scholarly journals Numerical Analysis of the Anisotropy and Scale Effects on the Strength Characteristics of Defected Rockmass

2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Xiabing Liu ◽  
Shaohui He ◽  
Dahai Wang
Keyword(s):  
Compression Test ◽  
Failure Modes ◽  
Scale Effects ◽  
Triaxial Compression ◽  
Influential Factor ◽  
Strength Characteristics ◽  
Uniaxial Compression Test ◽  
Mechanical Parameters ◽  
Strength Parameters ◽  
Strength Behavior

Discontinuous defect in the rockmass is a key influential factor in controlling the strength behavior, and how to estimate the anisotropic strength and scale effect on the defected rockmass is the remaining challenging focus in engineering application. In the present study, intact tuff samples cored from the Xiabeishan tunnel engineering in situ are conducted by experiment tests (i.e., uniaxial compression test, triaxial compression test, and Brazilian tensile test) to obtain the corresponding mechanical parameters. Results from the numerical simulations using the particle flow code (PFC) by the flat-jointed model (FJM) are performed to match the macroparameters from experimental results. It is observed that numerical results have good agreement with the macroscopic mechanical parameters of intact samples including UCS, BTS, triaxial compression strength, and corresponding deformation parameters. Finally, a series of uniaxial and confining compression tests are conducted by using a synthetic rockmass (SRM) method which is coupled with the discrete element method (DEM) and discrete fracture network (DFN). Then, the anisotropy and scale effects on the strength characteristics of the defected rockmass are investigated. The results show that defects have a vital effect on the failure mode and strength behavior of the rockmass in the research region. The strength parameters are changed with the specimen size. The REV size of the considered defected rockmass is regarded as 5 × 10 m, and this size is also influenced by the confinement level. The anisotropy of macroscopic strength parameters is found in the considered defected rockmass, whose stress-strain curves and failure modes are also discussed.

Study on Acoustic Emission and Failure Modes of Rock in Uniaxial Compression Test

2011 ◽  
Vol 261-263 ◽  
pp. 1393-1400
Author(s):  
Ji Liang Zhang ◽  
Chang Hong Li
Keyword(s):  
Compressive Strength ◽  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Compression Test ◽  
Failure Modes ◽  
Soft Rock ◽  
Development Stage ◽  
Uniaxial Compression Test ◽  
Whole Process ◽  
Shear Rupture

Based on uniaxial compression test, the mechanical properties and acoustic emission characteristics of rock had been obtained, including the relationship between AE and time, AE and stress level, and so on, in the whole process of rock failure. Research shows AE rate of rock has the subparagraph features obviously. There are three obvious AE sections for the higher strength elastic-brittle rock: First section is compaction stage, corresponding stress is 10% of compressive strength of rock; Second section is crack-development stage, corresponding stress is 80% of compressive strength; Third section is rupture stage, corresponding stress is the compressive strength. Furthermore, AE signals for the rupture stage is strongest. The law is still correct in cycle loading conditions. However, the subparagraph phenomenon isn’t clear for elastic-plastic rock, and the AE peak is lagging behind the ultimate strength of rock, the AE signal in the decline stage of strength is the most intensive and strong. The lagging phenomenon is due to X-shear rupture model of soft rock. The significant stress concentration in cone tip between the two relative extrusion cones leads to local rock broken seriously. Then, many acoustic signals have been observed.

Experimental Study of the Mechanical Properties of the Low Elastic Modulus Concrete

2013 ◽  
Vol 357-360 ◽  
pp. 727-731
Author(s):  
Min Sheng Zheng ◽  
Xiao Hua Ma ◽  
Guo Qiang Liang
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Compression Test ◽  
Failure Modes ◽  
Triaxial Compression ◽  
Unconfined Compression ◽  
Strength Theory ◽  
Unconfined Compression Test ◽  
Test Instrument ◽  
Low Elastic Modulus

By using the 2000kN static and dynamic triaxial test instrument the mechanical properties of the low elastic modulus concrete is studied. The results of the experiment show that the failure modes of the unconfined compression test is crushing-type and the failure modes of the triaxial compression test is shearing-type. Utilizing the Mohr - Coulomb strength theory to design the low elastic modulus concrete cut-off wall is more in line with the actual engineering, but utilizing the first strength theory to design the dam cut-off wall is safer.

scholarly journals Triaxial Permeability Experimental Study on Deformation and Failure Processes of Single-Fractured Rock Specimens

