Bearing Capacity Of Rock Mass Research Articles

A comparative study on the estimation of ultimate bearing capacity of rock masses using finite element and limit equilibrium methods

Most rock masses are excellent foundation materials due to their bearing capacities of MPa. However, the ultimate bearing capacity of rock masses should be accurately estimated in the design of structures with high foundation loads. In this study, the ultimate bearing capacities of a strip footing built on rock masses with different geotechnical properties are determined using the finite element method (FEM) and the failure criterion of Hoek & Brown. The results of FE-analyses are compared to those obtained from the limit equilibrium methods (LEM) in the literature. It has been shown that the FEM with associated flow rule and Terzaghi`s limit equilibrium method give similar failure surfaces for most cases, and the ratio of ultimate bearing capacities determined according to the Terzaghi´s method to FEM varies between 1.5 and 4. In cases, in which the failure surfaces obtained from both methods differ, this ratio can rise up to 11.aring capacities determined according to the Terzaghi´s method to FEM varies between 1.5 and 4. In cases, in which the failure surfaces obtained from both methods differ, this ratio can rise up to 11.

The influence of the void shape in the bearing capacity of rock mass with a superficial void

In this study is proposed a chart that allow estimating the reduction of bearing capacity due to the existence of a superficial void in a rock mass. It is contemplated the influence of different shapes and size of the void in relation to the foundation. The reduction of the bearing capacity is analyzed through the Finite Difference Method. In the numerical model, six possible cavity shapes are considered, with three different sizes and depths. Calculations are made considering eighteen types of rock masses, modelled by the H&B failure criterion. The results demonstrate that the critical depth where the cavity no longer influences the bearing capacity varies considerably depending on the geometric variables (size, shape and location of the void). In addition, it is observed that the relation between the bearing capacity obtained considering the rock mass with and without void is not affected by the geotechnical parameters of the H&B failure criterion. According to the results analyzed and graphic output, the variation in the stress distribution in the rock mass and the change of the failure mechanism under the different hypotheses studied can be observed. The results are presented in chart that facilitate to directly estimate the reduction of the bearing capacity of a rock mass with void based on geometric parameters.

Analytical and Numerical Solutions for the Effect of Seepage on the Bearing Capacity of Rock Masses

Analytical and Numerical Solutions for the Effect of Seepage on the Bearing Capacity of Rock Masses

Precising the Bearing Capacity of Rock Masses Subjected to the Loads of Adjacent Footings Considering Two Failure Mechanisms

Precising the Bearing Capacity of Rock Masses Subjected to the Loads of Adjacent Footings Considering Two Failure Mechanisms

Qualitative and Quantitative Investigations on the Failure Effect of Critical Fissures in Rock Specimens under Plane Strain Compression.

To investigate the failure effects of critical fissures in rock specimens subjected to plane strain compression (PSC), five types of internal fissures in rock specimens were designed and twelve PSC tests were conducted for two lithologies based on the discrete element method (DEM). The results were analyzed in terms of the fracture mode, data characteristics, and crack evolution. The results indicated the following. (1) The rock samples with a critical fissure under PSC showed a weak face shear fracture mode, which was influenced by lithology, fissure angle, and fissure surface direction. (2) There were four critical expansion points (CEPs) of axial stress of the rocks under PSC, which were the stage signs of rock materials from local damage to complete fracture. The rock-bearing capacity index (RockBCI) was further proposed. (3) The bearing capacity of rock samples with horizontal fissures, fissures whose angles coincided with the fracture surface, and fissures whose surface was perpendicular to the lateral confine direction was the worst; their BCI2 values were found to be 80.6%, 70.8%, and 56.9% of the rock samples without any fissures, respectively. The delayed fracture situation under PSC was identified and analyzed. (4) The crack evolution followed the unified law of localization, and the fissures in the rocks changed the mode of crack development and the path of the deepening and connecting of crack clusters, as well as affecting the time process from damage to collapse. This research innovatively investigated the behavior characteristics of rock samples with a fissure under PSC, and it qualitatively and quantitatively analyzed the bearing capacity of rock mass from local damage to fracture.

