International Journal of Engineering, Transactions B: Applications (1728144X)36(8)pp. 1532-1547
A series of large-scale laboratory model tests in a unit cell was performed to explore the behaviour of loose sandy soil due to improvement. An unreinforced and geogrid reinforced granular blanket, a single end-bearing stone column, and their combination were used for this purpose. Since the rupture of the geosynthetic reinforcement in the reinforced granular blanket has never been experimentally investigated. A novel method of installing the geogrid was used. Thus, geogrid was allowed to completely mobilize and fail under loads. In this investigation, load-settlement characteristics have been generated by continuing loading even after geogrid rupture until the desired settlement. Parametric studies were carried out to observe the effect of important factors, such as the blanket thickness and the layout of geosynthetic sheets, including the number and place of geogrid layers within the granular blanket. Reinforcing the blanket with geogrid while changing the usual form of the load-settlement characteristics has had a significant effect on enhancing load-carrying capacity and reducing settlement. It can be said using a stone column, granular blanket, or combination of both techniques to boost load-carrying capacity was more effective than reducing settlement. However, the effect of single-layer and double-layer geogrid reinforcement on settlement reduction depends on their placement within the granular blanket. In addition, the efficiency of improvement methods has been superior under looser bed conditions. The best layout was to arrange one layer of geogrid near the top of the blanket or two layers in the middle and near the top. © 2023 The author(s)
Iranian Journal Of Science And Technology, Transactions Of Civil Engineering (22286160)46(2)pp. 1359-1374
Predicting the accurate hydrodynamic pressure at plunge pool bottoms due to the impact of plunging high-velocity jets is essential in assessing the stability of the bed rock blocks and concrete slabs. In this context, the subsequent scour depth evaluation is essential. The regression-derived model of multiple nonlinear regression (MNLR) and two intelligent models of artificial neural network and adaptive neuro-fuzzy inference system are developed to predict the hydrodynamic pressure mean and hydrodynamic pressure fluctuations at flat and scoured plunge pool bottom. By running statistical analysis on a wide range of large-scale experimental data, it is revealed that, in general the intelligent models outperform the regression-derived equations of MNLR. The average values of RMSE and R2 in the prediction of hydrodynamic pressure coefficients are improved to 0.054 and 0.87, respectively. Nevertheless, due to its simplicity the empirical equations based on MNLR model are accurate enough for engineering applications. These equations predict both the dynamic pressure mean and root mean square of pressure fluctuations at flat bottoms and scoured bottoms more accurately than the available equations for this purpose, with 70% and 90% of data within 20% range of discrepancy, respectively. An empirical equation of pressure fluctuation at SB is introduced for the first time in this study. © 2021, Shiraz University.
Proceedings of the IAHR World Congress (2521716X)pp. 2744-2750
Predicting the efficiency of plunge pools in dissipating the dynamic energy of impinging high-velocityjets of free spillways is essential for assessing the stability of the bed and subsequent scour depth. In this study, a large-scale physical model is developed to assess the energy dissipation of the plunge pools at the bottom. A wide range of hydraulic conditions including impinging jet velocity and plunge pool water depth is considered, resulting in plunge pool Froude number Frp up to 8 which is in the prototype range (Frp=Vj/(gY)0 5, where, Vj is jet velocity at impact on pool surface, g and Y are acceleration due to gravity and water depth, respectively). The hydrodynamic pressures mean and fluctuation at plunge pool bottom are measured at the impinging jet centerline (stagnation point, SP). Buckingham theorem is applied to introduce non-dimensional parameters, among them is the plunge pool efficient parameter (n) which relates the mean hydrodynamic pressure head at the bottom and the kinetic head due to jet velocity at the plunge pool water surface. Results indicate that n varies between 0.1 and 0.95 depending on the magnitude of Y/Dj (Dj is jet diameter at water surface) and Frp. The multiple nonlinear regression-derived model (MNLR) are developed to predict the efficient parameter of plunge pool (n). Statistical analysis of empirical model indicates that the energy dissipation is accurately predicted by the model, the average values of RMSE and R2 are 0.04 and 0.95, respectively. The model can be applied in practice for the preliminary design purposes. © 2022 IAHR.
