• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.845-848
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• 2008

In this study, through the Batch Plant in field which is carrying out in the country, this research is going to grope the development of Ready-mixed Shotcrete that can improve the construction of shotcrete, and long-term durability. Accordingly, in this study, the Batch Plant in field which is only for shotcrete will be chosen in random so that can be aware the problems of the Batch Plant in field, and when the results come out, the shotcrete system will be prepared that is based on the results of rsearch, and also can be used in preparation index of shotcrete. Moreover, the results will be able to improve an efficent tool that can increase shotcrete quality.

• 한국터널공학회:학술대회논문집
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• 2005.04a
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• pp.251-258
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• 2005

In this study, a new concept for simulating a long-term mechanical degradation mechanism of shotcrete in tunnels has been proposed. In fact, it is known that the degradation takes place mainly by internal cracks and reduced stiffness, which results mainly from volume expansion of shotcrete and corrosion of cement materials, respectively. This degradation mechanism of shotcrete in tunnels appears similar to those of the most kinds of chemical reactions in tunnels. Therefore, the mechanical degradation induced by a kinds of chemical reaction was generalized and mathematically formulated in the framework of thermodynamics. The numerical model was implemented to a 3D finite element code, which can be used to simulate behaviour of shotcrete structures undergoing external forces as well as chemical degradation in time. A number of illustrative examples were given to show the feasibility of the model in tunnel designs with consideration of long-term degradation effect of shotcrete quantitatively for increase of long-term safety of tunnels.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.468-476
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• 2007

Generally, the strength of the field shotcrete is heavily dependent on the field mixing and spraying conditions so that it is different from the strength of the shotcrete mixed in laboratories. As a support member, the early strength of shotcrete unlike concrete as structural material is very important to the initial stabilization of the excavation face in tunnels. Therefore, the field methods to efficiently test the early strength of shotcrete have been highly required. This paper aimed to verify the pneumatic pin penetration test and the point load test for measuring the early strength of the field shotcrete. Through a series of uniaxial compression, pin penetration, and point load tests for the range of the early shotcrete strength, two equations to estimate reliably the uniaxial compressive strength by the pin penetration and the point load tests were derived. Field tests in working tunnel were carried out in order to estimate the economic efficiency. As a result, pin penetration method was proved to be the most effective method for testing the early strength of the field shotcrete.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.64-71
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• 2009

The stresses acting on shotcrete lining of tunnel have been measured virtually by monitoring instruments installed during construction. However, the malfunction of instrument and the lack of consistency of signal have always been controversial, but re-installation of instrument after construction of tunnel lining is practically impossible. Therefore, authors have carried out the study to develop a new technique for estimating the stress acting on shotcrete lining during and after construction. In the technique, stresses of shotcrete lining can be estimate by the measurement of deformation of free face. Therefore, the relationships between the stresses of shotcrete lining and deformation of free surface are indispensable factor. In this paper, the parametric study using 2D FEM analysis was carried out to estimate the relationships between the stress level acting on the tunnel shotcrete lining and the deformation near the free face (e.g. artificial crack in this study). The distribution of stresses of shotcrete lining is also investigated in this study as the preliminary investigation for the large-scale tunnel lining test and detailed 3D FEM analysis.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.131-140
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• 1994

Recently, tunnels are increasingly constructed in this country with the increased construction of highways, high-speed railways and subways. Shotcreting is one of the major processes in the tunnel construction. Many problems, however, exist in the current shotcreting practice. The purpose of the present study is, therefore, to explore the problems in the current shotcreting practice, to derive an optimum mix for efficient shotcreting, To this end, extensive experimental study has been conducted. Optimum mixes with high quality and economy were derived. The present study provides a firm bast: in our country to apply high-quality shotcrete in tunnel construction.

