146 publications from this institution
Chongqing is a mountain city in western China with a complex geological environment, which brings many difficulties to the construction of large sections of underground projects. In order to avoid serious problems in the construction of Guobo Station with large sections, intensive coring and laboratory tests were carried out to obtain the rock mass properties in detail. The boreholes reveal that the lithology of the rock mass in the project area consists mainly of mudstone and a small area of sandstone. The uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS) of mudstone are highly scattered, which are 4.43~42.43 MPa and 0.66~4.30 Mpa, respectively, but they all show a lognormal distribution. The average UCS of sandstone is 65.31 MPa, and the BTS is 3.06 MPa. Meanwhile, the softening coefficients of mudstone and sandstone are 0.33 and 0.73, which indicate that the water content has a great influence on the mechanical properties of the rock. For the in situ stress field, the relationship between the three principal stresses is as follows: the maximum horizontal principal stress > minimum horizontal principal stress > vertical principal stress, and the lateral pressure coefficient is 2.11~5.71. Based on the present experimental results, it is proposed that the potential risks of excavation include: (1) bias pressure (2) high in situ stress; (3) surrounding rock deterioration.
The soft-hard interbedded rocks are often encountered in rock engineering such as mining engineering, tunnel engineering, and natural gas engineering. In this study, the horizontal soft-hard interbedded composite rock-like material (HSHC) specimens were prepared with different thickness ratios of rock-like layers, and a series of uniaxial compression tests were performed by using a self-designed loading mold. A parameter R was defined for the HSHC specimens, which is related to the thickness ratio of the soft and hard rock-like layers, the length-width ratio, and the mechanical parameters of the soft and hard rock-like materials. R was regarded to characterize the strength properties of the HSHC specimens. The test results showed that the axial strength of the HSHC specimens decreases first and then tends to be constant with increasing of R. Digital image correlation (DIC) technique was used to investigate the strain evolution and crack propagation process of the HSHC specimens. The displacement variation trend of the specimen can be roughly divided into three stages: stable deformation stage, rapid crack growth stage and instability failure stage. The failure mode of the HSHC specimens was mainly splitting tensile failure along the bedding plane. Meanwhile, a simplified mechanical model of laminated rock mass under uniaxial compression is established. The strength variation trend predicted by this model is consistent with the experimental results. The present study can reveal the failure mechanism of soft-hard interbedded rock mass at the bottom of the tunnel under the action of large horizontal stress after excavation.
This study presents a peridynamic model formulated using the micromodulus function and bond deformation. The model is derived by establishing energy equivalence between a modified virtual internal bond (VIB) and a peridynamic bond. To address surface effects in peridynamics, a stress-based correction method utilizing nodal stress is introduced, enhancing the model’s numerical accuracy. The model was implemented using an in-house Cython code and validated through the following numerical examples: a plate under traction, a plate with a hole under displacement boundary conditions, a uniaxial compression test on granite with a deformation-based mixed-mode bond failure criterion, and a comparison with an existing strain-based peridynamic model. For the plate under traction, the deformation-based method performed similarly to the strain-based model in the loading direction and better in the unloaded direction. The stress concentration obtained from the proposed model (240 MPa) near the hole in the rectangular plate simulation differed from FEM (252 MPa) by 4.7%. The granite test predicted a UCS of 111.88 MPa and a Young’s modulus of 20.67 GPa, with errors of 0.1% and 1.57%, respectively, compared to the experimental data.
The uniaxial compression tests of plate-shape granite samples containing two prefabricated holes on each side,prepared from Iddefjord granite blocks in Norway,are carried out by Instron hydraulic servo control testing machine in laboratory.The axial stress,axial and lateral strain,acoustic emission(AE) counts and failure modes of the samples are monitored during the tests.The splitting cracks occur near the holes' vertical surface and parallel to the loading direction when the loading stress increases to a certain value.Some characteristics of rockburst phenomena such as rock block ejection and slabbing failure can be observed around the prefabricated holes under high compressive stress.The failure modes of samples always initiate from the splitting fractures around the holes under uniaxial compression.By observing the AE counts rate curve,it is shown that more jumping mutation points appear in the curve than that of intact rock samples.Based on the experimental studies,numerical models are validated by FLAC3D(3 dimensions fast lagrangian analysis of continua).The principal stresses distributions in the samples are obtained by the elastic model analysis,while the failure process is studied by the Mohr-Coulomb strain softening model.The modes of failure zones are monitored and characterized by the AE count events.Most failure zones are failed in tension and connected together to form as splitting fractures parallel to the vertical boundary of the holes.The numerical results are almost the same as the laboratory tests.The research results,to some degree,reveal the formation mechanism of slabbing fractures,which are usually parallel to the excavation boundary surrounding underground openings in hard rocks under high in-situ stresses.
