Mohr Stress Circle Research Articles

Discrete element analysis and analytical method on failure mechanism of retaining structures with narrow granular backfill

AbstractAscertaining failure mechanism is a prerequisite of the derivation for earth pressure against retaining structures. Retaining structures constructed adjacent to existing structures and excavation with narrow backfill have become common in practical engineering. The backfill width has a significant effect on the failure mechanism, requiring further study. In this study, a series of discrete element analyses are conducted to investigate the shear localization in soil mass behind retaining structures with narrow backfill in the active and passive limit states at the grain scale. Furthermore, the distribution characteristic of failure surfaces in soil mass is discussed from three aspects: the development of the failure surface, the state of soil mass behind retaining structures, and the shape of the failure surface. Based on the typical nonlinear failure mechanisms observed in particle rotation contours with various backfill widths and interface friction angles, the failure mechanisms behind retaining structures with narrow spacing are categorized into three types according to the backfill widths. According to the stress characteristics of interfaces under different failure mechanisms, the variational method and Mohr stress circle analysis are adapted to analytically obtain the failure surfaces behind the retaining structure with narrow backfill. Comparisons with results obtained by the discrete element simulation show a reasonable agreement. In addition, a series of parameter studies are conducted to investigate the effect of backfill widths and interface friction angles on the failure mechanism.

Effect of Loading Direction on Deformation and Strength of Heterogeneous Paleo Clay Samples

Landslides result from weak surfaces with varying rock-soil properties, posing a significant concern for engineering and accurate deformation analysis. This study investigated the macroscopic physical and mechanical properties of paleo clay specimens during triaxial compression testing, aiming to elucidate the deformation mechanisms exhibited by these specimens under varying loading directions at both the loading and unloading ends, and numerical simulation methods were carried out to simulate actual engineering scenarios. The analysis encompasses deformation patterns, stress–strain relationships, Mohr stress circles, and numerical simulation failure cloud diagrams for soil samples under different loading directions. The results showed that the loading end of heterogeneous specimens exhibited noticeable deformations. Alteration of the loading direction induced variations in the failure mode. The position and size of the deformations for the only iron-manganese clay, loading end iron-manganese clay, and loading end reticulated clay samples changed with the clay layer at the loading end of the sample. Moreover, the stress–strain curves under different loading directions were different, with strain hardening and strain softening appearing in the two loading directions, respectively. The results of this study contribute to an in-depth understanding of the impact of the loading direction on the deformation and strength of paleo clay, thereby providing a foundation for landslide prevention and control measures.

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths.

To investigate the strength and failure characteristics of silty mudstone using different stress paths, silt-like mudstone specimens were subjected to triaxial unloading tests. The results indicate the following. (1) When subjected to equivalent initial deviator stress levels and differing confining pressures, the peak stress, residual stress, and elastic modulus, exhibited during unloading, increased concordantly with greater initial confining pressure. Both the peak strain and residual strain increased with rising initial confining pressure. The increase in peak strain and residual strain initially decelerated, then noticeably increased, before ultimately decreasing again. Additionally, the unloading failure time and strain rate demonstrated a negative correlation as the confining pressure increased. (2) Under different initial deviatoric stress conditions, the peak stress, residual stress, and residual strain, under unloading confining pressure conditions, decreased as the initial deviatoric stress levels elevated. Conversely, the peak strain and elastic modulus initially increased, then decreased under increasing initial deviatoric stress conditions. The unloading failure time and strain rate were both observed to decrease as the initial deviatoric stress levels increased. (3) Utilizing the Mohr stress circle enabled the characterization of the shear strength variation in the specimens during the unloading process. The cohesion and internal friction angle remained relatively consistent across the different unloading stress paths appraised, with cohesion being greater in path I versus path II, whereas the internal friction angle exhibited an inverse relationship. (4) The specimen failed during unloading due to lateral expansion caused by unloading confining pressure and collapse failure. The failure fracture surfaces predominantly manifested shear failure morphologies.