Ground Characteristic Curve and Convergence Confinement Method - A case study

Ground Characteristic Curve (GCC) describes the relationship between the initial stress of rock mass and the displacement of rock mass on the boundary of tunnels. Another way that indicates the relationship of support pressure and the level of Convergence Confinement of tunnels by percent. The using GCC to design supports in the underground construction has many advantages to ensure full utilization of the loading bearing capacity of rock mass, and release a part of initial stress in the rock mass around tunnels. However, this method is limited in the field of underground mines in Viet Nam. This article analyzed and applied GCC and Convergence Confinement Method (CCM) to design the supports of underground constructions and applied them to the geological conditions of the Nam Mau coal mine - Vinacomin. The research results show that at the geological conditions of the drift at level +125 in Nam Mau coal mine, TH section steel ribs with flange width 124 mm, section depth 108 mm, weight 21 kg/m, maximum support pressure 1.98 MPa, and spacing 700 mm were applied. Results of research in this method can be applied to design rock supports for deep roadways and other drifts in the underground mines in Quang Ninh province of Viet Nam. By a factor of safety, mobilized support pressure, wall displacement of roadways, and convergence of roadways the designation and selection of rock support around roadways will become clearer. Near future this method should be widely applied in the combined protection design in deep roadways in underground mines in Viet Nam. Although the method has great advantages, it is still necessary to have complete and detailed monitoring data of the geological and hydrogeological conditions in the area under consideration.

Numerical Simulation of Large Compression Deformation Disaster and Supporting Behavior of Deep Buried Soft Rock Tunnel with High In Situ Stress Based on CDEM

Large compressive deformation of tunnels is a phenomenon involving plastic deformation and failure of surrounding rocks and often refers to the weak surrounding rock self-bearing capacity loss or partial loss. This research discusses the formation and evolution of large compressive deformation and effectiveness of the combined support of high in situ stress tunnel. From the new perspective of large deformation disaster caused by the structural failure of high in situ stress surrounding rock to clarify it, this paper illustrates the mechanism of progressive cracking and large deformation of high in situ stress soft rock tunnel from the aspects of the formation of self-bearing system, deformation evolution of the surrounding rock, mechanical properties of the surrounding rock, and failure characteristics. Accordingly, the continuous and discontinuous numerical simulation methods are used. The following conclusions are drawn by comparing the simulation results of surrounding rock under combined support with no support. (1) The supporting structure constitutes the self-supporting system with the surrounding rock and plays the roles of codeformation and load-bearing. (2) The support structure has evident reinforcing effect on the rock mass in the relaxation zone, thereby leading to the phenomenon of weakened rock mass failure. Moreover, the shear area develops to the compaction zone. (3) The supporting structure improves the bearing capacity of rock mass in the relaxation zone. It also increases the surrounding rock stress and reduces the range of the compaction zone. Simulation results verify that the combined support measures have a good suppression effect on the large compressive deformation, thereby providing a reference for similar projects and research on the large compressive deformation of soft rock.

Discussion on “Ultimate Bearing Capacity of Rock Masses under Square and Rectangular Footings”

Discussion on “Ultimate Bearing Capacity of Rock Masses under Square and Rectangular Footings”

Application of discontinuity layout optimization method to bearing capacity of shallow foundations on rock masses

AbstractThe discontinuity layout optimization (DLO) method is applied to obtain the bearing capacity of rock masses where it is necessary to consider a non‐linear resistance law. In rock mechanics, it is widely accepted the modified Hoek & Brown failure criterion, developed for homogeneous and isotropic rock masses. The results obtained with the DLO method are compared with those obtained from the analytical solution and using the finite differences method (FDM). To validate the DLO numerical method, the same hypotheses of the analytical solution are adopted: plane strain conditions, associated flow rule, Hoek & Brown material, and weightless rock. The research analyses the results of a numerical and analytical study based on a sensitivity study varying the three parameters that characterize the rock mass (rock type, uniaxial compressive strength, and geological strength index) and shows the need to adopt an adequate linearization of the non‐linear failure criterion in the numerical calculations. Furthermore, numerical results are obtained considering the self‐weight of the rock mass, using both DLO, considering the intermediate secant linearization proposed in this investigation, and FDM, implemented in a widely accepted geotechnical software. After comparing the results, the advantages and limitations of the DLO method are pointed out.

Effect of Load Inclination on the Bearing Capacity of Jointed Rock Foundations

In this paper, upper bound method of limit analysis is used to obtain the vertical and inclined bearing capacity of rock masses containing two orthogonal joint sets. The spacing of the joint sets is assumed to be large compared to the footing width. Different orientation angles are considered for the joints, and the Mohr–Coulomb failure criterion is employed for both the intact rock and the joint sets. Analytical expressions are derived for the bearing capacity of a strip footing resting on a jointed rock subjected to vertical loading. Then, the effect of load inclination on the bearing capacity is incorporated into the analytical equations by means of inclination coefficients. The findings are compared to the other solutions existing in the literature. The results of this study show that increasing the joint friction angle leads to decreasing the inclination coefficient. Moreover, increasing the joint orientation angle with respect to the horizontal direction results in decreasing the inclination coefficients. The obtained results are presented in tabular form that can be used easily for practical purposes.

