FLAC3D Software Research Articles

Study of the Stability Control of Rock Surrounding Longwall Recovery Roadways in Shallow Seams

The rock pressure appearance of longwall faces in shallow seams is generally violent, and roofs and supports are susceptible to damage during equipment extraction. Stability control of the rock surrounding longwall recovery roadways allows safe and rapid equipment extraction. Herein, via theoretical analysis, numerical simulations, and field observations, the stability control of the rock surrounding recovery roadways is studied to ensure the release of the accumulated rock pressure on the roof, the working resistance of the supports and the reasonableness of the recovery roadway support design. Pressure-relief technology is introduced to release the accumulated rock pressure before equipment extraction, and a discriminative approach is proposed to determine the breaking and articulated forms of key strata and broken blocks, respectively. On this basis, mechanical models of roof instability are established based on four key stratum structures in the overburden of shallow seams. Methods for calculating a reasonable working resistance for supports are discussed. Finally, Liangshuijing Coal Mine and Fengjiata Coal Mine are taken as research objects to evaluate the roof stability of recovery roadways based on observations of weighting characteristics. The support working resistances and reasonable recovery roadway widths under three key stratum structures are determined. Considering the time effect of plastic zone development, the support design of recovery roadways is optimized. FLAC2D software simulates the surrounding rock control effect of two support designs, and roof subsidence curves are obtained. The results show that the key to equipment extraction in shallow seams is to ensure that supports have reasonable working resistances and to improve the support of recovery roadways. The results provide a reference for the selection and extraction of supports in shallow seam faces.

Seismic behavior of cantilever wall embedded in dry and saturated sand

The embedded cantilever retaining walls are often required for excavation to construct the underground facilities. Significant numbers of numerical and experimental studies have been performed to understand the behavior of embedded cantilever retaining walls under static condition. However, very limited studies have been conducted on the behavior of embedded retaining walls under seismic condition. In this paper, the behavior of a small scale model embedded cantilever retaining wall in dry and saturated sand under seismic loading condition is investigated by shake table tests in the laboratory and numerically using software FLAC2D. The embedded cantilever walls are subjected to sinusoidal dynamic motions. The behaviors of the cantilever walls in terms of lateral displacement and bending moment are studied with the variation of the two important design parameters, peak amplitude of the base motions and excavation depth. The variation of the pore water pressures within the sand is also observed in the cases of saturated sand. The maximum lateral displacement of a cantilever wall due to seismic loading is below 1% of the total height of the wall in dry sand, but in case of saturated sand, it can go up to 12.75% of the total height of the wall.

A 3D Creep Model considering Disturbance Damage and Creep Damage and Its Application in Tunnel Engineering

Based on the Kachanov damage theory and elastic wave theory, considering the long-term creep damage from time dimension and instantaneous disturbance damage from space dimension, we presented a 3D damage creep model and converted it to difference expressions in order to write into the finite difference software FLAC3D. Then, according to the results of creep tests, we conducted parameter inversion of our damage creep model with the help of the particle swarm optimization (PSO) method. Finally, the damage creep model was applied in a railway tunnel project in Yunnan to simulate the tunnel deformation. Compared with the Burgers model and the model considering only creep damage, our model which considers both creep damage and disturbance damage yielded more reasonable results.

Research on the safe mining depth of anti-dip bedding slope in Changshanhao Mine

Safe mining depth constitutes the key to the open-pit mine development, it is significant to research the safe mining depth. First, According to the field geological investigation and geophysical exploration, the existing landslides were summarized and analyzed to obtain the potential destabilization and failure modes in mine, which laid the effective reference for the slope stability analysis in the Changshanhao mine. Then, The entire three-dimensional calculation model of north-east pit was established through FLAC3D software. According to the calculation results of displacement nephograms, plastic zone and shear strain, it was concluded that the entire instability might occur during excavation of the north-east pit in accordance with the designed final boundary. Following, ten sections of north-east pit were selected to calculate the slope stability through 3DEC software, and four types of mining depth elevation designed for each section were considered. According to the numerical calculations of each slope stability under different mining depths, for ensuring the mining safety of north-east pit, the boundary that is 84 m higher than the final boundary is recommended, thus the safe mining depth elevation and ultimate stable slope angle were determined as 1216 m and 38 degrees, respectively. Under the proposed safe mining depth condition, the slope of north-east pit can keep its stability, laying a basis for the safe mining depth determination of similar open-pit slopes.

