Search Results (20)

The implantable capsule grouting pile is a novel pile foundation technology in which a capsule is affixed to the side of the implanted pile to facilitate grouting and achieve extrusion-based reinforcement. This technique is designed to improve the bearing capacity of implanted piles in coastal areas with deep, soft soil. This study conducted model tests involving multiple grouting positions across different foundation types to refine the construction process and validate the enhancement of bearing capacity. Systematic measurements and quantitative analyses were performed to evaluate the earth pressure distribution around the pile, the resistance characteristics of the pile end, the evolution of side friction resistance, and the overall bearing performance. Special attention was given to variations in the lateral friction resistance adjustment coefficient under different working conditions. Furthermore, an actual case analysis was conducted based on typical soft soil geological conditions. The results indicated that the post-grouting process formed a dense soil ring through the expansion and extrusion of the capsule, resulting in increased soil strength around the pile due to increased lateral earth pressure. Compared to conventional piles, the grouted piles exhibited a synergistic improvement characterized by reduced pile end resistance, enhanced side friction resistance, and improved overall bearing capacity. The ultimate bearing capacity of model piles at different grouting depths across different foundation types increased by 6.8–22.3% compared with that of ordinary piles. In silty clay and clayey silt foundations, the adjustment coefficient η_s of lateral friction resistance of post-grouting piles ranged from 1.097 to 1.318 and increased with grouting depth. The findings contribute to the development of green pile foundation technology in coastal areas. Full article

Ground-source heat pumps (GSHPs), despite their high efficiencies, are still not as cost-effective as air-source heat pumps, especially in urban environments, due to the necessity of drilling/excavation. Integrating GSHPs into existing geo-structures, such as underground tunnels, can play a vital role in reducing the overall costs of GSHP systems and promoting their use in cities. Tunnels can be realized through artificial ground freezing (AGF) by using probes for circulating the freezing fluid, which are left in the ground once the tunnel is completed. The novelty of the present work lies in the proposal of a sustainable reuse of AGF probes as ground heat exchangers (GHEs). The idea of converting AGF probes is both sustainable and cost-effective for GSHPs, as it can reduce installation costs by eliminating the drilling/excavation process. A test was performed for the first time in the Piazza Municipio metro station in Naples, Southern Italy, where several AGF probes, initially used for the construction of two tunnels, have then been converted into GHEs. The probes have been connected to a testing device called the energy box. The experiments included testing the heat transfer in the recovered AGF probes through cooling and heating operations. This work presents a numerical simulation of a test that has been validated against experimental results. Full article

This study aims to ensure that the maximum crack width of underground working linings for compressed air energy storage (CAES) meets the allowable limit under high internal pressure conditions. Drawing on crack width calculation methods from hydraulic tunnels, this study proposes a design method for segmented linings with preset seams. The method accounts for the shear mechanical behavior of the sliding layer, with parameters determined through laboratory testing. A typical case study validates the reliability of the crack width calculation method that accounts for lining damage and plasticity. The study determined, from an engineering case, that six seams are optimal when the lateral pressure coefficient λ is below 1, while four seams are more suitable when λ > 1. Additionally, reinforcement ratios and retractable joints of the segmented lining were designed for the case. When the surrounding rock quality is lower than that of hard rock mass and gas pressure exceeds 12 MPa, monolithic cast-reinforced concrete linings often fail to meet the allowable crack width limits. However, segmented linings offer greater flexibility, as they can still meet the requirements even with fair-quality rock mass. These findings provide critical theoretical foundations for the design of CAES workings under high internal pressure. Full article

In-seam seismics is one of the main methods for detecting small geostructures in a coal seam working face, using the velocity and energy attenuation characteristics. When the receiver coupling is poor or geological anomaly is strong, the stability and accuracy of the inversion results are affected greatly. In order to improve the stability and enrich the parameters of the inversion, this paper proposes a channel wave multi-attribute tomography method. Based on the theoretical analysis, the formulas for calculating the spectral ratio, arc length, and bandwidth parameters of the channel wave were obtained. A two-dimensional numerical simulation was used to analyze the attenuation characteristic and exploration potential of three attribute parameters of the channel wave. Through the field measured experiment, the exploration effect of the three attributes was realized and compared. In conclusion, the effectiveness of the channel wave multi-attribute tomography method in characterizing geological structures within coal seams was successfully demonstrated and verified. This approach offers a novel and robust solution for channel wave data processing and exploration, significantly enhancing the prevention of mine water damage. Full article

