Experimental study on biaxial dynamical compressive test and PFC2D numerical simulation of artificial rock sample with single joint

Dynamic biaxial compression tests and Particle Flow Code numerical simulations of the cement mortar specimens with a single joint were carried out to study the mechanical properties and crack evolution of artificial rock samples with a single joint. The effects of lateral stress 2, loading rate V , the dip angle β (between the vertical loading direction and the joint) on the biaxial compressive strength b, and the evolution lawof crackwere investigated. Test results showed that; (1) when both the dip angle β and the loading rate V remained unchanged, the biaxial compressive strength b increased with the increase in the lateral stress 2, while 2 had no obvious effect on the crack evolution law; (2) when both the dip angle β and the lateral stress 2 were kept unchanged, the loading rate V had an insignificant effect on the biaxial compressive strength b and the crack evolution law; (3) when both the lateral stress 2 and the loading rate V were constant, the biaxial compressive strength b decreased first and then increased with the increase in the dip angle β ; however, the dip angle β did not significantly affect the crack evolution law. The conclusions obtained in this paper are presented for the first time

Numerical simulations of horizontal bearing performances of step-tapered piles

In this study, we tried to understand the horizontal bearing performances of step-tapered piles using numerical simulations. The influence of the geometric parameters, e.g. the diameter (D) and the distance (L), and the length (H) of the pile were considered, and the soil distribution imposed on the horizontal bearing capacity of the piles was simulated. Numerical results show that when the other geometrical parameters of step-tapered piles are kept unchanged: (a) the increasing diameter (D) of the enlarged upper part of step-tapered piles improves the horizontal ultimate bearing capacity of step-tapered piles; (b) reduced distance (L) improves the horizontal ultimate bearing capacity of the step-tapered piles; (c) Increasing length (H) of the enlarged upper part of steptapered piles increases the horizontal ultimate bearing capacity; (d) the reduced length (H) decreases the bending moment of the pile body. Higher soil strength surrounding the enlarged upper part of step-tapered piles can increase the horizontal ultimate bearing capacity of step-tapered piles. The change of soil strengths at the end of the step-tapered piles does not influence the horizontal ultimate bearing capacity of step-tapered piles

Uniaxial compression test and numerical simulation of rock-like specimen with T-Shaped cracks

In this study, the uniaxial compression test and PFC2D numerical simulation were carried out on the artificial rock specimen with T-shaped prefabricated fractures. The effects of the lengths l1, l2 of the main fractures, the length l3 of the secondary fracture, and the angle β between the secondary fracture and the loading direction on the uniaxial compressive strength and crack evolution law of specimen were studied. The research results show that the change of l1, l2 and β has obvious effect on the compressive strength and crack growth of the specimen, but the change of l3 has little effect on the compressive strength of the specimen. When l3 = 40 mm and l1 ≠ l2, the angle β influences on the crack propagation and failure mode of the specimen

Experimental study on shear mechanical properties of cement mortar specimen with through-step joints under direct shear

In this study, direct shear tests were carried out on cement mortar specimens with single-ladder, single-rectangular, and double-rectangular step joints. Consequently, the shear strength, and crack shape of specimens with these through-step joints were analyzed, for understanding the influence of the through-step joint’s shape on the direct shear mechanical properties. The results of the investigation are as follows: (1) Under the same normal stress, any increases in the height h of the step joint causes an initial-increase-decrease in the shear strengths of specimens with single-ladder and double-rectangular step joints, causing a type-W variation pattern for the specimens with single-rectangular step joint. More essentially, when normal stress and h are constant, the shear strength of specimens with a single-ladder step joint is the greatest, followed by specimens with a double-rectangular step joint, and then specimens with a single-rectangular step joint is the least. (2) Furthermore, given a small h and low normal stress, specimen with a single-ladder step joint mainly experiences shear failure, whereas specimens with single-rectangular and double-rectangular step joints mainly generate extrusion milling in the step joints

NO2 Retrieval from the Environmental Trace Gases Monitoring Instrument (EMI): Preliminary Results and Intercomparison with OMI and TROPOMI

Onboard the Chinese GaoFen-5 (GF5) satellite, the Environmental trace gases Monitoring Instrument (EMI) is a nadir-viewing wide-field spectrometer that was launched on May 9, 2018. EMI measures the back-scattered earthshine solar radiance in the ultraviolet and visible spectral range. By using the differential optical absorption spectrometry (DOAS) method and the EMI measurements in the VIS1 band (405–465 nm), we performed retrievals of NO2. Some first retrieval results of NO2 from EMI and a comparison with OMI and TROPOMI products are presented in this paper. The monthly mean total vertical column densities (VCD) of NO2 show similar spatial distributions to OMI and TROPOMI (r > 0.88) and their difference is less than 27%. A comparison of the daily total VCD shows that EMI could detect the NO2 patterns in good agreement with OMI (r = 0.93) and TROPOMI (r = 0.95). However, the slant column density (SCD) uncertainty (0.79 × 1015 molec cm−2) of the current EMI algorithm is relatively larger than OMI. The daily variation pattern of NO2 from EMI in Beijing in January 2019 is consistent with TROPOMI (r = 0.96). The spatial distribution correlation of the tropospheric NO2 VCD of EMI with OMI and TROPOMI is 0.88 and 0.89, respectively, but shows an overestimate compared to OMI (15%) and TROPOMI (23%), respectively. This study demonstrates the capability of using EMI for global NO2 monitoring