Shotcrete Lining Research Articles

Long-term deterioration of lining in tunnels

The long-time degradation of sprayed concrete lining in tunnels was studied using three-dimensional finite element method. During the tunnel excavation the rock deformation and forces in the primary shotcrete lining were observed. The gradual degradation of reinforced shotcrete support over a period of time, its perpetual deterioration under the influence of different physical, chemical, mechanical and biological agents and ground pressure was simulated by reduction of the Young′s modulus, cohesion and friction angle to study the impact of this reduction on the stress distribution and overall stability of the tunnel support system consisting of rock mass, shotcrete and the inner lining. Substantiating shotcrete shell deterioration, the progressive increase of stresses in the inner lining and stress dissipation into the surrounding ground was observed. This provided the possibility to illustrate the main attribute of a particular deterioration process on the basis of the obtained stress distributions of the support elements.

Investigation of surface and subsurface displacements due to multiple tunnels excavation in urban area

Underground structures are currently widely used and are built as urbanism develops. The interactions between perpendicularly crossing and parallel tunnels in the Tehran region are investigated by using a full three-dimensional (3D) finite difference analysis with elastic-plastic material models. Special attention is paid to the effect of subsequent tunneling on the support system, i.e., the shotcrete lining and rock bolts of the existing tunnel. Eventually, as the tunnels are excavated at certain levels, the interaction between the tunnels will certainly have a significant influence on both stress distribution and consequently deformations. Since multilayer tunneling is a three-dimensional phenomenon in nature, 3D numerical solutions must be utilized for analyzing effect of perpendicularly crossing tunnels at various levels. As Tohid twin tunnels and Line 7 pass beneath the Line 4 metro tunnel, changes in stress distribution, deformations, and surface settlements are studied for various conditions and the results are presented in this paper. Consequently, it is shown that there is a significant interaction between tunnels that necessitate certain preventive measures to maintain a stable tunneling operation.

Adhesion Strength at the Shotcrete–Rock Contact in Rock Tunneling

An increasing number of tunnels have been constructed worldwide for a diverse range of infrastructure projects, including highways, subways, railways, and various utilities. As a result, tunnel engineers are increasingly aware of the importance of safe and economic tunnel construction. Peck (1969) addresses the following three issues in terms of tunnel construction: maintaining stability and safety during construction, minimizing unfavorable impacts on third parties, and performing the intended function over the life of a project. Among these issues, the first is directly related to the behavior and stability of the tunnel support system. In rock tunneling, the New Austrian Tunneling Method (NATM) is a widely used tunneling method in which the shotcrete liner acts as the main support. Shotcrete is sprayed on the tunnel excavation surface very shortly after being excavated and supports the ground load in conjunction with the rock bolt and the steel rib. Barrett and McCreath (1995) explained the failure modes for the shotcrete liner (Fig. 1). It has been shown that the behavior of the shotcrete liner is highly dependent on the adhesion strength at the shotcrete–rock contact. For example, if this strength is sufficient enough, then the mode of failure may be a direct shear failure. Otherwise, the shotcrete liner may fail under a flexural condition. In addition to the behavior of structural characteristics, sufficient adhesion strength can merge the surrounding ground and the shotcrete liner into a single body, increasing tunnel stability. Therefore, the adhesion strength at the shotcrete– rock contact can influence the failure mode for the shotcrete liner, which, in turn, can impact the overall tunnel stability. This indicates a need for a better understanding of this adhesion strength. An adhesion strength test method (Swedish Standard 1987) from Sweden drills two circular slots with a doublediamond drill. Here, the inner circular slot is drilled through the substrate and shotcrete, and the test equipment is attached to the shotcrete drill core for the pullout test. The test method can be used only for relatively stiff shotcrete. Brennan (2005) explains a shotcrete bond test method from the International Concrete Repair Institute (ICRI). This method uses a core bit to drill the applied shotcrete and substrate, and then attaches a rigid steel disk to the top of the core by using epoxy. Then, the test equipment applies some tensile load to the disk until it fails. This test method is similar to the direct test of tensile bond strength by the American Concrete Institute (ACI 2004) or the American Society for Testing and Manuals (ASTM 2004). A thin spray-on liner (TSL) has been developed and used in the mining industry since the 1990s. Ozturk and Tannant (2010) compare various adhesion test methods based on TSL and suggest a pulloff test of an elevator bolt (33 mm in diameter) attached to the liner with strong epoxy. This test uses a thin-walled diamond core bit to isolate the test area by overcoring. Ozturk (2012) provides a method for calculating the liner–substrate adhesion M. Son (&) Department of Civil Engineering, Daegu University, Jillyang, Gyeongsan, Gyeongbuk 712-714, South Korea e-mail: mson@daegu.ac.kr

