Application of transient Rayleigh wave in detection of tunnel lining void area

Transient Rayleigh wave detection is a high-precision nondestructive detection method.At present,it has been widely used in shallow exploration,but rarely used in tunnel lining quality detection.Through the tunnel lining physical model experiment,the layout defects of the double-layer reinforcement lining area were detected and the Rayleigh wave velocity profile and dispersion curve were analyzed after data process-ing,which finally verified the feasibility and accuracy of Rayleigh wave method in detecting the tunnel lining void area.The results show that the method is not affected by the reinforcement inside the lining,the shallow detection is less disturbed and the accuracy is higher,and the data will fluctuate slightly with the deepening of the detection depth.At the same time,this method responds quite accurately to the thickness of the concrete,allowing for the assessment of the tunnel lining’s lack of compactness.This method has high efficiency,good reliability,and simple data processing,and is suitable for nondestructive detection of internal defects of tun-nel lining structure.

Case Study on Synchronous Construction Technology for Secondary Lining of Large-diameter Single track Shiel Shield-bored ored Tunnel

The synchronous construction of the secondary lining during the boring of large-diameter shield faces challenges such as the design of the lining jumbo,the high requirements on the performance for the lining jumbo,the organization of the construction activities in the small and confined area,the horizontal transportation for shield boring and high safety management requirements.A super-long invert lining construction jumbo,as well as the matching California switch,is developed,which provides solution for the confliction between the invert lining construction and the horizontal transportation.The procedure and method for the synchronous operation of the shield boring and the secondary lining are developed by referring to the synchronous construction of the secondary lining during the boring of the TBMs in hard rocks.Due to the adoption of the synchronous operation of the shield boring and the secondary lining,the construction period is shortened and the construction cost is reduced.The paper can provide reference for the synchronous construction of the secondary lining in similar projects in the future.

Load laws of composite lining in mountain tunnel model tests and numerical simulation validation

Currently,model tests are increasingly being used to simulate the construction of mountain tunnels,but the support structure of the model tests does not show the composite lining,and the force laws of the composite lining are not yet clear.In this research,the force variation of composite lining under three cases in model tests of deep-buried tunnels were carried out with the surrounding rock grade and installation time as the variation factors.The test results reveal that:(1)The suitable method to reduce the contact load between the secondary lining and primary support is to enhance the primary support in the soft and weak surrounding rock.Correspondingly,for ClassⅢsurrounding rock and better quality of surrounding rock,the primary support can lag behind the excavation face a certain distance.(2)The axial forces of the bolts tend to rise with concentration of 0.4 kN-0.7 kN after the secondary lining was installed.(3)With or without two to three excavation cycles delayed,the load sharing ratio of the secondary lining of the Class III surrounding rock is less than 10%.Finally,the numerical simulation verifies the feasibility of the model tests.

Study on Crack Propagation Parameters of Tunnel Lining Structure Based on Peridynamics

The numerical simulation results utilizing the Peridynamics(PD)method reveal that the initial crack and crack propagation of the tunnel concrete lining structure agree with the experimental data compared to the Japanese prototype lining test.The load structure model takes into account the cracking process and distribution of the lining segment under the influence of local bias pressure and lining thickness.In addition,the influence of preset cracks and lining section formon the crack propagation of the concrete lining model is studied.This study evaluates the stability and sustainability of tunnel structure by the Peridynamics method,which provides a reference for the analysis of the causes of lining cracks,and also lays a foundation for the prevention,reinforcement and repair of tunnel lining cracks.

Fiber optic sensing and performance evaluation of a water conveyance tunnel with composite linings under super-high internal pressures

For long-distance water conveyance shield tunnels in operation,the high internal water pressure may cause excessive deformation of composite linings,affecting their structural integrity and serviceability.However,the deformation and failure characteristics of lining structures under internal water pressure are not well investigated in the literature,particularly for three-layer composite linings.This study presents an in situ experimental investigation on the response of two types of composite linings(i.e.separated and combined lining structures)subjected to internal pressures,in which a fiber optic nerve system(FONS)equipped with distributed strain and displacement sensing nerves was employed to monitor the performance of the two composite linings during testing.The experimental results clearly show that the damage of the tunnel lining under different internal pressures was mainly located in the self-compaction concrete layer.The separated lining structure responded more aggressively to the variations in internal pressures than the combined one.Moreover,two evaluation indices,i.e.radial displacement and effective stiffness coefficient,are proposed for describing the changes in the structural bearing performance.The effective stiffness coefficients of the two types of lining structures were reduced by 39.4%and 29.5%,respectively.Considering the convenience of field monitoring,it is suggested that the average strains at different layers can be used as characteristic parameters for estimating the health conditions of lining structures in service.The analysis results provide a practical reference for the design and health evaluation of water conveyance shield tunnels with composite linings.

