30 research outputs found
Experimental and Numerical study of earth slope reinforcement using ordinary and rigid stone columns
Get PDFEarth slopes stabilization is one of the main issues focused on by are in geotechnical engineer. Use of stone columns is one of approaches well increasing the safety factor of earth slopes of the soil embankments; furthermore, it is economical besides the simplicity and ease it exhibits in implementation. . The present paper aims at an experimental comparison of the Ordinary Stone Column (OSC) and Rigid Stone Column (RSC) behaviors in sandy slope. These tasks were carried out by constructing embankment sandy slope and, then, saturating it with rain and, finally, loading increment. The experimental results, obtained in laboratory modeling through taking advantage of three-dimensional finite difference method, have also been verified. Laboratory modeling and numerical analyses results have shown that the existence of rigid stone column in the middle of slope (as the optimal placement location) enhances sandy slope stability up to 1.36 times compared with slope reinforced by ordinary stone columns
Coupled effect of tire-derived aggregate and geogrid on lateral earth pressure on high-filled cut-and-cover tunnels
Get PDFFor the possibility of using valuable lands with plateaus terrain, the High-filled cut-and-cover tunnels (HFCCTs) are considered a practical and successful solution. The HFCCT is first constructed and then backfilled in layers in the trench, which is different from traditional tunnel construction methods. Because the high amount of backfill soil above the HFCCT produces ultrahigh earth pressure, it is necessary to use load reduction methods to reduce the earth pressure on the HFCCT, which will reduce the tunnel designing structure loads and increase safety. This study describes two load reduction methods using a combination of tire-derived aggregate (TDA) and geogrid. Abaqus CAE 2019 software, based on the finite element method, was employed to analyze and examine the lateral earth pressure (LEP) reduction progress and mechanism. Several influential factors, including the geogrid presence effect, the TDA form, the TDA thickness, and the distance between the top of the HFCCT and the bottom of the TDA were studied. The analysis results focused on changes in average LEP, relative vertical displacement of the HFCCT backfill soil prisms, and the effect of geogrid presence on the top of the TDA. This study found that the factors are influential and have significant effects on the average LEP reduction on the HFCCT through the load reduction mechanisms, which include relative vertical displacements of the HFCCT backfill soil prisms and soil arching, where the average LEP on the top of the HFCCT model reduced from 303 kPa to 125 kPa (58.745% reduction in the average LEP)
Effect of the chemical compounds of soil on the stability of excavation wall: A case study
Get PDFChemical compounds of soils can remarkably affect the stability of the excavation wall. This is highlighted in soils with fine grain materials. Inter-particle chemical cementation (IPCC) increases soil cohesion and, in turn, provides more stable excavations. This study evaluates the effect of soil chemical compounds on the stability of an excavation excavated in the west of Iran, Kermanshah city. It adopted the 2D finite element method (2DFEM) to evaluate the physical stability of the excavation. In the excavation examined here, the maximum depth that could be excavated with no need for support was 36m. In contrast, according to simulation results, the maximum possible depth for an excavation with soil cohesion of 6kPa and friction angle of 33 degrees, derived from direct shear test, is 6m. As per the results of this investigation, iron oxide, aluminum oxide, and silicon oxide increase the soil's cohesion containing the clay mineral montmorillonite by 10 folds and increase its shear strength by 127%
Predicting three-dimensional displacement around the tunnel and its impact on the value of Q-system
