scholarly journals In Situ Needle Penetration Test and Its Application in a Sericite Schist Railway Tunnel, Southwest of China

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 4) ◽  
Author(s):  
Jiaxing Dong ◽  
Runxue Yang ◽  
Chenggang Guo ◽  
Meiqian Wang ◽  
Yonghong Wu ◽  
...  
Keyword(s):  
Large Deformation ◽  
Soft Rock ◽  
Reference Value ◽  
Surrounding Rock ◽  
Mechanical Parameters ◽  
Penetration Index ◽  
Needle Penetration ◽  
Joint Direction ◽  
Rock Tunnel

Abstract The sericite schist is a typical metamorphic soft rock. Large deformation of surrounding rock often occurs in the construction of a tunnel in this stratum. Due to the broken rock mass structure and poor mechanical strength in Baishitou tunnel project of Dalin line of Southwest railway, it is impossible to prepare standard samples for a traditional rock mechanical test. Therefore, we chose penetrometer (SH-70) for an in situ test. Firstly, we monitored the deformation of typical sections and analyzed the characteristics of large deformation of soft rock in the tunnel. Secondly, we tested the needle penetration index of fresh excavation face and side wall. Then, we estimated some mechanical parameters of sericite schist by a needle penetrometer and Hoek-brown criterion and discussed the acquisition of mechanical parameters of soft rock. The results show the following: (1) the characteristics of extrusion rock tunnel are summarized as large deformation, fast deformation rate, and obvious construction disturbance. (2) The reference value of penetration index of sericite schist (the vertical joint direction) is 3.90~7.77 N/mm, and the parallel joint direction is 1.27~2.99 N/mm. (3) The uniaxial compressive strength estimated by a penetrometer is 0.78~8.53 MPa, and the strength of the surrounding rock is negatively correlated with the amount of deformation. Therefore, it can be considered that the insufficient strength of surrounding rock is the fundamental reason for large deformation. (4) The reference value of cohesion of sericite schist estimated by a penetrometer is 0.203 MPa, and the reference value of internal friction angle is 18.224°. Compared with the common estimation methods, the penetrometer is more convenient and economical, which can provide a new idea for obtaining the mechanical parameters of sericite schist soft rock tunnel.

Judgement Method for Surrounding Rock Stability of Guanjiao Tunnel Based on Catastrophe Theory

2011 ◽  
Vol 90-93 ◽  
pp. 2307-2312 ◽  
Author(s):  
Wen Jiang Li ◽  
Su Min Zhang ◽  
Xian Min Han
Keyword(s):  
Plastic Strain ◽  
Catastrophe Theory ◽  
Soft Rock ◽  
Surrounding Rock ◽  
In Situ Monitoring ◽  
Engineering Practice ◽  
Stability Of Surrounding Rock ◽  
The Stability ◽  
Rock Tunnel

The stability judgement of surrounding rock is one of the key jobs in tunnel engineering. Taking the Erlongdong fault bundle section of Guanjiao Tunnel as the background, the stability of surrounding rock during construction of soft rock tunnel was discussed preliminarily. Based on plastic strain catastrophe theory, and combining numerical results and in-situ data, the limit displacements for stability of surrounding rock were analyzed and obtained corresponding to the in-situ monitoring technology. It shows that the limit displacements obtained corresponds to engineering practice primarily. The plastic strain catastrophe theory under unloading condition provides new thought for ground stability of deep soft rock tunnel and can be good guidance and valuable reference to construction decision making and deformation managing of similar tunnels.

scholarly journals Analysis on Loose Circle of Surrounding Rock of Large Deformation Soft-Rock Tunnel

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Rui Wang ◽  
Yiyuan Liu ◽  
Xianghui Deng ◽  
Yu Zhang ◽  
Xiaodong Huang ◽  
...  
Keyword(s):  
Large Deformation ◽  
Theoretical Calculations ◽  
Rapid Development ◽  
Field Tests ◽  
Soft Rock ◽  
Strength Criterion ◽  
Surrounding Rock ◽  
Distribution Law ◽  
Geological Conditions ◽  
Rock Tunnel

With the rapid development of tunnel construction in China, deep buried and long tunnel projects are emerging in areas with complex engineering geological conditions and harsh environment, and thus large deformation of tunnels under conditions of high in situ stress and soft rock becomes increasingly prominent and endangers engineering safety. Therefore, it is of great significance to control the deformation and improve the stability of surrounding rock by analyzing the thickness and distribution law of loose circle according to the unique mechanical properties and failure mechanism of surrounding rock of large deformation soft-rock tunnel. Based on unified strength theory, this paper deduces the radius calculation formula of the loose circle by considering the influence of intermediate principal stress. Furthermore, the theoretical calculations and field tests of the loose circle in the typical sections of grade II and III deformation of Yuntunbao tunnel are carried out, and the thickness and distribution law of loose circle of surrounding rock of large deformation soft-rock tunnel is revealed. The results show that the formula based on the unified strength criterion is applicable for a large deformation tunnel in soft rock.

