Use Of Shotcrete Research Articles

3D concrete printing for tunnel linings: Opportunities and challenges

The use of shotcrete for hard rock tunnel linings has drawbacks such as irregular surfaces and rebounds. By contrast, extrusion-based 3D concrete printing presents a promising solution with precise deposition and reduced rebound. This study discusses the potential of 3D printing for tunnel linings, focusing on mitigating shear failure and addressing interfacial detachment. Achieving high strength early for stable adhesion to rock surfaces is paramount for countering shear failure. A twin-pipe pumping system was introduced utilizing a helical static mixer to blend concrete involving chemical triggers, effectively managing the stiffness and fluidity during pumping. In addition, the adhesion to the substrate must be addressed. Based on the above discussion, this study offers insights into the fundamental challenges, paving the way for advancing extrusion-based 3D concrete printing for tunnel linings.

Experimental and Numerical Study on Unreinforced Brick Masonry Walls Retrofitted with Sprayed Mortar under Uniaxial Compression

The use of shotcrete or sprayed mortar is a common construction alternative to retrofit unreinforced brick masonry (URM), and extensive research has already been carried out in this area. However, most studies have been conducted on lateral strength, for example, eccentric compression or seismic forces. On the other hand, there are few studies about uniaxial compression, and the results of most studies confirm a strong relationship between the thickness of the retrofitting layer and whether it is a double-sided retrofitting section. However, most studies are exclusively experimental, with few samples, and lack numerical analysis; therefore, deeper research is required on this issue. In this sense, this paper combined experiments and finite element (FE) simulations to further study the uniaxial compression. A series of cyclic uniaxial compression experiments on URM retrofitting with sprayed mortar were performed. The experimental results were used to calibrate the FE model. Using these calibrated FE models, more variable parameters were run so that more reference results could be obtained. Moreover, the resulting damageable model of FE will be useful for studying the behavior in the inelastic phase. Results found that the compression strength of most composite walls retrofitted with sprayed mortar increases with the thickness of the sprayed layer and can improve the construction defects of the masonry itself. An over-thin sprayed layer reduces the range of the elastic phase of the composite wall. This phenomenon tends to stabilize with increasing thickness. The ultimate strength of the composite masonry is generally positively correlated with the overall increase in the thickness of the sprayed mortar but may cause a negative contribution to the ultimate strength of the composite masonry when the sprayed layer is too thin. The contribution of double-sided spraying to the ultimate strength of the composite wall was not as large as expected, but the contribution to the improvement of the elastic modulus of the wall was significant.

Geofoam: A potential for Indonesia’s soil problem II

Indonesia is a country with a fair amount of hills and mountains. Having a tropical climate and high rainfall, landslides/slope failures are a common occurrence in Indonesia. According to the Indonesian National Board for Disaster Management, 355 slope failures occurred in 2019, with 81 casualties. To aggravate the problem, global warming and climate change result in extensive dry period and higher intensity rainfall. Slope failures can become more frequent in the near future. Common mitigation of slope failure includes construction of retaining structures, or by reducing water infiltration by the use of shotcrete. In this paper, the use of geofoam to mitigate slope failures is introduced, followed by a case study.

Improving the Effectiveness of Strengthening Slopes of the Embankment

A study was conducted to assess the stability of soil slopes of the subgrade of roads and railways. The main causes of destruction (erosion) and loss of stability of the soil slope of great steepness are considered. The modern methods of strengthening and protecting the slopes of the embankment from erosion and sliding under its own weight are analyzed. The method of strengthening slopes with shotcrete is considered in detail. Recommendations are given on increasing the efficiency of the use of shotcrete while strengthening the soil slopes of the subgrade embankment. Mathematical modeling of the stability of the slopes of the subgrade with a laying from 1: 1 to 1: 0.25 is carried out, the stability of the steep slopes is also considered. Using modern software systems, the finite element method has been used to evaluate the stress-strain state and stability of the slope of the subgrade.

