A Comparative Study of the Cracking Effect of Induced Joints of Various Spatial Formations

Haifeng Li,Bo Yang,Bingqi Li

doi:10.1155/2019/7876503

Abstract

The use of induced joints is a common cracking control measure used in the design of roller compacted concrete arch dams. Currently, in some projects in which radial twisted joints were used, during the construction period, some cracks appeared around the induced joints while the joints themselves failed to open. From the fracture mechanics point of view, this problem is related to the variations in the spatial formation of the induced joint planes. In this study, we formulated numerical examples involving square plate and cylindrical arch dam with joints of various planar spatial formations and used the virtual crack-closure technique and the Richard brittle fracture criterion to obtain the equivalent stress intensity factor of the joint plane, and we studied the joint plane stress intensity factor based on the variations in the joint plane formation angle. Based on the reciprocal of the normalized stress intensity factor, we obtained the equivalent strength correction coefficient for induced joints of varying plane angles, referred to in this study as the joint plane formation factor ψα, in order to reflect the influence of varying joint plane formations on the induced joint cracking. Our study results show that as the joint plane angle continuously increases, it is more difficult for the induced joints to open, which implies a gradual increase in the equivalent strength of the joint plane. Therefore, in the actual design of rolled concrete arch dams, the straight transverse joint layout should be used for induced joints. If the use of the radial twisted joint layout is necessary, the joint plane angle should not exceed 10°.

Highlights

In the roller compacted concrete (RCC) arch dam projects, the planes of transverse joints and induced joints are generally planar, folded, or curved [1]; considering their spatial formation, the planar induced joints are straight transverse joints, while folded and curved joints can be considered radial twisted joints
At a slope of 30∘, and when the joint plane angle increased to 5∘, the stress intensity factor of the transverse and twisted joint planes decreased by 1%; at a 10∘ angle, the factor decreased by 2%; at a 20∘ angle, the stress intensity factor of the transverse joint decreased by 2.5%, while that of the twisted joint decreased by 5%; at a 25∘ angle, the transverse
Based on the analysis presented above, the following conclusions can be drawn from the study: (1) As the joint plane angle increases, in all cases, the joint plane stress intensity factor decreases by varying degrees

Summary

Introduction

In the roller compacted concrete (RCC) arch dam projects, the planes of transverse joints and induced joints are generally planar, folded, or curved [1]; considering their spatial formation, the planar induced joints are straight transverse joints, while folded and curved joints can be considered radial twisted joints (see Figure 1). In some projects that use radial twisted joints, a phenomenon has been observed in which some cracks appear around the induced joints before their opening and prior to the impoundment of the dam This problem occurred in an RCC arch dam located in the southwest China, where the radial twisted joint layout was employed for induced joints (see Figure 2 for details). Some researchers have studied the problem of noncoplanar induced joint layout based on fracture mechanics [3] and discussed the feasibility of an oblique layout of induced joints but have simplified the noncoplanar induced joint cracking into two planar problems: within the horizontal plane and within the vertical plane perpendicular to the radial direction.

Results

Discussion

Conclusion