Search Results (33)

Based on FLAC3D finite element analysis and field measurements, this paper studies the synchronous excavation of the deep foundation pit and the adjacent underground channel in the 17th section of the Beijing Metro Line 10 Phase II project. Due to the very tight schedule and deadline, an underground channel has been added between the double-arch tunnel and the deep foundation pit and excavated synchronously with the deep foundation pit. The minimum distance between the two excavations is 5 m. It was found that (1) the underground channel excavation destroys the intact structure of the soil around the channel and foundation pit on a larger scale, which affects the formation of soil arch behind the retaining pile and thus increases the lateral pile displacement, and the addition of anchor cables at the north and south sides of the foundation pit is not necessary; (2) if conditions permit, it is the safest to excavate the underground channel first and then the foundation pit; (3) the primary interaction spacing between the two adjacent excavations is the same depth as that of the foundation pit, and when the spacing increases to twice the depth of the foundation pit, there is basically no interaction; (4) compared with the solid and heavy soil, the adjacent existing underground channel is like a “hollow, elastic, light” tube and more sensitive to the foundation pit excavation, whose uplift and deformation rebound could exert a force on the surrounding soil and then enlarge the lateral displacement of the retaining pile. Full article

This study aims to identify the most suitable pre-reinforcement support measures to prevent TBM jamming when passing through the fractured zone of a gully fault. Given the high likelihood of jamming in such areas, the research focuses on selecting the most effective support system by considering factors such as surrounding rock stability, strata displacement, support structure stress, and cost-effectiveness. Theoretical analysis is employed to predict TBM jamming risks, based on design data, a 10 m gully unit and fractured rock mass were established at 75 m in the excavation direction with assigned parameters. Support effects of pipe curtains, grouting, anchors, and arch supports were analyzed under four conditions: chemical grouting, conduit installation, advanced pipe grouting, and double-layer pipe grouting. On-site verification reveals that TBM jamming occurs when the resisting torque on the cutter exceeds the maximum torque the cutter can generate. For the gully fault, pre-reinforcement measures are essential to stabilize the surrounding rock. Among the different methods, surface drilling reinforcement is the most effective. It significantly improves the surrounding rock’s stability, reducing the plastic zone’s depth by approximately 52.3% compared to the advanced pipe shed method. The axial force on the anchors decreases by 77.9–83.8%, arch stress is reduced by 68.9–90.8%, and tunnel deformation is minimized by 2.13–50.78%, all of which contribute to enhancing the safety of the initial support structure. On-site coring results, TBM boring parameters, and deformation monitoring data confirm that the surface drilling pre-reinforcement method outperforms the grouting pre-reinforcement for the pipe shed, ensuring the safe excavation of TBM in the gully fault conditions. These findings provide valuable insights for TBM tunnel construction in similar geological environments. Full article

Research on the calculation method of deep-buried surrounding rock pressure is an important subject in engineering mathematics. The existing calculation methods are mainly the two-hole closely spaced tunnel, double-arch tunnel, three-hole closely spaced tunnel, and three-arch tunnel. The four-hole closely spaced double-arch tunnel has the characteristics of both the double-arch tunnel and closely spaced tunnel, and its surrounding rock pressure distribution is more complicated. In this paper, the research is carried out based on Protodyakonov’s theory and the concept of process load. The influence of the post-construction tunnel on the supporting structure of the pre-construction tunnel is also considered. The calculation model of the surrounding rock pressure of the deep-buried four-hole closely spaced double-arch tunnel is established, and the calculation formula of the surrounding rock pressure is deduced and verified. Finally, the influences of the rock column parameters, excavation procedure, tunnel span, and middle partition wall on the surrounding rock pressure are analyzed. Full article