Rehabilitation of Portal Subsidence of Heybat Sultan Twin Tunnels: Selection of Shotcrete or Geogrid Alternatives

The occurrence of karst phenomenon is one of the common problems in carbonate rocks in the presence of water. The rock masses constituting the ground surface are mostly of sedimentary types among which carbonate rocks are widely observed. It is therefore necessary to accept such a geological hazard in many projects. Some of the rehabilitation methods for karstic subsidence include grout injection, filling with concrete or shotcrete and making use of geosynthetic products. Few studies have been carried out on the application of the geosynthetic products. Limy rocks form the main lithology of a large part of the 72 km long access road tunnel designed for the Iraqi-Kurdistan. The occurrence of a karstic subsidence with a volume of about 2250 m3 in the portal of Heybat Sultan tunnels revealed the necessity of examining and selecting one of these rehabilitation methods. Concerns about the repetition of such collapses in other tunnels, especially in the 6740 m long Korek twin tunnels that is the longest tunnel of the Middle East located in the vicinity of the project, has doubled the importance of the issue. This paper aims to render an account of the use of shotcrete and geogrid to rehabilitate the subsidence of the portal of Heybat Sultan tunnels. The modeling results with the FLAC numerical finite difference code showed that the displacement amount of the host rock mass after implementing the second method would be 2.9 times less than the first method. Geogrid also reduces the axial forces exerted to the tunnel supporting system up to 43 tons.

Bond strength of reinforcing bars encased with shotcrete

As the use of shotcrete (sprayed concrete) to build full-depth structural elements increases in North America, the encapsulation quality of reinforcing bars has become a subject of growing concern. In this investigation, the influence of the mixture consistency and the size of imperfections (created deliberately) behind reinforcing bars on the bond strength of the bars was studied using shotcrete “pull-out” specimens sprayed with the dry-mix process. However, as the desired range of the imperfection sizes could not be obtained, cast-in-place “pull-out” specimens were built with artificially created voids. This strategy allowed to study the reduction of the bond strength by knowing the precise size of the voids. The results suggest that the best bond performance of a bar is obtained, given an appropriate spraying technique, when the optimal combination between the mixture consistency and the airflow rate is used. Moreover, reinforcing bars encased with shotcrete slip less, relative to concrete, than those encased with cast-in-place concrete because of the high compaction with which the mixture is placed. Additionally, a void’s transversal length (in contact with the bar) of about 20% of the bar’s nominal perimeter was found to be the threshold beyond which an important change of the bond performance occurs.

SHOTCRETE IN MINE CONSTRUCTION

This article deals with concerns of construction of subsurface structures with the use of shotcrete as a support, the samples of mine construction with application of shotcrete have been shown, in particular projected mine with vertical well bore. The calculation method for construction of well bore with the use of shotcrete support has been stated, the major analytical relationships have been set out, a graph showing the growth of strength in a support has been generated for several sites according to the results of actual geotechnical survey. The research of properties of concrete with fast development of strength has been implemented for mine engineering and construction of transportation infrastructure. The results of experimental analysis of shotcrete with organo-mineral and chemical additives have been listed. Performance improvement of physical and mechanical properties of shotcrete has been proven when the complex active nano agent added into composition of the binder. Improved kinetics of development of strength related to accelerated admixture helps in proportioning concrete compositions for practically any firm and medium-firm grounds during construction of support of subsurface structures.

Structural and material properties of Mini notched Round Determinate Panels

Large use of shotcrete, especially in mining and underground operations, pushed the introduction of the Round Determines Panels (RDP) test as an effective design tool for the required toughness of the concrete mix. Nevertheless, structural more than material properties can be obtained from it and there are serious concerns related to safety of experimental operations and to their costs. In order to overcome these flaws, a recent study introduced the mini notched RDP test and showed that it is possible to correlate the energy absorbed by RDP samples with equal thicknesses but different diameters. Along this line, the present study focuses on the influence of the thickness of RDP samples on their toughness; an experimental campaign has been carried out, showing that the absorbed energy is thickness-dependent; in order to validate the results, a simple analytical model has been developed, able to provide for a direct relation between the absorbed energy and the material fracture energy. As a consequence, a new design procedure based on these findings has been proposed, allowing for the use of conventional designing tools together with the mini notched RDP test. Finally, hypothesis introduced in the analytical model have been verified both experimentally and by means of a non-linear numerical model.

