scholarly journals Numerical Evaluation on Dynamic Response of Existing Underlying Tunnel Induced by Blasting Excavation of a Subway Tunnel

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Jixue Zhou ◽  
Yi Luo ◽  
XinPing Li ◽  
Yunhua Guo ◽  
Tingting Liu
Keyword(s):  
Tensile Stress ◽  
Subway Tunnel ◽  
Railway Tunnel ◽  
Adjacent Structures ◽  
Blasting Excavation ◽  
Traditional Drill ◽  
Full Face ◽  
Drill And Blast ◽  
Blasting Method ◽  
Peak Value

In Southwest China, most regions are mountainous, where traditional drill-and-blast method is adopted to excavate relatively harder rocks. However, blasting would cause vibration to adjacent structures and might result in damage or even failure. This paper considers a case where subway tunnel is overlying an existing railway tunnel, while the excavation requires blasting method. Vibration and stress distribution are calculated via Dynamic Finite Element Method (DFEM) for both full-face excavation and CD method. Result shows that vibration induced by CD method is only 28% of that caused by full-face blasting with same distance. Peak vibration is located on the lining facing the blasting source, while peak tensile stress is on the other side of the contour due to the reflection of stress wave on strata boundary. And peak value of tensile stress induced by full-face blasting is capable of causing lining failure; thus full-face blasting is not suggested within 40 m beyond the underlying tunnel axis. However, CD method has shown much advantage, since blasting within 25 m is also considered safe to the underlying tunnel. But when the blasting source is as near as 12 m within the underlying tunnel, the CD method is no longer safe.

scholarly journals The Efficiency of Large Hole Boring (MSP) Method in the Reduction of Blast-Induced Vibration

2021 ◽  
Vol 11 (4) ◽  
pp. 1814
Author(s):  
Min Seong Kim ◽  
Sean Seungwon Lee
Keyword(s):  
Urban Areas ◽  
Cost Effective ◽  
Base Case ◽  
Large Hole ◽  
Promising Alternative ◽  
Geological Information ◽  
Drill And Blast ◽  
Smooth Blasting ◽  
Alternative Designs ◽  
Blasting Method

Drill and blast is the most cost-effective excavation method for underground construction, however, vibration and noise, induced by blasting, have been consistently reported as problems. Cut blasting has been widely employed to reduce the blast-induced problems during underground excavation. We propose that the large hole boring method using the state-of-the-art MSP (Multi-setting smart-investigation of the ground and pre-large hole boring) machine (“MSP method”) can efficiently improve vibration reduction. The MSP machine will be used to create 382 mm diameter empty holes at the tunnel cut area for this purpose. This study assessed the efficiency of the MSP method in reducing blast-induced vibration in five blasting patterns using a cylinder-cut, which is a traditional cut blasting method. The controlled blasting patterns using the MSP method demonstrated up to 72% reduction in blast-induced vibration, compared to the base case, Pattern B, where only cylinder-cut and smooth blasting method were applied. Therefore, the MSP method proves to be a promising alternative for blasting in sensitive urban areas where non-vibration excavation techniques were initially considered. Geological characteristics of 50 m beyond the excavation face can be acquired through the proposed real-time boring data monitoring system together with a borehole alignment tracking and ground exploration system. The obtained geological information will be a great help in preparing alternative designs, and scheduling of construction equipment and labour during the tunnel construction.

Continuous Belt Mucking Technology of China Railway Tunnel Construction

2012 ◽  
Vol 268-270 ◽  
pp. 664-672
Author(s):  
Ya Ting Sun ◽  
Zhi Rong Mei ◽  
Jun Wei Zhang
Keyword(s):  
Conservation Policy ◽  
The Other ◽  
Tunnel Construction ◽  
Frozen Ground ◽  
Railway Tunnel ◽  
Scheme Design ◽  
Construction Methods ◽  
Comprehensive Benefit ◽  
Equipment Configuration ◽  
Blasting Method

The conventional mucking system of tunnel construction in China has a series of deficiencies and stubborn problems. Tunnel mucking technologies matched with different tunnel construction methods have been analyzed systematically and the continuous belt mucking methodology which is appropriated with drilling-blasting method was presented. The continuous belt mucking technology includes mucking scheme design and mucking equipment configuration. Compared with the conventional mucking methods, the comprehensive benefit can be fully demonstrated by the new continuous belt mucking system. On the other hand, the predominance on environmental protection of the continuous belt mucking technoloty matches up with the conservation policy. The technology would be widely applied in long tunnels and tunnels embedded in frozen ground and located in bitter cold plateau. The economic benifis and contribution to society of continuous belt mucking technology would be remarkable.

