Settlement Of Vault Research Articles

Force analysis and treatments for Lidong tunnel of Renxin expressway crossing karst caves

There are several large karst caves at haunch part of the Lidong Tunnel during construction, together with inrush water due to high pressure within these caves. In light of it, this paper takes YK342+113 section as an example and adopts finite difference software FLAC 3D, so as to analyze tunnel deformation when crossing karst caves under six different working conditions, including with or without karst cave, before and after karst treatment, along with support locations. According to analysis results: First, the wall rock mainly had deformation at tunnel vault when evacuating at the third bench, which is a critical monitoring focus for tunnel construction; Second, karst cave treatment contributed to better conduct forces on both sides of wall rock, thus reducing vault settlement, while not affecting horizontal convergence and upturn of vaults; Third, treatment measures were proved to be effective in minimizing wall rock deformation by comparing deformation curves under different conditions; Fourth, after treatment measures, the angular points within the cave’s chamber had stress concentration, which might cause secondary collapse. Field monitoring data revealed that the final settlement of the tunnel vault was relatively consistent with the numerical analysis results, with a distinct change in daily settlement after initial support construction. By integrating numerical analysis and field monitoring, the rationality of the karst treatment plan was fully verified, providing a valuable reference for similar projects.

Gas Pipeline Response to Underlying Straight-Wall Arch Tunnel Construction

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.

Mechanical characterization of subway tunnel construction in urban shallow distributed karst stratums

To address the challenges posed by rapid urban and population growth, China has undertaken extensive urban subway construction. In order to explore the mechanical characteristics of subway tunnel construction in urban shallow karst environment, based on the first phase project of Guiyang rail transit line 3, the concept of “distributed Karst” is proposed according to the occurrence characteristics of karst in urban environment. The dry ice and model soil were used to characterize the karst strata, and the similar model test study on the influence of different volume karst rates on subway tunnel construction was carried out. The influence of tunnel excavation on surrounding rock disturbance, internal force of arch structure and ground settlement under distributed karst stratum condition is studied comprehensively. The following key findings emerged:(1) Karst presence causes an abrupt change in the release curve of surrounding rock earth pressure. Higher degrees of karst development result in smaller changes in earth pressure on the arch top and shoulder after tunnel excavation, with final earth pressure changes of 91.1 kPa, 83.5 kPa, and 74.8 kPa for volumetric karst rates of 5%, 10%, and 20%, respectively. (2) Distributed karst in the tunnel arch has a limited impact on the lateral excavation displacement of the arch girdle but significantly affects the vertical settlement of the tunnel vault. Increasing volumetric karst rates by twofold (from 5% to 10% and 20%) reduces arch settlement by 48.9% and 55.6%, respectively. (3) At volumetric karst rates of 5%, 10%, and 20%, the axial force values at the tunnel top are 58.2 kN, 52.8 kN, and 50.3 kN, while the corresponding bending moment values are 49.6 kN-m, 37.1 kN-m, and 26.0 kN-m, respectively, indicating a more significant difference in bending moment values than axial force values. (4) Karst presence leads to increased surface settlement, with a 48.8% increase in peak ground settlement observed as the volumetric karst rate rises from 5% to 20%.

Stability of the loess tunnel foundation reinforced by jet grouting piles and the influence of reinforcement parameters

The special geological characteristics of loess, such as collapsibility and vertical joint development, usually bring great difficulties to the construction of tunnel inverts. Effectively resolving the subsidence of the tunnel bottom, shortage of the bearing capacity, and uneven subsidence caused by weak loess has been a key challenge during the construction and operation of loess tunnels. Jet grouting piles are widely used because they can effectively improve the geological characteristics of loess and enhance the stability of the foundation. To investigate the reinforcement effect of jet grouting piles in loess tunnel foundations and the effect of changes in the geometric parameters of jet grouting piles on the stability of tunnel foundations, centrifugal model tests and numerical simulations were used to analyse the mechanical properties and the deformation characteristics of the tunnel lining. The results show that the deformation of the loess tunnel bottom caused by the operation and construction can be reduced effectively by using jet grouting piles, but the surrounding rock pressure and settlement of the tunnel vault will be increased at the same time. The length of the jet grouting piles has a better impact than the diameter to improve the reinforcement effect on the stability of the foundation, and the deformation of the tunnel bottom and the stress of the surrounding rock at depth are reduced greatly. Based on the relationship between the length and the reinforcement efficiency of jet grouting piles, the length of jet grouting piles is recommended to be 5–12 m.