No full textHaving knowledge of stability of an underground space depends on stresses and strains around it. Creating underground tunnels leads to significant changes in the rock mass stress. Therefore, to achieve the necessary stability, stresses and deformations around the tunnel must be examined carefully. Usually, stress-strain behavior analysis is conducted in two-dimensional mode. This paper was conducted to compare two-dimensional and three-dimensional analysis of deformation around the tunnel proposed as new work in relationship between the two-dimensional and three-dimensional deformation. Then, its impact on the value of Q-system in seismic mode is studied. Two-dimensional analyses are usually conservative. Therefore, the proposal relationship between two-dimensional and three-dimensional mode will lead to reduced costs and save in support materials. The results of different analyses in the intact and sparsely jointed rock masses show that displacement around the tunnel is greater in two-dimensional analysis compared with three-dimensional analysis. However, in the heavily jointed rock masses, displacement around the tunnel is lower in two-dimensional analysis than three-dimensional one. As three-dimensional analyses are closer to reality, results of equations proposed in this paper can be used to calculate three-dimensional displacement. Different analyses for intact or sparsely jointed rock masses carried out in 2D and 3D states. According to conclusions made, the new equation proposed between 2D (U_2D) and 3D (U_3D) displacement. Data obtained by local measurements (3D) and the results of the 2D analyses for heavily jointed rock masses were compared. Then relationship between 2D and 3D displacements in the heavily jointed rock masses proposed. The results of this research have been applied for tunnel of Gavoshan Dam in West of Iran. There is good consistency between equations proposed in this paper and three-dimensional analyses
Performance of Reinforced Stone Column using Geotextile & Geogrid Encasements in Triaxial Test
No full textThe use of stone columns is one of the effective ways to increase the bearing capacity of soils. An alternative system that can provide sufficient lateral confinement to support stone columns and increase bearing capacity is geosynthetic encased stone columns. These methods have been well utilized in Europe and South America. If the soil bed requires excessive confinement, the use of geotextile and geogrid encase around the stone columns is one way to improve the performance of these load-bearing members. This study aims to compare the behavior of geotextile and geogrid layers in reinforcing stone columns in standard Ottawa sand. In this study, a series of triaxial experiments in the undrained state was used. In the lowest confining pressure case, the load-bearing capacity for the geotextile reinforced column will be 1.18 times higher. Whereas for the geogrid-reinforced stone column, the load-bearing capacity is 1.31 times higher. In this study, standard Ottawa sand, gravel with a unit weight of 17 kN/m3 and a friction angle of 47.8°, geotextile and geogrid layers, and triaxial test apparatus are used. Triaxial specimens were 10 cm in diameter and 20 cm in height. Stone column dimensions of 2 cm in diameter and 20 cm in height are selected, respectively. Due to the limitations in the laboratory and the simulation of natural conditions, the unit weight of sand samples and stone columns made in triaxial test molds were selected as 15 and 17 kN/m3, respectively. Precipitation is used to fabricate cylindrical sand samples for triaxial testing. In this method, firstly attach the membrane to the underside of the triaxial apparatus and fasten the detachable bifurcation mold to the membrane and attach the membrane to the detachable mold walls by suction pumping about 2 bars. The aim is to create a homogeneous sample with uniform rainfall velocity to obtain a sample with evenly possible porosity. The method of precipitation depends on two parameters, one is the intensity of rainfall (amount of sand poured in a given volume at a specified time), and the other is the height of the sand fall, which is the distance between the sand outlet from the precipitation tank to the sand bed. The important point is that to achieve the same porosity, and this distance must be kept constant throughout the precipitation process. After construction, the test is performed according to ASTM D7181-11. Triaxial CU experiments on Ottawa sand were carried out in three cases: unreinforced, reinforced using geotextile encased stone column and reinforced using geogrid encased stone column. In triaxial experiments, three confining pressures of 200, 300, and 400 kPa were used
FE ANALYSIS OF UNDERGROUND DAM AND IMPORTANT POINTS IN UNDERGROUND DAM-A CASE STUDY, ABKHORI UNDERGROUND DAM