• The Journal of Engineering Geology
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• v.24 no.1
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• pp.81-89
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• 2014

Stress measurements of shotcrete lining were performed to evaluate the stability of the primary lining and to determine the thickness and the construction timing of the secondary lining. The current situation of stress measurements of shotcrete and problems related to judging the safety of shotcrete linings are presented, based on the results of several case studies. An improved method of performing stress measurements on shotcrete lining is also presented. In evaluating the safety of shotcrete lining, the use of absolute values of measured stresses would improve the reliability of the measurements.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.4
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• pp.305-311
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• 2005

Shotcrete adhesive strength in large section tunnels in jointed rock masses plays an important role in preventing rock block from falling and shotcrete debonding due to blasting vibration. Nevertheless, it has not been considered as a major factor such as shotcrete compressive strength in design and construction. For this reason, the purpose of this study is to analyze the effect on shotcrete adhesive strength for large-sectioned tunnels. First, the parametric study using numerical model similar to Holmgren's punch-loaded test was executed for various range of adhesive strength. It shows that the shotcrete bearing capacity is linearly proportioned to the adhesive strength between shotcrete layer and blocks. And then, distinct element analysis of a jointed rock tunnel for an adhesive strength of 1 MPa and a conventional fully-bonded condition between the shotcrete layer and the excavation face was compared in order to evaluate the effect of the shotcrete adhesive strength.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.1-15
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• 2004

The development of high-performance shotcrete lining is essential in improving the long-term durability of tunnels and in introducing single-shell tunnelling methods, where shotcrete as well as rockbolts are used as permanent support members. In this paper, new and advanced admixtures to improve shotcrete performance are introduced. In addition, requirements for mechanical properties as well as test items for quality control of shotcrete are summarized. A case study on the application of the pneumatic pin penetration test which can estimate compressive strength of shotcrete more easily and quickly is also illustrated. Previous studies to analyze the behaviors of shotcrete lining by considering its transient hardening and to carry out the sensitivity analysis of the design parameters of shotcrete lining are discussed to give fundamental concepts on rock-support interactions. Representative single-shell tunnelling methods where high-performance shotcrete lining is applied as a permanent support are also introduced.

• Advances in concrete construction
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• v.15 no.5
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• pp.333-348
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• 2023

Fast infrastructure development boosts the demand for shotcrete. Despite sand and stone being the most common coarse and fine aggregates for shotcrete, excessive exploration of these materials challenges the ecological environment. This study utilized an industrial solid waste, high-titanium heavy slag, blended with steel fibers to form Wet Shotcrete of Steel Fiber-reinforced High-Titanium Heavy Slag (WSSFHTHS). It investigated its workability, shotcrete performance and mechanical properties under different water-to-cement ratios, fly ash content, superplasticizer dosage, and steel fiber content. The tunnel excavation and support were investigated by conducting finite element numerical simulation analysis and was used in 3 tunnel lining pipes in Zhonggouwan tailing pond. The major findings are as follows: (1) The water-to-cement ratio (w/c ratio) significantly impacted the compressive strength of WSSFHTHS. The highest 28-day compressive strength of 60 MPa was achieved when the w/c ratio was 0.38; (2) Adding fly ash improved the workability and shotcrete performance and strength development of WSSFHTHS. The best anti-permeability performance was achieved when the fly ash constituted 15%, with the lowest permeability coefficient of 4.596 × 10-11 cm/s; (3) The optimum superplasticizer dosage for WSSFHTHS is 0.8%. It provided the best workability and shotcrete performance. Excessive dosage resulted in water bleeding and poor aggregate encapsulation, while insufficient dosage decreased flowability and adversely affected shotcrete performance; (4) The dosage of steel fibers significantly impacted the flexural and tensile strength of WSSFHTHS. When the steel fiber dosage was 45 kg/m³, the 28-day flexural and tensile strengths were 8.95 MPa and 6.15 MPa, respectively; (5) By integrating existing shotcrete techniques, the optimal lining thickness was 80 mm for WSSFHTHS per simulation. The results revealed that after using WSSFHTHS, the displacement of the tunnel surrounding the rock significantly improved, with no cracks or hollows, similar to the simulation results.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.177-192
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• 2010

The field measurements on the shotcrete lining are usually performed during the tunnel construction. However, the credibility of the measurements is not certain because of the non-stress related strains occurring in the shotcrete, the uncertainty of the deformation modulus of the shotcrete, and the intrinsic difficulties involved in the strain measurements in the shotcrete. The problem related to the field measurements on the shotcrete is investigated using the review of the previous studies and the field measurement performed for this study. A method for the correction of stress measurements at the shotcrete lining, considering the non-stress related strains, is suggested using the literature review and the actual measurements obtained from the non-stress shotcretes. The deformation modulus used for the calculation of the stress acting on the shotcrete is also suggested.