Frost heaving force considering synchronous damage to tunnel lining and surrounding rocks under freeze—thaw cycles

In areas with seasonal freezing,when the tunnel lining concrete is saturated with water infiltrating the interior,the lining and the surrounding rocks will simultaneously freeze.However,the current calculation of the frost heaving force fails to consider the synchronous damage to the lining and surrounding rocks under freeze-thaw cycles.Therefore,as per the elastic calculation model of the frost heaving force and model of steady-state heat transfer of circular tunnels,this study introduces the frost heaving rate of lining and surrounding rocks.First,the analytical solution of frost heaving force is obtained for simultaneous frost heaving of lining and surrounding rocks under any steady-state temperature field.Then,based on the fracture theory and meso-damage mechanics,the damage variables of lining and surrounding rocks under freeze-thaw cycles are extracted,representing their elastic modulus and porosity.Finally,the formula of frost heaving force for synchronous damage to the lining and surrounding rocks at any steady-state temperature field is obtained.The calculation results demonstrate that the lower the temperature inside the lining,the greater the frost heaving force.With the increasing number of freeze-thaw cycles,frost heaving force tends to gradually increase initially,reaching a peak value at 85 freeze-thaw cycles,decreasing to 80%of the peak value at 140 cycles before reaching a constant value.The lining participates in frost heaving,increasing the frost heaving force.The initial increase rate of frost heaving force is 15.7%.Changing the fitting coefficients s1 and s2 of the lining and surrounding rocks can effectively control the magnitude of the frost heaving force in the tunnels.

NuBot:A Magnetic Adhesion Robot with Passive Suspension to Inspect the Steel Lining

The steel lining of huge facilities is a significant structure,which experiences extreme environments and needs to be inspected periodically after manufacture.However,due to the complexity(crisscross welds,curved surface,etc.)of their inside environments,high demands for stable adhesion and curvature adaptability are put forward.This paper presents a novel wheeled magnetic adhesion robot with passive suspension applied in nuclear power containment called NuBot,and mainly focuses on the following aspects:(1)proposing the wheeled locomotion suspension to adapt the robot to the uneven surface;(2)implementing the parameter optimization of NuBot.A comprehensive optimization model is established,and global optimal dimensions are properly chosen from performance atlases;(3)determining the normalization factor and actual dimensional parameters by constraints of the steel lining environment;(4)structure design of the overall robot and the magnetic wheels are completed.Experiments show that the robot can achieve precise locomotion on both strong and weak magnetic walls with various inclination angles,and can stably cross the 5 mm weld seam.Besides,its maximum payload capacity reaches 3.6 kg.Results show that the NuBot designed by the proposed systematic method has good comprehensive capabilities of surface-adaptability,adhesion stability,and payload.Besides,the robot can be applied in more ferromagnetic environments and the design method offers guidance for similar wheeled robots with passive suspension.

Semi-analytical solution for internal forces of tunnel lining with multiple longitudinal cracks

Longitudinal cracks on the tunnel lining significantly influence the performance of tunnels in operation.In this study,we propose a semi-analytical method that provides a simple and effective way to calculate the internal forces of tunnel linings with multiple cracks.The semi-analytical solution is obtained using structural analysis considering the flexural rigidity for the cracked longitudinal section of the tunnel lining.Then the proposed solution is verified numerically.Using the proposed method,the influences of the crack depth and the number of cracks on the bending moment and modified crack tip stress are investigated.With the increase in crack depth,the bending moment of lining scetion adjacent to the crack decreases,while the bending moment of lining scetion far away from the crack increases slightly.The more the number of cracks in a tunnel lining,the easier the new cracks initiated.

Insulating Permanent Lining of Calcium Hexaluminate Based Castable for 300t Ladle in Baosteel

Minimizing of heat loss of liquid steel through the ladle lining led to the integration of increasing insulation function of the permanent lining and high-quality insulating layer between the permanent lining and the ladle steel shell.In this paper,a study was made on physical and thermomechanical properties and corrosion resistance of calcium hexaluminate based castables.The chemical and physical properties of CA6 based castables fabricated in this work can fulfill general requirements of the permanent lining in ladle.The permanent linings of CA6 based castables offer superb thermal insulation and corrosion resistance,compared to conventional refractory systems of 300t ladle in Baosteel.Both functions of insulation and safety work effectively in whole process of ladle operation.