No full textمدیریت منابع آب در کشور های کم آب از جمله ایران از موارد اجتناب ناپذیر است. یکی از راههای موثر مدیریت منابع آب احداث سد های زیرزمینی است. سد های زیرزمینی به منظور ذخیره و کنترل آب زیرزمینی طراحی و احداث می شوند تا آب قابل شرب در دسترس قرار گیرد. از محاسن سد های زیرزمینی نسبت به سدهای احداث شده بر روی سطح زمین، تبخیر بسیار کم و بهداشتی ماندن آب در مخزن سد است. از طرف دیگر اجرای سد های زیرزمینی در مناطق کویری تاثیر منفی بر محیط زیست ندارند زیرا از جریان آب شیرین به محیط های شور کویر جلوگیری می شود. در این مقاله روش اجزای محدود برای تحلیل سد زیرزمینی در منطقه ی کویری استان سمنان ارائه گردیده است. همچنین نکات موثر طراحی و اجرایی این گونه سد ها ارائه می گردد که در طراحی و اجرای صحیح این گونه سد ها بسیار موثر هستند. نتایج حاصل از تحلیل پایداری و تغییر مکان سد، نتایج خوب و قابل قبولی می دهد. در پایان این چکیده گزاف نیست اگر گفته شود که با توسعه و پیشرفت احداث سد های زیرزمینی در دنیا می توان از جنگ های آینده ی بشر بر سر آب شیرین جلوگیری کرد
Experimental investigation of the effect of using expanded polystyrene geofoam and geogrid in different forms on vertical earth pressure on high-filled cut-and-cover roadway tunnel
No full textAbstractUsing high-filled cut-and-cover tunnels (HFCCTs) can provide a practical and ideal solution for the possibility of using highly demanded lands with plateaus terrain. The huge amount of HFCCT backfill soil produces ultrahigh vertical earth pressure (VEP). Therefore it is necessary to use load reduction methods and mechanisms to reduce the VEP on the HFCCT, which will reduce the risks and increase safety by reducing the tunnel designing loads. This experimental study describes methods of VEP reduction on the HFCCTs using expanded polystyrene (EPS) geofoam as a compressible material in two different forms without and with the presence of geogrid on top of the EPS. Several important factors, including the effect of geogrid presence on top of the EPS, the EPS form, the EPS thickness, and the distance between the bottom of the EPS and the top of the HFCCT discussed and studied. It determined from the study results that the mentioned factors have significant effects on the VEP reduction on the HFCCTs through their roles in the VEP reduction mechanisms. This study adopted two VEP reduction mechanisms; relative vertical displacements of the HFCCT backfill soil prisms and soil arching. The mentioned two mechanisms caused a significant reduction in the VEP on the top of the HFCCT, where the best result was a 76.0% reduction in the VEP on the HFCCT
A NEW APPROACH FOR STABILITY ANALYSIS OF SOIL SLOPES USING A LIMIT EQUILIBRIUM METHOD
No full textSlope stability analysis is used in a wide variety of geotechnical engineering problems such as embankments, road cuts, open-pit mining, excavations, canals, landfills, etc. The limit equilibrium method is the most popular approach in slope stability analyses. In this study, a new limit equilibrium method is proposed that can satisfy the forces and moment without any assumptions. In this method, circular or non-circular slip surface has been considered and slices are intended along the radius of the slip surface. Innovation of this research is in the form of slices in circle sector which could eliminate the common simplifying assumptions in the equilibrium equations. The forces and moment equilibrium equations have been applied without any simplifying assumptions and expected that this method can achieve lower error in determining the safety factor. In order to calculate the safety factor using the proposed method, a numerical model has been developed. In this model, the soil slope characteristics such as slope geometry, soil strength properties, seismic coefficient and also water level are considered as input. Then sliding wedge is introduced and on the basis of number of divisions that the user defines, sliding wedge is discretized. In the next step, the coordinates of each node of these slices are determined. To compute the safety factor, a process should be taken that satisfies the force and moment equilibrium equations simultaneously. To achieve this goal, the iterative method (trial and error) is used in this study. In order to evaluate the proposed method and the efficiency of the developed model, several tests with different conditions are solved. The mentioned test results are in good agreement with the results of other methods that satisfy all of the equilibrium equations
An experimental and numerical investigation of reinforced slope using geotextile encased stone column
No full textApplication of Spatial Supporting Construction as an Effective Method for Stabilising a Landslide
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