Highway tunnel construction in mountainous areas of China has been developing rapidly. The influence of drilling and blasting on the existing tunnel structure has become a key factor affecting the safety and stability of tunnel construction. The double-arch tunnel has unique structural characteristics. The propagation characteristics of blasting vibrations and the resulting stress responses exhibit a certain level of complexity. There is little research on the influence of single-line blasting excavation of double-arch tunnel on the other line tunnel. This paper analyzes the blasting vibration of a double-arch tunnel by ANSYS/LS-DYNA. The propagation law of blasting vibration velocity and stress distribution law of blasting vibration in different sections of the tunnel is revealed. At the same time, the relationship between the peak particle velocity (PPV) and tensile stress is established, and the threshold vibration velocity is proposed. It provides a scientific basis for tunnel design and construction. The propagation of blasting vibration in the adjacent roadway is affected by the middle pilot tunnel. The peak vibration velocity of different parts decreases with the increase in distance. The monitoring of vibration velocity and stress in section A of the right line of the adjacent tunnel should be strengthened, especially in the tunnel vault, blast-facing side wall, and arch foot. The difference in vibration strength across different tunnel parts provides a basis for optimizing the structure. It helps strengthen the parts susceptible to vibration during the design stage of the multi-arch tunnel, improving the tunnel’s safety and stability. Full article

Water and sand leakage in shield tunnels has become more of a research interest in recent years. On the other hand, accidents involving underground engineering can take many forms and occur often. These accidents pose a risk to people’s lives as well as their property, and it is imperative that studies on underground engineering catastrophes be conducted without delay. In this paper, a technique for indoor model tests for disaster and erosion in shield tunnels is utilized to investigate the process of crater, water, and sand leakage evolution in shield tunnels. The change in water pressure at the leaking joint is inversely proportional to the magnitude of the water input rate, and the change in soil pressure is inversely proportional to the distance from the leakage joint. Both changes occurred in the same direction. Notably, the soil’s initial effective stress was also considered to maintain compatibility with actual engineering works. The preliminary findings suggest that soil-effective stress may cause erosion resulting in the soil arching effect. Tests with one and two leakage spots were carried out using this foundation. Compared to the scenario where two leakage sites are opened simultaneously, it was discovered that opening the two leakage points one after the other might result in a more extensive erosion area of superposition. The double leakage point test results indicate that the point where leakage occurs first causes another leakage point because the erosion area created when two leakage points are opened successively will be larger than the erosion area created when two leakage points are opened simultaneously. When two leakage points under a tunnel are close to each other, the width and depth of the soil erosion groove under the tunnel caused by the two leakage points leaking one after another are significantly larger than those caused by two leakage points leaking simultaneously and are also substantially larger than a single leakage point. After a leakage disaster occurs in the tunnel, the water and soil pressure near the leakage point will continue to decrease. The closer the leakage point, the greater the reduction. Until the leakage erosion converges, the water and soil pressure will tend to stabilize. Full article

Due to the complexity of construction sequence and the extended duration required to construct super large section tunnels, the selection of excavation method critically influences the stability of the surrounding rock and support structures. In this work, the Xiaoyuan Tunnel project in Jiangxi Province serves as the research background for employing ABAQUS software to simulate the variations in displacement and stress within the rock and support structures under three different excavation methods. The simulated results are subsequently compared and verified against monitoring data. The findings indicate that the three-benching seven-step method releases more stress (maximum principal stress value reaches 0.621 MPa) from the surrounding rock and support structures than the other methods, resulting in stress concentrations. Therefore, it is of vital significance to complete the initial support in time and seal the tunnel opening quickly. The maximum principal stress values caused by three excavation methods all appear at the arch foot position, highlighting the need for prompt reinforcement of stability support there. Compared to the CRD method and the three-benching seven-step method, the tunnel vault’s settlement value caused by the double-side drift method is reduced by 14% and 19%, respectively. Furthermore, the largest disturbance of the surrounding rock occurs under the CRD method, while the double-side drift method minimizes such disturbances, making it the preferred choice for the construction of super large section tunnels. These insights are invaluable for guiding the selection and optimization of construction methods for such tunnels. Full article

