Analysis of Circular Reinforced Tunnels by Analytical Approach

Abstract This paper addresses the problem of quantifying the mechanical contribution of rockbolts installed systematically around tunnels (regularly spaced around the tunnel) excavated in rock masses. Assuming that the mechanical contribution of grouted rockbolts is that of increasing internal pressure within a broken rock mass, a new procedure for computation of ground response curves for a circular tunnel excavated in strain softening material and then reinforced with systematically active grouted rockbolts is presented. In this work, the equation of the ground response curve for a tunnel which has been reinforced with passive grouted rockbolts is also derived. The proposed model allows one to take into account the effect of the distance of the bolted section to the tunnel face, the effect of increasing rockbolts spacing, the influence of increasing pretension load in calculating of the ground response curve, and the effect of increasing the cross-section area of rockbolts. The results show that decreasing rockbolts spacing increases the support system stiffness rather than preloading of them

Large Aftershock Routing to Reduce Earthquake Fatalities and Injuries (Case Study, Sefidsang Earthquake on April 5, 2017 in Northeastern of Iran)

سابقه و هدف: بررسی تجارب مرتبط با زمین‌لرزه‌های گذشته بویژه در کشورهای توسعه نیافته و در حال توسعه مانند ایران حاکی از این نکته است که علاوه بر تلفات و مصدومیت‌های ناشی از رخداد زمین‌لرزه اصلی، پس‌لرزه‌های بزرگ این زمین‌لرزه‌ها نیز معمولا در افزایش پیامدهای یاد شده موثرند. در این پژوهش با هدف کاهش تلفات و مصدومیت‌های ناشی از رخداد پس‌لرزه‌های بزرگ به ارائه روشی کاربردی در زمینه پیش‌بینی این پس‌لرزه‌ها پرداخته شد. روش بررسی: روش بررسی بکار گرفته شده در این پژوهش بر مبنای تحلیل آماری داده‌های مربوط به پارامترهای مبنایی پس‌لرزه‌های اولیه از جمله زمان رخداد، عمق‌کانونی و بزرگی آن‌ها با هدف شناسایی زمان رخداد پس‌لرزه‌های بزرگتر برای اطلاع رسانی و تخلیه به موقع افراد بازمانده در سازه‌های نامقاوم است. در اين پژوهش از تئوري سكون‌لرزه‌اي(فاصله زمانی بین رخداد پس‌لرزه‌ها) و تحليل داده‌های نرمال شده عمق و بزرگی پس‌لرزه‌هاي اوليه براي شناسايي زمان و میزان آسیب‌پذیری ناشی از رخداد پس‌لرزه‌هاي بزرگ براي زمين‌لرزه فروردین ماه 1396 سفید سنگ در شمال شرق ايران استفاده شد. نتایج: تحلیل داده‌ها در این پژوهش حاکی از این نکته است که رابطه مشخصی بین فاصله زمان بین بزرگی و سکون‌لرزه‌ای پس‌لرزه‌های اولیه وجود دارد که این رابطه می‌تواند مبنای تحلیل مورد نظر درخصوص پیش‌بینی زمان رخداد پس‌لرزه بزرگ قرار گیرد. نتیجه‌‌گیری: نتايج حاصل از اين پژوهش حاكي از آن است كه با تحلیل همزمان داده‌های نرمال شده عمق و بزرگی برمبنای سکون‌لرزه‌ای بین پس‌لرزه‌ها می‌توان به پيش بيني دقيقي از زمان و آسیب‌پذیری ناشی از پس‌لرزه‌های بزرگ دست یافت.  How to cite this article: Fatemiaghda SM, Saket A, Sadeghi H, Fahimifar A. Large Aftershock Routing to Reduce Earthquake Fatalities and Injuries (Case Study, Sefidsang Earthquake on April 5, 2017 in Northeastern of Iran). Irtiqa imini pishgiri masdumiyat. 2021;9(2):92-101.Background and Objectives: Examining experiences related to past earthquakes, especially in developing countries suggest that in addition to fatalities and injuries caused by the main earthquake the large aftershocks also have effect to increasing the mentioned consequences. In this Research has presented a practical method in predicting the large aftershocks with the aim of reducing fatalities and injuries caused by their occurrence. Materials and Methods: The survey method used in this study is based on statistical analysis related to basic parameters of the primary aftershocks such as: time occurrence, magnitude with aim of prediction of time the large aftershock for alarm and evacuation to people from non-resistant buildings. In this research has used seismic quiescence theory (time distance between aftershocks event) and analysis of the normalized data of depth and magnitude of primary aftershocks for the prediction of time and vulnerability level caused of the large aftershocks in Sefidsang earthquake in northeast of Iran. Result: Data analysis suggests that there is the definite relationship between magnitude and seismic quiescence of primary aftershocks that this relationship can be base of analysis for prediction of the time of the large aftershocks.                                                                                                  Conclusion: The results of this study indicate that predicting the time and the rate of vulnerability of the large aftershocks can be obtained by combining the outputs of the two aforementioned analyzes.   How to cite this article: Fatemiaghda SM, Saket A, Sadeghi H, Fahimifar A. Large Aftershock Routing to Reduce Earthquake Fatalities and Injuries (Case Study, Sefidsang Earthquake on April 5, 2017 in Northeastern of Iran). Irtiqa imini pishgiri masdumiyat. 2021;9(2):92-101