Optimum Support Design for Openings Considering Intact Rockmass in Production Level of Maddhapara, Granite Mine, Maddhapara, Dinajpur, Bangladesh

Maddhapara Granite mine is the only Hardrock underground mine, which is contributing to infrastructure development of Bangladesh. It was established in 1995 by the North Korean contractor (NAMNAM).Over the past few years it was observed that in some of the vital area of the pit bottom, appears to be vulnerable, where needs to be taken special consideration to make sure the safe working environment for the miners and equipment machinery as well. The authors of this research have taken an attempt to identify and overcome such problem by a research program. In this research, our outcome has been established that the, optimum support have to be determined by using Rock Support Interaction Analysis for rock mass in production level. During design stage, it was considered that the total rock mass is intact (based on initial geological survey data), means there are no wedges along the opening. However a little amount of geological abnormality anticipated in the production level during construction phase. Due respect to that, our research recommended that, there has to be a little amount of support is needed for any kinds of openings in first category of rock, in second category it has to be considered by shotcreting of different thickness of lining in roof and the sidewall. In third category of rock, support system has to be considered by rock bolting and latter shotcrete the roof and side wall. Finally 2.3, 4.6 and 10.73 m openings in third category of rock there needs to be 0.0095m 0.015m and 0.026m fiber reinforced shotcrete and 3m bolt length and blot spacing with 1.5, 1, 0.95m respectively in roof and inside wall 0.006m, 0.015 and 0.045m shotcrete lining have to be considered for safe mining work.

Nonlinear Finite Element Analysis of Shotcrete Lining Reinforced with Steel Fibre and Steel Sets

Nonlinear Finite Element Analysis of Shotcrete Lining Reinforced with Steel Fibre and Steel Sets