Study of Damaged Zone around Circular Opening Using Acoustic Emission Technique

One of the methods used to investigate the damaged zone in rock structure is the acoustic emission method. This method is based on receiving the elastic waves that are produced by deformation and cracking of the rock mass around the underground excavation. In this research, a study is conducted on the rock samples by a numerical method to investigate the damaged zone caused by the excavation of circular space on it. For this purpose, 33 cube samples of three different material types including sandstone, concrete, and cement-plaster mortar are prepared. A circular hole is drilled in the center of each sample. The hole diameter is 20 or 25 mm. The samples are loaded uniaxially or biaxially with different stress rates. It is tried to study the acoustic events occurring in the samples during the test, and their locations are investigated. Then the experiments are evaluated by a numerical method using the FLAC3D software and some developed codes. The relation between the sample damaged zone where the acoustic events have occurred during the loading period and the numerical elements that reach a degree of tensile and shear yield is studied. The results obtained show that the amount of cumulative acoustic parameters in cement-plaster mortar specimens is more than the others. In fact, the finer grains, the more amounts of energy and counts will be produced. Also, the results show that with increase in the lateral pressure and loading rate, the amount of cumulative energy and counts decreases.

Analysis of Ground Settlement in Metro Tunnel Construction with Shield Tunneling Method

With the continuous development of underground space, subway tunnel construction methods are constantly updated and developed. And shield tunnel method has become one the most common methods of subway tunnel construction. However, shield construction is often accompanied with the occurrence of surface subsidence. There may be a collapse of the surface when the surface settlement reaches a certain amount and the up buildings on the surface may be seriously influenced. The construction model was established based on FLAC3D software by using the engineering geological characteristic parameters of the study area and the observation data of ground subsidence during construction, which was compared and verified with the field vmonitoring value, and the subsidence was simulated and predicted. Using FLAC3D to establish a settlement prediction model for tunnel excavation and record the space-time changes of surface subsidence, it can better reflect the land subsidence situation and law in the horizontal and vertical directions of the axis of the subway tunnel.

The effect of engineering geology on the rock load and squeezing potential in Lot2 of Imamzadeh-Hashem tunnel

The load entering from the ground surrounding on the tunnel’s lining is one of the effective parameters in the designation of a tunnel. The amount of this parameter, which is called Rock load in a rocky environment, depends on several factors such as the overburden thickness, geological and geomechanical conditions and the depth of tunnel. In the present study, the amount of rock load for the Lot 2 of Imamzadeh Hashem Tunnel (L2IHT) has been evaluated using various methods and the effect of geological characteristics of the rock units on the tunnel route has been investigated. For this purpose, different methods for estimating the rock load were introduced firstly, and then the amount of this parameter for the tunnel was estimated using these methods. To evaluate the thickness of the plastic zone around the tunnel, the numerical method, finite difference code of FLAC3D software, has been used. Comparison of the results obtained from different methods and their analysis indicates that the rock load applying from H-4 and H-10 rock units is more than the other units. This happens because of the specific geological characteristics of these rock units such as high degree of crushing due to the geological factors and being in the faulted zone. Therefore, it is required for the stronger lining of the tunnel in the range of these units.

