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The pipe jacking method is gradually attracting increasing levels of attention and is becoming an important method for constructing underground engineering. However, jacking large-size concrete pipes in urban core areas subjected to complicated geological conditions is still a big problem preventing the employment of the pipe jacking method, and further studies related to pipe jacking are required. This paper presents a case study on the construction of three parallel large-size reinforced concrete circular pipes in the upper-soft and lower-hard composite formations, in which the construction work was implemented using the slurry balance pipe jacking method with the sequence of jacking the 1# and 3# pipes prior to the 2# pipe being implemented in field construction. This case study was implemented by employing numerical simulations with the aforementioned pipe jacking sequence, which focused on the stress and deformation variations of the reinforced concrete circular pipes, as well as the vertical settlement of the ground surface during the jacking processes, and considering the influences from the excavation pressure and grouting pressure of the drag-reducing thixotropic slurry. The simulation results revealed that a higher excavation pressure from the pipe jacking machine can easily induce an excessive pushing and squeezing effect of the excavated soil with the uplift phenomenon, while the increasing grouting pressure can be used to reduce the overall vertical settlement of the ground surface, whereas an excessive grouting pressure may have no effectiveness on protecting the reinforced concrete circular pipes. This work provides the numerical foundations for investigating the behavior of jacked parallel large-size reinforced concrete circular pipes. [ABSTRACT FROM AUTHOR]

Strain-hardening cementitious composites (SHCC) are an attractive construction material with obvious advantages of large strain capacity and high strength, as well as excellent workability and easy processing using conventional equipment. Moreover, SHCC can be designed with varied mix proportions in order to satisfy various requirements and expectations to overcome the shortages of existing construction materials. However, the behavior of SHCC in the structural application is varied from that of SHCC material, which is reviewed and presented in this paper, focusing on the flexural and shear behavior of the SHCC member and the SHCC layer used for strengthening reinforced concrete (RC). The reviewed results demonstrate that both the zero-span tensile behavior of the stress concentration and the uniaxial tensile behavior of the bending effect can influence the crack propagation patterns of multiple fine cracks in the SHCC strengthening layer, in which the crack distribution within the SHCC layer is limited near the existing crack in the RC substrate member in the zero-span tensile behavior. Moreover, the crack propagation patterns of the SHCC strengthening layer are changed with varied layer thicknesses, and the SHCC strengthening layer, even with a small thickness, can significantly increase the shear load carrying capacity of the shear strengthened RC member. This work provides the foundations for promoting SHCC material in the structural application of repairing or retrofitting concrete structures. [ABSTRACT FROM AUTHOR]

The cracks caused by fracture of concrete lining have adverse impacts on the tunnel structure, considering the influences of serviceability and durability. In this paper, a particular case study of a newly built tunnel structure is presented for a certain amount of longitudinal cracks, focusing on the inducement of cracking and effect of concrete fracture. An integrated field investigation is implemented to characterize the spatial distribution of longitudinal cracks and detailed site situations, and the temperature difference of concrete within the lining is as inducement according to a series of reliable experiments. To further understanding of the lining structure performance influenced by fracture behaviors, two groups of numerical models based on finite element software are simulated for reinforced concrete and concrete cross sections, respectively. Among the numerical models, a simplified crack model is applied for damaged lining structure, considering the realistic width and depth of cracks. Ultimately, different safety factors are adopted not only for verifying the stability of cracks but also for getting the differences of structural safety under maintenance work. Situations of crack are in accordance with the real conditions in situ, besides the maintenance work is proved as essential and effective methods in this damaged tunnel. [ABSTRACT FROM AUTHOR]

This paper presents a numerical shear stress transfer model for investigating the shear fracture behaviour of strain-hardening cementitious composites (SHCCs) for strengthening reinforced concrete (RC) structures. The model focuses on the transferred shear stress on the crack surface of the SHCC, taking account of the contributions from both the contact stress of the matrix and the bridging stress of the fibres. The numerical results demonstrate that the proposed shear stress transfer model can appropriately evaluate the shear fracture behaviour of SHCCs for RC strengthening, in which the fibre bridging effect on the crack surface of the SHCC has much influence on the shear fracture behaviour of the SHCC strengthening layer. [ABSTRACT FROM AUTHOR]

A numerical approach for evaluating the behaviour of strain-hardening cementitious composites (SHCCs) for reinforced-concrete (RC) seismic strengthening is presented. The method takes account of the seismic tensile strain capacity of SHCCs for RC strengthening, which is affected by the presence of cracks within the RC and varying layer thickness of the SHCC, the shear transfer behaviour of SHCC layers on the crack surface, which is contributed to by both the contact effect and the fibre bridging effect on the crack surface, and the seismic compressive constitutive law of SHCCs. In the numerical approach, a zero-span tensile model is adopted for reflecting the tensile strain capacity of SHCCs for RC strengthening, and a shear stress transfer model is applied for reflecting the respective contributions of both contact stress and fibre bridging stress for shear stress transfer behaviour of the SHCC on the crack surface. The effectiveness of the numerical approach is confirmed through the comparison between the experimental investigation and numerical analysis, in which the numerical result is coincided with the experimental one. [ABSTRACT FROM AUTHOR]

This paper presented a experimental investigation into the advantage of RC member with shear strengthening using strain hardening cementitious composites (SHCC), focused on the crack pattern of SHCC strengthening layer and its obvious advantage for increasing the shear load carrying capacity of the strengthened RC member. Especially, the shear failed SHCC member was also adopted to reflect the reduced multiple fine crack distribution in SHCC strengthening layer. Moreover, the contributions of matrix and reinforcing fiber for shear load carrying capacity of SHCC strengthening layer were also calibrated respectively, and the shear load carrying capacity of SHCC strengthening layer was assumed as the sum of load carried by matrix and reinforcing fiber. This work provided experimental foundations for RC member with shear strengthening using SHCC. [ABSTRACT FROM AUTHOR]

Strain hardening cementitious composites (SHCCs) have obvious advantages when used to strengthen reinforced concrete (RC) structures - high tensile and compressive strengths, as well as large tensile strain in uniaxial tensile behaviour. However, when used for flexural strengthening of RC members, the ductility of SHCC is reduced and the cracking behaviour of the SHCC strengthening layer varies with different layer thicknesses. In this paper, a zero-span tensile model using a fictitious material is proposed to assess the cracking behaviour of SHCC used for RC flexural strengthening, considering the localised behaviour of the SHCC on the cracked RC substrate member. In the model, the crack in the RC substrate member is represented by an artificial crack formed by two areas of fictitious material. The proposed model can evaluate the cracking behaviour of SHCC layers of varying thickness used for flexural strengthening of RC members. [ABSTRACT FROM AUTHOR]