Analysis on the Dynamic Characteristics of Cross-Tunnel Structures under Wheel-Rail Impact Forces

The dynamic behaviour of cross-tunnel structures under the wheel-rail impact forces of heavy-haul trains is complicated. This paper establishes an impact force excitation input model to simulate the wheel-rail vertical forces of rail welded joints. The calculated results of the correction formula of wheel-rail vertical forces for seamless rail joints are in good agreement with the measured data and meet the accuracy requirements. The present paper describes a 1/50 scale model experiment based on the case of the newly-built Jing-Zhang Railway underneath the existing Tang-Hu Heavy Haul Railway. Numerical simulation analysis uses FLAC3D to simulate the experiments and investigate the dynamic soil pressure characteristics under different factors. The test and numerical results showed that the dynamic responses of the upper tunnel monitoring points are stronger than the lower tunnel, but the maximum vertical settlement of the lower tunnel vault is bigger and prone to damage. As the depth increases, the stress of the surrounding rock interlayer at each monitoring point gradually decreases. In-depth, the surrounding rock stress decreased approximately non-linearly with increasing surrounding rock grade and surrounding rock interlayer thickness.

Analysis of the Interaction Effects of Shield Structure Oblique Passing under an Existing Tunnel

The interaction mechanism between a two-lane shield tunnel and an existing tunnel during oblique underpass is a matter of widespread concern in the engineering community, and knowledge in this area remains crude. In the construction of subway tunnels in mountainous cities with huge topographical fluctuations, internal forces and deformations are inevitable in existing tunnels. To verify the applicability of existing shield construction technology and empirical parameters to the Guiyang area, a systematic and refined numerical analysis was conducted on the shield passing under the existing tunnel section of the Tao-Hua interval of Guiyang Metro Line 3. In this paper, the accuracy of the numerical simulation is verified by comparing the calculated results with the data measured in the field; the settlement pattern that appeared above the existing tunnel during the construction of the shield with slurry hardening is analyzed; the internal forces, lateral deformation, and torsional deformation of the existing tunnel caused during the excavation of the new tunnel are obtained based on the numerical simulation results; finally, the effect of the old and new tunnels on the torsional deformation and settlement of the existing tunnel under different spatial intersection angles is studied. The results show that the internal forces, lateral deformation, and surface settlement of the existing tunnel due to the diagonal underpass show obvious asymmetric characteristics. Additionally, the existing tunnel experiences local irrecoverable torsional deformation, with the maximum torsional deformation occurring at the intersection of the old and new tunnels, and the spatial intersection angle of the old and new tunnels has a great influence on the maximum settlement of the tunnel vault and arch bottom, which shows a negative correlation.

Analysis of the Causes of the Collapse of a Deep-Buried Large Cross-Section of Loess Tunnel and Evaluation of Treatment Measures

To address the problem of the collapse of the roof of the Bailuyuan tunnel during construction, the causes of collapse were analyzed, targeted treatment measures were proposed, and the effects of the treatment measures were evaluated through on-site monitoring and three-dimensional numerical simulations. The results showed that the particular characteristics of loess and the synergy of groundwater were the internal causes of the tunnel’s collapse as well as, to a certain extent, atmospheric precipitation. Therefore, the combination of multiple factors contributed to the tunnel’s collapse. Untimely monitoring and measurement, as well as the low initial support parameters, reflect a lack of human understanding of the collapse. Based on the analysis of the causes of the collapse, comprehensive treatment measures for inside and outside the tunnel are proposed, which are shown to be effective and to be capable of preventing the occurrence of further collapses. After the collapse treatment, the measured maximum settlement of the tunnel vault was 65.1 mm, the maximum horizontal convergence was 25 mm, the maximum surrounding rock pressure was 0.56 MPa, and the maximum stress on the steel arch frame was 54.34 MPa. Compared with the original design plan, the vertical stress, horizontal stress, and shear stress of the surrounding rock obtained from numerical simulation after the collapse treatment were greatly reduced, the reduction rate at the vault reached 50%, and the safety factors of the initial support positions after treatment met the specification requirements. The research results can provide engineering guidance for the design and construction of large-section tunnels crossing deep-loess strata, and they are of important engineering significance.