International Journal of Engineering, Transactions B: Applications (1728144X)35(5)pp. 1056-1063
Clay soil may be subjected to heat in various applications, such as nuclear waste burial sites and high voltage transmission lines. The impact of heat on clay soil's physical and mechanical properties has been explored in previous studies. However, previous studies have mainly focused on the mechanical properties of clay soil without stabilizers, and the effect of heat on the properties of the stabilized clay soil is scarcely studied. The present paper has analyzed and studied the combined effects of heat and cement on the settlement properties of kaolinite clay soil. To conduct the study, kaolinite clay mixed with various degrees of cement was exposed to a range of 25 to 600 degrees Celcius. The results showed that the coefficient of consolidation gradually decreased by increasing heat up to the dehydroxylation point. An increase in heat up to 200 degrees Celcius resulted in increasing the coefficient of consolidation in the specimens containing cement. In specimens containing 10 percent of the cement at temperatures higher than 200 degrees Celcius, the coefficient of consolidation in room temperature decreased by 73 percent compared to kaolinite. Moreover, the void ratio increased in kaolinite specimens without cement when subjected to heat up to 400 degrees Celcius. By increasing the heat, the void ratio decreased in specimens containing 10 percent cement. © 2022 Materials and Energy Research Center. All rights reserved.
Amirkabir Journal of Civil Engineering (2588297X)54(7)pp. 2641-2660
Monopile is the most common type of foundation for onshore and offshore wind turbines. As the wind blows in different directions, wind load alternately applies in different directions during the life cycle of the wind turbine. In this paper, the influence of the alternating change of wind load direction on the response of wind turbine piles is studied. The functional performance of the soil-pile system is simulated with a bounding surface soil behavior model presented by Dafaliad-Manzari that is implemented in FLAC3D software. The softening and hardening effects of soils due to cyclic load patterns are incorporated into the model in a convenient manner. The results show that in monopiles, alternative change in the direction of loading results in the decrease in the maximum horizontal displacement and rotation up to 16% in comparison with the uni-directional loading mode. This difference in vertical displacement is about 100%. Residual displacement and rotation in the horizontal direction also decrease 13% and 18%, respectively. Alternating change of loading causes upward moves of the monopile; the pile moves upward from its original level. In general, the change of loading direction causes a significant change in the pile response, although the values of this difference vary in different parameters and for altered loading modes. © 2022, Amirkabir University of Technology. All rights reserved.
Archives of Civil and Mechanical Engineering (16449665)21(2)
Civil engineering projects deal with different risks over their life-cycle. Generally, risk sources are categorized into three types of cost, time, and project quality. The Modified Advanced Programmatic Risk Analysis Model (MAPRAM) is one of the leading approaches in this field that can assess the risks of the project on its whole life cycle. Electricity transmission lines have always been one of the most costly and time-consuming infrastructure projects. The costs of these projects play a significant role in a country's development budget. Given the considerable time and cost of constructing the foundations for power transmission towers, providing an economical design will significantly help in reducing duration and budget of these projects. In this study, using MAPRAM, first, different types of foundations of power transmission lines were studied; then the optimal foundations were introduced for a specific place as a case study, shaping a general framework to appoint the optimal foundation for power transmission lines in different areas. The foundations studied in this study included: pad & chimney foundation, auger foundation, steel grillage foundation, concrete piles, and helical piles. Initially, different types of foundations were designed, and then, the costs of each foundation in a whole life-cycle were estimated. Next, the risks and probability of their occurrence were identified for each type of foundation. Finally, the appropriate foundation was determined for the studied soil samples by performing an optimization process. © 2021, Wroclaw University of Science and Technology.