An alternative to the fault-valve model

This paper proposes a mechanism called the mode-switching model that is presented as an alternative to the fault-valve model. This mechanism is relevant to open-flow, low-porosity, fluid-saturated systems deforming by pressure solution creep. As opposed to most constitutive models discussed in the geological literature, the yield envelope is capped at high normal stresses, as demonstrated by experimental studies. A low-permeability rock has relatively high pore fluid pressure for a given input fluid flux. This increases the dissolution rate for quartz that in turn leads to a higher-permeability rock, low fluid pressure for the same flux and decreased quartz solubility and deposition, returning to a low permeability. This cycle continues indefinitely so long as the rock mass is stressed, a fluid flux is applied, and pressure solution operates. The high fluid pressure drives the Mohr stress circle to the tensile end of the yield envelope resulting in crack-seal and extensional veins. The low fluid pressure drives the Mohr stress circle to the cap end of the yield envelope resulting in laminated veins in rocks undergoing mineral reactions with large net volume losses coupled with solute transfer. Failure at the cap end of the yield envelope results in displacement discontinuities inclined at high angles to σ 1. Previously, these orientations have been taken to represent reactivated normal faults, an integral component of the fault-valve process. In the model presented, the yield surface prohibits the system ever reaching super-lithostatic pressures. The process of effective stress-driven switching between tensile and cap ends of the yield envelope arises from competition between dissolution and deposition, and is independent of any seismic events, fault reactivation or the episodic breaching of an impermeable seal. It provides a unifying, self-consistent concept for the interpretation of joints, faults and veins in hydrothermal systems.

Influence of Water Saturation Time on Microstructure and Mechanical Properties of Jointed Limestone

In order to study the influence of water saturation time on the mechanical properties of jointed limestone, the joint limestone samples with a crack length of 20 mm and a crack angle of 30° are saturated with water for 0, 1, 3, 5 and 7 days and tested with the RMT-150C mechanical test machine. The results show that the water saturation time has a significant effect on the stress-strain curve, peak strength, elastic modulus, crack development and failure characteristics of the jointed limestone. There is a step rise or fall phenomenon near the peak stress. The peak strength and elastic modulus of the joint limestone are significantly negatively correlated with the saturated time. Compared with that of the saturated 0-day sample, the peak compressive strength of the saturated 1-day, 3-day, 5-day and 7-day samples was decreased by 16.5%, 24.7%, 43.6%, and 47.7%, respectively, and the elastic modulus decreased by 11.0%, 32.0%, 45.0%, and 67.9%, respectively. Saturated water cracks the skeleton particles of the limestone samples, and the length of the microscopic pores and fissures increased gradually. The phenomenon that the number and length of cracks increase with the increase of the water saturation time will weaken the mechanical properties of the jointed limestone. The physical and chemical reactions, lubrication, and pore water pressure produced by water-saturated water-rock interactions make it easier for the Mohr stress circle to reach the limit equilibrium state. Saturated water reduces the degree of fragmentation of the sample, and the integrity of the fracture surface is higher after failure. The findings in this paper are helpful to further reveal the mechanism of the crushing of supports and the frequent occurrence of water gushing accidents at the working face in the Xinhua region of northwestern Guizhou.

Effect of Freeze-Thaw Cycles on Mechanical Properties of an Embankment Clay: Laboratory Tests and Model Evaluations

Freeze-thaw (FT) cycling is a crucial issue in seasonal frozen regions and it will influence the mechanical properties of soils, which must be strictly considered for embankment engineering. This study conducted a series of unconsolidated and undrained triaxial tests under various closed-system FT cycles to investigate the mechanical properties of a typical embankment clay from China. Results indicated that the stress-strain curves changed from strain hardening or stabilization to softening during FT cycles. The elastic modulus was obviously weakened by FT cycles and declined sharply after the first FT action. The failure strength gradually reduced with the accumulation of FT cycles and eventually tended to be stable when the FT cycles reached 10, and the attenuation range was approximately 6–22% compared with the condition before FT cycles. Moreover, a phenomenological model on the failure strength was established by results of the tested clay in this study and validated to be robust through multiple sets of different clays data from other published literatures. Based on that, combined with the Mohr stress circle equation and envelope theory, an innovative method for rapidly obtaining the shear strength was proposed. The ensuing discoveries were that the cohesion was damaged in the course of the first few FT cycles and then kept basically constant after 10 cycles, while the internal friction angle was not sensitive to FT cycles. The normalized empirical formula was deduced and can simultaneously apply to the strain hardening, stabilization, and softening curves given the effect of FT cycles.

Interfacial Shear Performance of Epoxy Adhesive Joints of Prefabricated Elements Made of Ultra-High-Performance Concrete.