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Recovery of carbon and cryolite from spent pot lining of aluminium reduction cells by chemical leaching

A two-step alkaline-acidic leaching process was conducted to separate the cryolite from spent pot lining and to purify the carbon. The influencing factors of temperature, time, and the ratio of liquid to solid in alkaline and acidic leaching were investigated. The results show that the recovery of soluble compounds of Na3AlF6 and Al2O3 dissolving into the solution during the NaOH leaching is 65.0%,and the purity of carbon reaches 72.7%. During the next step of HCl leaching, the recovery of soluble compounds of CaF2 and NaAl11O17 dissolving into the HCl solution is 96.2%, and the carbon purity increases to 96.4%. By mixing the acidic leaching solution and the alkaline leaching solution, the cryolite precipitates under a suitable conditions of pH value 9 at 70 °C for 2 h. The cryolite precipitating rate is 95.6%, and the purity of Na3AlF6 obtained is 96.4%.

Simulation Study on Reinforcing Overburden to Prevent and Cure the Rupture of Shaft Lining

For preventing and curing the rupture disaster of shaft lining effectively, according to the additional force theory of shaft lining fracture, more than forty tests were carried out on the large scale test rig on the basis of simulating theory. The influence of the position of aquifer, the reinforcing scope of aquifer, reinforcing distance and the strength of grouting cemented mixture on the value and variation law of the axial additional force on shaft lining is studied. The relationships between the reinforcing parameters and the axial additional force on shaft lining are obtained, which provides the theoretic foundation and construction design parameters for the method of reinforcing strata by grouting to prevent and cure tbe rupture disaster of shart lining.

Footprint of harmful substances in spent pot lining of aluminum reduction cell

Spent pot lining(SPL) from aluminum reduction cells is considered to be hazardous materials due to containing a large amount of soluble fluoride salts and trace toxic cyanides. The distribution of fluorides and cyanide in a 350 kA cell operated for 2396 days was analyzed and the footprint and corrosion mechanism of the harmful substances in SPL were also studied. It is found that the fluorides are mainly concentrated in the cathode carbon block and the layer of dry barrier under the cathodes, which is closely related to permeability of the cathodes and dry barrier the fluorides penetrate in. Cyanide has a low concentration in the cell center and a high concentration in the sidewall, which is positively related to the air amount entering into the areas in the cells.

Unified analytical solution for deep circular tunnel with consideration of seepage pressure,grouting and lining

A new unified analytical solution is presented for predicting the range of plastic zone and stress distributions around a deep circular tunnel in a homogeneous isotropic continuous medium. The rock mass, grouting zone and lining are assumed as elastic-perfectly plastic and governed by the unified strength theory(UST). This new solution has made it possible to consider the interaction between seepage pressure, lining, grouting and rock mass, and the intermediate principal stress effect together. Moreover, parametric analysis is carried out to identify the influence of the related parameters on the plastic zone radius. Under the given conditions, the results show that the plastic zone radius decreases with an increasing cohesion, internal friction angle and hydraulic conductivity of lining and unified failure criterion parameter, respectively; whereas the plastic zone radius increases with the growth of elasticity modulus of lining. Comparison of results from the new solution and the other published one shows well agreement and provides confidence in the new solution proposed.

Time-dependent safety of lining structures of circular tunnels in weak rock strata

Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding rock.Thus,the safety of the tunnel lining in weak strata is strongly correlated with time.In this study,we developed an analytical method for determining the time-dependent pressure in the surrounding rock and lining structure of a circular tunnel under a hydrostatic stress field.Under the proposed method,the stress–strain relationship of the fractured surrounding rock is assumed to conform to that of the Burgers viscoelastic component,and the lining structure is assumed to be an elastomer.Based on these assumptions,the viscoelastic deformation of the surrounding rock,the elastic deformation of the lining structure,and the coordinated deformation between the surrounding rock and lining structure were derived.The proposed analytical method,which employs a time-dependent safety coefficient,was subsequently used to estimate the durability of the lining structure of the Foling Tunnel in China.The derived attenuation curve of the safety coefficient with respect to time can assist engineers in predicting the remaining viable life of the lining structure.Unlike existing analytical methods,the method derived in this study considers the time dependency of the interaction between the surrounding rock and tunnel lining;hence,it is more suitable for the evaluation of lining lifetime.