scholarly journals Analysis of Surrounding Rock Creep Effect on the Long-Term Stability of Tunnel Secondary Lining

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Xiaoqian Zhang ◽  
Chengmin Wei ◽  
Heng Zhang
Keyword(s):  
Stress Measurement ◽  
Soft Rock ◽  
In Situ Stress ◽  
Calculation Model ◽  
Surrounding Rock ◽  
In Situ Stress Measurement ◽  
Rock Creep ◽  
Secondary Lining ◽  
Rock Tunnel

The secondary lining failure of deep buried soft rock tunnel often occurs, which is obviously related to the time factor. The formation mechanism of this phenomenon is studied in this paper. Therefore, the combination of in situ stress measurement and neural network inversion is used to analyze the distribution characteristics of in situ stress. At the same time, the creep characteristics of surrounding rock are tested in laboratory, and the key parameters are obtained. Combined with the characteristics of surrounding rock, the calculation model is established by using discrete element simulation technology and considering the joints of surrounding rock. According to the above multiple information, the stress characteristics of the secondary lining in different time periods are analyzed creatively. Finally, the method of setting arch and adding anchor bolt in key parts is proposed, and significant effect results are obtained.

scholarly journals Research on the Large Deformation Prediction Model and Supporting Measures of Soft Rock Tunnel

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Junying Rao ◽  
Yonghu Tao ◽  
Peng Xiong ◽  
Chongxin Nie ◽  
Hao Peng ◽  
...  
Keyword(s):  
Large Deformation ◽  
Soft Rock ◽  
Surrounding Rock ◽  
Rock Deformation ◽  
Maximum Displacement ◽  
Deformation Prediction ◽  
Significant Difference ◽  
Rock Tunnel ◽  
Surrounding Rock Deformation ◽  
Bolt Support

The weak surrounding rock has the characteristics of easy softening, poor integrity, low mechanical strength, etc., which makes it easy to induce different degrees of deformation and damage under excavation disturbance and then seriously affects the stability of the tunnel. Carrying out soft rock tunnel deformation prediction research and designing the supporting structure according to the predicted value is of great significance to engineering construction and design. Based on the grey theory, the large deformation of the vault, shoulder, and waist of the soft rock tunnel are predicted, and then the specific bolt support is designed in the maximum predicted value (Smax·R) area. The control effects of different bolts, spacing (d), length (L) on the maximum displacement (Smax·M), and maximum stress (σmax·M) the surrounding rock are analyzed by numerical simulation. Results show that the gray model has high prediction accuracy, the best prediction time is one week, and the maximum error is only 2.99%; with the decrease in d, resin bolt support has a significant supporting effect compared with mortar bolt support, with Smax.M and σmax·M reduced by 64.38% and 10.35%, respectively; as the L of bolt increases, compared with the mortar bolt support, the resin bolt support has a more obvious restraining effect on the surrounding rock deformation, and Smax·M and σmax·M are reduced by 28.20% and 10.00%, respectively; when 4.5 m < L < 6.0 m and 0.6 m < d < 0.7 m, resin bolt support should be adopted; in other ranges, mortar bolt support or resin bolt support has a less significant difference in controlling surrounding rock deformation.

Application of Long Anchor in Support Optimization of Soft Rock Tunnel

2013 ◽  
Vol 368-370 ◽  
pp. 1614-1624
Author(s):  
Yang Sun ◽  
Jian Ping Chen ◽  
Wei Zheng ◽  
Li Yu
Keyword(s):  
Soft Rock ◽  
Surrounding Rock ◽  
Parameters Optimization ◽  
In Situ Monitoring ◽  
Rock Deformation ◽  
New Thought ◽  
Supporting Structure ◽  
Rock Tunnel ◽  
Surrounding Rock Deformation

supporting structure parameters optimization is always a research focus in soft rock tunnel. Combined with Youfangping tunnel in Guzhu highway, the scheme of long anchor supporting has been provided. Usually the length of systematic anchor was determined according to experience, it often not reasonable. In order to determine the length of anchor, in-situ wave velocity test and theoretical calculation was used, and with the consideration of safety and economy, the length of anchor was determined as 4.5m finally; At the same time combined with in-situ monitoring measurement, two test sections was selected, and with the comparison of the designed supporting scheme and the original strong supporting scheme, it can be found that: no matter from the sight of surrounding rock deformation, stress applied on surrounding rock or force pattern of supporting structure, the supporting form by lengthening anchor can control surrounding rock deformation more effectively, can improve the bearing capacity of surrounding rock fully and improve the effect of supporting structure. And the supporting scheme of long anchor was more reasonable than the strong supporting scheme. This long anchor supporting scheme can provided new thought to supporting design of soft rock tunnel in Guzhu highway.