Application of ultra-high-performance concrete (UHPC) in joints can improve the impact resistance, crack resistance, and durability of structures. In this paper, the direct shear performance of ultra-high-performance concrete (UHPC) adhesive joints was experimentally studied. Twenty-four direct shear loading tests of UHPC adhesive joints were carried out considering different interface types and constraint states. The failure modes and load-slip curves of different interfaces were studied. Results indicated that passive confinement could enhance the strength and ductility of the interface; the average ultimate bearing capacity of the smooth, rough, grooved, and keyway specimens with passive restraint were, respectively, increased by 11.92%, 8.91%, 11.93%, and 17.766% compared with the unrestrained ones. The passive constraint force changes with the loading and finally tends to be stable. The epoxy adhesive has high reliability as a coating for the UHPC interface. The adhesive layer is not cracked before the failure of the specimen, which is also different from the common failure mode of adhesive joints. Failure of all specimens occurred in the UHPC layer, and the convex part of the groove interface shows the UHPC matrix peeling failure; the keyway interface is the shear damage of the key-tooth root, and the rest of the keyway showed UHPC surface peeling failure. According to the failure mode, the shear capacity of UHPC keyway adhesive joints under passive restraint is mainly provided by the shear resistance of key teeth, the friction force of the joint surface, and the bonding force of the UHPC surface. The friction coefficient was determined based on the test results, and the high-precision fitting formula between the shear strength of the UHPC surface and the passive constraint force was established. According to the Mohr stress circle theory, the proposed formula for direct shear strength of UHPC bonded joints under passive constraint was established. The average ratio of the proposed UHPC adhesive joint calculation formula to the test results was 0.99, and the standard deviation was 0.027.

Analysis of force and displacement of anchor systems under the non-limit active state

This paper proposes a concept of soil shear strength exertion around an anchorage section to analyze and calculate the anchor’s force and displacement. First, based on the Mohr stress circle, the numerical relationship between the value of the internal friction angle exertion, the value of the cohesion exertion, and the displacement are established under the non-limit active state. According to the interaction mechanism between the anchorage section and the surrounding soil, this paper obtains the corresponding relationship between the value of the soil’s shear strength exertion and displacement under the non-limit active state. Then, according to the load transfer principle of the anchorage section, the basic differential equation is established. The differential equation of the relative displacement distribution along the length of the anchorage section under the non-limit active state is further derived. And the calculation and analysis formula of the shear stress and relative displacement in the anchorage section considering the process of the soil shear strength exertion is also obtained. Finally, this paper compares the calculation method with the hyperbolic model calculation method for the same example. The results verify the accuracy of the calculation method.

Study on Optimization of Shallow Section Coal Pillar Width of Gently Inclined Medium-Thickness Coal Seam

This paper takes a coal mine gently inclined medium-thickness coal seam as the object. Firstly, the principal stress characteristics and displacement characteristics of roadway surrounding rocks after roadway driving along goaf under section columns with different breadthes were analyzed by simulation method, and the roadway stability was evaluated to determine the reasonable breadth. The results show that when the breadth of column is 4 m, the Mohr stress circle of the pillar intersects the strength envelope and the roof and side displacement of roadway are significant; when the breadth is 6 m, the Mohr stress circle on both flanks of the pillar intersects at the strength envelope and the roof and side displacement of roadway are significant; when the breadth is 8-12 m, the Mohr stress circle of surrounding rock is separated from the strength envelope and the surrounding rock displacement meets the production needs. Therefore, it is in a stable state. 8-12 m is the reasonable width range of coal pillar. Secondly, through the actual project verification, the 8 m wide coal pillar is the most reasonable for the shallow part of the gently inclined medium-thickness coal seam.

Experimental investigation on shear performance of fiber-reinforced high-strength concrete dry joints

In order to consider the seven parameters including joint types, confining stress levels, fiber lengths, fiber shapes, fiber types, volume ratios of fibers, and reinforcement of key specimens, seventeen pairs of shear key specimens were cast and tested. The effects of the above seven parameters on the shear behavior and shear capacity of fiber-reinforced high-strength concrete (FHSC) dry joints were obtained. Analysis of the test results shows that the type of joint has a great influence on the shear behavior of specimens. Compared with HSC specimens, the cracking stress, ultimate stress, and ductility of FHSC specimens were improved. The average cracking stress is increased by 46.4%, and the average ultimate stress is increased by 25.3%, and the average ductility is increased by 30.9%. Within a certain range, the ultimate stresses of FHSC specimens increase with the increases of confining stresses, fiber lengths, and fiber volume ratios. The end-hook steel fibers have a greater effect on the ultimate stresses than the two other types. Then, the calculating formula for the shear capacity of dry joints was summarized. Based on the existing test data, the calculated results of different formulas were compared and analyzed. It was found that the calculated results of the formula suggested by AASHTO agreed best with the test results for single-keyed specimens, while the formulas suggested by Buyukozturk predicted the shear capacity well for multi-keyed specimens. Also, considering the effect of fibers on the concrete strength, a calculating formula for FHSC was proposed based on Mohr's stress circle principle, which was in a good agreement with the test data.