Khouzani, M.A.,
Zeynalian dastjerdi, M.,
Hashemi esfahanian, M.,
Mostofinejad, D.,
Farahbod, F.,
Shahadifar, M. Journal of Building Engineering (23527102)44
Several roofing systems have been proposed given their significance in concrete structures, in terms of time and resources. A biaxial voided slab system is introduced to improve the solid slab system's performance by creating voids in the concrete and removing ineffective material. In this study, the bending behavior of voided slabs is investigated numerically. For this purpose, a numerical ABAQUS model is presented and then verified using available experimental results. Then, a parametric study was carried out focusing on the plastic balls and their spacing, steel cages, and the position of plastic balls relative to the slab height. As shown in this paper, the presence of plastic balls improves the flexural capacity, because of steel cages. However, the spacing between plastic balls and their position have not a significant effect on flexural behavior. Finally, the numerical results were compared with the ultimate moment capacities from ACI 318-19, AS 3600-18, EC2 2004, and CSA A23.3-19, and were shown that considering steel cages have better consistencies with numerical results. © 2021 Elsevier Ltd
Structural Concrete (14644177)21(1)pp. 291-302
In some of biaxial voided slabs, spherical or ellipsoidal plastic balls enclosed in steel cages are used to eliminate ineffective concrete. To investigate the bending and shear behavior of this system, five full-scale specimens were cast including two bending specimens for investigating bending capacity and cracking distribution as well as three shear specimens used to study the shear capacity, cracking distribution, and concrete casting effect on the shear behavior. Moreover, the effects of the steel cage rods were studied on the bending and shear capacity. It was found that while both solid and biaxial voided specimens exhibited almost similar failure mode, both the bending and shear capacity of biaxial voided specimens were affected by the steel cages. In contrast, the voided specimens exhibited a significantly lower shear capacity than the solid ones while the different concrete casting methods had no effects on the capacity and behavior of biaxial voided specimens. Finally, a comparison was made with experimental results and ACI 318-14, MC 2010, and Eurocode 2 recommendations. © 2019 fib. International Federation for Structural Concrete
Structures (23520124)27pp. 1075-1085
The numerous advantages of solid slabs, including adequate rigidity, appropriate fire resistance, and sound insulation, have further extended the system's applications. The main disadvantage of this system is, however, its extreme weight, especially in long spans. Since concrete is not involved in bearing in the tensile zone, its removal can lower the weight without affecting the load bearing of the slab. In a number of systems, named biaxial voided slabs, ellipsoidal or spherical sacrificial plastic balls are used to create voids within the concrete. As this system has just been introduced, considerable uncertainties have been raised about one-way and two-way shear behaviors of the system. Accordingly, four full-scale specimens were built in order to investigate these behaviors. Two one-way and two two-way full-scale shear specimens with dimensions of 3500 × 1200 × 200 mm and 2300 × 2300 × 200 mm (length × width × height) were constructed, respectively. These specimens were used to compare the shear capacity, cracking distribution, and deflection in solid and biaxial voided specimens. Also, the effect of vertical rods of steel cages on the shear behavior was investigated. The results show the steel cages clearly contributed to shear bearing; and although the shear capacity of voided specimens was less than solid ones, the failure mode of all specimens was shear. Finally, a new method was proposed to predict the ratio of shear capacity of biaxial voided slabs to solid slabs. Hence, the proposed method can predict the ratio of biaxial voided capacity to solid slab capacity with an adequate precision. © 2020 Institution of Structural Engineers
Journal of Constructional Steel Research (0143974X)161pp. 385-399
A new yielding damper with pure torsional mechanism is introduced and investigated in this paper. Story shear force is transferred to the proposed device using special details to produce pure torsion without shear force and bending moment in the damper pipes. Hence, energy dissipation capacity of damper material could be efficiently used. Some relationships for structural characteristics of the proposed damper including initial stiffness, yielding and ultimate strength and load-displacement relation, are derived analytically. This is done by assuming a bi-linear curve for steel material considering its strain hardening. Ten specimens of this pure torsional damper were tested under cyclic loading. The hysteresis curves indicate a stable and well-shaped cyclic behavior. Results also show high energy absorption capacity and ductility for this damper. Widespread yielding and uniform stress distribution across the entire thickness of the pipe wall of the damper results in high equivalent viscous damping ratio from 38% to 48%. The structural characteristics of the tested specimens were compared with analytical relationships. In addition, a parametric study was conducted based on the analytical equations. © 2019 Elsevier Ltd
International Journal of Rock Mechanics and Mining Sciences (13651609)82pp. 10-21
To investigate the stability of ground surrounding shallow tunnel, an important step is to study the medium using the stress-strength method. The method includes the longitudinal convergence along tunnel. The studies done up to now are concentrated on the deep tunnels in the form of presenting a longitudinal deformation profile (LDP). It expresses relation for unsupported tunnel wall/crown by various researchers in terms of distance from excavation face along the tunnel. Of course, the effect of soil strength parameters is not considered in the relations yet. It is attempted in the current research work to propose a new concept of Longitudinal Convergence Profile (LCP) as alternative to Longitudinal Deformation Profile LDP. Then, a series of 3-dimensional analyses are conducted on a sample with conventional stratified environment observed in metropolitans. Finally, to include the effect of soil strength parameters, i.e., modulus of elasticity, cohesion and internal friction angle of soil on the LCP, a new set of relations is suggested. © 2015 Elsevier Ltd.