Significant Analysis of Soft Rock Tunnel Disaster-Causing Factors Based on Orthogonal Test

2012 ◽  
Vol 594-597 ◽  
pp. 1331-1337
Author(s):  
Jian Ping Chen ◽  
Ying Xu ◽  
Chang Qun Zuo ◽  
Yi Yi
Keyword(s):  
Large Deformation ◽  
Pressure Coefficient ◽  
Soft Rock ◽  
Tectonic Stress ◽  
Surrounding Rock ◽  
Joint Spacing ◽  
Dependent Relationship ◽  
Side Pressure ◽  
Dependence Relationship ◽  
Rock Tunnel

The impacting effect of lithological features, tectonic stress, the mechanical parameters, structure surface contrasts were comparative analysis, to explore the effect from mentioned factors to surrounding rock-lining in schist tunnel. In order to make sure the dependence relationship of large deformation with these factors, the significant and interaction on large deformation in rock-mess and lining mechanical mechanism were studied according to the experiment data and statistics theory. The result shows that elastic modulus E, side pressure coefficient λ, and joint spacing S have obvious influence on the mechanical properties of surrounding rock-lining, and there is interaction among them. Furthermore, the influence of the interaction between S and λ to rock-lining is found to be significant, and there is an obviously dependent relationship between anchor failure and joints spacing. Therefore, when discussing the reduction measures to avoid the large deformation, the most appropriate method is to study it in overall factors and with the interaction.

scholarly journals Application of Constant Resistance and Large Deformation Anchor Cable in Soft Rock Highway Tunnel

2019 ◽  
Vol 2019 ◽  
pp. 1-19 ◽  
Author(s):  
Xiaoming Sun ◽  
Bo Zhang ◽  
Li Gan ◽  
Zhigang Tao ◽  
Chengwei Zhao
Keyword(s):  
Large Deformation ◽  
Support System ◽  
Field Tests ◽  
Soft Rock ◽  
Internal Force ◽  
Surrounding Rock ◽  
Gansu Province ◽  
Tunnel Engineering ◽  
Anchor Cable ◽  
Constant Resistance

Muzhailing Highway Extra-long Tunnel in Lanzhou, Gansu Province, China, belongs to the soft rock tunnel in the extremely high geostress area. During the construction process, large deformation of the soft rock occurred frequently. Taking the no. 2 inclined shaft of Muzhailing tunnel as the research object, an NPR (negative Poisson’s ratio) constant resistance and large deformation anchor cable support system based on high prestress force, constant resistance, and releasing surrounding rock pressure was proposed. The characteristics of the surrounding rock under the steel arch support and NPR anchor cable support were compared and analyzed by using 3DEC software. A series of field tests were conducted in the no. 2 inclined shaft, and the rock strength, displacement of the surrounding rock, deep displacement of the surrounding rock, internal force of steel arch, and axial force of anchor cable were measured to study the application effect of the NPR anchor cable support system in tunnel engineering. Moreover, the 3DEC numerical simulation results were compared with the field test results. The research results show that the application of NPR constant resistance and large deformation anchor cable support system in tunnel engineering has achieved good results, and it plays a significant role in controlling the large deformation of the tunnel surrounding rock.

The Bench Method Numerical Simulation of Soft Rock Tunnel

2013 ◽  
Vol 438-439 ◽  
pp. 949-953
Author(s):  
Hao Bo Fan ◽  
Jin Xing Lai ◽  
Dan Dan Hou
Keyword(s):  
Numerical Simulation ◽  
Measurement Data ◽  
Soft Rock ◽  
Simulation Method ◽  
Internal Force ◽  
Surrounding Rock ◽  
Supporting Structure ◽  
Highway Tunnel ◽  
Tunnel Design ◽  
Rock Tunnel

This paper based on Chaoyang tunnel by bench method excavation, using the finite element numerical simulation method, simulates the surrounding rock displacement of soft rock tunnel and the stress characteristics of supporting structure to get the various stages of tunnel surrounding rock stress, strain and the internal force changes of tunnel supporting structure. After the analyses of the numerical simulation results and field monitoring measurement data, the safety and rationality of the method are determined. The research provides certain reference for highway tunnel design and construction.

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