• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6D
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• pp.615-622
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• 2012

The aim of shotcrete is to increase the bearing capacity and to protect the excavated surface from erosion by preventing falling of rock mass. Shotcreting method is divided into two types as dry process and wet process. Since 1997, wet process method has been used more frequently than dry process method in field works. The failure to bond, so called rebound, occurs in many case during shotcrete works. The excess amount of rebound has a significant effect on the total construction cost. For example, material and craft-man cost increases, the shooting time delays due to deceleration of work execution stage, work efficiency of craft-man decreases and additional cost to remove the muck generates. In this study, therefore, the experimental analysis of rebound amount and strength was conducted by analyzing the actual construction data for wet process type of shotcreting method upon accelerator contents. Also, the effective and rational method was suggested, which can be actually implemented in the Korea construction sites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.3988-3997
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• 2010

Shotcrete was a mortar or concrete that is pneumatically projected at high velocity onto a subject. It has been applied for tunneling, underground big-spaces, slope stabilization. Shotcrete is increasing use in structure repair. The dry-mix shotcrete require a smaller equipment, easy maintenance, possible of very-earlystrength materials than wet-mix shotcrete, which make this process attractive and economic for structural repairs. It is common practice core compressive strength to the dry-mix shotcrete quality control. This test is very difficult estimating eraly-strength of Very-Early-Strength Dry-Mix Shotcrete. The purpose of this research was to analyze the correlation of test results among cube test, core test, pullout test and maturity. The correlationship analysis of test results among cube test, core test, pullout test and maturity showed more than 90%.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 1995.03a
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• pp.1-26
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• 1995

Key aspects of the Norwegian Method of Tunnelling (NMT) are reviewed. These include a predictive method of support design using the six-parameter Q-system of rock mass characterisation. The rock mass rating or Q-value is updated during tunnel driving. The designed tunnel support generally consists of wet process, steel fibre reinforced shotcrete combined with fully grouted, untensioned rock bolts, Even in poor rock conditions S(fr) + B usually acts as the final rock reinforcement and tunnel lining. Since it is a drained lining, it is very economic compared to cast concrete with membranes. Light, free-standing steel liners are used to prevent water affecting the runnel environment. Rock mass conditions, and hence lining design and cost estimation can be assessed by careful use of seismic surveys. Relationships between the P-wave velocity, the rock mass deformation modulus and the Q-value have recently been established, where tunnel depth, rock porosity and the uniaxial compression strength of the rock are important variables. The rock mass modulus estimate, and simple index testing of the joints, provide the key input which joints are discretely represented (either in two dimensions with the UDEC code or in three dimensions with the 3DEC code) is generally favoured compared to continuum analysis. The latter may give a misleading impression of uniformity and deformations tend to be understimated. Q-system NMT designs of S(fr) + B (fibre reinforced shotcrete and bolting) are numerically checked and adjustments made to bolt capacities and shotcrete thickness if overloading is evident around the modelled profile.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.4
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• pp.25-32
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• 2010

High performance shotcrete has been recently researched partly as a result of high consensus on high strength and durability. However, they are very initial step compared from the advanced countries. For instance, they has been mainly on high strength or durability without any consideration on pumpability and shootability which are very crucial on workability. The purpose of this dissertation was to make a high performance wet-mix shotcrete (high workability) which would solve the general problems of wet-mix process in Korea. For this, the main experimental variables were selected to be silica fume(0.0, 4.5, 9%), air entrained agent(0.0, 0.005%). Rheology with IBB rheometer was measured for evaluating pumpability and shootability as well as pump pressure, rebound rate and build-up thickness. The conclusions from a series of experiments were as follow: The results of analyzing the effects of AE agent and silica fume on rheology indicated that AE agent reduced both of flow resistance(G) and torque viscosity(H) and silica fume increased flow resistance (G) and reduced torque viscosity(H). An increase in the value of torque viscosity(H) produces an increase in the requried pumping pressure. These result indicated that the reduction of torque would work better at improving pumpability. And an increase flow resistance(G) improved shootability(increase build-up thickness and reduce rebound).