Upper bound solution for the bearing capacity of two adjacent footings on rock masses

In this paper, the effect of the adjacency of two strip footings on bearing capacity of rock masses was investigated using the upper bound analysis and finite element method. The modified Hoek-Brown nonlinear failure criterion was used for the rock mass. The effect of various parameters such as the distance between the two footings, Hoek-Brown parameters, surcharge pressure and unit weight of the rock mass on the ultimate bearing capacity of rock masses were also investigated. The results show that if the distance between the two footings is significant, the failure lines occur beneath each footing will not interfere with the failure lines beneath the other adjacent footing and each footing behaves as a single one. The maximum distance for which the two footings affect each other can be obtained from the charts presented in this paper. By reducing the distance between the two footings, the bearing capacity will increase firstly and then decrease. Finally, when the two footings touch each other, the ultimate bearing capacity of the two footings will be equal to the ultimate bearing capacity of a single isolated footing with a width twice the width of each footing.

Upper bound solution for the bearing capacity of rock masses considering the embedment depth

The effect of the embedment depth is one of the most important issues in calculating the bearing capacity. The results of the previous studies show that in most cases, it was assumed that the footings are rested at the ground surface and the effect of the embedment depth was considered by applying an equivalent surcharge load to the ground surface. In this paper, the influence of the embedment of the footings on the bearing capacity of weak rock masses was investigated using the upper bound method of limit analysis. The modified Hoek–Brown failure criterion was used for the rock mass. The embedment depth of the footings was considered directly in the upper bound calculations. According to the obtained results, considering the embedment depth results in increasing the ultimate bearing capacity, which cannot be anticipated correctly in the methods which replace the embedment depth by an equivalent surcharge. The results of this paper were presented in the form of a design table that can be used easily in practical applications.

Effects of Embedment Depth of Foundations on Ultimate Bearing Capacity of Rock Masses

The embedment depth of footings is an essential factor affecting the bearing capacity of base material. In most bearing capacity determination methods, the effect of the embedment depth was considered by applying an equivalent vertical stress to the ground surface. This simplifying assumption excludes the effect of the shear strength of the rock mass at the levels above the footing base. In the present paper, a bearing capacity equation was obtained for rock masses in which, the effect of the embedment depth of the footing was considered directly without replacing its equivalent vertical stress. Using the upper bound method, the Hoek–Brown failure criterion was employed for the rock mass. The results revealed that the incorporation of the embedment depth results in considerably greater bearing capacity than the cases in which, an equivalent surcharge was used. Therefore, it is important to consider the footing embedment depth for optimal design of foundations.

Experimental Study on the Mechanical Properties and Crack Propagation of Jointed Rock Mass Under Impact Load

A drop hammer impact test on jointed rock masses is carried out in this study. According to the analysis of the effect of different joints on the strength, the deformation and the damage of jointed rock masses, the law of the mechanical properties and crack propagation of jointed rock masses is observed under impact load. First, when the dip angle and the number of the joint are greater, the dynamic bearing capacity of rock masses will be weaker. Meanwhile the deformation and the damage of rock masses will increase. Then, when the impact load is small, the dynamic compression deformation of jointed rock mass is mainly due to the normal closure of joints. After the impact load increased, more microcracks are produced around the joints. These cracks will gradually spread along the joints and finally lead to the damage of jointed rock masses. Besides, the joint can increase the stress waves energy dissipation and weaken the propagation of the stress waves in the rock mass. The study provides a reference for the dynamic analysis of fractured rock masses and the excavation support of surrounding rock mass in deep mining of mines.

Ultimate bearing capacity of rock masses under square and rectangular footings

This paper investigates the ultimate bearing capacity of Hoek-Brown rock masses under square and rectangular footings using three dimensional finite element analyses. Analyses were conducted for different dimensions of footings and also for various rock mass properties.The results obtained show that the bearing capacity increases with increasing rock mass Hoek-Brown parameters. Furthermore, by increasing dimensions of the footings, total tolerable load will increase. It is also concluded that in the case of square and rectangular footings, three dimensional bearing capacity analyses should be performed, while the existing two dimensional methods result in over estimation of the bearing capacity.