Effect of Hydrogen on the Fracture Behavior of High-Strength Cr-Mo Steel

2006 ◽  
Vol 512 ◽  
pp. 55-60 ◽  
Author(s):  
Mao Qiu Wang ◽  
Eiji Akiyama ◽  
Kaneaki Tsuzaki
Keyword(s):  
Tensile Stress ◽  
Power Law ◽  
High Strength ◽  
Maximum Tensile Stress ◽  
Maximum Principal Stress ◽  
Slow Strain Rate Test ◽  
Diffusible Hydrogen ◽  
Thermal Desorption Spectrometry ◽  
Stress Concentration Factors ◽  
Peak Value

We examine the hydrogen embrittlement susceptibility of a high-strength AISI 4135 steel by means of a slow strain-rate test (SSRT) using notched round bar specimens. Hydrogen was introduced into the specimens by electrochemical charging and its content was measured by thermal desorption spectrometry (TDS). It was found that the maximum tensile stress decreased in a power law manner with increasing diffusible hydrogen content. Finite element method (FEM) calculations demonstrated that the peak value of the maximum principal stress and the peak value of the locally accumulated hydrogen concentration at the maximum tensile stress were in good agreement with one power law relationship for the specimens with different stress concentration factors.

An experimental investigation on the tensile stiffness in layered rock interface using the digital image correlation technique

2020 ◽  
Vol 13 (2) ◽  
pp. 65-79
Author(s):  
Xiong Dong ◽  
Yang Huanqiang ◽  
Liu Yang ◽  
Wang Xiaowei
Keyword(s):  
Digital Image Correlation ◽  
Tensile Stress ◽  
Digital Image ◽  
Image Correlation ◽  
Tension Stress ◽  
Displacement Curve ◽  
Layered Rock ◽  
Tensile Stiffness ◽  
The Law ◽  
Peak Value

Tensile stiffness of interfacial layered rock is the basis of studying the law of interlaminar propagation of hydraulic cracks. We used similar materials to make simulated specimens of sand-mud layered rock with prefabricated cracks, and used the digital image correlation (DIC) technique together with the three-point bending (TPB) test to obtain the strain field near the prefabricated crack tip in tensile state. Combined with the tensile stress in the corresponding area calculated by the load of the tester, the tensile stress-displacement curve at the interface of layered rock is obtained, and the tensile stiffness and interfacial fracture law at the interface of layered rock is calculated by the curve. The results show that in the process of tensile failure, before reaching its peak value, the interfacial tension stress of layered rock has a linear elastic deformation stage followed by a short hardening stage. Upon reaching the peak value, it is accompanied by interfacial failure and macro-cracks, and then the load decreases and enters the softening stage, which results in the complete destruction of the interface. The tensile stiffness values of layered rock with different sizes vary greatly, which indicates that the interfacial tensile stiffness values are sensitive to the specimen size and have a size effect. The results are of great significance to the study of the law of hydraulic fracture propagation in the interface of layered rock.

scholarly journals Excavation Method of Reducing Blasting Vibration in Complicated Geological Conditions

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Lixiang Xie ◽  
Wenbo Lu ◽  
Jincai Gu ◽  
Gaohui Wang
Keyword(s):  
Back Analysis ◽  
Blasting Vibration ◽  
Underground Engineering ◽  
Engineering Construction ◽  
Vibration Data ◽  
Geological Conditions ◽  
Blasting Excavation ◽  
The Stability ◽  
Site Test ◽  
Blasting Method

Drilling and blasting method as a common excavation method is widely used in the underground engineering construction. However, in the complicated geological conditions, the path of blasting excavation available has limitation, and then the larger blasting vibration is produced, which influence the stability and safety of the protected structure. To effectively reduce the blasting vibration by optimizing the blasting excavation method, firstly, the site test on blasting vibration is conducted to obtain the blasting vibration data; secondly, the LS-DYNA software is applied to simulate the vibration generated by blasting in site test, based on back analysis on the blasting vibration, the mechanical parameters of the rock mass are obtained, and they are used to simulate six different types of blasting excavation method. According to the analysis on them, the reasonable blasting excavation method is proposed to reduce the blasting vibration which can satisfy the blasting safety regulation.