Evaluation on the Potential Use of Shotcrete Lined High Pressure Tunnel at Upper Tamakoshi Hydroelectric Project

Optimization of rock support is a key factor for successful use of underground space for hydropower development in the Himalaya. Therefore, finding innovative, optimum and economic solution will be the only way to guarantee such optimization. A main issue is to determine the extent of hydraulic fracturing and assess the water leakage possibility during the operation of such tunnels. The leaked water not only causes economic loss but also may severely affect the stability of tunnel, valley side slopes and the environment.The use of fully concrete/steel lined pressure tunnels against hydraulic fracturing in the rock mass is a costly alternative. Hence, it is advantageous to explore possibilities of minimizing the length of the concrete or steel lining in high pressure tunnels and shafts. A proper assessment of hydraulic fracturing of the rock mass plays an important role in this endeavor.This paper evaluates whether or not hydraulic fracturing (splitting) will occur at the 4,746m long shotcrete-lined high pressure headrace tunnel of 456 MW Upper Tamakoshi Hydroelectric Project (UTKHEP). The Upper Tamakoshi HEP is a high head project (gross head 822m) and the proposed shotcrete lined high pressure headrace tunnel will experience maximum hydrostatic pressure head of 40 bar (400m water column) at normal plant operation. To check the possibility of hydraulic fracturing, both deterministic and two dimensional numerical modeling techniques have been used. In addition, the paper also highlights the importance and challenges to be faced while estimating representative input variables needed for both deterministic and numerical modeling.DOI: http://dx.doi.org/10.3126/hn.v10i0.7118 Hydro Nepal Vol.10 January 2012 73-80

Shotcrete for structural and architectural restoration of concrete shell built in 1905

The Herbivora Building at the Cincinnati Zoo (Cincinnati is a city in southern Ohio, in the midwestern USA), presently housing elephants, giraffes and rhinos, was constructed in 1905. This unique building is one of the earliest examples of reinforced concrete shell roof construction in the United States. The building experienced severe structural and architectural deterioration over a long service life, and was restored in a series of phased projects after 75 years of service. The restoration of structural integrity and the replacement of architectural features and appearance was achieved through the use of shotcrete (also called gunite or pneumatically applied or sprayed concrete) applied to walls, teams, window openings and the dome roof structure.

Health and safety in shotcreting: ITA Working Group on Shotcrete Use in Tunnelling

This report summarizes the responses to a questionnaire, distributed to ITA member countries, on health and safety in shotcreting. The report deals with the following aspects of this topic: use of shotcrete; influence of dust on the human body; regulation and guidelines regarding dust concentration; efforts to reduce dust production; efforts to reduce dust emission and improve personal protection; and demands for Research and Development of shotcrete. An appendix presents the various countries' specific responses to the questionnaire.

Waterproofing of tunnels by the use of shotcrete : Astad, U; Heimli, P Proc International Congress on Tunnels and Water, Madrid, 15–18 June 1988V1, P393–397. Publ Rotterdam: A A Balkema, 1988

Waterproofing of tunnels by the use of shotcrete : Astad, U; Heimli, P Proc International Congress on Tunnels and Water, Madrid, 15–18 June 1988V1, P393–397. Publ Rotterdam: A A Balkema, 1988

Shotcrete for underground support V

This proceedings consists of papers presented at the Engineering Foundation Conference held in Uppsala, Sweden on June 3-7, 1990. They are divided into sections concerned with the design of shotcrete linings, wet mix shotcrete processes, shotcrete additives, fiber-reinforced shotcrete, and case histories. The first section on the design of shotcrete linings explores the need to develop and refine shotcrete lining systems to provide optimum tunneling efficiency and economy. Next, the benefits of wet mix shotcrete processes are discussed. This is followed by papers on the use of additives to enhance shotcrete properties. Another method of enhancing shotcrete properties, fiber reinforcement, is also presented. Finally, case histories provide an entire spectrum of shotcrete usage ranging from difficult ground control problems in Zimbabwe mines to the use of shotcrete as a major support element in the Channel Tunnel Project.

