The reasonable prediction of ground frost heave provides guiding significance for tunnel construction that uses artificial ground freezing technique. Single-pipe freezing theory, which considers the ...freezing point of soil and assumes the constant surface temperature of a freezing pipe, is suggested for solving the radius of the freezing front before the closure of the frozen wall. By contrast, the radius of the freezing front after the closure of the frozen wall can be calculated using flat-panel freezing theory, which considers the freezing point of soil and determines the average temperature of the freezing pipe circle. On the basis of these suggestions and the analytical prediction proposed by Cai et al. (2014), an improved analytical prediction of ground frost heave was established by the stochastic medium theory according to the formation process of the frozen wall. The improved analytical prediction was applied to an actual tunnel freezing project. Then, the heaving and horizontal displacements of the ground surface are obtained, which agree well with the field-measured data. The effectiveness and practicality of the improved analytical prediction are verified in this study.
•Frost heave and thawing settlement of Gongbei Tunnel are predicted.•Transient temperature variation effect of soil is developed in numerical simulation.•Orthotropic deformation characteristics of ...soil is considered.•Effectiveness of Freeze-sealing pipe-roof method is verified.
The port section of the Gongbei Tunnel of the Hong Kong Zhuhai Macao Bridge is constructed by the freeze-sealing pipe-roof method, a new construction method that combines the pipe-roof and artificial ground freezing techniques. If the frost heave and thaw settlement of the ground are not effectively predicted and controlled during tunnel construction, then the surrounding environment of the tunnel will be adversely affected. In this study, thermophysical and mechanical parameters such as frost heave ratio and thawing settlement coefficient are obtained by the laboratory test of frozen-thawed soil. Then, the frost heave and thawing settlement laws of the ground are simulated by the full-coupled analysis method of transient temperature and displacement according to the secondary development technology of the ABAQUS finite element software considering the orthotropic deformation characteristics of frozen soil during the construction of the Gongbei Tunnel. The numerical simulation results show that the maximum vertical frost heave displacement of the stratum is 164.47 mm and the maximum horizontal frost heave displacement of the stratum is 53.80 mm, while the maximum vertical thawing settlement displacement of the stratum is −69.45 mm and the maximum horizontal thawing settlement displacement the stratum is −43.89 mm. Moreover, the error of the maximum vertical frost heave displacement between numerical simulation and field measurement is only 5.89 mm, which shows that the numerical simulation method proposed in this paper has high prediction accuracy.
Abstract To address the problems of the conventional composite supporting structures (CCSSs) such as insufficient anti-dislocation performance and deformation capacity, this study used Engineered ...Cementitious Composite (ECC) lining sections instead of the traditional lining sections and optimized support design parameters, resulting in the development of novel ECC-RC composite supporting structures (ECSSs) of tunnels passing through active fault. The dislocation response characteristics and their parameter sensitivity of the ECSS was revealed by way of 1/25-scale fault dislocation model tests and finite element analysis. The test results show that the mechanical response characteristics and the failure modes of the CCSS and the ECSS are similar under reverse fault dislocation. Compared with the CCSS, the anti-dislocation performance of the ECSS is significantly improved by introducing of the ECC lining and optimizing the design parameters. The vertical deformation of the ECSS and the range of influence under the same dislocation are significantly decreased, and the strain are reduced to different degrees. This phenomenon shows that by improving the material properties, shortening the spacing of aseismatic joints and optimising the thickness of the shock absorption layer, the stress conditions and applicability under deformation of the structure are improved. The ECSS benefits from the crack resistance and toughening effect of fibres, the degree and scope of cracking of the ECSS are significantly reduced compared with those of the CCSS, and internal and external through cracks and local spalling are absent. The results of finite element analysis show that the overall damage degree of the ECSS is decreased and the damage range is increased by decreasing the strength of the surrounding rock in the fault zone. The fault dislocation response pattern of the ECSS varies depending on the fault type. The damage degree caused by different fault types follows the order of normal fault, strike-slip fault, and reverse fault from large to small. However, the damage range caused by the strike-slip fault is significantly larger compared to normal fault and reverse fault. In the design of fault resistance, the surrounding rock conditions of the fault zone and the form of fault dislocation should be considered.