Rockfall is considered the main geohazard in mountainous areas with steep morphology. The main objective of this study is to assess the rockfall hazard in the cultural heritage site of the Monastery of Agia Paraskevi, Monodendri, in northern Greece, where a recent rockfall event occurred, destroying a small house and the protective fence constructed to protect the Monastery of Agia Paraskevi. To evaluate the rockfall potential, engineering geological-oriented activities were carried out, such as geostructurally oriented field measurements, aiming to simulate the rockfall path and to compute the kinetic energy and the runout distance. In addition, using remote sensing tools such as Unmanned Aerial Vehicles (UAVs), we were able to inspect the entire slope face and detect the locations of detached blocks by measuring their volume. As a result, it was concluded that the average volume of the expected detached blocks is around 1.2 m³, while the maximum kinetic energy along a rockfall trajectory ranges from 1850 to 2830 kJ, depending on the starting point (source). Furthermore, we discussed the level of similarity between the outcomes arising from the data obtained by the traditional field survey and the UAV campaigns regarding the structural analysis of discontinuity sets. Full article

A rock mass is mainly subjected to a high internal pressure load in the lined rock cavern (LRC) for compressed air energy storage (CAES). However, under the action of long-term cyclic loading and unloading, the mechanical properties of a rock mass will deteriorate, affecting the long-term stability of the cavern. The fissures in the rock mass will expand and generate new cracks, causing varying degrees of damage to the rock mass. Most of the existing studies are based on the test data of complete rock samples and the fissures in the rock mass are ignored. In this paper, the strain equivalence principle is used to couple the initial damage variable caused by the fissures and the fatigue damage variable of a rock mass to obtain the damage variable of a rock mass under cyclic stress. Then, based on the ANSYS 17.0 platform, the ANSYS Parametric Design Language (APDL) is used to program the rock mass elastic modulus evolution equation, and a calculation program of the rock mass damage model is secondarily developed. The calculation program is verified by a cyclic loading and unloading model test. It is applied to the construction project of underground LRC for CAES in Northwest China. The calculation results show that the vertical radial displacement of the rock mass is 8.39 mm after the 100th cycle, which is a little larger than the 7.53 mm after the first cycle. The plastic zone of the rock mass is enlarged by 4.71 m², about 11.49% for 100 cycles compared to the first cycle. Our calculation results can guide the design and calculation of the LRC, which is beneficial to the promotion of the CAES technology. Full article

In order to reduce the risk of early freezing damage to cement-based materials in winter construction, lime powder was used to improve the properties of the Portland cement–sulphoaluminate cement (PC–CSA) composite system at low temperatures. In this study, the effects of lime powder dosage on the properties of a PC–CSA blended system with two proportions (PC:CSA = 9:1 and 7:3) at −10 °C were investigated, and the mechanisms of improvement were revealed. The results showed that the compressive strength of the PC–CSA composite system was effectively improved, and the setting time was shortened by the addition of lime powder. Lime powder could effectively act as an early heating source in the PC–CSA composite system, as the maximum temperature of samples exposed to sub-zero temperatures was increased and the time before dropping to 0 °C was prolonged by the addition of lime powder. The extra CH generated by the hydration of lime powder provided an added hydration path for C₄A₃$\overline{\mathrm{S}}$, which accelerated the formation of AFt at each stage. Frozen water as well as the early frost damage were effectively decreased by lime powder because of the faster consumption of free water at an early stage. The modification of the hydration products also contributed to the denseness of the microstructure. Full article

As one of the raw materials of basic magnesium sulfate cement (BMSC), the activity of light-burned magnesium oxide (MgO) has an important effect on the hydration rate, hydration products, and mechanical properties of BMSC. To reveal the influence of packaging method, storage environment, and storage time on the activity of MgO and the mechanical properties of BMSC, an experiment was conducted by using ordinary woven bags, peritoneal woven bags, and plastic and paper compound bags to store the finished BMSC and the raw materials (light-burned MgO, MgSO₄·7H₂O, fly ash, and a chemical additive) under the conditions of natural environment, sealed environment, and wet environment, respectively. Comparative analysis of the effects of packaging method, storage conditions, and storage time on the activity of MgO and the mechanical properties of BMSC was performed through the mechanical strength test of mortar specimens. The results showed that in a sealed environment, the loss of a-MgO content in light-burned MgO was minimized, which was more conducive to keeping the mechanical properties of BMSC stable. In the wet environment, the mechanical strength of BMSC was significantly reduced in the early stage (1 day) due to the significant reduction in the activity of MgO, and the mechanical strength of the finished BMSC and prepared BMSC after 120 days of storage was still lost, regardless of the packaging method. However, the storage environment and packaging method had relatively little effect on the late mechanical strength (28 days) of BMSC. It is advisable to use ordinary woven bags for packaging in natural and sealed environments as this is more economical for engineering applications. Plastic and paper compound bags are superior to ordinary woven bags and peritoneal woven bags in wet environments. Full article