吹付コンクリートの強度と変形特性に関する研究

In the last decade, the use of shotcrete in tunnel construction has rapidly increased and the shotcrete has become an important element of the modern tunnel support techniques. Nevertheless, the properties of shotcrete have not been sufficiently investigated.This paper presents the results of an experimental program to evaluate the properties of shotcrete relevant to the tunnel support systems. In the experiments the cubic specimens were prepared and tested to obtain the mechanical properties, especially the strength and Young's modulus in relation to curing time. From these results, the relationship among the uniaxial compressive strength, Young's modulus, curing time, failure strain and ultrasonic velocity are proposed and their relevancy are discussed.

Soil nailing supports excavation : Nicholson, P L; Boley, D L Civ Engng, N YV55, N4, April 1985, P44–47

Excavation for the PPG Headquarters complex in Pittsburgh, Pa. was critical because the site is adjacent to three historically important buildings. Soil nailing, a method of in situ earth reinforcement, was used at these three areas. One method, which had been tested at the University of California, involves use of shotcrete and wire mesh to support the excavation face with reinforcing members grouted into the soil mass behind the face. This, however, was not satisfactory for the Pittsburgh site, so a modified method was used. Columns were drilled, pressure grouted and reinforced; then the reinforcing nails were drilled and pressure grouted. No movement of the three buildings was detected during excavation and construction of the new buildings.

Precast reinforced concrete lining competes with NATM : Wagner, H Tunn Tunnlg, V14, N8, Sept 1982, P15–18

Over the years, price considerations have meant that European practice has favoured the use of shotcrete and in-situ concrete lining in preference to precast concrete elements. These elements would usually be of the bolted type and be used in conjunction with shield driving. Only with the introduction of single shelled waterproof reinforced concrete rings has it been possible, with the improvements in sealing systems gained from cast-iron linings, for this type of lining to regain its popularity. (A)

Use of shotcrete to increase the rate of roadway drivage (in German) : Riedel, H; Schmidt, K Neue Bergbautech, V11, N8, Aug 1981, P443–447

Use of shotcrete to increase the rate of roadway drivage (in German) : Riedel, H; Schmidt, K Neue Bergbautech, V11, N8, Aug 1981, P443–447

Putting the NATM into perspective : Brown, E T Tunn Tunnlg, V13, N10, Nov 1981, P13–17

A commentary on the features of the New Austrian Tunnelling Method (NATM) is intended to reconcile apparent misunderstandings concerning the tunnelling technique. Main elements of the NATM philosophy as they appear to the author, are tabulated. A description of the NATM by one of its originators states that the system incorporates surface stabilisation by a shotcrete lining. This necessary use of shotcrete was open to doubt according to the author. From a review of the central features of the NATM, such as conservation and mobilisation of rock strength, it is concluded that the NATM is a soundly based system of providing support in which instrumentation monitors the performance of the structure. The NATM is said to be open to conflicting interpretations, while its successful application requires a high degrees of understanding of support mechanics and geological interpretation. (TRRL) (TRRL)

Use of shotcrete for permanent linings underground : Sjostrom, O Proc 1st International Symposium on Storage in Excavated Rock Caverns (Rockstore 77), Stockholm, 5–8 Sept 1977, V3, P585–591. Publ Oxford: Pergamon Press, 1978

Use of shotcrete for permanent linings underground : Sjostrom, O Proc 1st International Symposium on Storage in Excavated Rock Caverns (Rockstore 77), Stockholm, 5–8 Sept 1977, V3, P585–591. Publ Oxford: Pergamon Press, 1978

Use of shotcrete as a structural element in mine workings support (in Polish) : RULKA, K MATEJA J PRZEGL. GORN. V32, N5, MAY, 1976 P193–198

Use of shotcrete as a structural element in mine workings support (in Polish) : RULKA, K MATEJA J PRZEGL. GORN. V32, N5, MAY, 1976 P193–198