Bearing capacity of shallow foundation under cyclic load on cohesive soil

Abstract The bearing capacity of shallow foundations under static loads has been widely studied by various authors. In contrast, the bearing capacity under dynamic loads has been solved indirectly by adopting an equivalent pseudostatic approach or by means of reduction coefficients. The study of the problems related to cyclic loads has focused mainly on the behavior of granular soils. However, in the case of cohesive soils, these began to be studied in detail as a result of the Northridge, Kocaeli and Chi-Chi earthquakes that took place in the 90s. The object of the present work is to evaluate the influence of pore pressure in the calculation of bearing capacity of shallow foundation on cohesive soil and dynamically requested. This research is based on the results of cyclic simple shear tests carried out with samples from the Prat port (Barcelona). A pore-water pressure generation equation is proposed that depends on the effective vertical stress “in situ” (σ’ov), static shear stress (τo), cyclic shear stress (τc), and void ratio (e0). The formulation was implemented to the finite difference software FLAC2D, by which the bearing capacity of foundations can be determined. The proposed formulation can calculate the maximum cyclic load (CL) that a cohesive soil can resist before failure by cyclic softening, as a consequence of cyclic loads transferred by a shallow foundation. The practical application of this research is to provide a chart to calculate the bearing capacity of cohesive soils requested by cyclic loading (CL). This application takes into account the properties of the ground, the static load capacity (Phe) and the effective load outside the foundation ( q ). In addition, the formulation is validated in the application of a real case.

Dynamic failure processes and failure mechanism of soil slope under random earthquake ground motions

Understanding the failure processes and failure mechanism of slopes is essential in the seismic design of slopes. However, the effect of ground motion uncertainty on slope failure is unclear (for example, whether the slope failure processes differ under different ground motions). This study investigated the failure processes and failure mechanism of a soil slope subjected to random earthquake ground motions. Non-stationary random earthquake ground motions were generated based on the improved orthogonal expansion method and dynamic problems were solved using the FLAC3D software. We attempted to determine the slope sliding surface by analyzing the dynamic strain time history of monitoring points. Statistical results obtained using the probability density evolution method revealed that the slip surface extended from the toe to the crest of the slope during the earthquakes and that only one slip surface could be determined under an earthquake scenario. Additionally, the slip surface, time of failure, and failure duration differed under different earthquakes. The strain development patterns also differed and four typical failure modes were identified based on these patterns. The slope risk was assessed based on the sliding mass uncertainty. The proposed framework can be useful in evaluating slope failure processes and for seismic design in the field of slope engineering.

Investigating the Effect of Geocell Changes on Slope Stability in Unsaturated Soil

The purpose of this research is to investigate the performance and efficiency of reinforced slope in the stability of geocell layers in unsaturated soil conditions. Slope reinforced with geocell acts like a beam in the soil due to the geocell having a height (three-dimensional). Due to its flexural properties, it has moment of inertia as well as bending strength, which reduces the displacement and increases the safety factor of the slope. Taking into consideration unsaturated conditions of soil contributes a lot to making results close to reality. One of the well-known models among elastoplastic models for modeling unsaturated soils is Barcelona Basic Model, which has been added to the FLAC2D software by codification. Changes in thickness, length and number of geocell layers are remarkably effective on slope stability. The results show that the geocell's reinforcing efficiency depends on the number of layers and depth of its placement. As the depth of the geocell's first layer increases, the lateral and vertical side elevation of the upper part of the slope increases with respect to the elevation. Load capacity increases with increasing geocell length. By increasing the length of the geocell layer, the joint strength, the mobilized tensile strength, and the bending moment are increased. At u/H = 0.2, an increase in the bending momentum of about 20% occurs with increasing geocell thickness. In u/H = 1, the increase in bending momentum is 10.4%. In addition, by increasing the thickness of the geocell, the Value of moment of the inertia increases and, as a result, the amount of geocell reinforcement bending moment increases.

Damage Evolution Mechanism of Extraction Structure During Mining Gently Dipped Orebody by Block Caving Method

The layout of single transportation level and multiple production levels in one panel made it possible to mine gently dipped orebody by block caving method. However, with the collapse of the orebody in the main sublevel, the ground pressure damage of the extraction structure in the vice sublevel presented some specific characteristics. In order to study the damage evolution mechanism of ground pressure in extraction structure during the process of mining gently dipped orebody, a numerical simulation model was established by using finite difference software FLAC3D, Mohr–Coulomb strength criterion was adopted in calculation. The stress state of the extraction structure in the vice sublevel after each step was monitored and analyzed separately. The research results show that: undercutting in the main sublevel can aggravate the ground pressure damage of the extraction structure in front of an advancing undercut front in the vice sublevel while undercutting in the main sublevel can reduce the probability of secondary occurrence of ground pressure damage in the vice sublevel. The results are beneficial to the guidance of mining gently dipped orebodies in block caving method.

