전산유동역학을 이용한 절리 거칠기 및 주입재 특성에 따른 그라우트 주입 시 압력 손실 해석

Numerical analyses using CFD on the pressure losses of the grout flow with variation of joint roughness and grout features

Abstract

암반 내 그라우팅은 불연속면 내부에 시멘트 그라우트재를 주입하여 주변지반을 강화하는 목적으로 사용된다. 현장에서 다상의 그라우트재의 주입 시 거동특성 및 주입경로인 3차원 절리면의 형태가 사전파악되지 않으므로 정량적인 설계가 어려운 분야중 하나이다. 따라서 현장에서의 그라우트 주입 거동특성을 나타내는 GIN (Grouting Intensity Number) 지표를 이용하여 주입 모니터링을 통해 적절한 시공관리를 수행하는 것이 최적이 방안이다. 본 논문에서는 그라우팅 주입 시 절리면의 거칠기 등급과 물시멘트(W/C)비에 따라 발생하는 압력의 손실을 전산유동해석을 수행하여 조사하였다. 절리면이 거칠수록 그리고 물시멘트비가 높을수록 주입 시 마찰저항은 크게 발생하였으며 해당 결과를 각 조건별 상관식으로 정리하였다.

Grouting for the rock joint is to strengthen the rock strata by infiltrating cement grout materials into the rock joints. Grouting is one of a field of study which is difficult to develop deterministic and quantitative design approach because of multiphase behaviors of grout materials and 3 dimensional features of rock joints. Therefore, GIN (Grouting Intensity Number) can be a good index with appropriate monitoring of pressure and volume of grout. In this paper, we investigate the effects of joint roughness (JRC) and rheology of cement material during the infiltration of cement grout material into rock joint through CFD (computational fluid dynamics) analyses. With rough joint surface and increase of WC ratio, the frictional resistance during the grouting increases. The results have been summarized with polynomial correlations.

Fig. 1. GIN envelope, target and zero flow path for the controlled grouting process

Fig. 2. Schematic of grout injection

Fig. 3 Topographic profile of a joint along x-axis

Fig. 4. A correlation between standard deviation and Z₂

Fig. 5. Grid generation process (aperture = 0.3 mm)

Fig. 6. Joint surface profile according to the JRC (aperture = 0.3 mm)

Fig. 7. Herschel-Bulkley, Power-Law model of the shear stress and shear rate of change

Fig. 8. The velocity profile of joint surface (W/C = 1, aperture = 0.3)

Fig. 9. Pressure by position along the joint (kPa)

Fig. 10. Variation of required injection pressure affected by W/C, aperture and JRC (kPa)

Table 1 A correlation between Standard deviation, Z₂ and JRC

Table 2. Grout material properties

Table 3. Boundary condition

Table 4. Required pressures for a constant grout injection of 3 l/min with different joint apertures and roughness (kPa)

Table 4. Correlations of K_p with aperture and JRC

Table 4. Correlations of K_p with aperture and JRC (continue)