Function mechanism and analytical method of a double layer pre-support system for tunnel underneath passing a large-scale underground pipe gallery in water-rich sandy strata: A case study

The Dongping No.1 Tunnel of the Guangdong–Foshan Loop Line Intercity Railway in China passes an existing large-scale underground pipe gallery in water-rich sandy strata through the undercutting method. During construction, controlling the underground pipe gallery deformation is difficult because the water-rich sandy strata can easily become unstable. To deal with this problem, this paper proposes a double layer pre-support system (DLPS) consisting of pipe shed and horizontal jet grouting piles, whose function mechanism is explored from the viewpoint of passive protection and active reinforcement. The deformation transferring path of the DLPS is described as follows: tunnel excavation → lower pre-support deformation → deformation of the soil between the upper and the lower pre-supports → upper pre-support deformation → underground pipe gallery deformation. Considering the influence of geological conditions, the proposed DLPS has two failure modes, namely, excessive settlement of the tunnel vault and excessive deformation of the overlying underground pipe gallery. The mechanical model and analytical method of the DLPS were established according to the theory of beam resting on elastic foundation. Comparing the computed and measured settlement values revealed that the established model is reliable because it could reflect the interaction characteristics of the upper pre-support, the lower pre-support, and the middle soil. Finally, multiple factor analysis was conducted to ascertain the influence of typical calculating parameters, and the deformation characteristics of the DLPS under different influence factors were obtained. The design suggestions for key parameters could provide reference for similar practical engineering in the future.

Analysis on construction deformation characteristics of Da-Puling tunnel by monitoring measurement

Tunnel monitoring and measurement is the guarantee of tunnel construction safety and implementation of dynamic parameter design; relying on the surface settlement, vault settlement and convergence deformation in the tunnel during the construction of Da-Puling tunnel on Guangxi expressway, based on the monitoring data, the stress situation and deformation characteristics of the tunnel are analyzed; the results show that the construction parameters of Da-Puling tunnel are basically reasonable, and the portal section is the key to the control of the whole construction parameters, the settlement of the tunnel vault in the V-Class surrounding rock of the portal section is about 4 times of the convergence deformation, which is mainly caused by the gravity of the overlying soil layer. The settlement of the tunnel vault in the IV-class surrounding rock is close to the convergence deformation, and the stress release deformation in the loose area of the tunnel surrounding rock is the main one. The monitoring and analysis in the construction process provides reliable data for design and construction in time, and ensures the smooth progress of tunnel construction.

Study on the supporting time of the secondary lining of the highway tunnel with weak surrounding rock

Based on the Dongxiu tunnel project of Liyu highway under construction in Guangxi province of China, this paper attempts to study the supporting time of the secondary lining of the highway tunnel with weak surrounding rocks. Firstly, the measurement data of typical section of the tunnel is fitted and used to reveal the evolution law of the settlement of the tunnel vault and peripheral convergence of the sidewall. Then the three-dimensional simulation is carried out to verify the rationality of the evolution law. After that, the supporting time of the secondary lining is determined relying on the results of field monitoring and numerical simulation. The results show that, both the settlement of the tunnel vault and the peripheral convergence for the Dongxiu tunnel can be characterized by exponential function, and it is reasonable to construct the secondary lining at 24th-25th day after excavation. The results can not only guide the subsequent construction on site but also provide reference for the determination of supporting time of the secondary lining of similar tunnel projects.

The angle for setting foot reinforcement bolt based on the failure mode of shallow tunnel in loess

During the construction of shallow tunnel in loess, installation angle of foot reinforcement bolt (FRB) has a significant effect on settlement at tunnel vault. In this paper, according to the failure modes of shallow tunnel in loess, considering the internal force transmission, deformation coordination, and arch foot displacement between the steel frame and the FRB, a mechanical calculation model for joint load-bearing and displacement of the steel frame for primary support and the FRB is proposed, and found that the maximum anti-sliding force is at angle of 47 degrees of FRBs. The calculated angle is used at different sections of the Jianzicha No. 2 tunnel, measured settlement and deformation of the tunnel vault in field tests showed the angle is applicable in construction. By using the finite element simulation, the influence of anchor pipe angle on the settlement of tunnel vault was studied. The results showed that, FRBs at 47 have the best effect in controlling settlement.