3D Numerical Simulation of the Influence of Drilling-blasting Subway Construction on Subgrade Settlement

Based on the tunnel between Junfeng road-Xiliuzhuang of Qingdao metro, the tunnel excavation model is established by FLAC3D software. The established calculation model mainly includes:(1) Free field boundary conditions are adopted around and at the bottom of the model;(2) The blasting load is simulated by triangle pulse wave;(3) According to the peak value V of the surface velocity, the peak value Pmax of the velocity in the triangular pulse wave is calculated by Sadovsky formula;(4) The calculation results show that the vertical settlement of subgrade is more significant when compared with horizontal settlement;(5) the calculation results are in good agreement with the field monitoring data. It shows that the method can simulate the dynamic characteristics of the model and reflect the dynamic response of subgrade settlement.

Numerical Analysis of The Three Piles of Facing Each Other

In order to study the deformation and stress characteristics of the pile under the action of landslide thrust. Taking the Suo Er Tou landslide in Gansu Province, China as the engineering background, In the paper the numerical analysis model by establishing the finite difference software FLAC3D of geotechnical engineering is analysed the displacement and bending moment of the pile. The anti-slide pile adopts pile element, soil constitutive model uses Mohr-Coulomb. The results show that the displacement of the piles at the top of the pile and the section of the pile are basically equal, but the horizontal displacement values are not equal above the sliding surface. In the sliding surface, the bending moment of the front pile is smaller than the bending moment of the back pile, but the bending moment of the front pile at the top of the pile is larger than the bending moment of the back pile.

Study on the Supporting Features of Composite Soil Nailing Wall

This paper was based on a deep foundation pit support project in Beijing. FLAC3D software was used to simulate the excavation and support process of the foundation pit in detail according to design parameters and geological conditions. The experiment data of the horizontal and vertical displacements of walls, the axial forces of soil nailing and prestressed anchor cables during excavation and support process of the foundation pit provided a technical reference for the site construction and ensured the safety of the whole project.

Application research of a prestressed anchor cable‐pile‐slab wall supporting structure for multistage high fill slopes

AbstractWhen carrying out engineering constructions in a mountainous area with complex geological conditions, high fill slopes commonly need to be strengthened. At present, several of the main supporting structures have unique defects and shortcomings when used in the reinforcement of high fill slopes. Therefore, this paper proposes to apply a prestressed anchor cable‐pile‐slab wall structure to high fill slope support engineering, relying on the long‐term monitoring results of an actual project and using the finite difference finite element software FLAC3D to model the supporting structure. The displacement of the slope, the earth pressure behind the pile, the internal force of the supporting structure and the distribution of the anchor cable force are analyzed comprehensively and systematically. The analysis and study show that the prestressed anchor cable‐pile‐slab wall supporting structure can effectively strengthen a filled slope and control its horizontal displacement to improve its overall stability. The analysis results are used to optimize and improve this approach, which provides a new direction for the reinforcement of high fill slopes, and the results can provide a better reference for the reinforcement and design of fill slopes.

Analysis of Supporting Mechanism of Steel Arch Frame in Tunnel Collapse

As the steel arch can withstand the rock load immediately, this is widely used in tunnel collapse treatment. Firstly, the steel arch mechanism and mechanical model in tunnel collapse supporting had been studied. Then the modeling points and solutions of the finite difference software FLAC3D were pointed out, and the effects of steel arches and steel arches with different spacings were simulated. This paper analyzed the stress field of rock, displacement field of rock and stress behavior of steel in different conditions, the following conclusions: (a) Steel arch can inhibit stress concentration of the foot arch, while the dome appears to reduce the scope of the low stress areas, and it can effectively inhibit the vertical displacement of the vault and floor; (b) The maximum axial force and bending moment were increased with the increase in the arch steel arch spacing; (c) The maximum axial force steel arch occurs mainly at the crown, while the maximum bending moment occurs mainly in the arch and vault at the waist, and arch at the moment was very small. There were basically consistent with the mechanics calculations.