Mechanical Behavior of Segmented Lining Structure of Tunnel under Acting Ground Fractures in Xi’an Zone

2011 ◽  
Vol 261-263 ◽  
pp. 1778-1783
Author(s):  
Sheng Jun Shao ◽  
Fang Tao She ◽  
Juan Fang
Keyword(s):  
Tensile Stress ◽  
Mechanical Behavior ◽  
Compressive Stress ◽  
Three Dimensional ◽  
Vertical Displacement ◽  
Maximum Tensile Stress ◽  
Internal Force ◽  
Subway Tunnel ◽  
Lining Structure ◽  
Pass Through

Xi’an ground fracture, caused by the extraction of groundwater and the movement of fault under soil strata, is a geo-hazard. The movement of ground fracture originates the uneven settlement of upward block and downward block. In Xi’an ground fracture region, the segmented lining structure was adopted in subway tunnel to pass through the ground fracture, so as to adapt for the uneven settlement. Three-dimensional elastic-plastic finite difference method was applied to simulate the initial lining structure, second segmented lining structure, surrounding soils and ground fracture. The horizontal and vertical displacement of segmented lining structure, surrounding soils pressure and internal force of segmented lining structure in subway tunnel were analyzed by the calculation results. The knowledge on mechanical behavior of segmented lining structure passing through an active ground fracture and surrounding soils was shown as following. The relative vertical displacement between segmented lining structure sects beside the ground fracture increases remarkably with the movement of ground fracture, and the segmented lining structure located in upward displaceent block near ground fracture originates notable rotary. Tension or compression deformation occured in the deformation joint between adjacent segmented lining structures near the ground fracture.There was a significant change in the contact pressure of the first sect of lining structure in the upward displace block. Under the same uniform settlement at the bottom of upward diaplacement block, the relativly vertical displacemtn on the surfaceof ground fracture strata without tunnel equals 50cm, but the relativly vertical displacement between adjacent segmented lining structure at ground fracture is 18.2cm on the design level of arch top of lining strcutre. the maximum tensile stress of segmented lining structure is 2.02MPa, the maximum compressive stress of segmented lining is 3.49MPa. In conclusion, segmented lining structure can adapts to the uneven settlement caused by the movement of ground fracture. Though maximum tensile and compressive stress of sengmented lining structure passing through the active ground fracture is bigger than the general lining structure located in soils strata without the ground fracture, the segmented lining structure constructed by the steel fibre concrete can bear with the maximum tensile stress.

scholarly journals Analysis of Load-Bearing Capacity of Initial lining in Tunnels

2021 ◽  
Vol 9 (VII) ◽  
pp. 3954-3960
Author(s):  
MD Waquar Alam
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Bearing Capacity ◽  
Element Model ◽  
Time Dependent ◽  
Load Bearing Capacity ◽  
Load Bearing ◽  
Full Face ◽  
Ground Condition ◽  
Drill And Blast

Large displacements during excavation are regularly observed in Squeezing ground condition and Rock-burst condition with high overburden. The expected displacement has to be estimated prior to excavation to provide enough allowance for the displacements. The support system need to be well-suited through the estimated imposed strains. As the estimated displacements and thus the strains in the support depend upon the load-bearing capacity of support. The ratio of uniaxial compressive strength of rock mass to maximal insitu stress determines tunnel integrity in the weak region.This ratio estimates the requirements of initial lining to control strain to a stipulated level. The elasto-plastic theory may deliver definitive forecasts providing the strength limitations of rock masses are identified accurately. With the help of empirical analysis, the development of displacements for diverse advance rates and supports can be concluded. As a consequence, a quantitative finite element model based on an advanced built-in model is designed to analyse the load-bearing efficiency of initial lining although taking into consideration the time-dependent and non-linear material behaviour of initial lining. The time-dependent excavation mechanism of the drill-and-blast approach for tunnels guided by full face excavation is considered in the finite element model. The material parameters for the initial lining were computed based on case studies- (A Chibro-Khodri Hydropower Tunnel).