Deformation Response Induced by Surcharge Loading above Shallow Shield Tunnels in Soft Soil

In the case of sudden surcharge loading, shallow shield tunnels in areas with soft soil experience substantial deformation responses. It is very important to understand the different loading modes and control measures above the shallow shield tunnels in soft soil for improving the safety of tunnel structure and reducing the influence of deformation. In this study, a three-dimensional numerical model of shallow shield tunnels in soft soil is established with FLAC. Ground and tunnel deformations are analyzed under different loading modes, and the effects of different deformation control measures are also studied. The numerical simulations in this paper show that the surface and tunnel deformation responses vary when induced by different loading modes above shallow shield tunnels in soft soil. After surface hardening with a 20-cm-thick layer of C20 concrete, the surface settlement is effectively controlled, and the uneven longitudinal settlement of the tunnel vault is improved. However, controlling the height of the surcharge is the most direct deformation control method. When the height of the surcharge is reduced from 6 m to 4 m and 2 m, the maximum ground settlement is reduced by 37.8% and 69.4%, respectively, and the maximum longitudinal settlement of the tunnel vault is reduced by 35.3% and 65.2%, respectively. During the operation of shallow shield tunnel in soft soil area, sudden surcharge loading should not be allowed. In the inevitable case, the surcharge loading on one side of the tunnel should be prevented and the surcharge loading height should be strictly limited.

Optimization Research of Construction Methods and Parameters of Large-span City Coastal Tunnel in Horizontal Layered Rockmass

Hou, F.-J.; Han, X.-M.; Li, S.-C., and Li, W.-J., 2019. Optimization research of construction methods and parameters of large-span city coastal tunnel in horizontal layered rockmass. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 232–236. Coconut Creek (Florida), ISSN 0749-0208.A city coastal tunnel was a four-lane road tunnel. Maximum excavation width of tunnel reached to 19.51 m in Class IV surrounding rock. The surrounding rock of tunnel was medium-thick horizontal layered limestone. To obtain the mechanical parameters of transverse isotropic material, some tests, including rock mechanics test, on-site structural characteristics survey of rockmass, bearing plate test and numerical back analysis, field test of shear strength, were conducted. Then numerical simulation were adopted to study the reasonable excavation method and parameters of tunnel in Class IV surrounding rock. To verify effectiveness of the conclusion, stress of shotcrete and steel frame of primary support of tunnel were monitored on site. Research showed that normal elasticity modulus of rockmass was obviously less than transverse elasticity modulus, and it have remarkable transverse isotropy. Settlement of vault was the main deformation in horizontal layered surrounding rock. The failure characteristic of layered rockmass were rock-falling in spandrel and delaminating collapse of vault. Bench method could be employed in Class IV surrounding rock to speed up the construction progress. Stress test results of shotcrete and steel frame of support structure indicated the tunnel was safe under the optimized excavation method and parameters.

Evaluation of a tunnel in Yunnan using CRD construction method

According to the surrounding rock conditions of Re Shuitang Tunnel NO.2, it is analyzed whether the CRD method is suitable for such surrounding rock conditions. By comparing and analyzing the distribution of plastic zone of surrounding rock during construction and the displacement deformation of tunnel monitoring point, the tunnel is constructed. The plastic zone of the middle arch and the arch is obviously changed, and should be reinforced. The settlement of the right vault and the side wall is larger than the left side, which is about 19.8% and 21.9%. According to the analysis results, the vault should be reinforced in advance during tunnel construction to prevent collapse and ensure construction safety, and provide reference for future construction.

Effect analysis of grouting reinforcement ring considering fluid solid coupling

Geological hazards such as instability of surrounding rock and leakage of water are easily occurred in subway tunnels crossing water rich sand layers. Based on the principle of fluid solid coupling in porous media, this paper studies the plastic zone distribution of surrounding rock and reinforcement ring, vertical settlement of tunnel vault and water seepage of tunnel before and after grouting reinforcement for water rich sand layer. Considering the compressibility of rock mass, the relationship between porosity, permeability and volume strain is further deduced and simplified. A set of numerical calculation formula is set up to study the change of physical parameters of the water rich sand layer before and after grouting to determine the grouting effect and select the thickness of the best grouting reinforcement ring. The results show that the deformation and water permeability of the tunnel decrease with the increase of the thickness of the grouting reinforcement ring. The thickness of the grouting reinforcement ring is the most reasonable when the thickness of the reinforcing ring reaches a certain value, and the thickness of the grouting reinforcement ring is designed to be 5~6m. The research results have been successfully applied in the grouting project of Qingdao Metro stone elderly bathing beach. The reliability of the numerical simulation is verified by comparing the data from the field monitoring and measurement, providing reference for the related projects.