Study on the Structure Optimization of h-Type Anti-Slide Pile

Compared with the traditional anti-slide pile, the h-type anti-slide pile has larger overall lateral stiffness, more reasonable structure stress, and can resist the greater landslide thrust. However, due to the short development history, there are relatively few studies on h-type anti-slide pile, and its structural design is not perfect. Numerical software Flac3d was used to optimize the structural parameters of h-type anti-slide pile, and the results showed that the optimal beam stiffness was 3 times of the front and rear piles, the optimal rear pile depth was 0.28 times of the length of the rear pile, and the front pile depth was 0.5 times of the length of the front pile.

Investigation on lateral bearing capacity of monopile under combined vertical-lateral loads and scouring condition

Nowadays offshore wind turbines have been widely used for wind energy exploitation. The lateral bearing capacity of monopile is important to ensuring the safe operation of monopile based offshore wind turbines. As one of the most used forms of foundations for offshore wind turbines, the monopile is subjected to vertical loads induced by its own weight and superstructures, and lateral loads engendered by winds and waves, simultaneously. Meanwhile, scouring is often formed by the flushing of sea currents, which may affect the lateral bearing capacity of the monopile. Thus, it is important to investigate the lateral bearing capacity of the monopile subjected to combined vertical-lateral loads and scouring condition. The loading device for the laboratory test of the monopile was designed to obtain the reasonable factors of the finite difference model, and the lateral bearing capacity of the monopile subjected to combined vertical-lateral loads and scouring was further investigated by numerical simulation software FLAC3D. The results show that the vertical load has little effect on the lateral bearing capacity of the monopile. Scouring can reduce the lateral bearing capacity and the bending moment of the monopile obviously and make the position of the maximum bending moment move towards the monopile-end.

Seismic analysis of the zaouiat ait mellal twin tunnels of Agadir motorway (Morocco)

Underground structures, such as tunnels, are vital for ensuring all kinds of transportation; and being buried under the surface makes them exposed to soil dynamics. Added to the moderate seismic activity in Morocco, the stability of tunnels is put to the test. This paper examines the interaction between the ZAM (Zaouit Ait Mellal) twin tunnels between the cities of Marrakesh and Agadir, using the Difference Element Method provided by FLAC 2D software. The acceleration is introduced as the one related to the historic event of El centro 1940 with free-field boundary conditions in the numerical model, with three configurations: tunnel 1 without tunnel 2, tunnel 2 without tunnel 1 and tunnel 1 with tunnel 2. The results of the simulations indicate that the differences values of the maximum displacement, axial force and bending moment on structural elements are very noteworthy from the configuration of the tunnel (single) to the twin tunnels in order to prove the interaction between these latter under seismic loading.

Study on the Stability of a Transition Section from Soft to Hard Surrounding Rock Based on the Solid‐Fluid Coupling Effect

To study the stability of a transition section of a tunnel from soft to hard surrounding rock under seepage conditions, FLAC3D software was used to numerically simulate the transition section of the Laomushan Tunnel from the Shiqian to Yuping (Dalong) Expressways in Guizhou Province, China, and to explore different working conditions. The characterization of the tunnel seepage field, stress field, and displacement field and the analysis of the force of the primary lining support structure describe the influence of the seepage field on the stress field distribution and displacement field changes. The reliability of the calculation results is verified by comparison with displacement measurements collected during field monitoring. The design values of the primary support structure parameters of the transition section from soft to hard surrounding rock of the Laomushan Tunnel basically met the strength requirements. The research results provide references for the design and construction of similar projects.