Experimental investigations on the mechanical properties of rocks containing a single discontinuity

PhD ThesisAn extensive experimental programme was undertaken to investigate the strength and deformational characteristics of six rock types containing a single joint under various loading and straining conditions. A monitoring system was set up using a microcomputer controlled logger and the required computer programs for data logging and processing were also developed. For the purpose of achieving reliable findings the effects of system constraints on the experimental results in triaxial testing of jointed specimens were investigated. On the basis of a satisfactory end-specimen condition the results of triaxial compressive tests performed on the specimens of three rock types, containing artificial joints at different orientations, are presented, and the effects of joint inclination, confining pressure (0-70 MPa) and joint surface roughness on the mechanical behaviour of jointed specimens were investigated. A method to calculated volumetric strain in the rock specimens has been developed and the volumetric strain, lateral strain and instantaneous Poisson's ratio for both intact and jointed specimens are calculated. Time-dependency of jointed rocks for the three cases of different constant strain rates, changing strain rates and stress relaxation at various points on the complete stress-strain curve has examined. The failure criteria applicable to jointed media are reviewed and the necessary parameters for an appropriate failure criterion have been defined. The stick-slip characteristics of jointed rocks are investigated and two types of stick-slip phenomena are introduced in conjunction with the type of rock and type of testing system.The Iranian Ministry of Culture and Higher Education: The Amir Kabir University of Technology

Nov način analiziranja plitkih in globokih tunelov ob upoštevanju gravitacije

A new, elasto-plastic, analytical-numerical solution, considering the axial-symmetry condition, for a circular tunnel excavated in a strain-softening and Hoek–Brown rock mass is proposed. To examine the effect of initial stress variations, and also the boundary conditions at the ground surface, the formulations are derived for different directions around the tunnel. Furthermore, the effect of the weight of the plastic zone is taken into account in this regard. As the derived differential equations have no explicit analytical solutions for the plastic zone, the finite-difference method (FDM) is used in this study. On the other hand, analytical expressions are derived for the elastic zone. Several illustrative examples are given to demonstrate the performance of the proposed solution, and to examine the effect of various boundary conditions. It is concluded that the classic solutions, based on the hydrostatic far-field stress, and neglecting the effect of the boundary conditions at the ground surface, give applicable results for a wide range of practical problems. However, ignoring the weight of the plastic zone in the analyses can lead to large errors in the calculations.Članek predstavlja novo analitično-numerično rešitev za krožni tunel v deformacijsko popuščajoči in Hoek-Brownovi hribini, ob upoštevanju pogojev osne simetrije. Izpeljani so izrazi za določitev sprememb začetne napetosti in robnih pogojev površine tal v različnih smereh okrog tunela. Pri tem so upoštevani tudi vplivi teže v plastični coni. Ker izpeljane diferencialne enačbe ne predstavljajo eksplicitne analitične rešitve za plastično cono, se v študiji uporablja metoda končnih razlik (MKR). Izpeljani pa so analitični izrazi za elastično cono. Učinkovitost predlagane rešitve in učinek različnih robnih pogojev sta ponazorjena z več pojasnjevalnimi primeri. Ugotovljeno je, da dajejo klasične rešitve, ki temeljijo na oddaljeni hidrostatični talni napetosti in zanemarjajo vpliv robnih pogojev na površini tal, uporabne rezultate za veliko praktičnih problemov. Vendar pa lahko neupoštevanje teže v plastični coni v analizah privede do velikih napak v izračunih

