Reliability analysis of supporting pressure in tunnels based on three-dimensional failure mechanism

Based on nonlinear failure criterion,a three-dimensional failure mechanism of the possible collapse of deep tunnel is presented with limit analysis theory.Support pressure is taken into consideration in the virtual work equation performed under the upper bound theorem.It is necessary to point out that the properties of surrounding rock mass plays a vital role in the shape of collapsing rock mass.The first order reliability method and Monte Carlo simulation method are then employed to analyze the stability of presented mechanism.Different rock parameters are considered random variables to value the corresponding reliability index with an increasing applied support pressure.The reliability indexes calculated by two methods are in good agreement.Sensitivity analysis was performed and the influence of coefficient variation of rock parameters was discussed.It is shown that the tensile strength plays a much more important role in reliability index than dimensionless parameter,and that small changes occurring in the coefficient of variation would make great influence of reliability index.Thus,significant attention should be paid to the properties of surrounding rock mass and the applied support pressure to maintain the stability of tunnel can be determined for a given reliability index.

Influence of the liquefied soil layer distribution on the seismic response of rectangular tunnel

In order to obtain the seismic responses of the soil-rectangular tunnel structure,based on the PL-Finn constitutive model,four different conditions,namely,the liquefied soil around the rectangular tunnel,the liquefied soil below the rectangular tunnel,the liquefied soil on either side of the tunnel and the structure on non-liquefied soil,are compared.In accordance to the time at which a large deformation occurs,the possibility of destruction from hard to easy follows a descending order:the liquefied soil all around the structure,the liquefied soil on the bottom of the structure,and the liquefied soil on the two sides of the structure.The area of large deformation is mostly beneath the two arch angles of the tunnel floor.The soil on the two sides,especially close to the structure,is the hardest to liquefy and deform.The large deformation of soil caused by the liquefaction appears after the peak seismic value occurs.The higher the input seismic value is,the easier a large deformation can take place.With the same input of peak ground motion,the total displacement vector of the structure and differential displacement of the side-wall are in accordance with an order from large to small in the three situations:when the saturated sand is on two sides,all around the structure,and on the bottom of the structure.

Power allocation and mode selection methods for cooperative communication in the rectangular tunnel

For the multipath fading on electromagnetic waves of wireless communication in the confined areas,the rectangular tunnel cooperative communication system was established based on the multimode channel model and the channel capacity formula derivation was obtained.On the optimal criterion of the channel capacity,the power allocation methods of both amplifying and forwarding(AF) and decoding and forwarding(DF) cooperative communication systems were proposed in the limitation of the total power to maximize the channel capacity.The mode selection methods of single input single output(SISO) and single input multiple output(SIMO) models in the rectangular tunnel,through which the higher channel capacity can be obtained,were put forward as well.The theoretical analysis and simulation comparison show that,channel capacity of the wireless communication system in the rectangular tunnel can be effectively enhanced through the cooperative technology;channel capacity of the rectangular tunnel under complicated conditions is maximized through the proposed power allocation methods,and the optimal cooperative mode of the channel capacity can be chosen according to the cooperative mode selection methods given in the paper.

Investigating Effect of Tunnel Gate Shapes with Similar Cross Section on Inserted Forces on Its Coverage and Soil Surface Settlement

According to technology development and relative facilitation in digging and underground structures, ways, highways, all types of tunnels, underground train network, and other underground settle, storage are number of structure built and developed in advanced countries. In most situation, tunnel digging operations are done years after its construction or are not recorded in new structures regulations;therefore, this research investigates soil settlement and inserting force to tunnel coverage by limiting studies about effects of tunnel shapes on soil settlement using Plaxis, Seismo Signal, and Seismo Aspect. This study shows that rectangular tunnel has the most settlement in soil surface and circular tunnel has the least settlement but horseshoe tunnel has similar behavior to circular tunnel;however, earth subsidence level by digging this tunnel is more than circular tunnel. In addition, sectional shape has direct effect on inserting forces on tunnel coverage.

Prototype Loading Tests on Full-Ring Segmental Lining of Rectangular Shield Tunnel

A series of full-scale loading tests are performed for a prospective subway tunnel with a rectangular shape including two reliability tests: one stagger-jointed three-ring reliability test, and one ultimate failure test on a single ring. Comprehensive measuring programs are designed to record the deformation of both lining structure and joints and the stresses of concrete, bolts and reinforcements. Experimental results show that in both the single-ring and three-ring loading cases, the long sides of tunnel cross section bend inwards while the short sides of tunnel cross section bend outwards. The inner part of joints opens while the outer part of joints closes at places experiencing positive moment and vice versa. Joint's rotational stiffness varies at different locations. Concrete cracking and crushing are the chief damage modes, and they are closely related to the distribution of bending moment. Stagger-jointed fabrication significantly increases the overall rigidity of lining system, which thereby greatly reduces the deformation of both concrete lining and joints in comparison with the single-ring case. It is shown that the routinely-used uniform rigidity model is conservative and the preliminary design can be optimized by applying an effective rigidity ratio(ERR) of 0.5.

Experimental analysis on the interaction between underground structures and sand layer under groundwater level change

Groundwater level change stands a momentous role in affecting the geotechnical construction stability and safety of underground structures.Global warming and active underground construction cause conspicuous changes in the groundwater level,which further leaves an impact on the underground structures’serviceability.To reveal the interaction between underground structure and soil under groundwater level change in the sand layer,model tests of circular transportation tunnel and rectangular utility tunnel were carried out.With the self-designed experimental equipment and innovative experimental methods,the changes in tunnel stress,bending moment,buoyancy,and vertical displacement of the rise and drawdown of the groundwater level in the sand layer were studied.The results revealed the developments of concentrated structural forces during the rising and falling process of the groundwater water level,indi-cating critical locations that should be strengthened.Meanwhile,both tunnels showed the same movement trend:settling first,floating afterwards and settling at last.And it is concluded that no reduction is required when calculating buoyancy in sands using measured pore pressure.Conclusions can provide a notable reference for future related research and engineering designs.