The pre-bored grouted planted (PGP) pile has been more and more used in recent years, but its precise disturbance effect in soft soil areas has not been studied deeply. Therefore, a comparative field test for the disturbances by PGP pile and driven pile construction in deep soft ground was carried out. It revealed that the excess pore pressure caused by the two kinds of piles decreases with the increase of radial distance, and the influence range is less than 7.5 d (d is pile diameter). The maximum excess pore pressure generated by PGP pile construction is about 100 kPa smaller than that generated by driven pile construction. The comparison of the soil pressure and lateral displacement between the two piles is related to the depth and soil type. The typical result is that the soil pressure caused by PGP pile construction is half that of the driven pile, and the maximum lateral displacement of the PGP pile is 50.7~53.8% of that of the driven pile. The noise generated during PGP construction was lower but continuous, and the maximum value at the same distance was reduced by 8 to 15% than the driven pile. The test results reveal the construction disturbance effect of PGP pile and provide a reference for the selection of pile construction method in soft soil areas. Full article

As an energy-efficient and low-carbon technology, ground-source heat pumps are promising to contribute to carbon neutrality in the building sector. A crucial component of these systems is the ground heat exchanger, which has been extensively studied through sandbox experiments. These experiments play a vital role in understanding heat transfer characteristics and validating simulation results. In order to facilitate the improvement of ground heat exchangers and the development of ground-source heat-pump systems, this article provides a comprehensive summary of existing sandbox experiments. The borehole sandbox experiments are classified into the single borehole experiment, borehole group experiment, seepage experiment, and multi-layer soil experiment. It was observed that the heat transfer efficiency of a single spiral tube is only 80% compared to that of a double spiral tube. Moving on to energy-pile sandbox experiments, they are further divided into mechanical performance, thermal performance, and thermal-mechanical coupled performance tests. It was revealed that the heat transfer distance of a single U-shaped energy pile in the radial direction is three times greater than in the vertical direction. For the mentioned sandbox experiments, the sandbox design, experiment conduction, testing conditions, and result analyses are summarized. To improve the sandbox experiments, there are still some difficulties in building a similarity experiment, testing the temperatures in a small error, controlling the boundary conditions accurately, and testing the thermophysical properties of soil accurately. Furthermore, the perspectives of sandbox experiments of ground heat exchangers are also proposed. The sandbox experiments under complex environment conditions or with novel composite energy geo-structures or ground heat exchangers with new materials and new technologies would be further investigated. By addressing these aspects, this review aims to provide guidelines for the design, construction, operation, and optimization of sandbox experiments for different ground heat exchangers, ultimately promoting the wider adoption of ground-source heat pumps in achieving carbon neutrality. Full article

Due to the proposal of China’s carbon neutrality target, the traditional fossil energy industry continues to decline, and the proportion of new energy continues to increase. New energy power systems have high requirements for peak shaving and energy storage, but China’s current energy storage facilities are seriously insufficient in number and scale. The unique features of abandoned mines offer considerable potential for the construction of large-scale pumped storage power stations. Several countries have reported the conversion of abandoned mines to pumped storage plants, and a pilot project for the conversion of an underground reservoir group has been formalized in China. A feasibility study that considered the natural conditions, mine conditions, safety conditions, and economic benefits revealed that the construction of pumped storage power stations using abandoned mines could ameliorate several economic, ecological, and social problems, including resource utilization, ecological restoration, and population resettlement. The construction of pumped storage power stations using abandoned mines not only utilizes underground space with no mining value (reduced cost and construction period), but also improves the peak-load regulation and energy storage urgently needed for the development of power grid systems. Combined with the underground space and surface water resources of the Shitai Mine in Anhui, China, a plan for the construction of a pumped storage power station was proposed. The challenges faced by the current project were evaluated, further research suggested, and demonstration projects established in order to help achieve carbon peaking and carbon neutrality goals. Full article