Dynamic mass variation and multiphase interaction among steel, slag, lining refractory and nonmetallic inclusions: Laboratory experiments and mathematical prediction

The mass transfer among the multiphase interactions among the steel, slag, lining refractory, and nonmetallic inclusions during the refining process of a bearing steel was studied using laboratory experiments and numerical kinetic prediction. Experiments on the system with and without the slag phase were carried out to evaluate the influence of the refractory and the slag on the mass transfer. A mathematical model coupled the ion and molecule coexistence theory, coupled-reaction model, and the surface renewal theory was established to predict the dynamic mass transfer and composition transformation of the steel, the slag, and nonmetallic inclusions in the steel. During the refining process,Al_(2)O_(3) inclusions transformed into Mg O inclusions owing to the mass transfer of [Mg] at the steel/refractory interface and(Mg O) at the slag/refractory interface. Most of the aluminum involved in the transport entered the slag and a small part of the aluminum transferred to lining refractory, forming the Al_(2)O_(3) or Mg O·Al_(2)O_(3). The slag had a significant acceleration effect on the mass transfer. The mass transfer rate(or the reaction rate) of the system with the slag was approximately 5 times larger than that of the system without the slag. In the first 20 min of the refining, rates of magnesium mass transfer at the steel/inclusion interface, steel/refractory interface, and steel/slag interface were x, 1.1 x, and 2.2 x,respectively. The composition transformation of inclusions and the mass transfer of magnesium and aluminum in the steel were predicted with an acceptable accuracy using the established kinetic model.

Railway tunnel concrete lining damaged by formation of gypsum,thaumasite and sulfate crystallization products in southwest of China

The railway tunnel concrete lining exposed to sulfate-bearing groundwater beyond 40 years in southwest of China was investigated. Field investigation, sulfate ions content and corroded products analysis, macro/microscopic test were carried out. Results show that under the tunnel concrete lining structure and its served environmental conditions, sulfate solutions permeate concrete lining and accumulate on windward-side of concrete lining, resulting in the increase of sulfate ions content on windward-side and the diffusion of sulfate ions from windward-side to waterward-side, which cause the concrete lining of windward-side damaged seriously but the waterward-side of concrete lining is still in perfect condition. It is confirmed that structural characteristic of tunnel and environmental conditions lead to physical attack with the leaching of concrete and sodium sulfate crystallization as well as chemical corrosion with formation of gypsum in high sulfate concentration and formation of thaumasite in proper temperature rather than formation of ettringite. These achievements can provide academic and technical supports for understanding the deterioration mechanism of concrete lining as well as constructing railway tunnel under sulfate attack.

Experimental study on sliding shaft lining mechanical mechanisms under ground subsidence conditions

Aimed at more than 60 shaft linings damaged in Huaibei, Datun, Xuzhou and Yanzhou mine areas, this paper presents a new type of sliding shaft lining with asphalt blocks sliding layer. By model test, it is obtained that the deformation characteristics and the mechanical mechanisms of the sliding shaft lining under the condition of ground subsidence. The research results provide a testing basis for the sliding shaft lining design. By now, this kind of sliding shaft lining had been applied in 9 shafts in China and Bangladesh.

Research on Stress and Strength of High Strength Reinforced Concrete Drilling Shaft Lining in Thick Top Soils

High strength reinforced concrete drilling shaft linings have been adopted to solve the difficult problem of supporting coal drilling shafts penetrating through thick top soils. Through model experiments the stress and strength of such shaft linings are studied. The test results indicate that the load beating capacity of the shaft lining is very high and that the main factors affecting the load bearing capacity are the concrete strength, the ratio of lining thickness to inner radius and the reinforcement ratio. Based on the limit equilibrium conditions and the strength theory of concrete under multi-axial compressive stressed state, a formula for calculating the load-beating capacity of a high strength reinforced concrete shaft lining was obtained. Because the concrete in a shaft lining is in a multi-axial compressive stress state the compressive strength increases to a great extent compared to uni-axial loading. Based on experiment a formula for the gain factor in compressive strength was obtained： it can be used in the structural design of the shaft lining. These results have provided a basis for sound engineering practice when designing this kind of shaft lining structure.

Effect of Tension on Friction Coefficient Between Lining and Wire Rope with Low Speed Sliding

In order to obtain the exact friction coefficient between lining and wire rope, the tension of wire rope is studied as a factor which affects this coefficient. A mechanical model of a wire rope subjected to axial load was established to determine the torque of the wire rope. The contact motion between lining and wire rope was regarded as a screw rotation and the axial force of the lining resulting from the torque of the wire rope was analyzed. Theoretical formulas relating tension of the wire rope and the friction coefficient was obtained. Experiments between lining and wire rope with low sliding speed were carried out with friction tester made by us. Experimental results show that increment of the friction coefficient is proportional to that of the tension of the wire rope with a low sliding speed. The experimental results agree with the theoretical calculation; the errors are less than 6%, which oroves the validity of the theoretical model.