Application of Integrated Forecasting Model Based on Multiple Variables in Tunnel Vault Settlement

The settlement of tunnel vault, which is a complicated process that includes combined actions of multiple factors together, is difficult to calculate accurately with mathematical model. In the actual construction process, the surrounding rock often changes, so we must strictly control the tunnel vault settlement to meet design requirements. Traditional prediction models can obtain only a rough estimate of the vault settlement by using the monitoring data to fit and forecast its changes. To solve the problem, this paper constructs a time-series model, GM (1, 2) model, and BP model with input variables to predict the settlement of the vault. The effectiveness of the model is verified by examples, which show that the GM (1, 1) prediction model of a single variable is completely ineffective. To avoid the lower prediction accuracy of single model and use the complementary advantages of different models, this paper establishes an integrated prediction model based on the above three models, and its weighting coefficient is determined by the application of the entropy method. The model is applied to Baimiaozi Tunnel for testing, which provides high-speed travel from Baoji to Hanzhong (two cities in Shanxi Province). The integrated model is effective in practice and has a high prediction accuracy.

Construction mechnical effect of highway tunnelwith four lanes in layered rockmass

Jiangshuiquan tunnel was a highway tunnel with four lanes. Its maximum excavation cross section was 170.1 m2 in Class III surrounding rock. The host rock was horizontal layered limestone, and it have obvious transverse isotropy. Based on laboratory experiments and site survey of rockmass structure, mechnical parameters of rockmass were determined. Numerical simulation and field test were used to study the deformation and failure characteristics of tunnel, pressure of surrounding rock, stress of shotcrete and lattice girder. It was concluded that lateral elasticity modulus of rockmass was obviously bigger than vertical elasticity modulus. Settlement of vault was the main deformation form of surrounding rock. Rock-falling in spandrel and delaminating collapse of roof were the common failure phenomenon. Setting rock bolt in vault was necessary in horizontal layered rockmass. Compared wtith other postions, pressure of surrounding rock, stress of shotcrete and steel frame of the vault were relatively small.

The Comparison of Tunnel Engineering Construction Methods for Renhechang Tunnel Crossing Underneath Existing Tunnel on Lanzhou-Chongqing Railway

Problems often exist in construction of transportation tunnels, such as the effect of new tunnels constructed close to existing structures. Solving this magnificent problem by carefully choosing tunnel construction methods will be beneficial to minimize effects on existing structures while ensuring the newly constructed tunnel is both time-consuming and economical. Three representative engineering methods-the benching tunneling method, the Center Diaphragm method and the Cross Diaphragm method-are compared in controlling the settlement of new tunnel vault and the deformation of the existing tunnel. Finally checking the simulation results by comparing with field measurement data.

Three Dimensional Numerical Analysis of Ground Settlement Induced by Shield Tunneling

The fine numerical simulation is used to study the ground settlement of complex stratum owing to shield construction by ANSYS program. It is shown that the closer the distance between soil layer and the axis of tunnel is, the smaller the disturbance of construction is, the obvious the ground surface settlement is. The value of the maximum settlement at the center of the surface is 7.4mm. The maximum settlement of vault is 14mm. The ground subsidence in cross section distribution is shaped of normal distribution. The closer the distance between soil layer and ground surface is, the smaller the vertical displacement is, the bigger the width of settlement trough of soil layers is. The width of settlement trough is 25m. The volume loss rate of shield tunnel is about 0.32%. The width coefficient of ground settlement trough is 0.56. The tendency of ground settlement decrease to become gentle with the advance of shield construction. The ground settlement keeps constant after tunnel face advancing to 30m.

Stability Analysis on Rectangular Transition Section Tunneling in Beiwan Horsehead Region of No. 7 Subway

The settlement of ground and vault by tunneling has important effect on construction safety and normal operation of urban transport system. The soils around reserved shaft of Beiwan region in No.1 section of Beijing Metro Line No.7 are backfilled and complex. In order to tunnel safely and keep surrounding structures safe, the stability of rectangular transition section by tunneling of Beiwan horsehead region is analyzed. Based on the data of surface survey, drilling, prediction detection of the strata and engineering design, the software of 3D FLAC is used to study the vault and ground settlements during the excavation of six pilot tunnels of rectangular transition section, and the results are also compared with the results of in-situ monitoring. The research shows that the results of numerical simulation and in-situ monitoring are matched very well, the ultimate ground settlement will be 17 mm when the transition tunnel is excavated by non-shrinkage (WSS) pre-grouting method and CRD method, and meets with the requirements of standard specification. Therefore, the six-pilot-tunneling method is good for keeping the transition tunnel stable.