Research on dynamic characteristics of cutter breaking frozen soil and optimal drum rotation speed of the new shaft tunneling machine.

To improve the efficiency of frozen soil excavation, the new shaft tunneling machine was developed. The new shaft tunneling machine exerts pressure on the frozen soil through the cutter under the joint action of its own gravity, the drum rotational force and the inertia force, and the frozen soil is damaged. By unique way of breaking frozen soil to improve the efficiency of frozen soil excavation, the drum rotation speed is one of the factors affecting the performance of frozen soil excavation. This article applies SolidWorks software to establish the model of cutter breaking frozen soil, takes advantage of Hyper Mesh finite element software coupled with LS-DYNA solver to acquire the regular pattern of change in the force change, frozen soil stress-strain and specific energy of cutter crushing frozen soil, etc., which analyzes the destruction of frozen soil when the drum of the new shaft tunneling machine is rotating at the speed of 25-40 rpm. Combine with field test to investigate the mechanism of cutter breaking frozen soil under the optimal drum rotation speed. The investigation results demonstrate that: when frozen soil's self-bearing capacity is lower than the force of cutter, it breaks up and detaches from the soil body, and frozen soil undergoes tensile, compressive and shear damages. For this research, it is instructive for practical engineering.

Study on Influence Mechanism of Short-Cut BF Dispersion Morphological Behavior on Concrete Properties Based on Meso Scale.

The orientation, distribution, and contact point density of BF (basalt fiber) in the concrete matrix play significant roles in the mechanical properties of BF concrete, but represent a weak point in current research. It is meaningful to study the morphological characteristics of BF in concrete. In this study, the transparent model test and joint blocking method were innovatively adopted to investigate the correlation of dosage with the BF morphological parameters and concrete mechanical properties. A focus on a BF dosage of 0-7.5 kg/m3 and the contribution index of fibers Cf was defined. Furthermore, NMR and CT techniques were used to observe the changes in the microstructure of BF concrete. The experimental results show that the BF contribution index Cf reaches the largest value when the BF content is around 3 kg/m3, approximately 2.7; in this case, the mechanical properties of BF concrete were also optimal, and the Cf was only 2.34 when the BF content was 7.5 kg/m3. NMR and CT test results show that there is a strong correlation between the BF morphological parameters and the distribution of pore structure in the concrete matrix. The overlapping contact of BF clusters led to the penetration of pores, which led the macro-pore proportion to increase dramatically. The increase in the macro-pore proportion is the main reason for the deterioration in concrete performance. In addition, these macro-pores may have adverse effects on the chloride ion permeability of BF concrete.

Pore Structure Characterization of Tailing Bed and Dewatering Mechanism at nm-µm Scales Under Shearing.

The preparation of high-density tailings is a prerequisite for cemented paste backfill technology, and the flocculated fine tailings of sealed water leads to challenges in the slurry thickening of tailings. Shearing conditions can compact the micro floc structure to improve the underflow concentration. The nm-µm scales of pore characteristics and connectivity are essential for the dewatering process. The computed tomography (CT) results show that the underflow concentration increases from 62.3 wt% to 68.6 wt% after undergoing rake shearing at 2 rpm, and the porosity decreases from 42.7% to 35.54%. The shearing conditions reduces the spheres and sticks by 43.14% and 43.3%, respectively, from the pore network model (PNM). The seepage flow states were affected by the changes in the pore structure. The maximum surface velocity and the maximum internal pressure decrease after undergoing shearing. Shearing conditions can break the micro floc structures, and the fine particles can fill in the micron-scale pores by gravity and shearing conditions, resulting in the forced drainage of water into the pores. Shearing conditions can break the thickening floc network structures; natural fine particles can fill the micron-scale pores by gravity and shearing conditions. The upward seepage of sealed water along the µm-scale pore channel causes a higher bed concentration. However, the sealed water in the nm-scale pores cannot flow upward due to water cohesion and particle adhesion resistance.