scholarly journals Vibration Failure of Young Low-Temperature Concrete Shaft Linings Caused by Blasting Excavation

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Lidong Xie ◽  
Zhaoxing Dong ◽  
Yanjun Qi ◽  
Ruohua Qiu ◽  
Qiang He
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Tensile Strength ◽  
Vibration Velocity ◽  
The Finite Element Method ◽  
Dynamic Tensile Strength ◽  
Cumulative Energy ◽  
Blasting Excavation ◽  
Shaft Lining ◽  
Blasting Method

The freezing-blasting method constitutes the only available technique for excavating mining shafts within water-bearing bedrock. This study explores the effects of vibration damage to young C65 concrete shaft linings caused by close-range blasting excavation using the finite element method. C65 concrete test specimens were made in the laboratory and then cured at −7°C, and the elastic modulus, compressive strength, and longitudinal wave velocity were tested. The allowable dynamic tensile strength of the concrete for each mold of the shaft lining was obtained according to the observed strain rate of the concrete shaft lining using a regression formula. The finite element simulation results are basically consistent with the in situ measurements, thereby attesting to the validity of the numerical simulation. The blasting-induced vertical peak vibration velocity of the first mold of the concrete shaft lining reached 20∼25 cm/s, which far surpasses the allowable vibration velocity range (i.e., 2∼3 cm/s) in the Safety Regulations for Blasting for newly cast concrete between the initial setting and an age of 3 d. The tensile stress of the first concrete mold calculated by the finite element method is approximately equal to the theoretical tensile stress, both of which are smaller than the dynamic tensile strength of concrete. The cumulative energy sustained by the shaft lining of each mold and the allowable values of the dynamic tensile strength were obtained. The growth rate of the dynamic tensile strength of the subsequent molds was larger than that of the cumulative energy, and thus the safety of the shaft lining gradually improved. The C65 concrete would therefore not experience tensile failure after the shaft lining has sustained multiple rounds of blasting loads. This finding can provide a basis for safety considerations when employing the freezing-blasting method to construct mining shafts in water-bearing bedrock.

scholarly journals Study on the Face Stability of a Metro Tunnel in a Silty Clay Layer Constructed Using the Full-Face Method

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1069
Author(s):  
Zhien Zhang ◽  
Mingli Huang ◽  
Chunbo Yu ◽  
Xiaojian Fu
Keyword(s):  
Soft Soil ◽  
Horizontal Displacement ◽  
Silty Clay ◽  
Subway Tunnel ◽  
Tunnel Face ◽  
The Core ◽  
Cut Method ◽  
The Face ◽  
Full Face ◽  
Subway Tunnels

The horizontal displacement of the soil at the face of the subway tunnel is symmetrically distributed along the central axis of the tunnel, which is larger in the middle and smaller at both sides. The displacement is related to the size of the excavation face. If the excavation area is too great, the horizontal displacement of the tunnel face will be too large, easily leading to tunnel face collapse. For this reason, tunnel builders often use the core-keeping ring-cut method to build subway tunnels. A large section is divided into several small sections to reduce the soil displacement caused by soil excavation. With the continuous promotion and application of mechanized construction in the field of tunnels, mechanized full-section construction will gradually be performed in urban subway tunnels. Once the change in construction method from the core-keeping ring-cut method to the full-face method is made, the issue of how to maintain the stability of the tunnel working face (especially the soft soil stratum) becomes the focus of attention. Taking silty clay as the research object, this paper studies the displacement law of core soil with regard to the tunnel face under the condition of full-face excavation by using theoretical analysis, numerical simulations, and outdoor tests. According to the research results, the extrusion displacement of the tunnel face is the main cause of tunnel displacement. We optimize the construction parameters of glass fiber anchors to strengthen the tunnel face and provide theoretical guidance for the safe construction of subway tunnels.

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