운영중인 도로터널의 측벽하부 숏크리트 보강에 의한 단면확대

도심지내 기존터널을 단면확대 시공하는 경우, 터널내 교통흐름을 유지하기 위하여 '<TEX>${\sqcap}$</TEX>'형태의 프로텍터를 설치한다. 터널내 프로텍터를 설치하면 터널 측벽하부에서 작업공간이 협소하여 록볼트 시공이 불가능해 질 수가 있다. 본 연구는 터널의 측벽하부에서 록볼트를 시공하지 않고 숏크리트만으로 보강하여 터널단면을 확대된 할 경우, 터널구조물의 안정성과 보강되는 최적의 숏크리트 두께를 제시하는데 목적이 있다. 본 연구를 위하여 3차선 NATM 도로터널을 4차선 NATM 도로터널로 확대 시공하는 경우에 대하여 수치해석을 수행하였다. 수치해석결과, 4차선 NATM 도로터널의 측벽하부에서 록볼트를 시공하지 않은 경우의 천단변위와 상반 내공변위는 록볼트를 시공한 경우와 거의 유사하였다. 다만, 하반 내공변위 및 숏크리트 응력은 록볼트를 시공하지 않은 경우가 록볼트를 시공한 경우보다 최대 0.57 mm 및 최대 1,300 kN/<TEX>$m^2$</TEX> 크게 나타났다. 터널 측벽하부에서 록볼트를 시공하지 않아 추가 발생한 하반 내공변위와 숏트리트 응력은 25 cm인 기본 숏크리트 두께의 20%(25 cm<TEX>${\rightarrow}$</TEX>30 cm)만 증가시켜도 저감시킬 수 있다. The protector with the shape of '<TEX>${\sqcap}$</TEX>' in cross section can be set up in the tunnel, which can be constructed for enlargement of cross section, to keep traffic flow in the tunnel. It is impossible to install the rockbolt in the side wall of tunnel due to a limited space between the protector and cutting surface of side wall. The objective of this study is to suggest the optimum thickness of shotcrete lining without rockbolt on the side wall and to evaluate the stability of tunnel enlarged. Numerical analysis was performed to evaluate the displacement at the center of tunnel, the convergence of tunnel, and the stress in shotcrete lining in 4-lane NATM road tunnel enlarged from 3-lane NATM road tunnel. The vertical displacement at the center of tunnel and the convergence of crown in the tunnel with rockbolt in the side wall were almost similar to those in the tunnel without rockbolt in the side wall. The convergence of bench/invert and the stress in shotcrete lining without rockbolt on the side wall were greater maximum 0.57 mm and 1,300 kN/<TEX>$m^2$</TEX> than those with rockbolt in the side wall. The increased convergence and the stress in shotcrete lining can be reduced in incerasing of thickness of shotcrete lining about 20% (5 cm) of standard thickness, 25 cm, of shotcrete lining.

Use of explosive energy in applying the shotcrete lining

The basic circuit design of erection of shotcrete lining in vertical excavations of round cross-section as well as the calculation algorithm of key parameters of a way for the basic industrial explosives are considered.

The Saint Martin La Porte access adit (Lyon–Turin Base Tunnel) revisited

This paper presents the monitoring data collected over a period of five years from January 2006 to December 2010, during which the Saint Martin La Porte access adit of the Lyon–Turin Base Tunnel was excavated through a Carboniferous Formation, a highly heterogeneous, overstressed and in cases anisotropic rock mass exhibiting a squeezing behaviour. The interest of these data stems from the information which became available along a significant tunnel length in the same rock mass, where a novel excavation and support method was adopted with highly deformable elements inserted in the shotcrete lining which allowed for controlled deformation, rate of deformation and stress in the rock mass and in the supports. A description of the geological and geomechanical conditions met and of the tunnel response in different cross sections is given in terms of developed convergences, rates of convergence, strain distributions around the tunnel and ahead of the face, including the state of stress in the supports. In conclusion an attempt is made to characterise the Carboniferous Formation in terms of the extent of squeezing and in view of the future excavation of the Base Tunnel.

Use of Synthetic, Fiber-Reinforced, Initial Shotcrete Lining at Devil's Slide Tunnel Project in California

Fiber-reinforced shotcrete is widely used as a temporary excavation support in the construction of transportation tunnels and in other civil applications that are performed with the Sequential Excavation Method. Traditionally, steel fibers have been used in tunnel construction; however, the use of synthetic fibers is becoming more common. At the Devil's Slide Tunnel Project, on Highway CA-1 in Pacifica, California, a synthetic fiber mix was used to achieve the contract initial lining performance. The synthetic (polypropylene) fiber was used throughout the excavation phase of the twin highway tunnels and was tested with the round determinate panel test (ASTM C1550) for its capability to absorb energy after shotcrete section failure (flexural strength). The contract required the ASTM C1550 test to produce at least 320 J at 40 mm of deflection after 7 days. This paper discusses the testing program and summarizes its results. The overall performance of the fiber-reinforced shotcrete liner is discussed and evaluated on the basis of its reaction to deformation and its use in the tunnel.

