Shuang You

Under high-density urban underground development conditions, excavation of a large-section tunnel overcrossing an existing tunnel with ultra-small clearance may induce unloading-induced rebound of the underlying ground, thereby causing uplift deformation of the existing tunnel. Three-dimensional finite element analysis and field monitoring were conducted to compare the deformation-control performance of different control-measure combinations and to assess the sensitivity of key parameters of the bench-beam uplift-resistant system. The results showed that, under the basic structural condition of the composite three-layer lining system, the combined control scheme limited the maximum uplift of the existing tunnel to 4.71 mm, corresponding to a reduction of 33.10% relative to the baseline condition. However, compared with the bench-beam uplift-resistant system alone, the addition of surface pre-grouting produced only a further reduction of 0.10 mm, indicating a relatively limited incremental contribution to uplift control under the investigated conditions. Among the parameters considered, pile length exerted the greatest influence on the uplift response of the existing tunnel, followed by pile diameter and the equivalent stiffness of the pipe-jacking capping beam, whereas the number of section-steel members had the smallest influence. When the pile tip extended to approximately 0.5D below the invert of the existing shield tunnel, where D denotes the outer diameter of the existing tunnel, the marginal benefit of further increasing pile length gradually diminished. Field monitoring further revealed a spatially non-uniform vertical deformation response of the existing tunnel after implementation of the comprehensive control scheme. The measured deformation trends and response characteristics were generally consistent with the numerical results. These findings provide a useful reference for the selection of deformation-control measures and the design of uplift-resistant structural parameters in similar large-section tunnel overcrossing projects with ultra-small clearance.

In recent years, deformation disasters in mine shafts have occurred frequently, posing a threat to mine safety. The nonlinear coupling relationship between shaft surrounding rock deformation and rock mass mechanical parameters is a key criterion for surrounding rock stability. However, existing machine learning prediction methods are rarely applied to shaft deformation, and issues such as poor accuracy and generalization of single models remain. To address this, the study proposes a feature-weighted Stacking ensemble model, which considers 15 feature variables; using RMSE, MAE, R², and inter-model MAPE correlation as evaluation metrics, GBDT, XGBoost, KNN, and MLP are selected as base learners, with Lasso linear regression as the meta-learner. Prediction errors are corrected by weighting the outputs of base learners based on prediction accuracy. Experiments show that, using MAPE as the evaluation metric, the improved model reduces the error by 2.59% compared with the best base learner KNN, by 6.83% compared with XGBoost, and by 0.18% more than the traditional Stacking algorithm, making it suitable for predicting weak surrounding rock shaft deformation under multi-feature conditions.

With the increasing demand for renewable energy sources, shallow geothermal energy has become a reliable alternative energy source for building heating and cooling. In this paper, we present a methodology for estimating the shallow geothermal potential to meet heating demand for a public building. Firstly, the geothermal reserves and the cooling heating demand of the building are evaluated. Then the simulation model of hybrid ground source heat pump system is established, which aims at solving the problem of soil heat accumulation. Finally, one-year and five-year variation of performance parameters of hybrid ground source heat pump system are calculated. Our results indicate that hybrid ground source heat pump system could effectively solve heat accumulation problem and reduce traditional energy consumption.

The development of urban rail transit has led to an increase in the number of large section subway tunnels crossing existing tunnels. This study combines the actual engineering of the Yanggongqiao Station Longzhuayan Station section tunnel of Chengdu Metro Line 17 Phase II project crossing the existing Line 7 shield tunnel, and uses on-site investigation, monitoring, and numerical simulation methods to evaluate the construction impact. Based on this, measures such as bench pile reinforcement, pre grouting, and parameter optimization are proposed. In practical applications, the comparison between monitoring and simulation results shows that these measures effectively control the deformation of existing tunnels, providing important references for similar projects.