Rock Mechanics and Rock Engineering (07232632)46(2)pp. 341-357
The focus of this study is the empirical hydromechanical behaviour of the Ostur dam site rock mass. The area surrounding the dam mostly consists of diorite and andesite, with primary fractures and hydrothermal veins. The hydromechanical behaviour of the rocks was determined using 500 water pressure tests at 5-m intervals. The hydrothermal veins and 2,739 discontinuities were studied and mapped along the dam axis. As a result, it was possible to design an optimum grout curtain for the dam axis. The empirical hydromechanical behaviour of the rock was studied to determine water flow and grout pressurised flow during the field tests that were conducted on two representative A-series grouting operation boreholes (one borehole for each abutment). The secondary permeability index (SPI), Lugeon value (LU), rock quality designation (RQD) and cement take (CT) values are presented and compared in this article. It is concluded that permeability and groutability are mostly controlled by the specifications and characteristics of the veins, especially in shallow areas and lower depths. A procedure is proposed based on a comparison of the trends in the RQD-SPI and LU-CT, and it is suggested that the areas with diverging trends require no treatment and that those with converging trends require heavy treatment. Additional complementary studies that were conducted during the construction stage have validated these results. © 2012 Springer-Verlag.
Rock Mechanics and Rock Engineering (07232632)43(3)pp. 305-320
The results of geotechnical explorations, engineering geological investigation (including laboratory and in situ tests) and field observations have been used, along with borehole logging charts, to obtain the rock mass geotechnical data. Based on the data, the rock mass along the Sabzkuh water conveyance tunnel route was classified by rock mass rating (RMR), Q-system (Q), rock mass index (RMi) and geological strength index (GSI) (3 methods). A new series of correlations were established between the systems based on the data collected from the study area. These relationships were then compared with those reported in the literature, and two new relations were recommended. The classifications were utilized to calculate mechanical properties (rock mass strength and deformation modulus) of the rock mass along the tunnel according to available empirical relations, and to distinguish the upperbound and lower-bound relations. © Springer-Verlag 2009.
The Bazoft dam diversion tunnel with length of 450 m and diameter of 9 m is to be excavated in left abutment of Bazoft dam and the currently under study. The lithology mostly comprises of jointed Asmari and Jahrum limestones. The tunnel passes the AS2 zone of Asmari formation belongs to dolomitic limestones of Miocene age. The rock mass discontinuities orientations were studied by a field survey and a statistical analysis. Also the borehole logs and outcrop surveys were used to determine the basic characteristics of the discontinuities. The rock mass surrounding the tunnel is classified using the Q, RMR and GSI methods. The engineering properties and temporary tunnel support systems were determined based on the methods. A series of 3D analytical (stress-strength method) and numerical continuum (FEM) stability analyses were conducted for the rock mass surrounding excavation face based on the excavation scheme proposed by the empirical method based on RMR for supported and unsupported tunnel. Based on the analyses, there is no need for intense support installation. For verification and to determine the influence area of the face, the longitudinal displacement profile values were extracted, drawn and compared with the available literature. © 2010 International Society for Rock Mechanics. All rights reserved.