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Taoli Xiao ◽  
Mei Huang ◽  
Min Gao
Keyword(s):  
Compression Test ◽  
Failure Modes ◽  
Triaxial Compression ◽  
Testing Machine ◽  
Peak Stress ◽  
Triaxial Compression Test ◽  
Permeability Test ◽  
Deformation And Failure ◽  
Seepage Pressure ◽  
Conventional Triaxial Compression

A series of rock-like specimens with specific sizes and fracture inclinations was created in the laboratory. The different effects of seepage pressure on the deformation and failure characteristics between a conventional triaxial compression test and a triaxial permeability test were studied using a servo-controlled testing machine. Furthermore, the change in the permeability of single-fractured specimens was explored based on a triaxial permeability test. The results were as follows. Compared with those observed in the conventional triaxial compression test, the peak stress and corresponding axial strain decrease under seepage pressure in the triaxial permeability test, while the deformation modulus increased. With the increase of fracture length, the peak stress of specimen decreases due to the seepage pressure and the specimen showed tensile failure horizontally. The failure mode of the single-fractured specimens was changed by the seepage pressure. A closed relationship was observed between the failure modes and the permeability-stress curves. A shear failure along the crack surface will occur when the permeability abruptly changed later than the peak stress point. The dramatic change in the permeability indicated that the permeability channel was extended or new seepage paths were created. These conclusions can provide a valuable theoretical reference for the numerical simulation of excavation and design in stability analysis of jointed rock masses.

Specimen size effects on behavior of loose sand in triaxial compression tests

2015 ◽  
Vol 52 (6) ◽  
pp. 732-746 ◽  
Author(s):  
Tarek Omar ◽  
Abouzar Sadrekarimi
Keyword(s):  
Shear Strength ◽  
Size Effects ◽  
Scale Effects ◽  
Triaxial Compression ◽  
Shear Banding ◽  
Specimen Size ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Shear Strength Parameters ◽  
Strength Parameters

Triaxial tests are often used to determine the behavior and strength characteristics of soils without due attention to the differences in specimen size. Several drained and undrained monotonic triaxial compression shear tests are performed in this study on three different specimen sizes of the same sand to investigate the influence of specimen size and scale effect on sand compression and shear behavior. The behavior of a sand specimen is strongly influenced by shear banding and specimen boundary conditions, which are manifested as specimen size effects in the test results of this study. The measured sand compressibility and shear strength parameters are employed to describe scale effects, and investigate specimen size effects in liquefaction triggering analysis. The results show that while larger specimens exhibit a less compressible behavior during isotropic compression, larger shear strengths and effective friction angles are mobilized in the smaller specimens during shearing. A number of geotechnical analyses can be significantly affected by variations in strength parameters of the same soil determined from different specimen sizes. While using small size specimens for determining shear strength parameters might result in an unconservative design, a large specimen size provides a more accurate representation of different soil strength conditions and field deformations.

scholarly journals Correlation between Uniaxial Compression Test and Ultrasonic Pulse Rate in Cement with Different Pozzolanic Additions

2021 ◽  
Vol 11 (9) ◽  
pp. 3747
Author(s):  
Leticia Presa ◽  
Jorge L. Costafreda ◽  
Domingo Alfonso Martín
Keyword(s):  
Compression Test ◽  
Ultrasonic Pulse Velocity ◽  
Ultrasonic Pulse ◽  
Pulse Velocity ◽  
Uniaxial Compression Test ◽  
Unconfined Compression Test ◽  
Pozzolanic Cement ◽  
The Relationship ◽  
Compression Resistance

This work aims to study the relationship between the compression resistance and velocity from ultrasonic pulses in samples of mortars with 25% of pozzolanic content. Pozzolanic cement is a low-priced sustainable material that can reduce costs and CO2 emissions that are produced in the manufacturing of cement from the calcination of calcium carbonate. Using ultrasonic pulse velocity (UPV) to estimate the compressive resistance of mortars with pozzolanic content reduces costs when evaluating the quality of structures built with this material since it is not required to perform an unconfined compression test. The objective of this study is to establish a correlation in order to estimate the compression resistance of this material from its ultrasonic pulse velocity. For this purpose, we studied a total of 16 cement samples, including those with additions of pozzolanic content with different compositions and a sample without any additions. The results obtained show the mentioned correlation, which establishes a basis for research with a higher number of samples to ascertain if it holds true at greater curing ages.

Sign in / Sign up

Export Citation Format

Share Document