Mechanical properties of steel and polymer fiber reinforced concrete

The present study aimed to investigate the influence of a number of fiber parameters including fiber type, content and hybridization on strength and ductility of polymer fiber reinforced concrete (PFRC) and steel fiber reinforced concrete (SFRC) used mostly in tunneling practices as the primary shotcrete lining. Numerous cylindrical and prismatic beams were casted and undergone various tests in which main previously mentioned fiber traits varied. It was understood that SFRC excels at every mechanical feature in comparison to PFRC; however, such transcendence found predominant in compressive strength but marginal in flexural and tensile strength. Despite being classified under different compressive strength classes (SFRC in the upper and PFRC in the lower class) according to EFNARC, both FRC types fell under a similar flexural class (at 4% of fiber fraction); a result possibly in debt to excellent bonding properties and more slender polymer fibers. Tensile strength of PFRC was measured lower than SFRC. Augmentation of fiber content positively affected mechanical characteristics of FRC at most cases. Hybridization of different fibers at a specific range of fiber mixing proportions was observed to have advantageous impacts on ductility and strength of a more corrosive resistant and cost efficient hybrid fiber reinforced concrete (HFRC)

New analytical approaches for evaluating the performance of systematic pre-tensioned fully grouted rockbolts in tunnel stabilization

In this paper, two new analytical approaches are presented on the basis of convergence-confinement method to compute both the ultimate convergence of circular tunnel and its plastic zone having been reinforced by systematically pre-tensioned fully grouted rockbolts. The models have two basic assumptions: (1) the grouted rockbolts increase the radial internal pressure within a broken rock mass by both the pre-tensioned force and the probable following induced force due to rock mass movement (2) tunnel convergence (specially short-term) occurs only due to reducing and diminishing of the radial constrained stress on tunnel surface provided by the working face. Hence, the values of both the pre-tensioned pressure and the mentioned radial constrained stress are specially taken into consideration in this paper. That is, according to their magnitudes, two different conditions occur: the magnitude of pre-tensioned pressure is greater than that of the constrained stress at bolt installation time and vice versa. The solutions are extended to each of conditions, and illustrative examples are solved. The proposed approaches predicting almost identical results show that pre-tensioning of grouted rockbolts will increase the efficiency and effectiveness of rockbolts

Investigating the Effects of Cement and Polymer Grouting on the Shear Behavior of Rock Joints

This study carried out a comparison between cement grouting and chemical grouting, using epoxy and polyurethane, with respect to their effects on the shear behavior of joints. Joint replicas, with three different grades of surface roughness, were molded and grouted by means of cement and epoxy grouts of various mixtures. To investigate their shear behavior, samples were subjected to direct shear tests under constant normal load (CNL) condition. According to the results obtained, grouting improves the overall shear strength of the rock joints. All the grouted samples yielded higher maximum and residual shear strength in comparison with the non-grouted joint. Grouting resulted in an improvement in the cohesion of all the samples. However, a fall in friction angle by 5.26° in the sample with JRC of nine was observed, yet it was reduced by 2.36° and 3.26° for joints with JRC of 14 and 19, respectively. Cement grouts were found to have a more brittle behavior, whereas the chemical grouts were more ductile. Higher amounts of cement used in the grout mixture do not provide as much cohesion and only increase the brittleness of the grout. As a result of being more brittle, cement grout breaks into small pieces and joint planes are in better contact during shearing; consequently, there would be less of a fall in friction angle as opposed to epoxy grout whose ductile characteristic prevents grout chipping; therefore, joint planes are not in contact and a greater fall in the friction angle occurs. There was no noticeable change in the cohesion of the larger grouted joints. However, the friction angle of both natural and grouted joints increased in the larger joint. This can be related to the distribution of random peaks and valleys on the joint surface, which increases with the joint size

Predicting tunnel boring machine performance through a new model based on the group method of data handling

The tunnel boring machine (TBM), developed within the past few decades, is designed to make the process of tunnel excavation safer and more economical. The use of TBMs in civil and mining construction projects is controlled by several factors including economic considerations and schedule deadlines. Hence, improved methods for estimating TBM performance are important for future projects. This paper presents a new model based on the group method of data handling (GMDH) for predicting the penetration rate (PR) of a TBM. In order to achieve this aim, after investigation of the most effective parameters of PR, rock quality designation, uniaxial compressive strength, rock mass rating, Brazilian tensile strength, weathering zone, thrust force per cutter and revolutions per minute were selected and measured to estimate TBM PR. A database composed of 209 datasets was prepared according to the mentioned model inputs and output. Then, based on the most influential factors of GMDH, a series of parametric investigations were carried out on the established database. In the following, five different datasets with different sets of training and testing were selected and used to construct GMDH models. Aside from that, five multiple regression (MR) models/equations were also proposed to predict TBM PR for comparison purposes. After that, a ranking system was used in order to evaluate the obtained results. As a result, performance prediction results of [i.e. coefficient of determination (R2) = 0.946 and 0.924, root mean square error (RMSE) = 0.141 and 0.169 for training and testing datasets, respectively] demonstrated a high accuracy level of GMDH model in estimating TBM PR. Although both methods are applicable for estimation of PR, GMDH is able to provide a higher degree of accuracy and can be introduced as a new model in this field