Kolmogorov entropy analysis of surrounding rock system in the processing of unloading for deep buried tunnels

Rock is a kind of physical nonlinear complicated medium, under deep buried condition the surrounding rock system deformation shows geometrical nonlinear characteristic, and the interaction between the two nonlinear mechanism makes the unloading of surrounding rock system evolving complexly. Based on the Lagrangian method and large deformation caculation method, both the double nonlinearity and nonlinear dynamics character of deep buried tunnel surrounding rock system under unloading are studied. The numerical model results show that the Kolmogorov entropy has been extracted from the evolution data in the unloading process of surrounding rock system. The analysis indicates that the typical chaos character has been demonstrated in the process of unloading for deep buried tunnel surrounding system and the rock mass energy dissipation is analyzed at the stage of unloading.     

Safety Assessment of Circular Arches Tunnel Evacuation on Surrounding Geotechnical Environment

Based on the stochastic medium theory, influence on the surrounding rock and soil by tunnel excavation was studied. formula for predicting movement and deformation of rock and soil mass caused by tunnelling were deduced. And especially for the tunnel with circular arch section, half analytic solution for this problem was put forward. Furthermore, a program was developed to compute the movement and deformation of the rock and soil mass resulted from excavation. The deformation failure criterion of stochastic medium for estimating the surroundings safety was provided and was applied in an engineering example, which proved that the results of the research were reasonable and significant for the tunnel safety construction.     

Stability Analysis for the Excavation Engineering Under Coupling Effect of Seepage from Heavy Rain and River Fluctuation

The seepage accident is very easily occurred, when the excavation engineering has been constructed in rainy season and it is very easily influenced by the coupling effect of seepage duo to heavy rain and water level fluctuation of neighboring river. So a coupling seepage equation that based on the theory of Dupuit has been established for the ground water in the layered foundation. And then, the water table surrounding the excavation engineering has been determined on the consideration of the coupling effect of seepage duo to heavy rain and water level fluctuation of river. In the meantime, by means of the theory of coupling analysis of stress and seepage and the software of Midas, a model of coupling analysis of stress and seepage has been built for the specific excavation engineering and the seepage destroy characteristics of this project has been researched.     

Elasto-plastic analysis on surrounding rock of roadways based on seepage, strain softening and dilatancy

According to seepage body force, strain softening and rupture expansion of rock mass, elastic-plastic mechanics theory, distribution laws of stress and displacement of surrounding rock in seepage field are derived, and relationships between different zonation range of the surrounding rocks, pore water pressure, strain softening and rupture expansion are established. The results show that the pore water pressure and rupture expansion rock mass have a more obvious impact on the surrounding rock rupture area than the plastic zone. Both the plastic zone and the rupture area are larger when the seepage field is considered. The impact of strain softening on both the plastic zone and the rupture zone of surrounding rock is very significant, and both seepage and strain softening rupture expansion affect deformation of surrounding rock of roadways obviously. It provides certain reference values for the roadway support engineering in seepage field.     

Load Calculation Method of Shallow Tunnel under Unsymmetrical Loadings in Broken Surrounding Rock

Tunnel portal section mostly faces unfavorable geologic and topographical conditions, such as broken surrounding rock, shallow and unsymmetrical loadings. The current Chinese code for design of road tunnel provides the load calculation method of tunnel under unsymmetrical. However, according to the mechanic and deformation characteristics of the tunnel lining on site, the assumption is not suitable for the shallow tunnel under unsymmetrical loadings in broken surrounding rock. Therefore, through engineering case analysis and results of three-dimensional numerical analysis, the failure mechanism of shallow tunnel under unsymmetrical loadings in broken surrounding rock is presented firstly, that is, deep buried side broken surrounding rocks slump down after excavation and squeeze the lining, which makes the lining deform outward and bear passive earth pressure. Through the failure mechanism, the surrounding rock mainly includes slumping area and passive area. Then the corresponding formulas are deduced based on limit equilibrium theory. Finally, a case study is adopted to verify the feasibility of the new method. It is show that the new method is more reasonable than the method of current code.     

Finite Element Analysis on Interaction of Neighboring Highway Tunnels under Construction

Recently, the construction of neighboring highway tunnels with small interval gets more and more in China. The construction of such tunnels proceeds usually by excavating one after another. The second tunnel is constructed with the surrounding rock disturbed by the first one. And the construction of second tunnel also has effect on the first excavated one. For revealing the interaction laws of such tunnel construction in combination with the engineering practice of Lanfeng tunnel at Jinshan Road in Chongqing, The FE numerical simulation analysis was used to study the characters of surrounding rock deformation, stress field, and plastic zone of the tunnel. From this analysis, it clearly shows that the excavation of second tunnel has significant influence on the first one. This study provides a scientific basis for design and excavation of neighboring highway tunnels.     

