차수용 박층 멤브레인의 직접전단실험에 관한 수치해석 연구

Numerical Study on Direct Shear Test of Composite Shotcrete with Sprayable Waterproofing Membrane

Abstract

차수용 박층 멤브레인은 폴리머로 구성된 재료로 기존 방수포(sheet membrane)와 비교했을 때, 시공에 있어서 뿜어 붙이는 방식을 사용하기 때문에 타설이 용이하고 상대적으로 높은 부착성능을 보이는 재료이다. 하지만, 차수용 박층 멤브레인은 최근에 개발된 재료로 그 성능이나 구조물과의 거동 양상은 충분히 보고되지 못한 실정이다. 따라서 본 연구에서는 차수용 박층 멤브레인이 삽입된 복합 숏크리트 재료에 대해 전단시험을 수행한 기존 연구 결과를 이용하여 차수용 박층 멤브레인의 전단거동을 수치해석적으로 접근하여 접촉면 특성을 파악하고자 하였다. 연구를 통해 숏크리트 사이에 시공된 멤브레인에 의해 숏크리트의 전단거동과는 다른 거동을 보여 일반적으로 사용되는 전단강도 방식으로 거동을 표현하는데에는 한계가 있었다. 이에 따라 수치해석 방법을 사용하여 직접 전단시험을 모사하였고 차수용 박층 멤브레인의 전단거동을 가장 효과적으로 표현할 수 있는 방안을 제시하였다.

A sprayable waterproofing membrane which has relatively high adhesive property onto concrete enables faster construction with better waterproof performance compared with a conventional sheet membrane. However, the sprayable waterproofing membrane is a recently developed material and its performance and behavior with structures are not sufficiently reported. Therefore, in this study, the shear behavior of sprayable waterproofing membrane was numerically analyzed using the results of previous studies of composite shotcrete with sprayable waterproofing membrane. From the previous study, shear behavior of shotcrete with sprayable waterproofing membrane was different from shotcrete case and there was a limitation to express the behavior of the interface in general shear strength method. Therefore, in this study, the direct shear test was numerically simulated using two contact models, and then the best suitable method to express the shear behavior of the sprayable waterproofing membrane was suggested.

Fig. 1. Schematics of waterproofing composite structure with shotcrete (modified after Holter, 2015)

Fig. 2. Coulomb friction model (modified after Kim, 2014)

Fig. 3. Typical traction-separation response (modified after SIMULIA, 2014)

Fig. 4. Examples of failed specimens after direct shear tests at σ_n = 0.5 MPa (Park et al., 2018) according to thickness of membrane; (a) t = 3 mm, (b) t = 5 mm and (c) t = 7 mm

Fig. 5. Peak shear strengths of interfaces in composite and double-layered shotcrete specimens at different normal stress conditions (Park et al., 2018)

Fig. 6. Numerical analysis for material property of sprayable waterproofing membrane; (a) modeling of tensile test and (b) comparison between laboratory test and numerical analysis

Fig. 7. Schematics of numerical model for direct shear test

Fig. 8. Numerical analysis results for direct shear test used Coulomb friction model

Fig. 9. Relationship of shear stress-displacement with analytical variables; (a) cohesive stiffness, (b) the maximum stress of damage initiation and (c) fracturing energy at contact surface

Fig. 10. Comparison with direct shear test result and numerical analysis

Table 1. Results of direct shear test by Park et al. (2018)

Table 2. Interaction properties with 3 mm thickness of waterproofing membrane

Table 3. Cohesive interaction properties of waterproofing membrane