In slurry pipe jacking, lubricant slurry is commonly used to sustain against the displacement and pressure of the overcut area and reduce the interface friction of pipelines. Therefore, a reasonable ...grouting pressure should ensure the stability of surrounding soils, which is raised as a new method in this study. Not only ensure the grouting pressure is not too small to support the stratum effectively and reduce the frictional resistance but also ensure that the grouting pressure will not be too large to produce excessive deformation and affect the surrounding environment. First of all, the influence of grouting pressure on the stability of surrounding soil is analyzed, and the mechanical model of slurry grouting expansion is established. Then, the minimum grouting pressure is designed from the critical balance between radial expansion tension by grouting and loose earth pressure by jacking excavation, and the maximum grouting pressure is designed from the critical expansion pressure caused by grouting splitting. Finally, the rationality of grouting pressure design is proved by the engineering example of a slurry pipe-jacking project near Haikou Meilan Airport and on-site GPR detection test. All these work aims to raise a new theoretical solution of grouting pressure and provide theoretical reference for similar projects.
This study aims to solve the problems of the high cost, heavy pollution and poor performance of traditional engineered cementitious composites (ECC) by adding modified Polyvinyl chloride (PVC) ...aggregate, Polypropylene (PP)-Polyvinyl alcohol (PVA) hybrid fiber and large amount of fly ash. The PVC aggregate is modified by pre-coating silica fume with a PP fiber volume content of 0.5%, PVA fiber volume contents of 1%, 1.5%, and 2%, PVC aggregate contents of 10%, 20%, and 30%, and fly ash volume content of 69%. Different properties and microstructures were studied by carrying out cube compression tests, splitting tensile tests, water absorption tests, drop hammer impact tests, scanning electron microscopy and nuclear magnetic resonance tests. According to the test results, under the same content of PVC aggregate, the use of modified PVC aggregate can, not only effectively avoid the decrease in strength and increase of water absorption, but also improve brittleness and impact failure energy. Regardless of the kind and content of fiber, the compressive strength and brittleness will decrease, while the splitting tensile strength, water absorption, and impact failure energy will increase. After adding 0.5% PP and 1.5% PVA fiber, the performance is ordinary and a negative mixing effect occurs. As more modified PVC aggregate is added, the strength of the ECC concrete with PP-PVA hybrid fiber and modified PVC aggregate added slowly decrease, while the water absorption and impact failure energy increase. Based on a comprehensive analysis of the test data, the reinforcement method of adding 1.5% PVA-0.5% PP hybrid fiber-30% modified PVC aggregate is superior to adding 1.5% PVA fiber, but slightly inferior to adding 2% PVA fiber. This study argues that the reinforcement method is of great significance for the promotion and application of ECC.
As the geological environment of highway tunnels becomes increasinlgy complex, sprayed engineered cementitious composites (ECC) has broad application prospects in the field of highway tunnel support. ...This study focuses on the shotcrete layer in the initial support of Wulingtou extra-long highway tunnel, the 1:4 scale model test of sprayed ECC layer under confining pressure was prepared. Its mechanical properties and real-time joint monitoring are determined using strain gauges, distributed optical fibers, and cameras. The results show that the maximum confining pressure of the sprayed ECC layer is 0.975 MPa with the maximum displacement of 15.497 cm, which outperforms ordinary shotcrete. The loading process of steel bars and sprayed ECC can be divided into three stages, with the change rate of these three stages showing an ascending trend. The failure mode is ductile, involving normal section, oblique section compression shear failure and bending shear failure. In addition, based on the similarity theory, the real mechanical characteristics of the sprayed ECC layer at the tunnel site can be predicted according to the experimental model.
