The deformation capacity of tunnel will be overestimated by small strain theory especially in high geostress and heavily squeezing rocks, the calculated wall convergence of tunnel may even exceed the ...excavated radius. Based on the Generalized Zhang-Zhu (GZZ) strength criterion, a new large strain solution for tunnel excavated in strain-softening rocks under high geostress is proposed by a semi-analytical approach. During calculation, the material nodes in the plastic zone of surrounding rock are generated automatically in each unloading step. The locations of these nodes are updated after each step and the governing equations are established on the updated state. The proposed procedure allows one to predict the rock stresses, strains, and deformations in a rational and rigorous manner, and it is validated by numerical simulation. Results show that the ground displacement calculated by proposed approach is in good agreement with that obtained by GeoFBA3D, which indicates that the proposed approach is capable in predicting the large deformation of surrounding rock. As long as the unloading radial pressure of each step δp is sufficient small, i.e., the number of material nodes in the plastic zone exceeds 40, the computational error can be neglected. Compared to HB strength criterion, the GZZ criterion can take into account the intermediate principal stress, which is beneficial to tunnel stability. The applicable conditions for large strain theory and small strain theory are given by parametric studies. Parametric studies show that the calculation error produced by small strain theory can reach 30% when the deformation of surrounding rock exceeds about 10%R0, therefore, a large strain theory is necessary for calculation.
•A new semi-analytical large strain solution for tunnel excavated in strain-softening rocks based on GZZ strength criterion.•Nodes are generated and updated automatically during calculation.•When the deformation of surrounding rock exceeds about 10%R0, a large strain theory is necessary for calculation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Numerous cold region tunnels have been constructed in recent decades. To prevent frost damage, problem of frost heaving force calculation is to be solved urgently. During the freezing process of cold ...region tunnels, temperature gradient occurs mainly in radial direction, whereas the temperature gradient in circumferential and axial directions is negligibly gentle. Hence, the surrounding rock of cold region tunnels freezes unidirectionally along the radial direction, which results in the transversely isotropic frost heave of surrounding rock. Therefore, an analytical elasto-plastic solution of frost heaving force is proposed, in which an anisotropic frost heave coefficient k is introduced to consider the transversely isotropic frost heave. And the surrounding rock is considered as ideal elasto-plastic material conforming to Mohr-Coulomb yield criterion in the solution. Moreover, the method to determine the elastic or plastic state of the surrounding rock after frost heave is proposed. For the condition that the frozen surrounding rock doesn't reach the plastic state, an elastic solution of frost heaving force considering the transversely isotropic frost heave is also established. Then, the analytical elasto-plastic solution is verified with the existing solutions and a model test, and proved to be reasonable and applicable. Finally, the influence of the related factors, such as the frost heaving property (the anisotropic frost heave coefficient and the volumetric frost heaving strain) of surrounding rock, the initial ground stress, and the mechanical parameters of surrounding rock on the frost heaving force and plastic zone radius is analyzed. Results show that as the anisotropic frost heave coefficient k increases, the frost heaving force increases significantly, which demonstrates that the transversely isotropic frost heave of surrounding rock has considerable impact on the frost heaving force and should be considered.
•Frost heave of surrounding rock is transversely isotropic in cold region tunnels.•An analytical elasto-plastic solution for frost heaving force in cold region tunnels is derived.•Use a coefficient to consider the transversely isotropic frost heave of surrounding rock in the solution.•Propose a method to determine the elastic or plastic state of the frozen surrounding rock.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A series of freezing experiments has been conducted to investigate the frost heaving property of saturated rock under unidirectional freezing condition. Results show that the frost heave parallel to ...the freezing direction is considerably larger than that perpendicular to the freezing direction, and the frost heave is isotropic on the plane perpendicular to the freezing direction. Thus, the transversely isotropic frost heaving property of saturated rocks under unidirectional freezing condition is proposed, in which the plane perpendicular to the freezing direction is the plane of transverse isotropy and the line parallel to the freezing direction is the axis of transverse isotropy. In cold region tunnels, the inflow of cold air leads to the unidirectional freezing of the surrounding rock along the radial direction of tunnels. Hence, the frost heave of the surrounding rock is transversely isotropic during the freezing process. The cylindrical surface constituted by the circumferential and axial directions is the surface of transverse isotropy and the line along the radial direction is the axis of transverse isotropy. Furthermore, an analytical solution for frost heaving force in cold region tunnels is derived, in which an anisotropic frost heave coefficient k is used to consider the transversely isotropic frost heave of the surrounding rock. The calculated results of the solution are compared with in situ measured data to prove the reasonability of the solution. Finally, the solution is used to optimize the design of the thermal insulation layer of a cold region tunnel.