Three Dimensional Load Analysis of Tunnel Linings Including Weathering Processes of the Shotcrete

In this study a three-dimensional finite element model was applied to simulate the process of tunnel excavation and lining installation. The emphasis was placed on the prediction of deformation and forces acting on the primary shotcrete lining during a NATM excavation in rock modelled with Mohr-Coulomb elasto-plastic material behaviour. Further investigations and development of the model were done by taking into consideration long-time behaviour of the primary support elements by decreasing the strength and stiffness parameters of the shotcrete shell and the influence on the final lining caused by this.

Influence of the Tunnel Shape on Shotcrete Lining Stresses

Abstract:Tunnel excavation is frequently carried out in rock masses by the drill and blast method and the final shape of the tunnel boundary can be irregular due to overbreaks. In order to investigate the effects of overbreaks a study of the effect of tunnel boundary irregularity has been carried out. This is done developing a computational tool able to take into account fuzzy variables (i.e., thickness of the beams of the bedded spring approach used for the model). The obtained results show that irregularity effects should be considered when a shotcrete lining is used as the final tunnel lining (for the case where the tunneling procedure does not permit a smooth surface to be obtained). This is crucial to obtain a durable lining.

Stability Analysis of Tunnel Surrounding Rock and Shotcrete Lining and Rock Bolts Based on Strength Reduction Finite Element Method

Based on the practical engineering ,by using the 3D-FEM of elastic-plasticity, a reasonable model for simulation of tunnel excavation and shotcrete lining and rock bolts builds up, surrounding rock using Mohr-Coulomb constitutive model of ABAQUS, lining using Concrete Damaged Plasticity constitutive model, and bolt using elastic-plasticity constitutive model. By using strength reduction finite element method, analysis for safety coefficient of stability of surrounding rock with primary shotcrete lining and rock bolts under the four limit state criteria. It is concluded that the appearance of divergence of the computation may precede by displacement of characteristic points, The safety coefficient of the running-through of the plastic zone of the surrounding rock and the running-through of the plastic zone of the shotcrete and a great amount of rock bolts yielding are less than the divergence of the computation and displacement of characteristic points.

Application of Shotcrete Linings under Sulfate Attack Environments

Shotcrete lining has been increasingly used in tunnel and underground structure since 1960. Cement in shotcrete is the most vulnerable to aggressive sulphate ions from the environment in the presence of moisture. Sulfate attack can change the chemical composition of the cement matrix.The sulfate attack can be caused by alkali sulfates or due to thaumasite form of sulfate attack (TSA). Based on the mechanism of sulfate attack in conrete, the features of the interaction of the sulfate bearing ground water with shotcrete linings are presented in this paper. Under sulfate attack environment, shotcrete durability and the specification of materials should be highlighted in design. The basic requirements to the shotcrete are high strength, low permeability and good homogeneity, which can be produced by well controlled wet process.

Influence of geometric factors on the punching load resistance of early-age fibre reinforced shotcrete linings

Understanding the early-age properties of fibre reinforced shotcrete (FRS) is critical to the accurate estimation of the time to safe re-entry under freshly sprayed FRS linings. Previous research in the field has indicated that shear failures dominate early-age load resistance and thereby govern the performance of a lining during the first few hours after spraying. This investigation has examined the influence of several geometric variables on shear resistance in a punching mode of failure. In particular, the research has addressed the influence of the size, shape, eccentricity, and inclination of punching loads on the apparent shear strength of an early-age fibre reinforced shotcrete (FRS) lining.