Experimental Study on the Shear Behaviors of PolypropyleneFiber-Reinforced Sand

With excellent water permeability and high shear strength S, fiber-reinforced sand (FRS) is an ideal material for subgrades and has promising application prospects. In this study, the FRS were formed by adding the randomly distributed fibers to the sand specimens. Based on the triaxial consolidated drained tests, the effects of factors such as fiber content ζ, fiber length lf, relative density Dr and confining pressure σ3 on the S of FRS were systematically investigated. The test results showed that the S of the FRS increased as ζ, lf, Dr and σ3 increased. Under axial loads, the stress-strain curve of the FRS exhibited a hardening trend. Under specific Dr and σ3, the S increment of the FRS had a strong linear relationship with ζ and lf. The Mohr's stress circle results showed that the FRS possessed not only frictional strength but also high cohesive strength. Based on the triaxial consolidated drained test results, the S of the FRS was calculated using the Zornberg model and Michalowski model. The calculation results showed that the S predicated by the Zornberg model differed significantly from the measured values. However, the S predicted by the Michalowski model were in good agreement with the measured values.

Active Earth Pressure Against Rigid Retaining Wall Considering Effects of Wall-soil Friction and Inclinations

This paper reports a new method for calculating the active earth pressure acting on inclined rigid retaining wall with inclined backfill, considering wall-soil interface friction angle. Based on Mohr-Coulomb strength theory and Mohr stress circle, new formulae of the active earth pressure and the active rupture angle are derived. The effects of internal friction angle, backfill-surface inclination, wall-back inclination on the active earth pressure and the active rupture angle are investigated. In order to facilitate calculation, special solutions of presented formulae are discussed under various particular conditions. Finally, the calculated results from the presented formula and existing formulae are compared with existing small-scale test results. The comparison shows that the presented method satisfactorily predicts active earth pressure.

Teaching Reform and Case Design of Blended Teaching and Learning on Material Forming Principle

Material forming principle is an important basic theory course of major in material forming and control engineering. Modern teaching modes, such as Blended Teaching and Learning, Flipped Classroom and MOOC, were analysized and the teching reform ideas were put forward according to the basic curriculum teaching characteristics and practical needs of the common universities of China. In combination with the contents of material forming principle, the teaching case design on Mohr Circle of Stress was carried out. It was shown the teaching quality and effect of curriculum difficulties can be improved in this course used Blended Teaching and Learning. It is of positive significance to teaching reform and practice on professional basic curriculum in commom university of China.

Scaling the 3-D Mohr circle and quantification of paleostress during fluid pressure fluctuation – Application to understand gold mineralization in quartz veins of Gadag (southern India)

In this study, orientations of 157 quartz veins occurring in metabasalts of the Gadag region (Dharwar craton, southern India) are used to plot the 3-D Mohr stress circle, which provides information about relative stress/fluid pressure (Pf) conditions, as well as stress state during Pf fluctuation. To scale the 3-D Mohr circle, vein orientation data are integrated with (a) available estimates from fluid inclusions of highest recorded Pf (390 MPa) and lowest recorded Pf (50 MPa) and (b) intrinsic rupture criterion that empirically quantify rock properties. Based on the scaled 3-D Mohr circle, the absolute magnitudes of the three principal stresses are quantified for high and low Pf. Of 157 veins investigated here, 14 veins are identified as having favourable orientation for dilation at high as well as low Pf. These 14 veins have a mean strike of 150°, which is similar to the orientation of the gold-bearing quartz lodes reported in the region. The effective normal stress (σ′n = σn−Pf) prevalent during dilation of fracture/fabric anisotropy with 150° strike is calculated to be −11.5 MPa at high Pf, and −1.0 MPa at low Pf. Thus, it is interpreted that in the Gadag region, a change in σ′n of 10.5 MPa prevailed during Pf fluctuation and associated separation of gold from the fluid.