Characterized by long spans, low aspect ratios, and intricate construction sequences, super-large cross-section tunnels present substantial construction risks. Therefore, the selection of the optimal excavation method and construction sequence is crucial for ensuring the safety of tunnel construction and minimizing project costs. This paper takes a super large transverse-section highway tunnel as a case study, employing field monitoring data combined with ABAQUS software to analyze the stress and deformation of surrounding rock and support structures under different excavation methods. The findings reveal that the deformation of surrounding rock and support structures excavated by the Double-Side Drift Method is smaller than those caused by the three-benching seven-step method and the CRD excavation method. Nevertheless, the significant stresses of surrounding rock and support structures are released by the Double-Side Drift Method, leading to potential stress concentrations. Thus, it is necessary to ensure the rapid completion of early support and quick sealing of the tunnel. Furthermore, the sixth process achieves smaller deformation (including arch displacement and surface settlement) of the tunnel, a shorter construction period, and lower economic costs when compared to other construction processes. Consequently, it can obviously be concluded that both the Double-Side Drift Method and the sixth construction process stand out as the most appropriate choices for excavating super large cross-section tunnels. The insights obtained from this study provide theoretical guidance for the design and construction of similar tunnel projects. Full article

Double-layer primary support is proposed to control the deformation of surrounding rock in tunnels within weak geological conditions, where engineering challenges such as large deformations, tunnel faces, and arch collapse are encountered. This approach is based on the principle of combined resistance and release. A combined approach of numerical modeling and on-site surveillance was utilized to analyze the displacement and stress state of the tunnel support structure at different construction stages of primary support for the second layer, using Xiejiapo Tunnel as an engineering case. The findings indicate that the implementation of two-layer primary support can mitigate the progression of large deformations effectively in weak surrounding rock; the sooner the primary support for the second layer is applied, the better the deformation control, and the later the application takes place, the more effectively the tension in the surrounding rock is diminished, whereby the self-supporting capacity of surrounding rock comes into its own. The force of the shotcrete is reduced. Considering the structural deformation and stress state, as well as combination of resistance and release, it is best to implement the primary support for the second layer 10 feet behind the primary support for the first layer. Full article

Research on the excavation mechanical properties of underpass tunnels has already had certain results, but only a few of them consider the effects of dynamic and static loads on the excavation mechanical properties of underground tunnels at the same time; particularly, there is a lack of research investigating double-line highway tunnels with angled underpasses of existing railway tunnels. In this paper, based on the tunnel project of the new double-line Shiqian Highway Tunnel passing under the Hurong Railway with an oblique angle, based on the method of over-advance geological prediction and investigations into the palm face surrounding the rock, the rock degradation caused by dynamic and static loads is quantified using the perturbation system. Additionally, the mechanical parameters of the rock under the influence of dynamic and static load coupling in the influence area of the cross-tunneling project are determined using the Hoek–Brown criterion, and the mechanical characteristics of the excavation of a tunnel under the double-lane highway tunnel passing under the existing railroad are constructed with the mechanical characteristics of the double-lane highway tunnel, taking into consideration the influence of the dynamic and static load coupling in a three-dimensional model. The results show that, in line with the new tunnel rock movement law for the top of the arch sinking, the bottom plate bulging, the side wall outward movement, the height and width of the arch, and the bottom plate arch show an increase with the tunnel excavation, while the side wall rock displacement effect is smaller; the left and right line tunnel disturbed area of the rule of change is similar; the existing tunnel bottom plate displacement is larger than the top plate and the left and right side wall, under the influence of the excavation time step. Typical profile point displacement is mainly determined by the distance from the excavation surface; von Mises stress extremes are observed in the top plate and side walls of the existing tunnel, which occur in the tunnel structure, and there are unloading and pressure-bearing zones in the bottom plate; the new tunnel has the same rock disturbance angle under the four calculation conditions and, based on the displacement control criterion, the excavation method is preferred and the upper and lower step blasting excavation method is recommended. Full article

