Investigation on Ground Collapse Due to Exfiltration of Shallowly Buried Water-Supply Pipeline

Pipeline exfiltration from damaged water-supply systems frequently causes soil erosion and ground subsidence, which jeopardizes the safety of pedestrians and vehicles and even causes casualties. Despite the severe consequences, it is difficult for engineers to give reliable assessments of pipeline exfiltration hazards. In this study, erosion processes were explored using model tests and coupled computational fluid dynamics–discrete element method (CFD-DEM) simulations. It was discovered that the erosion zone can be divided into two zones—the exfiltration zone and the seepage diffusion zone. When water pressure reached 2.412 × 10−2 MPa, local porosity approached 1.0, indicating there were no soil particles remaining. As pipeline pressure increased from 2.122 × 10−3 MPa to 2.412 × 10−2 MPa, ground failure transitioned from downward settlement to upward bulge, and the ground failure duration of the fractured prototype pipe was reduced by 22–28% (from 125 s to 98 s), with a standard deviation of less than 5. The established exponential decay model (v(t)=v0e(−αt),R2>0.89) enabled prediction of erosion duration. Based on the erosion height curve, the erosion duration and erosion area in similar engineering environments can be estimated, providing a reference for evaluating the risk of ground collapse due to pipe exfiltration

Multi-Scale Investigation on Bearing Capacity and Load-Transfer Mechanism of Screw Pile Group via Model Tests and DEM Simulation

Screw piles are widely used in infrastructure, such as railways, highways, and ports, etc., owing to their large pile resistance compared to unthreaded piles. While most screw pile research focuses on single pile behavior under rotational installation using torque-capacity correlations. Limited studies investigate group effects under alternative installation methods. In this study, the load-transfer mechanism of screw piles and soil displacement under vertical installation was explored using laboratory model tests combined with digital image correlation techniques. In addition, numerical simulations using the discrete element method were performed. Based on both lab tests and numerical simulation results, it is discovered that the ultimate bearing capacity of a single screw pile was approximately 50% higher than that of a cylindrical pile with the same outer diameter and length. For pile groups, the group effect coefficient of a triple-pile group composed of screw piles was 0.64, while that of cylindrical piles was 0.55. This phenomenon was caused by the unique thread-soil interaction of screw piles. The threads generated greater side resistance and reduced stress concentration at the pile tip compared with cylindrical piles. Moreover, the effects of pile type, pile number, embedment length, pile spacing, and thread pitch on pile resistance and soil displacement were also investigated. The findings in this study revealed the micro–macro correspondence of screw pile performance and can serve as references for pile construction in practice

Experimental investigation and evaluation of the performance of air-source heat pumps for indoor thermal comfort control

Air-source heat pumps (ASHPs) have been widely used in domestic buildings. However, the regulation performance of ASHPs for indoor thermal comfort control is influenced by the factors such as cold draft and slow response to the variation in room temperature. In this paper, a range of experiments was carried out for 14 ASHPs in an indoor environmental chamber under both cooling and heating conditions. A multi-index comprehensive evaluation model including the questionnaire survey method, the weighted scoring method and the quartile algorithm method was then adopted to analyze the tested data in order to give some intuitive indices to evaluate the regulation performance of ASHPs for indoor thermal comfort control. The results showed that unsatisfied factor of the overall thermal comfort under the cooling conditions was reached to 71 %. Besides, the precision of the temperature control was poor in both cooling and heating conditions, which manifesting ASHPs need a novel matched adjust mode and more intelligent control system to meet thermal comfort requirement. This study provided a reference basis for evaluating ASHP\u27s regulation performance on indoor thermal comfort

Study on the Performance of Fan-coil Unit in a Moderate Water Temperature Air Conditioning System

In this paper, the variation in the indoor temperature and humidity when FP85 series fan-coil units are used to treat indoor return air to its equilibrium point is analyzed based on the experimental comparison between an air conditioning system with a moderate water temperature and a conventional air conditioning system. Then, the influence of a chilled water supply temperature and tube numbers on the heat transfer performance of a fan-coil unit is simulated and analyzed by a coil simulation method. The experimental results show that when the temperature of the chilled water supply increased from 7 °C to 9 °C, the latent heat capacity of the 3-row FP85 fan-coil unit was reduced. As a result, the indoor humidity cannot be guaranteed in the comfortable range. As the chilled water supply was increased by 1 °C, the relative humidity of the indoor equilibrium point increased by 11.03%–12.05% accordingly. For the 6-row FP85 fan-coil unit, the temperature and humidity of the indoor equilibrium state can meet the design requirements of comfortable air conditioning,system with a chilled water supply temperature in the range of 9–12 ℃. Moreover, the simulation results state that the 4-row, 5-row, and 6-row FP85 fan-coil units can ensure an equilibrium indoor temperature and humidity in the comfortable range for an indoor return air with dry bulb temperature 27.01 °C and wet bulb temperature 19.51 °C, respectively. The heat exchange and dehumidification coefficients of the 4-row fan-coil unit decreased by 6.13% and 0.045, respectively, when the supply chilled water temperature increased by 1 °C. The heat transfer coefficient and dehumidification ability of the 4-row fan-coil unit are superior to that of the 5-row and 6-row fan-coil units. Therefore, the 4-row FP85 fan-coil unit is more appropriate for an air conditioning system with moderate water temperature. This study indicates that the air conditioning system with moderate water temperature has great application potential, and provides a theoretical basis for the design of air conditioning system with moderate water temperature

Multi-faceted performance analysis and optimization of a hybrid deep borehole heat exchanger heating system with latent heat thermal energy storage

Deep borehole heat exchangers (DBHEs) coupled with heat pump systems present a promising solution for building space heating. However, conventional heating systems have limited demand flexibility and ignored the potential of direct heating using DBHEs. Thus, this study proposed a hybrid DBHE heating system by integrating latent heat thermal energy storage (LHTES) and borehole direct heating (BDH), and evaluated its performance in terms of energy, exergy, economy, and flexibility. This work aimed to achieve a matching operation between the LHTES and the heat pump and quantify the performance improvement potential of the hybrid system. Firstly, a thermodynamic analysis was carried out based on a pilot project, showing that the seasonal performance factor (SPF) of the system can reach 4.3 under the high-temperature heat storage mode, with a 45.5% improvement in exergy efficiency. Based on the field-measured data, a transient model of the hybrid system was developed using TRNSYS and MATLAB. With the established model, the single and interactive impacts of multiple critical parameters on the system performance were explored. Subsequently, a multi-objective optimization was performed using artificial neural networks and a genetic algorithm by considering several scenarios with different geographical locations and electricity tariffs. The optimization results revealed a trade-off between the levelized cost of energy (LCOE) and the flexibility factor, both of which were highly sensitive to the tank volume of the LHTES. The case studies showed that the LCOE of the optimized hybrid system was decreased by up to 8.5%, while the SPF, exergy efficiency, and flexibility factor were improved by up to 20.3%, 3.0%, and 998.7% respectively, in comparison with the conventional system. Compared with the hybrid system without using LHTES, integrating LHTES led to a decrease in LCOE by up to 5.0% and an increase in SPF by up to 3.8%. This study demonstrated the potential of using such hybrid systems for building heating decarbonization