이산화탄소 격리저장시스템의 역학적 안정성 평가를 위한 주입온도 및 주입량 시나리오 해석

향후 국내에서 수행될 이산화탄소 지중저장 프로젝트의 성공적인 수행을 위해서는 현장 지질조건에 최적화된 주입 조건을 설계하는 것이 중요하다. 따라서 본 연구에서는 주입량 및 주입온도 등의 주입조건이 격리저장시스템의 역학적 안정성에 미치는 영향을 열-수리-역학 연계해석기법의 하나인 TOUGH-FLAC 해석기법을 이용하여 평가하였다. 저장시스템의 역학적 안정성은 기존 균열의 전단미끄러짐 발생가능성을 활동마찰각 및 응력원을 이용하여 분석하였다. 이산화탄소의 주입온도가 저류층의 초기온도보다 낮은 저온주입의 조건에도 열응력으로 인한 인장균열은 발생하지 않는 것으로 파악되었으나, 저류층에서 전단미끄러짐이 발생하는 결과를 보였다. 단위시간당 이산화탄소 주입량을 변화시킨 시나리오 해석에서는 단계별로 주입량을 감소시키는 주입시나리오에서 기존 균열들의 전단미끄러짐 발생 가능성이 가장 낮은 것으로 평가되었다. For a successful accomplishment of Carbon Capture Sequestration (CCS) projects, appropriate injection conditions should be designed and optimized for site specific geological conditions. In this study, we evaluated the effect of injection conditions such as injection temperature and injection rate on the geomechanical stability of CCS system in terms of TOUGH-FLAC simulator, which is one of the well-known T-H-M coupled analysis methods. The stability of the storage system was assessed by a shear slip potential of the pre-existing fractures both in a reservoir and caprock, expressed by mobilized friction angle and Mohr stress circle. We demonstrated that no tensile fracturing was induced even in the cold CO2 injection, where the injected CO2 temperature is much lower than that of the reservoir and tensile thermal stress is generated, but shear slip of the fractures in the reservoir may occur. We also conducted a scenario analysis by varying injected CO2 volume per unit time, and found out that it was when the injection rate was decreasing in a step-wise that showed the least potential of a shear slip.

Computational analysis of linear friction welding process and micromechanical modeling of deformation behavior for medium carbon steel

Finite element simulation of linear friction welding (LFW) medium carbon steel was carried out using the ABAQUS software. A two-dimensional (2D) coupled thermo-mechanical model was established. First, the temperature fields of medium carbon steel during LFW process were investigated. And then, the Mises stress and the 1st, 2nd and 3rd principal stresses fields’ evolution of the steel during LFW process were studied. The deformation behavior of LFW carbon steel was analyzed by using micromechanics model based on ABAQUS with Python code. The Lode parameter was expressed using the Mohr stress circle and it was investigated in detail.

Comparing the generalized Hoek-Brown and Mohr-Coulomb failure criteria for stress analysis on the rocks failure plane

Determination of mobilized shear strength parameters (that identify stresses on the failure plane) is required for analyzing the stability by limit equilibrium method. Generalized Hoek-Brown (GHB) and Mohr-Coulomb (MC) failure criteria are usually used for obtaining stresses on the plane of failure. In the present paper, the applicability of these criteria for determining the stresses on failure plane is investigated. The comparison is based on stresses on the real failure plane which are obtained from the Mohr stress circle. To do so, 18 sets of data (consist of principal stresses and angle of failure plane) presented in the literature are used. In addition, the values account for (VAF) and the root mean square error (RMSE) indices were calculated to check the determination performance of the obtained results. Values of VAF and RMSE for the normal stresses on the failure plane evaluated from MC are 49% and 31.5 where for GHB are 55% and 30.5, respectively. Also, for the shear stresses on failure plane, they are 74% and 36 for MC, 76% and 34.5 for GHB. Results show that the obtained stresses and angles of failure plane for each criterion differ from real ones, but GHB results are closer to the empirical results. Also, it is inferred that results are affected by the failure envelope not real failure plane. Therefore, obtained shear strength parameters are not mobilized. Finally, a multivariable regressed relation is presented for determining the stresses on the failure plane.