The mesoscopic structure of rocks determines their strength and deformation characteristics. The grain and pore size distribution of granite samples buried depth of 1600 m to 1900 m in a goldmine of Shandong Province are measured by polarizing microscope and low-field nuclear magnetic resonance. The splitting test is carried out and the acoustic emission signal is obtained in real time by using an electro-hydraulic servo press and PCI-2 acoustic emission collector. The relationship between meso-mechanics and acoustic emission characteristics of split granite is analyzed. The experimental result shows that there is no clear correlation between meso-grain size and pore size distribution. Rocks with larger mineral grains easily form inter-embedded structures between grains and grains, the bearing effect of grains is enhanced, and the tensile strength of rocks is improved. The level of stress concentration in the rock is closely related to the pore size of the rock, and the acoustic emission ringing count before the main rupture in the large aperture (0.1~10 mm) of the rock is more active than that of the small aperture rock (0.01~1 mm), and a large number of high frequency acoustic signals are induced by the penetration between the pores in the unstable failure stage and post-peak failure stage, the stress concentration is higher, and the energy release frequency is increased, however the energy released strength by a fracture is weak.

The heat exchanger can use shallow geothermal energy to provide regional heating and cooling demand in winter and summer. In this paper, a large-scale public building is taken as the example, and the energy system in the building is taken as the research object. Firstly, through the collection of geothermal drilling geographic information and geothermal data, the geothermal reserves and geothermal recoverable resources are evaluated. Secondly, the cooling and heating demand of the building is calculated by using HVAC simulation software. Then, the heat transfer capacity of a single pile is evaluated and the layout scheme of the underground heat exchange pile foundation of the building is given. The actual heating effect of the heat exchange pile foundation system is explored, and the heat transfer characteristics of heat exchange pile foundation under different working conditions are compared and analyzed. Finally, reasonable suggestions for the arrangement of heat exchange pile foundation are given.

In order to scientifically evaluate the thermal environment of the deep stope and its influencing factors, research was conducted on the thermal environment in Sanshandao Gold Mine, the theoretical calculations and structural analysis of heat release from 8 types of heat sources in the three sub-levels of -930 m, -945 m, and -960 m were carried out, and quantitative characterization was made on the influential degree of comprehensive heat release on the thermal environment, and it was clear that the heat release from the surrounding rock and mechanical and electrical equipment were the main parts at the deep mining site and the proportion of heat release from other heat sources is basically stable. Then, through the analysis of the influence factors of heat sources in the mining site, 17 evaluation indexes of the influence factors of the mining site thermal environment were sorted out, and the indexes’ weight was calculated based on the entropy weighting method, and it was learned that the largest weight of the influence on the thermal environment factors in a single excavation working face was the water gushing in the roadway. The TOPSIS method was used to comprehensively analyze and rank the thermal damage degree in the three middle sections. The results show that the degree of thermal damage in the -960 m is more severe than that in the -930 m and -945 m. This will provide some basic basis for the evaluation and prevention of thermal damage in deep mining projects, and is of great significance for improving mine production efficiency.

Compared with the small diameter and the single stratum shield tunnel, the surface subsidence is much greater when the large-diameter shield passes through the upper-soft and lower-hard stratum. In this case, it is particularly important to control the deformation of the embankment when the large-diameter shield passes underneath the embankment. Taking a tunnel project underneath the north embankment in Zhuhai as an engineering example, this paper investigates the deformation characteristics and safety control measures of a super-large-diameter (i.e., 15.80 m) shield tunnel underneath the embankment under complex stratum conditions in upper-soft and lower-hard strata, using on-site monitoring and three-dimensional numerical simulations. The results of the numerical simulation show that grouting can effectively reduce the settlement of the embankment. Grouting is applied to practical engineering, and the monitoring data are in agreement with the numerical simulation results. The surface subsidence of the embankment gradually increases as the shield tail leaves the monitoring section and finally stabilizes. After the shield machine has passed through the embankment, the horizontal deformation troughs on the embankment’s surface conform to the Gaussian normal distribution. The maximum settlement occurs in the area directly above the central axis of the tunnel. The deformation trough covers an area about four times the diameter of the tunnel on both sides of its center line.