•Frost heave of saturated rock during unidirectional freezing is transversely isotropic.•Frost heave of surrounding rock is transversely isotropic in cold region tunnels.•An analytical solution for frost heaving force in cold region tunnels is derived.•Use a coefficient to consider transversely isotropic frost heave in the solution.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This study introduces a novel segmented lining model designed to mitigate the challenges associated with tensile cracking in reinforced concrete linings within underground rock caverns subjected to ...high internal pressure. The proposed model comprises prefabricated reinforced concrete segments interconnected by bolts, with selected connectors designed to facilitate retractability. This unique feature enables circumferential deformation, effectively preventing concrete cracking and the subsequent loss of bearing capacity under high internal pressure conditions. Key components of the proposed segmented lining include the utilization of prefabricated segments for improved construction efficiency and quality control, secured interconnection through bolts to ensure a flexible yet robust assembly, and the incorporation of retractable connectors for controlled circumferential deformation. The presence of predetermined seams in the lining facilitates the transmission of elevated air pressure within the cavern to the surrounding rock, thereby minimizing damage to the rock structure and ensuring optimal utilization of the surrounding rock's bearing capacity. The study employs a systematic approach, deriving simplified mechanical expressions for the rock masses encompassing a cavern with high internal pressure. The stress evolution and mechanical response of the surrounding rock during the internal pressure increase are examined across distinct stages: elastic–plastic, plastic unloading, plastic loading, and plastic expansion. Case studies are conducted to investigate the influence of various factors on the gas storage capacity of the cavern supported by the segmented lining. Parameters such as the quality of the surrounding rock, cavern burial depth, spring stiffness of the retractable connector, and preset seam width of the lining are evaluated. Results demonstrate that the segmented lining not only averts lining cracking and damage but also markedly enhances the gas storage pressure within the cavern compared to conventional reinforced concrete linings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Fracture initiation, propagation, merging and branching in rocks are considerably complicated and commonly exhibit a great variety of patterns. How to characterize and capture the complicated ...fracturing process is still a challenging task for recent studies. In this study, a new double phase field model (DPFM) for mixed-mode fractures in rocks modified from triple shear energy criterion is proposed. We introduce two independent phase field variables to describe the tensile fractures and shear fractures individually. In the proposed DPFM, a new fracture driving force based on triple shear energy criterion is proposed and a hybrid formulation is adopted for constructing the new fracture governing equations. Differently from the existing phase field models, our new model can comprehensively consider the influence of cohesion, internal friction angles and intermediate principal stress. Uniaxial compression tests on rock specimens with an inclined flaw and double flaws are performed to validate our DPFM. We also test the fracture patterns of rocks with intermittent fissures in 3D compressive-shear tests. It is observed that the proposed new DPFM can capture the complicated fracturing processes and fracture coalescence types, which are in good agreement with the existing experimental and numerical results.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
It is essential to monitor the ground temperature over large areas to understand and predict the effects of climate change on permafrost due to its rapid warming on the Qinghai-Tibet Plateau (QTP). ...Land surface temperature (LST) is an important parameter for the energy budget of permafrost environments. Moderate Resolution Imaging Spectroradiometer (MODIS) LST products are especially valuable for detecting permafrost thermal dynamics across the QTP. This study presents a comparison of MODIS-LST values with in situ near-surface air temperature (Ta), and ground surface temperature (GST) obtained from 2014 to 2016 at five sites in Beiluhe basin, a representative permafrost region on the QTP. Furthermore, the performance of the thermal permafrost model forced by MODIS-LSTs was studied. Averaged LSTs are found to strongly correlated with Ta and GST with R2 values being around 0.9. There is a significant warm bias (4.43–4.67 °C) between averaged LST and Ta, and a slight warm bias (0.67–2.66 °C) between averaged LST and GST. This study indicates that averaged MODIS-LST is supposed to be a useful data source for permafrost monitoring. The modeled ground temperatures and active-layer thickness have a good agreement with the measurements, with a difference of less than 1.0 °C and 0.4 m, respectively.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•An innovative technology, tunnel lining GHEs was introduced.•The field test of tunnel lining GHEs was introduced.•The field test investigated the impact factors of heat transfer performance.