Study of Tunnel Supporting Effect

Based on the elastic theory, an analysis can be made on stress and plastic deformation under tunnel excavation and shotcrete support.FLAC 3D can be used to simulate the mechanical behavior of excavation and support, getting the deformation of surrounding rock stress and plastic without support and shotcrete. The results show that, the prestress applied on the anchor equals to the supporting force when the tunnel plastic zone disappears. This support improves the self bearing capacity of surrounding rock, effectively suppresses the expansion of the plastic zone after the tunnel excavation, and prevents further damage to the tunnel surrounding rock.     

Application of Uncertainty Average Clustering Measurement Model to Classification of Tunnel Surrounding Rock

Based on the uncertainty measurement theory, a uncertainty average clustering measurement model for tunnel surrounding rock classification was established. Due to the uncertain factors in judging the engineering quality of rock masses, seven indexes, i.e., the rock grade, rock weathering degree, rock mass structure, elasticity longitudinal wave velocity of rock mass, influence degree of geological structure, development of joint fissure and ground water regime, were used as the discriminating factors. the indexes functions of unascertained measurement of 20 sets of rock samples were established, and the centre of the classification was indicated by using the average of classification of samples. The weight of indexes was calculated by entropy weight theory, and a prediction for the classification of residual tunnel surrounding rock was carried out using the rules of credible recognition. Each of the 20 sets of tunnel surrounding rockmass samples was tested according to the model, and the correctness rate is 100%. The other 10 sets of tunnel surrounding rock samples were predicted by using this model. The results show that the uncertainty measurement model classification agrees well with the actual measured ones. Therefore, it shows that the uncertaity measurement model is effective, available and can be applied to classification of tunnel surrounding rock in underground engineering.      

Analysis on Interfacial Stress Between Surrounding Rock and Shotcrete Lining

According to the characteristics of interfacial stress between surrounding rock and shotcrete support, mechanical model of composite curved beame for support system of tunnel surrounding rock and shotcrete lining was established, considering the interfacial deformation coordination and the effects of bearing arch of surrounding rock. Then from static equilibrium of two differential elements, the differential equations for the radial displacement of composite curved beam were obtained. All analytic formulas of both interfacial stress and internal forces between surrounding rock and shotcrete lining by arbitrary distribution load were derived. And thus the mechanical condition of interface zone and the stress concentration position were obtained, which is convenient to assess the stability of surrounding rock and predict the safety. Finally, the analysis of tunnel project excavated by bench method showed that shotcrete lining made the formation of compressive stress zone in surrounding rock by transferring stress from the interface between surrounding rock and shotcrete, which is beneficial to improve the stability of surrounding rock.     

Rock Deformation, Stability Monitor Active Control About Excavation of Super-span Tunnel

According to the measurement during excavation of Jinzhou tunnel with four lanes in one cave which lies on the rebuilt highway from Shenyang to Dalian, this paper analyzes the rock deformation rule, discusses the reason of instability after a highway tunnel was excavated, emphasizes the necessity of the construction stability monitor and active control. The importance of support is Fresented with bolts and shotcrete to improve and enhance the carrying capability of the rock. It is necessary to insist on the rule of measurement and active control to ensure the safety and quality of tunnel construction.     

Study on Surrounding Rock Classification Refinement of Railway Tunnel and Application

For IV、V、VI levels of weak rock, because of different levels, The calculated load of tunnel surrounding rock according to the relevant specification was too different. Based on surrounding rock sub-classification method of current highway tunnel, the relation between the new surrounding rock classification and the elastic p-wave velocity refining that was used by railway tunnel was built. The phenomenon of elastic p-wave velocity cross overlap was avoided when surrounding rock classification was different in railway tunnel. For Ⅲ、V、V、VI levels of weak rock, the further refining was done by Vp in railway tunnel, in order to calculate primary support design pressure of surrounding rock, so the oversize difference of computation load value Between adjacent classification was avoided. Combining with a subway tunneling of Qingdao, comprehensive fuzzy identifying method is used to judge Surrounding rock classification level of refinement and adjust, which is more safe and economical for design and construction.     

Experimental Analysis of Construction Time Space Effect for Large Span and Flat Multi Arch Tunnel

For the large span and flat, together with the interaction effect of construction and disturbance of surrounding rock, the mechanical of large span and flat multi arch tunnel is very complicated, and the time space effect is different from that of two lane multi arch tunnel or separated tunnel. Adopting the “CTSSSRH”, the 3 D dynamic process of the tunnel construction was simulated. Analyzing the rule of surrounding rock displacement and stress with excavation, the time space effect of large span and flat multi arch tunnel was proposed.     

Influence Threshold Analysis on Railway Over-Cross Tunnels

Double-track railway over-cross tunnels were stuied by numerical simulation and regression analysis. A series of research on the influence of the construction of newly built tunnel to the existing one in different surrounding rock grades was carried out. According to the numerical simulation, 48 mechanical models were established, which considered various clearance, rock conditions and different construction sequences（building above or beneath existing one）. Based on regression analysis on the calculation results from the 48 models, the deformation prediction formulas for the existing tunnel's surrounding rocks and ballast bed were deduced. According to the high-speed rail allowed standard of roadbed deformation during operation, the minimum clear distance value by which the existing tunnel's operation would not be affected was recommended. Some analysis on the surrounding rock pressure's variation of the existing tunnel caused by new tunnel construction was done. Taking the variation amplitude as the evaluation criteria, a critical value of influenced clearance for railway over-crossing tunnels project is provided. Meanwhile, the results found that the tunnel cross the building had a smaller impact on itself compared with that of the tunnel which goes through the building.     