The mechanical response characteristics of mudstone from the ingate roadway of the west ventilation shaft in Yuandian No. 2 coal mine, Huaibei City, Anhui Province, China to dynamic loads were ...quantified in single- and cyclic-impact compression tests, using the split-Hopkinson pressure bar test device. The dynamic stress-strain relationships and the failure characteristics of mudstone samples under different impact loads were analyzed systematically. Considering the "rate effect" of the mudstone dynamic strength, the dynamic strength criterion of mudstone was proposed, and the dynamic damage constitutive model of mudstone was established, based on the statistical damage theory. In response to single-impact loads, with increasing impact pressure, the mudstone peak stress and strain gradually increased, and the peak stress and average strain rate increased nonlinearly. In response to cyclic-impact loads, with an increasing number of impacts, the mudstone peak stress first increased and then decreased, and the peak strain increased gradually. With increasing impact pressure, the number of impacts to the samples' failure decreased gradually. By parameter identification and comparative analysis of the test results, the proposed dynamic damage constitutive model of mudstone was validated. The model can be used for stability analysis of roadway-surrounding rock under dynamic loads.
Different from the traditional tunnel construction, the tunnel construction using artificial horizontal freezing technique needs to go through three stages: soil freezing, tunnel excavation and ...frozen soil thawing. Each construction stage will produce different degrees of ground deformation, which has a great impact on the surrounding environment of the tunnel. In this paper, the whole process theoretical prediction model of ground surface deformation is established based on the stochastic medium theory by introducing the parameters of ground loss rate and average degree of consolidation. Besides, the whole process numerical prediction model is established by programming the transient temperature volumetric strain of frozen-thawed soil based on ABAQUS. The theoretical and numerical prediction models are verified by the measured data of Fu-ba tunnel construction using local horizontal freezing technique. The results show that the ground surface deformation law obtained by the theoretical and numerical prediction models is basically consistent with the field measurement, and the prediction accuracy of the maximum vertical displacement of the ground surface is high. Besides, the numerical prediction model can accurately reveal the evolution law of the formation temperature field and displacement field, and the stress field of tunnel lining can be used as a reference for the design of tunnel structure. It is suggested that the combination of theoretical and numerical prediction models should be used to predict the whole process of ground surface deformation in the tunnel construction using artificial horizontal freezing technique, so as to take protective measures in advance.
In this study, rice husk ash (RHA) was explored as a strength enhancer for mortars containing waste rubber. The effects of RHA on the flow, mechanical strength, chloride resistance, and capillary ...absorption of rubber mortar were investigated by substituting up to 20% cement with RHA. The experimental results showed that the incorporation of rubber into mortar could be safely achieved by adding RHA as a cement substitute by up to 20% without compromising the compressive strength of mortar. Moreover, the RHA also exerted positive effects on the enhancement of the chloride resistance as well as the capillary absorption of rubber mortars, for which 15% RHA was found to be the optimal dosage.
Artificial liquid nitrogen freezing technology is widely used in urban underground engineering due to its technical advantages, such as simple freezing system, high freezing speed, low freezing ...temperature, high strength of frozen soil, and absence of pollution. However, technical difficulties such as undefined range of liquid nitrogen freezing and thickness of frozen wall gradually emerge during the application process. Thus, the analytical solution of the freezing-temperature field of a single pipe is established considering the freezing temperature of soil and the constant temperature of freezing pipe wall. This solution is then applied in a liquid nitrogen freezing project. Calculation results show that the radius of freezing front of liquid nitrogen is proportional to the square root of freezing time. The radius of the freezing front also decreases with decreased the freezing temperature, and the temperature gradient of soil decreases with increased distance from the freezing pipe. The radius of cooling zone in the unfrozen area is approximately four times the radius of the freezing front. Meanwhile, the numerical simulation of the liquid nitrogen freezing-temperature field of a single pipe is conducted using the Abaqus finite-element program. Results show that the numerical simulation of soil temperature distribution law well agrees with the analytical solution, further verifies the reliability of the established analytical solution of the liquid nitrogen freezing-temperature field of a single pipe.
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