• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.187-195
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• 2005

When a tunnel is excavated below groundwater table, the groundwater flow occurs towards the tunnel resulting in the seepage pressure. In this paper, the effect of groundwater flows on the behavior of shotcrete lining installed between ground-liner interfaces was studied considering permeability ratio between the ground and the shotcrete into account. Three-dimensional coupled finite element analysis was performed for this assessment. Seepage forces will seriously affect the shotcrete behavior since arching phenomena do not occur in seepage forces. A parametric study was conducted on the various tunnelling situations including interfacial properties between ground and shotcrete lining, the shape of tunnel cross-section and the thickness of liner, etc. Moreover, the convergence-confinement method (CCM) of a NATM tunnel considering seepage forces was proposed. The result showed that the more water tight is the shotcrete, the smaller is the convergence and the larger is the internal pressure. Therefore, the watertight fiber-reinforced shotcrete is found to be even more advantageous when used in under water tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.1
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• pp.41-51
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• 2006

This paper concerns the effect of lining interface adherence on the lining's load carrying capacity. A series of reduced scale laboratory tests and finite element anlayses were carried out with the aim of gaining insight into the effect of shotcrete lining adherence on the load carrying capacity of double shell lining. The results indicated among other things that the load carrying capacity of a double shell tunnel is significantly affected by the adherence between layers. Also revealed was that for cases with low lining layer adherence stress concentration may occur due to relative movement between the lining layers with this trend being more pronounced with increasing tunnel cover depth. Practical implications from the results of this study are discussed in great detail.

• 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.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.1
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• pp.23-31
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• 2003

Since the mid of 1990, permanent shotcrete tunnel linings such as Single-shell and NMT have been constructed in many countries for reducing the construction time and lowing construction costs instead of conventional in-situ concrete linings. Among essential technologies for successful application of permanent shotcrete linings, high performance shotcrete having high strength, high durability and better pumpability has to be developed in advance as an integral component. This paper presents the idea and first experimental attempts to increase early strength and bond strength of wet-mixed Steel Fiber Reinforced Shotcrete (SFRS) in spring water condition. In order to increase early behavior of SFRS, a new approach using high-early strength cement with alkali-free liquid accelerator has been investigated. From the test results, wet-mix SFRS with high-early strength cement and alkali-free accelerator exhibited excellent early compressive strength improvement compared to the ordinary portland cement and good bond strength even under spring water condition.

• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.167-177
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• 2009

This study investigates a failure mechanism of a tunnel shotcrete lining with respect to a concentrated load due to blocky rock mass. First of all, it is carried out to survey relevant researches to shotcrete failures by literature reviews and to numerically re-investigate the failure modes of shotcrete lining given by previous researches. Through this study, the failure modes are relocated with the conditions which induce each failure mode newly proposed by this study. In addition to this, the arching shape of tunnel lining, which has not been considered in the previous research despite of inherent geometrical characteristics in tunnels, is taken into consideration in numerical investigation on lining failure in this study. As a result, it is shown that more simplified failure modes can be found on the tunnel boundary condition and the corresponding failure condition to each mode can be different from ones of the previous study due to a tunnel arching effect.

• 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.8 no.3
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• pp.273-287
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• 2006

This study investigates the failure mechanism and load-carrying capacity of a single-shell lining which has no disturbance in transfer of shear force, with respect to a conventional double-shell lining which has separation between layers of shotcrete lining and secondary concrete lining by water-proof membrane. In order to evaluate the capacity, a 2-D numerical investigation is preliminarily carried out and then real-scale loading tests with tunnel lining section specimens are performed on the condition given by the numerical investigation. In the test, a concentrated load is applied for considering a released ground load or rock wedge load. Through this study, it appears that the single-shell lining takes the load-bearing capacity 20% higher than in case of the double-shell lining. In addition, a possibility of a composite single-shell shotcrete layer composed by multiple bonded layers partly involving different contents of high-capacity additives is shown thereby leading to use of less amount of the high-capacity additives on the condition of taking a similar load-bearing capacity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.597-604
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• 2015

When a tunnel is constructed by drilling and blasting operation, the excavated perimeter becomes uneven due to overbreak at the drill holes so that the thickness of shotcrete tends to be irregular. In this case, the conventional stress analyses for tunnel lining of a uniform thickness cannot be readily applicable. In this study, the profile of tunnel perimeter assumed to be sinusoidal in order to simulate the uneven tunnel perimeter and to control the thickness of shotcrete by using the amplitude and wavelength. By adopting the sinusoidal function to a theoretical solution of stress analysis for uniform lining, the range of axial stress of irregular shotcrete can be estimated. The applicability of the approximate solution has been verified by performing a series of numerical analyses for various conditions. It is shown that the axial stress of shorcrete is highly dependent upon the irregularity of shotcrete, together with the ground property and initial stress conditions. It is also shown the shear stress is dependent upon the wavelength, and the stress condition becomes unfavorable where the thickness of shotcrete is relatively small. The approach developed in this study shows that the stress state where the thickness is relatively small is unfavourable, and it is necessary to take complementary measures when installing shotcrete after blasting.

• Tunnel and Underground Space
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• v.27 no.4
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• pp.185-194
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• 2017

This technical paper is a study on the unique displacements of Shotcrete Lining at the mined tunnel during excavation period through deep consideration with real time data from monitoring instrumentations correlation with the numerical analysis to identify the rock stresses and the rock spring points at the working face of the Conventional tunnelling by the Drill and Blast, based on the geological face mapping results of the project NS2, Transmission cable tunnel project in Singapore. The created geometry of numerical model was prepared to the real mined tunnel construction site including, vertical shaft, construction adit, tunnel junction area, and 2 enlargement caverns. The convergence measurements by the monitoring instrumentation were performed during the tunnel excavation and shaft sinking construction stages to guarantee the safety of complicated underground structures.

• Tunnel and Underground Space
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• v.8 no.4
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• pp.307-320
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• 1998

Tunnel lining is the final support of a tunnel and reflects the results of the interaction between ground and support system. Recently it is very difficult to support and manage the tunnel because the cracks on tunnel lining cause many problems in supporting and managing tunnels. Therefore the analysis of the cracks is quite strongly required. In this study, mechanical behaviour of a tunnel lining was examined by model tests and by numerical analyses. Especially the model test was examined for double linings including shotcrete and concrete lining. The model tests were carried out under various conditions taking different loading shapes, horizontal stresses, thicknesses of linings and double lining, vault opening behind the concrete lining and rock-like medium surrounding the lining. Due to horizontal stress, compressive stress prevailed on the lining. Thus the bearing capacity of the lining increased. The existence of a vault opening behind the concrete lining reduced the bearing capacity by the similar amount of reduction of concrete lining thickness. Rock-like medium cast around the side wall of the lining restrained the deflection of the lining, and the bearing capacity for cracking and failure increased vary much. In numerical analyses a algorithm which can analysis the double lining by introduction of interface element was developed. And the results of the numerical analyses were compared with the results of the model tests.