The underground energy geostructure represented by the energy pile is one of the key paths for the cooperative development of underground space and geothermal energy. Because of its advantages of low cost, high efficiency and no extra occupation of underground space, it has become a feasible alternative to the borehole heat exchanger. The change in the temperature field of the energy pile and its surrounding ground not only affects the geological environment but also influences the thermomechanical performance and the durability of the structure. However, the temporal and spatial unsteady-state temperature distribution of piles and surrounding rock under typical intermittent and unbalanced thermal load conditions is still unclear. In this paper, a finite element model was applied to analyze the unsteady-state temperature distribution, and the thermomechanical behavior of the energy pile group was developed and verified. The temperature field distribution of pile and surrounding rock under typical intermittent working and unbalanced thermal load conditions were determined. Moreover, the thermomechanical behavior characteristics of the energy pile group were investigated. Finally, the influences of pile layout on the thermomechanical behavior of the energy pile group were identified by designing six different scenarios. The results indicate that under typical intermittent operation conditions, the temperature of the energy pile and surrounding ground near the heat exchange pipe varies periodically. For areas with unbalanced cooling and heating loads, long-term operation of energy piles leads to thermal accumulation, and the maximum temperature of energy piles occurs in the first daily cycle. In summer/winter working conditions, the increase/decrease in pile temperature induces axial compression/tensile stress. When the pile group is partially used as the energy pile, the non-energy pile acts as the “anchor pile”, and it generates the added tensile stress. Full article

This paper explored the relationship between acidic sulfate alteration, geostructural frameworks, and geomorphological changes that can be observed in active volcanic hydrothermal systems. The target area was Pisciarelli in the Campi Flegrei volcano, where diffuse acidic sulfate alteration and hydrothermal dynamics have been growing since 2012, causing a progressive deterioration of landscapes. Terrestrial Laser Scanner (TLS), photogrammetry of proximity survey, geological field work, mineralogical and geochemical analysis with Optical Microscopy (OM), electron microscopy, and energy dispersive micro-analysis (BSEM-EDS) and X-ray Powder Diffraction (XRPD) to characterize (and monitor) altered rock outcrops were repeatedly carried out in the area. We present the multi-temporal acquisition and analysis referring to Terrestrial Laser Scanning (TLS) datasets (2014 survey) with 3D-point clouds obtained from the Structure for Motion (SfM) photogrammetry (2021 survey) with a high-resolution digital camera aimed at evaluating volumetric changes on the mostly damaged and altered fault scarp. For each survey, we obtained a vertical Digital Elevation Model (DEM) and a true color RGB orthomosaic that provided the setting of the area at the different times and its evolution through their comparison. Changing sites were examined in the field and characterized for mineralogical and geochemical purposes. The investigated slope lost up to about 4 m³ of deposits between 2014 and 2021, mostly related to hydrothermal alteration induced by gas emissions and meteoric infiltration. Our methodological approach appears promising to evaluate evolution and rock-fall susceptibility of solfataric terrains subjected to hydrothermal dynamics. Full article

This paper proposes and demonstrates, in full scale, a novel type of energy geostructure (“the Climate Road”) that combines a ground-source heat pump (GSHP) with a sustainable urban drainage system (SUDS) by utilizing the gravel roadbed simultaneously as an energy source and a rainwater retarding basin. The Climate Road measures 50 m × 8 m × 1 m (length, width, depth, respectively) and has 800 m of geothermal piping embedded in the roadbed, serving as the heat collector for a GSHP that supplies a nearby kindergarten with domestic hot water and space heating. Model analysis of operational data from 2018–2021 indicates sustainable annual heat production levels of around 0.6 MWh per meter road, with a COP of 2.9–3.1. The continued infiltration of rainwater into the roadbed increases the amount of extractable heat by an estimated 17% compared to the case of zero infiltration. Using the developed model for scenario analysis, we find that draining rainwater from three single-family houses and storing 30% of the annual heating consumption in the roadbed increases the predicted extractable energy by 56% compared to zero infiltration with no seasonal energy storage. The Climate Road is capable of supplying three new single-family houses with heating, cooling, and rainwater management year-round. Full article