Forensic Investigations to Evaluate Sulfate-Induced Heave Attack on a Tunnel Shotcrete Liner

This paper presents the results of a comprehensive research study to determine the potential causes for an inordinate distress developed on a shotcrete liner material of a tunnel located near Dallas, TX. This tunnel was originally founded on a limestone material. Distress locations were identified where possible delamination of shotcrete layer and moisture leaks were either suspected or noticed. As a part of the research, rock cores and white powderlike substance behind the liner were collected around the distressed locations, and these cores and powder material were subjected to chemical, mineralogical, and engineering tests to understand the potential causes of this distress. Mineralogical tests, in particular, X-ray powder diffraction analysis on a powder material and gel-like substances collected on the liner, showed the presence of anhydrite, gypsum, and ettringite traces. High amounts of sulfate measurements in chemical and energy dispersive X-ray spectroscopy studies also showed that both gypsum and ettringite formations were possible in and around the limestone material. Upon hydration, mineral expansion of ettringite and anhydrite led to heaving and subsequent cracking of the adjacent shotcrete layer. Engineering characterization tests including unconfined compression strength (UCS), indirect tensile strength (ITS), and triaxial tests on rock cores embedded with a powder type sulfate material revealed that low strength cores were obtained near high distress zones and high strength cores were collected at low distress zones. The UCS values ranged from 6.2 (high distress) to 13.8 MPa (low distress) whereas the ITS values of the cores varied from 0.5 to 1.1 MPa for the same distress locations. This indicates the potential loss of strength of these rock materials from the presence of gypsum material in them. Possible methods to mitigate this heaving problem behind the liner are also discussed.

Ductile support design

AbstractTunnelling in weak ground under high overburden normally results in very high displacements and if a stiff support concept is applied, this requires a very high load‐bearing capacity. This has again and again proved to be both an uneconomical and an unsafe concept, leading to extremely high lining thickness and brittle failure behaviour. In order to avoid such problems, ductile support systems have been developed, which allow controlled deformation of the ground and plastic dissipation of excessive stresses accumulated in the lining. For the efficient design of such systems, the aspects of spatial and time‐dependent development of displacement, time‐dependent properties of shotcrete, and the load‐displacement behaviour of the ductile elements have to be harmonized.The requirements posed on a ductile support system are presented, together with simple principles for the determination of ground behaviour boundaries when the application of a ductile support becomes imperative. Recent developments of ductile elements for use with shotcrete linings are described, and their general performance and efficiency are reviewed. A method for calculation of shotcrete stresses using absolute displacement monitoring data is presented, allowing the identification of both inefficient (lining stresses too low and strongly variable in the cross‐section) or unsafe (lining stresses almost exceeding the strength) concepts and optimisation during construction.Bei Tunnelvortrieben in Gebirge geringer Qualität und hoher Überlagerung treten in der Regel große Verformungen auf. Bei steifem Ausbaukonzept ist zum Erzielen eines Gleichgewichts eine sehr hohe Ausbaukapazität erforderlich. Die Erfahrung hat gezeigt, dass steife Ausbauten sehr unwirtschaftlich sind, und dass ein Versagen der Schale oft trotzdem nicht verhindert werden kann, was zu Sicherheitsproblemen führt. Zur Lösung des Problems wurden schon vor geraumer Zeit duktile Ausbausysteme entwickelt, die einen kontrollierten Lastaufbau in der Auskleidung erlauben. Zur Auslegung eines solchen duktilen Ausbaus müssen die räumliche und zeitliche Entwicklung der Verschiebungen sowie die zeitabhängigen Eigenschaften des Spritzbetons und die Charakteristik der duktilen Elemente berücksichtigt werden.Eine Methode zur Ermittlung der Spannungen im Spritzbeton aus den Verschiebungsmessungen wird vorgestellt. Dies erlaubt eine einfache Abschätzung der Effizienz verschiedener Systeme sowie eine Optimierung der Auslegung duktiler Ausbauelemente.

The application of fibre reinforced shotcrete as primary support for a tunnel in flysch

The 10 m diameter Dekani motorway tunnel was constructed using the principles of the NATM method. The tunnel was located in a flysch geological sequence, which was classified as heterogeneous weak rock. The aim of the research presented in this paper was to examine whether fibre reinforced shotcrete can be successfully used as the only material for the primary tunnel lining in these geological conditions. The interpretation of the interaction between the fibre reinforced shotcrete lining and the surrounding rock, which was based on monitoring in a 60 m long test section, is presented in the paper. The development of the new mix of steel and polypropylene fibres and shotcrete is described and the results of the laboratory testing of strength, stiffness and post-crack strength are presented. The success of the field test led to the use of the fibre reinforced shotcrete for the primary lining in a 410 m long section of the tunnel. Significant savings were made in the use of time and material without compromising the quality of the final product.