Rock Mechanics and Rock Engineering (07232632)43(1)pp. 69-87
In this article, the shear behavior of discontinuities caused by bedding planes of weakness between two different rock types with high strength difference is investigated. The effect of roughness and compressive strength of joint wall in such discontinuities are studied. The designed profiles consist of two regular and three irregular artificial joints molded by three types of plaster mortars with different uniaxial compressive strengths. Firstly, it is demonstrated that the shear behavior of discontinuities with different joint wall compressive strengths (JCS) is different from rock joints with identical wall compressive strengths by showing that Barton's empirical criterion is not appropriate for the former discontinuities. After that, some correlation equations are proposed between the joint roughness coefficient (JRC) parameter and some surface statistical/fractal parameters, and the normal stress range of Barton's strength criterion is also modified to be used for such discontinuities. Then, a new empirical criterion is proposed for these discontinuities in such a way that a rational function is used instead of JRC log10(JCS/σ n) as i 0(σ c/σ n)a/[b + (σ c/σ n) a ] by satisfying the peak dilation angle boundary conditions under zero and very high normal stress (physical infinite normal stress causing zero peak dilation angle). The proposed criterion has three surface parameters: i 0, a, and b. The reason for separation of i 0 from JRC is indicated and the method of its calculation is mentioned based on the literature. The two remaining coefficients (a and b) are discussed in detail and it is shown that a shows a power-law relationship with b, introducing the coefficient c through b = c a . Then, it is expressed that a is directly related to discontinuity surface topography. Finally, it is shown that the coefficient c has higher values in irregular profiles in comparison with regular profiles and is dominated by intensity of peak dilation angle reduction (majorly related to the surface irregularity and minorly related to roughness). The coefficient c is to be determined by performing regression analysis on experimental data. © 2009 Springer-Verlag.
Empirical rock failure criteria generally relates lateral stresses to axial strengths by a particular equation in which uniaxial tensile and/or compressive strengths are to be estimated from the failure criterion by applying the obtained parameters from triaxial datasets into the criterion equation. In order to satisfy the exact amounts of uniaxial tensile and compressive strengths in a failure criterion, a rational function is proposed as a failure criterion for isotropic, dry and intact rocks to be used in both tensile and compressive regions. The proposed criterion is validated by using 59 series of accurate triaxial test datasets which are belong to 20 different rock types selected from the literature. It has been shown that the proposed criterion is capable of predicting the triaxial behavior of rocks in both tensile and compressive regions. There are two coefficients for the proposed criterion ('c' and 'd') which have been estimated for used rock datasets by applying brittle-ductile transition as an initial boundary condition. The most proper brittle into ductile boundary, the confinement in which ∂τ/∂ σn=0 or in other words when ∂σ1/∂σ3=1, has been determined (σ3=ησc) in such a way that the best triaxial predictions have been obtained. Also, the values of the criterion coefficients are discussed in detail. © ISRM International Symposium on Rock Mechanics, SINOROCK 2009.
Landslides (16125118)6(2)pp. 101-109
The Siruyeh landslide occurred at the eastern side of the Siruyeh valley, 22 km west of Semirom city, south of Esfahān on 25th March, 2005 with large dimensions (2,400 m long, 450 m wide with total area of 1 km2). The sliding mass blocked the Siruyeh River making a 35-m-high natural dam and 6-acre lake 570,000 m3 in volume that poses a potential threat for the area. The landslide occurred in soil and intensely weathered marls of the Tarbur and Kashkan Formations (upper Cretaceous-Paleocene age). The overall comparison and interpretation of the gathered evidence from satellite images, field trips, and laboratory tests show that the most important factors involved in triggering the Siruyeh landslide in order of importance are heavy precipitation and snow melt and intense concentration of faults and fractures as well as weathered and weak lithology. © 2009 Springer-Verlag.