Nonlinear Rheological Analysis on Tunnel Displacement Induced by Adjacent Excavation in Soft Clay

Deep excavation in soft clay often brings soil stress disturbance and soil deformation, which would bring differential settlement and structural cracks. It probably brings safety problems to adjacent underground tunnels. Therefore, it is necessary to predict tunnel displacement induced by excavation for tunnel’s security. A new method was proposed to estimate the heave of underlying tunnel induced by adjacent excavation verified by field measurements. The soil deformation by excavated soil gravity was analyzed by application of Boussinesq solution. The soil deformation by tunnel surface pressure was analyzed by Mindlin solution. The tunnel was assumed to be an elastic beam on foundation to simulate the tunnel, in which interaction analysis of tunnel and soil was employed. In consideration of rheologic soil, Viscoelastic model was employed to analyze soil nonlinear displacement with time in soft clay. Tunnel displacements were discussed by different excavation cases. A case study showed a good agreement between the results from the prediction and the measurement.     

Dynamic Construction Mechanical Behavior of a Deeply Buried Intersection Tunnel

Excavation of an intersection tunnel between independent double tunnels leads again to stress release and redistribution in the surrounding rock and the support structure of the chief tunnel, resulting in change of mechanical behavior of the rock mass an     

Advisable calculation heights of tunnel overlaying soil with earthquake coefficient method

The earthquake coefficient method is used for aseismatic calculation of tunnel in traffic tunnel specification in our country, but the method is not in accordance with the practical engineering and seismic damage when tunnel is buried very deep, because the inertia force of overlaying soil is overestimated. In order to improve the adaptability of earthquake coefficient method, it is necessary to modify it. In this paper, the aseismatic calculation based on earthquake coefficient method is carried out,and the limitation of the method is analyzed. Then earthquake coefficient method, response displacement method, and dynamic analysis method are applied to tunnels’ aseismatic calculation in V class surrounding rock at different widths of the cavity. Finally, the advisable calculation heights of tunnel overlaying soil with earthquake coefficient method in V class surrounding rock is presented, which can be referenced in aseismatic calculation of tunnel engineering.     

Reliability Analysis of Space Structural System in Deep buried Tunnel

Height of similar rockmass landslides in one tunnel section was processed with the statistical method in the existing design codes.However, the spatial variability within the similar rockmass length was not taken into account.In order to overcome the shortcomings, an equivalent deviation increasing function of the space rockmass landslides height σh(L) was put forward.And the Weibull Бοлοгин statistical theory for brittle materials failure was employed to find the equivalent compressive strength of tunnel secondary lining with different concrete volumes.As a result, the problem of space structural system reliability for the deep buried tunnel could be simplified as a plane problem.Taking the class Ⅲ deep buried rockmass in Jinzhou tunnel as an example, the characteristic values of joint spacing, variance upper limit of rockmass landslides height and the length of the tunnel to affect the system reliability were analyzed.And it was shown that the system reliability index increased with the increase of characteristic values.The system reliability index decreased gradually with the increase of variance upper limit of rockmass landslides height and the length of the tunnel.However, the reliability index would be towards a stable value at the end.     

Simulation Analysis of Spatial Distribution of Roadway′s Surrounding Rock Stress

To get the spatial distribution characteristic of roadway's surrounding rock stress, circular section roadway was taken as a case study. The solution of stress was got by using complex function method, and roadway's surrounding rock stress field was analysed after the solution of mapping space was transformed into the solution of roadway space. As a result, the visual diagram of stress field distribution of roadway's surrounding rock was obtained, which could describe intuitively stress distribution of roadway's surrounding rock at any position. Considering the influence of different radius and side pressure coefficients on surrounding rock stress field, the following conclusions have been obtainded: the peak value and direction of circular roadway's surrounding rock stress has nothing to do with the radius; when side pressure coefficient is less than 1/3,the roof can produce tensile stress; when side pressure coefficient is more than 3, the surrounding rock in two sides can produce tensile stress. And the change rule of hoop stress, radial stress, shear stress and the maximum and minimum of stress have also been generated.     

Real Simulation of 3 D Physical Model Testing for Metro Station Tunnel Construction

Based on the large scale conceptual model theory of similar material, a physical model of metro station tunnel excavation was simulated. The excavation process of metro station tunnel between existing double tubes also was simulated. Ground settling, soil deformation and displacement of specific points around tunnels were studied. The influence of a cast in place pile on reducing soil displacement was simulated. The dynamic mechanical behavior and deformation laws of the soil were obtained along with some useful conclusions. The conclusions are beneficial for guiding the construction and expanded excavation of metro station spaces between existing double tubes.