With the increasing construction of undersea tunnels in seismic-prone areas, accurately assessing their response to seismic conditions is crucial. To grasp the dynamic response of undersea tunnel structures to seismic waves, the shaking table test of water–sea–sea submarine tunnel is designed and carried out based on the methods of orthogonal design and fuzzy method. A comprehensive time-domain model is developed to capture the nonlinear dynamic interaction of ocean engineering structures, taking into account seismic waves, seawater, and saturated soil. The research results show that as the burial depth at each measurement point of the submarine tunnel increases, the acceleration response decreases and the horizontal displacement relative to the seabed surface increases. Comparing test and finite element simulation results reveals that under seismic loading, the strain distribution pattern of the tunnel section is mainly in the arch shoulder, waist, and foot with larger strain peaks, whereas the strain peaks at the arch top and the superelevation arch are smaller. Simultaneously, doubling the water pressure induces a slight increase in the overall strain response peak of the tunnel, with an indistinct relative displacement change rule. When a vertically polarized shear wave (SV wave) is vertically incident, different dynamic response indices will have different trends with the change in water level. This study may provide a reference for shaking table tests for saturated soil–submarine tunnels at complex sites. Full article

Temperature stress has a significant impact on the structural stress of (super) large-span tunnel lining, which can easily lead to structural fatigue damage and premature cracking. With the increasing scale and quantity of super large-span tunnels, the issue of temperature stress in secondary lining has attracted widespread attention. Previous studies have paid little attention to the influence of temperature stress on the structural internal forces of ordinary small–medium-span tunnels, but this influence cannot be ignored for super large-span tunnels. We take the Letuan Tunnel (a double-hole eight-lane tunnel) of the Binzhou-Laiwu expressway renovation and expansion project in Shandong Province as a case study and analyze the mechanical response of the secondary lining through on-site measurement. Moreover, a numerical simulation was conducted to evaluate the effects of self-weight and temperature stress on the secondary lining of the case tunnel. The results indicate that: the stress of the secondary lining concrete and steel bars is greatly affected by seasonal temperature changes. The compressive stress of the concrete and steel bars is significantly greater in summer than in winter, and the tensile stress is greater in winter than in summer. Furthermore, multiple measurement points have shown a phenomenon of transition between tensile and compressive stress states. The stress of concrete and steel bars fluctuates periodically with a sine function over time, with a fluctuation period of one year. The structural stress increases with the increase of summer temperature and decreases with the decrease of winter temperature. The fluctuation amplitude of stress in the inner side of the lining concrete and steel bars is greater than that on the outer side. Among them, the stress amplitudes of the inner and outer sides of the concrete are between 0.77–1.75 MPa and 0.44–1.07 MPa, respectively, and the stress amplitudes of the inner and outer steel bars are between 5–31 MPa and 7–13 MPa, respectively. The safety factors in summer are lower than those in winter. The minimum safety factors for secondary lining in summer and winter are 3.4 and 4.6, respectively, which can meet the safety requirements for service. The average axial forces of the secondary lining under the coupling effects of self-weight and temperature in winter and summer are 528 MPa and 563 MPa, respectively, which are significantly greater than the combined axial forces under their individual effects. The bending moment distribution of the secondary lining at the tunnel vault, inverted arch, wall spring and other positions under the coupling effect of self-weight and temperature is different from or even opposite to the bending moment superposition result under the two individual actions. The achieved results reveal that the influence of temperature stress on the service performance of the lining structure cannot be ignored, and the research results can provide useful reference for similar tunnels and related studies. Full article

The construction of underwater shield tunnels under high water pressure conditions and seepage action will seriously impact the stability of the surrounding rock. In this study, an analytical model for the strength of the two-lane shield tunneling construction under anisotropic seepage conditions was established, and a series of simulations were carried out in the engineering background of the underwater section of Line 2 of the Taiyuan Metro in China, which passes through Yingze Lake. The results show that: (1) the surface settlement has a superposition effect, and the late consolidation and settlement of the soil body under seepage will affect the segment deformation and the monitoring should be strengthened; (2) under the influence of the weak permeability of the lining and grouting layers, the pore pressure on both sides of the tunnel arch girdle is reduced by about 72% compared with the initial value, with a larger hydraulic gradient and a 30% reduction at the top of the arch; (3) within a specific range, the tunneling pressure can be increased, and the grouting pressure and the thickness of grouting layer can be reduced to control the segment deformation; (4) the more significant the overlying water level is, the larger the maximum consolidation settlement and the influence range of surface settlement. This study can provide a reliable reference for underwater double-lane shield tunnel design and safety control. Full article