A rational function is proposed as a failure criterion for isotropic, dry and intact rocks to be used in both tensile and compressive regions. The criterion is capable of predicting the triaxial behavior of rock under low confinements satisfying the exact values of uniaxial tensile and compressive strengths. The capability of the rational criterion is assessed by applying brittle-ductile transition and downward concavity boundary conditions into the criterion introducing ë and ã parameters. The sensitivity of the criterion response is analyzed by varying under variation of ë and ã parameters. It has been shown that the Hoek's rule of thumb for brittleductile transition could be used for all types of rocks in low confinements and the proper boundary between low and high confinements is obtained. It was also experimental that the acceptable envelope could be obtained for low confinements using a dataset including only two triaxial tests together with uniaxial tensile and compressive strengths. Also, the parameters and concavity of the criterion have been discussed. © ISRM International Symposium - 5th Asian Rock Mechanics Symposium 2008, ARMS 2008. All rights reserved.
Dams are constructed to control the surface runoff. One of the important points involved in grouting operation and cut off curtain design is the geological and hydrogeological investigation of the site and evaluation of its groutability. The commonly method used for determination of permeability coefficient is water pressure test (WPT). The test includes measurement of water pressure (P) and discharge (Q) pumped in the drilled boreholes and its graphical representation as (P-Q) diagrams which can be interpreted to give rock mass hydromechanical behaviour. Based on the test designation, in Ostur dam site, 400 water pressure tests were conducted and analyzed. Results of these tests are used to determine the type of hydrogeomechanical behaviour. In the other hand, the test grouting was also conducted in continuation of the (WPT) operation and the results have shown that the bedrock of this dam is impermeable, with very low groutability potential. However, the shallow part of rock mass is partly affected due to weathering. The type of flow in these parts is identified as turbulent. From the other side, the rock mass is also intersected in deep parts by hydrothermal veins. The flow type in these parts is different from the shallow parts. © ISRM International Symposium - 5th Asian Rock Mechanics Symposium 2008, ARMS 2008. All rights reserved.
The Gardaneh Rokh tunnel is being excavated with the length of 1300m it axis striking of N28. The height of tunnel section is 8.6m and its width is 13m. To characteristics of the discontinuities were recorded from 5 outcrops as survey stations. A series of laboratory tests was conducted on the intact rock samples selected from cores taken from two boreholes to get the physical and geomechanical properties. The rock mass along the tunnel enroute was divided into 5 structural zones and were then classified based on the Q and RMR systems. The required support systems were also determined according to the systems. Regarding tunnel stability analysis, the tunnel inlet section as the weakest zone of rock mass located in km 6+300 (structural zone 5) is numerically modelled and analyzed using PLAXIS software with and without support system. The excavation and support installation process was modelled in 3 phases. The results of the numerical modelling show that the crown and sidewalls instabilities are mainly reduced by installation of partial shotcrete support in crown and sidewalls. However, the support installation even in lower sidewalls may not substantially reduce the displacements in invert.
International Journal of Rock Mechanics and Mining Sciences (13651609)41(SUPPL. 1)
There are various structural and geological stratigraphies in study area. The main lithology includes the shale, marl, limestone and dolomite that belong to the Cambrian to upper Cretaceous besides Quaternary deposits. To identify the engineering and geotechnical characteristics of the rock mass along the tunnel route, the results of laboratory and in situ tests, geophysical explorations (geoelectrical methods), field observations and borehole logging charts have been used. The well-known rock mass classification systems for tunnelling purposes (RMR, GSI and Q-system) have been used. Using the GSI classification system for rock mass, the modified Hock- Brown criterion parameters of the rock mass for typical section were determined. The RMR was used to determine the required support for the entire length of tunnel. Also the Q system was used to compare the required support from Q system with the RMR system. Finally rock-support interaction analysis was conducted for a typical cross section of the tunnel. Using the above empirical and analytical methods, the required supports were compared for a typical section. © 2004 Elsevier Ltd.