Seafloor Polymetallic Sulfides Mechanical Property Test

Seafloor polymetallic sulfide specimens were developed according to engineering rock test method standard (GB/T 50266-2013). Seafloor polymetallic sulfide wet density and dry density were tested. Uniaxial compressive strength and triaxial compression strength of seafloor polymetallic sulfide were tested using rock mechanics test system MTS 815. Elasticity modulus and Poisson's ratio of seafloor polymetallic sulfide were calculated based on specimens stress-strain curves. Cohesion and internal friction angle were calculated based on specimens triaxial test Mohr stress circle. Test results show that seafloor polymetallic sulfide dry density average value is 2.6 g/cm3, wet density average value is 2.94 g/cm3. Uniaxial compressive strength and triaxial compression strength of seafloor polymetallic sulfide are unstable. Average value of the uniaxial compressive strength is 10.243MPa. Average value of triaxial compression strength test peak load is 47.166KN. Cohesion is 2.447MPa and internal friction angle is 38.04o.

Characterization of Strength of Intact Brittle Rock Considering Confinement-Dependent Failure Processes

As technologies for deep underground development such as tunneling underneath mountains or mass mining at great depths (>1,000 m) are implemented, more difficult ground conditions in highly stressed environments are encountered. Moreover, the anticipated stress level at these depths easily exceeds the loading capacity of laboratory testing, so it is difficult to properly characterize what the rock behavior would be under high confinement stress conditions. If rock is expected to fail in a brittle manner, behavior changes associated with the relatively low tensile strength, such as transition from splitting to the shear failure, have to be considered and reflected in the adopted failure criteria. Rock failure in tension takes place at low confinement around excavations due to tensile or extensional failure in heterogeneous rocks. The prospect of tensile-dominant brittle failure diminishes as the confinement increases away from the excavation boundary. Therefore, it must be expected that the transition in the failure mechanism, from tensile to shear, occurs as the confinement level increases and conditions for extensional failure are prevented or strongly diminished. However, conventional failure criteria implicitly consider only the shear failure mechanism (i.e., failure envelopes touching Mohr stress circles), and thus, do not explicitly capture the transition of failure modes from tensile to shear associated with confinement change. This paper examines the methodologies for intact rock strength determination as the basic input data for engineering design of deep excavations. It is demonstrated that published laboratory test data can be reinterpreted and better characterized using an s-shaped failure criterion highlighting the transition of failure modes in brittle failing rock. As a consequence of the bi-modal nature of the failure envelope, intact rock strength data are often misinterpreted. If the intact rock strength is estimated by standard procedures from unconfined compression tests (UCS) alone, the confined strength may be underestimated by as much as 50 % (on average). If triaxial data with a limited confinement range (e.g., σ3 ≪ 0.5 UCS due to cell pressure limitations) are used, the confined strength may be overestimated. Therefore, the application of standard data fitting procedures, without consideration of confinement-dependent failure mechanisms, may lead to erroneous intact rock strength parameters when applied to brittle rocks, and consequently, by extrapolation, to correspondingly erroneous rock mass strength parameters. It follows that the strength characteristics of massive rock differ significantly in the direct vicinity of excavation from that which is remote with higher confinement. Therefore, it is recommended to adopt a differentiated approach to obtain intact rock strength parameters for engineering problems at lower confinement (near excavation; e.g., excavation stability assessment or support design), and at elevated confinement (typically, when the confinement exceeds about 10 % of the UCS) as might be encountered in wide pillar cores.

Effect of block rotation on fault sealing: An example in Dongpu sag, Bohai Bay basin, China

Pre-existing faults or early formed faults may be reactivated or locked in subsequent evolution in a rift basin. The reactivation or sealing of a fault affects sedimentation in the related fault block, and in turn controls the accumulation of oil and gas. Based on fault mechanics of reactivation, this paper established equations denoting the angle range of the reactivated faults or frictional sliding faults by using Mohr stress circles. The results were applied to explain the sealing property of pre-existing faults or early formed faults in Dongpu sag. In the Dongpu sag, reactivation or sealing of the faults in fault blocks is supposed due to the rotation of the fault block which was caused by the activity of high order faults. For quantitative calculation of dip range for activated faults, the sum of the maximum and minimum principal stresses were determined by acoustic emission experiment based on the Kaiser effect of rocks, and the cohesion and inner frictional angle of rocks were measured by rock physical experiment. The calculations show, when the dips of early formed faults are from 87° to 45°, the faults will remain activation in the subsequent deformation. Otherwise, the faults will be locked as sealing faults. The results of petroleum exploration show that the peak dips of sealing faults are from 36° to 40°, and the most of sealing faults are those with dip angles less than 46–50°. These results indicate that a shallower fault is of better sealing property in oil and gas reservoirs than a steeper fault in Dongpu sag.