Monitoring the deformation of a temporary top heading invert using Time Domain Reflectometry

AbstractFor the objective evaluation of the structural safety of tunnel structures during the construction phase, continuous monitoring of all important structural elements (e.g. tunnel lining) and the tunnel face are of utmost importance. The temporary top heading invert, frequently used in sensitive areas of top heading drives, could not up to now be monitored with measuring equipment, because it is usually covered with infill to form a temporary haul road.The application of a Time Domain Reflectometry (TDR) measurement system makes it possible for the first time to detect, localise and quantify failures in the shotcrete lining. The calibration of the TDR measurement system in laboratory tests and the experience gained through a practical trial in the Lainzer tunnel in Vienna have made it possible to determine the capabilities and limits of this measuring system and demonstrate its readiness for practical use.

Effects of tunnelling on existing support systems of perpendicularly crossing tunnels

The interactions between perpendicularly crossing tunnels in the Sydney region are investigated using a full three-dimensional (3D) finite element analysis coupled with elasto-plastic material models. Special attention is paid to the effect of subsequent tunnelling on the support system, i.e. the shotcrete lining and rock bolts, of the existing tunnel. The results of the analysis show that in a region such as Sydney, with relatively high horizontal stresses, installation of the new tunnel causes the shotcrete lining of the existing tunnel to be in tension in the side facing towards the tunnel opening and in compression at the crown and invert. The pre-stressed rock bolts are usually tensioned more in the sections closest to the tunnel opening. For this particular study, if a new tunnel is driven perpendicularly beneath an existing tunnel, significant increases are induced in the bending moments in the shotcrete lining at the lateral sides of the existing tunnel and in the axial forces at its crown and invert. The increase in side bending moments causes further tensile cracking but the crown and invert stresses remain within the thresholds for both compressive failure and tensile cracking for shotcrete lining of typical concrete quality. Moreover, the driving of the new tunnel causes the tensile forces in the existing side rock bolts to increase and those in the existing crown rock bolts to decrease. In contrast, if the new tunnel is driven perpendicularly above the existing tunnel, compressive failure of the existing shotcrete lining is induced at the crown of the deeper tunnel for concrete of typical capacity and a significant tensile force increase of the existing rock bolts around the crown. It is concluded that in order to ensure the stability of the existing tunnel, local thickening is needed at the sides of the existing shotcrete lining if the shallow tunnel is installed first and local thickening is needed at the crown if the deep tunnel is installed first.

Design and Construction of the Venaus Powerhouse Cavern in Calcschists

AbstractThis paper examines the design and observed performance during construction, associated with staged excavation and support requirements of the Venaus powerhouse cavern, a component of the Pont Ventoux‐Susa hydroelectric scheme (in Northern Italy, near the city of Torino), which has been recently put into operation. This cavern, with a maximum height of 49 m, a length of 50 m, and a span of some 23 m, has been excavated in calcschists at a depth of 250 m below surface. Rock reinforcement consisted essentially of 9 to 15 m long primary rock anchors, for long term support, and 6 m long secondary rock dowels, together with a 25 cm thick reinforced shotcrete lining. Following comprehensive geological and geomechanical investigations with laboratory and in situ testing, design analyses have been performed by numerical modelling with both continuum and discontinuum methods. On the basis of the observed performance during early excavation of the upper cross section of the cavern, a discontinuum model, calibrated by back analysis procedures, was used for predicting the overall excavation stability. It is noteworthy that the design concepts adopted allowed this large cavern to be excavated and stabilized without the use of a cast‐in‐place concrete arch for roof support.