...Innovative tunnel lining ground heat exchangers (GHEs) were introduced in China for the first time and applied to Linchang Tunnel in Inner Mongolia. This paper is dedicated to studying this new technology based on a field experiment at Linchang Tunnel. The experiment investigated the heat transfer performance of tunnel lining GHEs and its impact factors, including the flow rate, inlet water temperature and pipe distance. The test results show that (i) the ground temperature at a pipe distance of 50cm cannot completely recover when the intermittent ratio is 1.1, but it can completely recover at a pipe distance of 100cm; (ii) the heat exchange rate presents a linear variation with the inlet temperature of the heat carrier liquid, and on average, the heat exchange rate increases 2.494W/m for every 1°C increase in the inlet temperature; (iii) the heat exchange rate increases exponentially as the flow rate increases; (iv) the heat exchange rate shows an exponential downward trend as the running time increases, and the heat exchange rate for a pipe distance of 50cm is always higher than that for a pipe distance of 100cm during the testing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
During the operation of compressed air storage energy system, the rapid change of air pressure in a cavern will cause drastic changes in air density and permeability coefficient of sealing layer. To ...calculate and properly evaluate air tightness of polymer sealing caverns, the air-pressure-related air density and permeability must be considered. In this context, the high-pressure air penetration in the polymer sealing layer is studied in consideration of thermodynamic change of the cavern structure during the system operation. The air tightness model of compressed air storage energy caverns is then established. In the model, the permeability coefficient and air density of sealing layer vary with air pressure, and the effectiveness of the model is verified by field data in two test caverns. Finally, a compressed air storage energy cavern is taken as an example to understand the air tightness. The air leakage rate in the caverns is larger than that using air-pressure-independent permeability coefficient and air density, which is constant and small in the previous leakage rate calculation. Under the operating pressure of 4.5–10 MPa, the daily air leakage in the compressed air storage energy cavern of Yungang Mine with high polymer butyl rubber as the sealing material is 0.62%, which can meet the sealing requirements of compressed air storage energy caverns. The air tightness of the polymer sealing cavern is mainly affected by the cavern operating pressure, injected air temperature, cavern radius, and sealing layer thickness. The cavern air leakage rate will be decreased to reduce the cavern operating pressure the injection air temperature, or the cavern radius and sealing layer thickness will be increased.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► Conducting the first field experiment of heat exchangers in diaphragm wall. ► Finding the difference between heat exchanger in diaphragm wall and in borehole. ► Investigating the influence of 4 ...factors on heat exchange rate in diaphragm wall.
To bury absorber tubes in diaphragm wall as heat exchanger is a new energy saving technology. This paper is dedicated to study this new technology based on the field experiment at Shanghai Museum of Nature History. By the experiment, the heat transfer performance of heat exchanger in diaphragm wall and its impact factors including heat exchanger type, water velocity, inlet water temperature and operation mode were investigated. The test results show that (i) the heat exchange rate of W-shaped heat exchanger reached to 66.3 and 73.7W/m for tube type (a) and (b) at the inlet temperature of 35°C, which are approximately 1.2–1.4 times higher than that of single U-shaped type (c); (ii) under the experimental condition, the reasonable water velocity is 0.6–0.9m/s; (iii) the exchange rate reached to 40.3, 66.3 and 85.0W/m at the inlet temperature of 32, 35 and 38°C, respectively, for tube type (a), every 1°C rise of inlet water will promote 15% heat exchange rate; (iv) in intermittent operation mode, the average heat exchange rate is 82.8W/m while 72.7W/m for continuous mode under the experimental condition, i.e., 14.7% higher than that in continuous mode.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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