Straight-wall arch cross-sections are usually designed at the entrance and exit tunnels of subway stations, and dense underground pipelines often cross these cross-sections at close range. Among these pipelines, gas pipelines have the highest risk level. Therefore, it is necessary to reduce the deformation influence of underground crossing construction on existing gas pipelines. Based on the No. 2 entrance and exit tunnel project of Zhongshan Road Station of the Hohhot Metro Line 2, using the methods of numerical simulation and field monitoring, this paper has particularly investigated the influence of straight-wall arch tunnel construction by applying the pre-grouting reinforcement and double-side drift method to the deformation of existing gas pipelines. The research results show that the double-side drift method is an efficient and sustainable construction method for straight-wall arch tunnels, which can effectively reduce the crossing construction disturbance to overlying gas pipelines. The measured maximum settlement of the existing gas pipeline is 18.46 mm, and the maximum settlement of the new tunnel vault is 22.86 mm, with both values satisfying the requirements for deformation control. The simulation results are consistent with the measured results of gas pipeline settlement. This study shows that the safety control scheme employed in the field with a tunnel excavation step of 6 m, stratum reinforcement with upper semi-section grouting, and a grouting reinforcement range of 2.0 m is reasonable and effective. This scheme can provide a reference for the deformation control of similar underground gas pipelines in the crossing construction of straight-wall arch tunnels at close range. Full article

A small clear-distance, double-arch tunnel under an asymmetrical load combines the characteristics of small clear-distance, tunnels and double-arch tunnels, and the influence of an asymmetrical terrain must be considered. Its construction stability is a problem worth studying. This paper used the Wengcun tunnel as the engineering background. Midas/GTS finite element analysis software was used to study the effects of eight excavation sequences and two excavation methods on tunnel stability. The results showed that the deformation and force of the tunnel were asymmetric under the asymmetrical terrain. Both middle partition walls were deformed towards the shallowly buried side, and the shallowly buried side was deformed to a greater extent. Excavating shallow side tunnels first can effectively mitigate the impact of asymmetric terrain. The arch settlement of the Center Diaphragm Excavation Method is 1.33 cm, which is smaller than the three-step excavation method of 1.48 cm; however, this difference is not significant. The Three-bench Excavation Method was more efficient. Based on the conclusion of a numerical simulation, the construction site adopted the construction sequence of excavating the shallowly buried side tunnel first and adjusted the excavation method to the Three-bench Excavation Method. Full article

The conventional support forms of foundation pit retaining piles include single-row piles, double-row piles, anchor-row piles, and so on. The double-row pile supporting structure is widely used in the deep foundation pit supporting the engineering of wharves, bridges, subways, tunnels, and high-rise and super-high-rise buildings. This study on double-row pile supporting structures mainly focuses on four aspects: (1) The influence of dimension parameters, such as pile diameter and pile length, and engineering parameters, such as pile spacing and row spacing, on the deformation control of a double-row pile structure and the stability control of foundation pits; (2) Influence of the soil arch effect on the stress and deformation of the double-row pile supporting structure; (3) Study on the deformation characteristics and rules of the components and the whole structure of the double-row pile supporting structure; (4) Study on the calculation model of pile-soil interactions. Based on the above four aspects, this paper summarizes the latest research status of the existing double-row pile supporting structure and its stress and deformation characteristics. The deformation characteristics and calculation model of the pile-soil interaction of double-row piles are reviewed and evaluated. Finally, the problems and deficiencies in the research on double-row pile support are summarized. These results provide a reference for future research on the double-row pile supporting structure of the foundation pit and the numerical analysis and calculation model and lay a solid foundation for further development of the theory. Full article