Numerical Analysis of the Seismic Response of Tunnel Composite Lining Structures across an Active Fault

The mechanical properties of high-toughness engineering cementitious composites (ECC) were tested, and a damage constitutive model of the materials was constructed. A new aseismic composite structure was then built on the basis of this model by combining aseismic joints, damping layers, traditional reinforced concrete linings, and ECC linings. A series of 3D dynamic-response numerical models considering the composite structure-surrounding rock-fault interaction were established to explore the seismic response characteristics and aseismic performance of the composite structures. The adaptability of the structures to the seismic intensity and direction was also discussed. Results showed that the ECC material displays excellent tensile and compressive toughness, with respective peak tensile and compressive strains of approximately 300- and 3-fold greater than those of ordinary concrete at the same strength grade. The seismic response law of the new composite lining structure was similar to that of the conventional composite structure. The lining in the fault zone and adjacent area showed obvious acceleration amplification responses, and the stress and displacement responses were fairly large. The lining in the fault zone was the weak part of the composite structures. Compared with the conventional aseismic composite structure, the new composite lining structure effectively reduced the acceleration amplification and displacement responses in the fault area. The damage degree of the new composite structure was notably reduced and the damage area was smaller compared with those of the conventional composite structure; these findings demonstrate that the former shows better aseismic effects than the latter. The intensity and direction of seismic waves influenced the damage of the composite structures to some extent, and the applicability of the new composite structure to lateral seismic waves is significantly better than that to axial waves. More importantly, under the action of different seismic intensities and directions, the damage degree and distribution area of the new composite structure were significantly smaller than those of the conventional composite lining structure.

Stress-Strain Calculation Method of Composite Lining considering the Creep Characteristics of Tunnel Surrounding Rock

Tunnels are generally designed for a sustained usage of 80 to 100 years, during which the safety of tunnel structures must be guaranteed. A common supporting form utilized in contemporary tunnel engineering is composite lining. To derive applicable parameters of the supporting form and therefore ensure the long-term safety of the tunnel structure, it is imperative to determine the extra acting force exerted onto the composite lining by the creep of the rock surrounding the tunnel and to calculate the stress-strain characteristics of composite lining. In the current study, this paper proposes an approach termed surrounding reinforcement, which is based on the homogenization method. Specifically, this paper defined the bolt force as the internal force of the surrounding rock, analyzed their viscoelastic-plastic properties using the unified strength theory, and derived an equation for calculating the stress-strain relationship of the composite lining. To further validate the method in tunnel structures, this paper applied the derived equation to a representative instance. The results of this paper show that the initial support force has also increased during the creep process of the surrounding rock, indicating that engineers should pay close attention to the coordination between the strength of initial support and the secondary lining and thus ensure an optimal distribution of the pressure from the surrounding rock when designing composite lining tunnel within weak strata. This paper proposes that the initial support not only would guarantee the tunnel safety during the construction stage but also could cooperate with the secondary lining to brace the stress caused by the creep, ensuring that the supporting structure stays stable across the whole period of tunnel operation. This paper provides an alternative to previous methods that is more comprehensive, with simpler calculations, and more applicable to the composite lining supporting design within weak strata.

A Case Study of Constraint Cross-Passage Construction in Urban Tunneling

The paper aimed at a detailed case study of cross-passage, which is forced to design and construct by connecting the station box and main tube tunnel of Marol Naka station in Mumbai Metro Line 3, since the marol Naka is densely populated area and elevated metro line is passing over an underground station, therefore further excavation of tunnel is done through the cross-passage. In these station, the cross- passage is constructed for public utilities for connecting the station box to the platform and also for the emergency exit. During tunnel construction, the cross passage is excavated after the main tunnel has been constructed. At the same time, the safety of the cross passage and the stability of the tunnel must be ensured by instrumentation and monitoring. Design of the cross- passage is achieved according to the principles of “New Austrian Tunnelling Method’ (NATM) and the composite lining structure is adopted. NATM is used to widen the station platform which is initially tunnelled by the TBM. The dimension of 230m long and 15m wide Marol Naka station has 16 cross-passages which are constructed connecting the station box to the platform; the observations and the designing part- Finite Element method is used in order to evaluate stress deformations induced on the cross-passage. Keywords: Cross passage, NATM, TBM, Finite element method, Marol Naka station, Emergency exit.

Analysis on water migration in freeze-thaw process of composite lining canal in seasonal frozen soil area

In order to quantify the migration rule of water in composite lining canal foundation soil during the freeze-thaw process, the outdoor prototype test is performed to prove the change rules of water in different positions and depths of the rigidflexible mixed composite lining canal foundation during the whole freeze-thaw cycle. The prototype observation test shows that during the freezing period, the water content within the 0~80cm depth of the canal foundation soil increases with the depth, and that within the depth of 80~160cm decreases gradually with the depth. In the freezing period, water accumulates in the depth of 60 ~ 80cm, with a maximum water transfer amount of +13.2%, which occurs at the canal bottom. In the thawing period, the maximum water content also occurs at the canal bottom, with a maximum water transfer amount of -11.0%. Through the laboratory test of soil samples, the water migration development and change rules of the canal foundation soil, under different moisture contents and temperature gradients are studied in unilateral pattern. In the case of the same top plate control temperature, soil samples with similar initial water contents have similar water transfer amounts. The samples with higher initial water content have higher water transfer amount, with higher water accumulation, normally accumulating in the depth of 16~18cm. The results indicate that high water contents make it easy to gather water in soil samples during the freezing period.

Research on the Algorithm for Composite Lining of Deep Buried Water Conveyance Tunnel

Composite lining of deep buried water conveyance tunnel for bearing high internal water pressure is a new type of applicable structure. However, up to date, no effective method is available to calculate the stress of the structure. In this paper, a simplified algorithm, which can be used to calculate the stress distribution of composite lining accurately but costs little computational resource, is proposed. This algorithm, which is based on the elastic theory, takes the effect of internal water pressure and surrounding rock on the composite lining into consideration, respectively. Then, the stress distribution of composite lining in infinite body is derived on the basis of Lame solution. Finally, a case study is followed by choosing a typical section of the Eastern Canal in Beijing of the South-to-North Water Diversion Project (SNWDP). This case study was analysed by using the simplified algorithm and verified by finite element method with ABAQUS. The results show that the stress distribution of composite lining can be obtained quickly and accurately with the simplified algorithm, which can provide a reference for other engineering designs.

Finite Element Analysis on Lining Structure of Diversion Tunnel in a Hydropower Station

Aiming at the high internal and external water pressure tunnels built in unfavorable geological bodies, this study proposes a novel type of composite support structure in which steel plates are poured inside concrete linings. Compared with traditional structures, it has the advantages of higher tensile strength, better crack resistance, and impermeability. Taking the diversion tunnel of a hydropower station as an example, based on linear and non-linear finite element simulations, mechanical properties of the steelconcrete composite lining structure for a hydraulic tunnel in soft surrounding rocks are analyzed. On this basis, the concrete crack control under this supporting condition is verified. Research results can provide a reference for the selection of reasonable steel plate thicknesses and reinforcement types in design.