Bearing capacity and slope stability assessment of rock masses at the Subasi viaduct site, NE, Turkey

This study investigates the bearing capacity of rock masses and stability of slopes at the Subasi viaduct site which is a part of the improvement project of the Artvin–Hopa government highway between KM 6 + 500 and 13 + 787 in NE Turkey. The geotechnical studies were performed in three stages. Firstly, the bearing capacity of moderately weathered andesitic tuff was evaluated using the empirical equations. Secondly, the major principal stress and vertical displacement due to the viaduct and traffic loadings at the level of foundations were determined by the finite element method (FEM). The vertical displacement value and comparison of bearing capacity and major principal stress show that any problem is not expected at the viaduct site in terms of the bearing capacity. Finally, the stability of slopes at the viaduct site was investigated using kinematic, limit equilibrium, and finite element method-based shear strength reduction analyses methods. It was concluded that no discontinuity controlled failures at the slopes are expected. However, a circular failure is possible to occur at the face slope excavated in highly weathered andesitic tuff. After support application, the long-term stabilization of face slope has been achieved. Consequently, it is suggested that the empirical, analytical, and numerical methods should be combined for a more reliable construction design.

Ultimate bearing capacity of rock masses based on modified Mohr-Coulomb strength criterion

•A method for calculating the bearing capacity of spread foundations in rock is presented.•Bearing capacity of spread foundations on rock masses based on modified Mohr-Coulomb strength criterion.•Charts and figures are presented for a quick obtaining of bearing capacity for shallow foundations.•Comparison of the ultimate bearing capacity using the Hoek and Brown criterion and the modified Mohr-Coulomb strength criterion.

Numerical Tests on Laterally Loaded Drilled Shafts Socketed in Rock

Ultimate lateral bearing capacity of rock mass is the base of the research of laterally loaded drilled shafts socketed in rock mass. The ultimate bearing capacity is often not available because of the limitation of loading ability in field tests. Numerical tests are used here to simulate the drilled shafts socketed in rock mass and expand the load-displacement curve obtained from field tests. Common methods of determining ultimate lateral bearing capacity are also analyzed and compared here. At last, a relatively accurate method of determining laterally loaded drilled shafts socketed in rock mass is recommended.

Modeling of Ultimate Bearing Capacity of Shallow Foundations resting on Jointed Rock Mass

Ultimate bearing capacity of jointed rock mass specimens, studied by distinct element software UDEC which allows explicit modelling of blocks of rock, is presented in this paper. Since the other numerical methods like FEM considers the rock mass as continuum, their applicability to anisotropic blocky rock masses remains doubtful. A series of numerical tests has been conducted, by developing a programme using fish functions, on rock mass having two orthogonal joint set with the joint orientation from 0° to 90°. Simple models have been assigned to rock material and joints. An experimental study was conducted by Bindlish (Bearing capacity of strip footings on jointed rocks, 2007) wherein a rigid footing placed on the top surface of the jointed rock mass was loaded up to the failure. The effect of the joint orientation and interlocking of rock mass on the ultimate bearing capacity of the rock mass was studied. The numerical findings by distinct element software UDEC on the ultimate bearing capacity of the jointed rock mass have been found to be close to the experimental results obtained by the author.

Distinct element simulation of ultimate bearing capacity in jointed rock foundations

In this paper, distinct element method numerical modeling is applied to evaluate bearing capacity of strip footing rested on anisotropic discontinuous rock mass. As yet, a little work has been carried out to investigate the effect of joint set orientation on the bearing capacity of rock mass. Generally, the overall behavior of rock mass under loading is very complicated and such analysis should include deformation determination, sliding along discontinuities and failure of rock material. Failure mechanism of rock mass depended on both geometrical parameters of joint sets and strength parameters of rock mass. In this research, it is assumed that rock mass contains one joint set, and therefore the anisotropy in bearing capacity and rock behavior is only due to the existence and orientation of the joint set. In this study, by assuming constant strength parameters and using Mohr–Coulomb failure criterion for the single joint set and nonlinear Hoek–Brown failure criterion for rock material, variation of the bearing capacity values and the type of failure mechanism of rock mass with different joint set dips is investigated. The obtained results indicate that the ultimate bearing capacity of rock mass containing one joint set varies between 27 and 86 % of intact rock.