characteristics of discrete blocks within the collapsed mass.A coupled"casing-drill rod"penetration model was subsequently established in Abaqus.Numerical results were validated against field drilling data obtained from the FS120CZ large-diameter rescue drilling rig.Building upon the validated model,a parametric sensitivity analysis was conducted,focusing on drilling speed,collapse body height,and rock block content.The results indicate that drilling speed can serve as the dominant control parameter.When the penetration rate increases from 1.0 to 4.0 m/h,drill rod torque rises by 49.05%,while casing resistance increases by 63.47%.More importantly,load fluctuations intensify in a nonlinear manner with increasing speed.This amplification effect can be attributed to the compounded enhancement of frictional interaction and cutting resistance at the drill-collapse interface under high-speed penetration conditions.In contrast,under shallow burial conditions,the height of the collapsed mass exerts only a limited influence on load magnitude.However,in rock-containing collapse bodies,force-time curves exhibit pronounced"serrated"oscillations,reflecting intermittent block engagement and release.Such instability can significantly increase the likelihood of slippage and sticking incidents.Overall,drilling speed and rock block content emerge as the primary parameters controlling rescue drilling safety.These factors should therefore be prioritized in operational planning and equipment regulation.Considering the strong force fluctuations induced by rock blocks,a pre-treatment strategy involving targeted removal of large blocks along the drilling trajectory is recommended.This measure can effectively reduce peak loads and load variability,thereby enhancing drilling continuity and operational safety.
The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag. Thus, improving the bottom structure is of great significance to reduce the aerodynamic drag of the train. In this study, computational fluid dynamics (CFD) based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes (RANS) equations and Realizable k-ε turbulence model were utilized for numerical simulations. Inspired by the concept of streamlined design and the idea of bottom flow field control, this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism. Three models, i.e., single-bogie model, simplified train model, and eight-car high-speed train model, were created and their aerodynamic characteristics were analyzed. The results show that the single-bogie model with streamlined design shows a noticeable drag reduction, whose power bogie and trailer bogie experience 13.92
Employing a combination of field measurements and numerical simulations, this study initially evaluates the impact of simplifying wheel-rail profile wear on the calculation results of vehicle performance indicators. Subsequently, it investigates the influence of time-varying wear of wheel-rail profiles on the vehicle's dynamic response, along with an analysis of change law in wheel wear depth and range under different wheel-rail profiles. The finding indicates that simplifying wheel-rail profile wear notably affect the accuracy of predicting wheel wear, with potential maximum prediction errors of up to 84 % compared to actual conditions. Furthermore, changes in the wheel-rail profile resulting from wear significantly impact the vehicle's straight-line running performance and curve negotiation performance, particularly in the early and later stages of wheel-rail wear. Moreover, profiles in the mid-term wear stage significantly exacerbates wheel wear depth, demonstrating a maximum increase 4.33 times higher than that of the standard profile.
The traditional methods for testing the sleeve grouting fullness of prefabricated structures generally face the technical challenges such as high detection cost and inability to detect in real-time. In order to solve these technical challenges, the detection method and instrument based on the piezoelectric testing principle were developed. Through the electrical properties tests of grouting materials and grouting-leakage cycle tests of transparent sleeves, the effectiveness of the piezoelectric method for testing grout leakage defects was analyzed. The research results indicate that measuring the voltage changes before and after the piezoelectric sensor is wrapped in the grouting slurry can effectively evaluate the sleeve grouting fullness. The voltage measured by the piezoelectric sensor is significantly reduced after the sensor is wrapped in the grouting material (full grouting). Then the voltage increases after grouting leakage (insufficient grouting), and decreases again after supplementary grouting (full grouting). Moreover, whether the piezoelectric sensor is placed horizontally or vertically, the voltage shows obvious changes, indicating that the piezoelectric method is less affected by the sensor laying mode. Considering that the vertical embedding method is more stable for piezoelectric data, it is recommended to use the vertical laying mode in engineering projects. Furthermore, through the prefabricated model tests, the threshold for judging grouting fullness using piezoelectric method was determined. The test results show that the threshold for determining the grouting fullness using piezoelectric method can be set to 0.40. That is to say, when the voltage value is less than 0.40, it can be determined as complete grouting, otherwise it can be determined as insufficient grouting. The case studies results indicate that the piezoelectric method meets the quality control requirements during the grouting process of prefabricated structural sleeves. The research results provide a new approach and practical reference for solving the quality detection problem of sleeve grouting.
Adequate station classification is of great importance for the study of passenger flow characteristics and the development of land around stations. To address the problem that it is difficult to accurately classify new stations before the opening of new lines due to unknown passenger flow data, this paper proposes a classification method for new line stations based on the mapping relationship between the built environment and subway passenger flow. First, we cluster existing stations and calculate the passenger flow characteristic intervals of each category of stations. Random forests are used to screen important built environment factors that affect the classification of categories. Second, based on the above characteristics of passenger flow and built environment, the mapping relationship between them is determined by logarithmic transformation fitting. Finally, we calculate the unknown passenger flow characteristics of new line stations according to the mapping relationship and built environment characteristics, and then realize the classification of new line stations. An example of the Beijing subway system is taken to verify the effectiveness of the method. The results show that the method can realize the early classification of station types before the opening of new lines, and has good classification effect and applicability.
