Through simulating a hot and humid environment of high-ground-temperature tunnel and taking advantage of mechanics performance testing, differential thermal analysis (DTA) technology, and scanning electron microscope (SEM) observation technology, the macroscopic and microscopic properties of cement-based materials and their performance improvement measures can be investigated. Also, the mechanism of improvement can be revealed from the perspective of the hydration degree and microstructure. The experimental results indicate that under the hot and humid environment of high ground temperature, adding fly ash could efficiently weaken the early high-temperature curing effect of cement-based materials, improving their physical properties. But the mechanical strengths of cement-based materials go through a transformation from increase to decline with the rise of fly ash, appearing a maximum value in the process. Meanwhile, the differential thermal analysis and the microstructure analysis show that a hot and humid environment enhances the pozzolanic activity of fly ash and an appropriate ratio of fly ash could improve the microstructure of cement slurry, but when fly ash covers more than 30% of the mix of cement-based materials, the quantity of the alkaline exciting agent, calcium hydroxide, is not enough to meet the needs of the active effect of fly ash and the hydration degree of fly ash becomes extremely low. Last, under a hot and humid environment of high ground temperature, fly ash saturation in cementing material should range from 20% to 30% in mass of total binder, which makes for long-term performance of cement-based materials.
In order to reduce the damage of blasting to rock mass and improve the half-hole rate of presplitting blasting, the dynamic finite element analysis software ANSYS/LS-DYNA is used to simulate and analyze the action process of sequential controlled blasting. The effects of the detonation delay time of the postblasting hole and the hole spacing of the postblasting hole on the crack formation of the sequential controlled presplitting blasting are studied. The results show that when the blast hole with a diameter of 42 mm is used for sequential controlled presplitting blasting and the first blast hole pitch is 60 cm, the reasonable detonation delay time is 80∼120 μs. When the detonation delay time is 80 μs, the reasonable postblast hole spacing is 60 cm. Field tests show that when reasonable optimized blasting parameters are used, presplit blasting with sequential control can reduce drilling workload and explosive consumption. The sequential controlled presplitting blasting not only increases the hole spacing but also plays a better role in protecting the surrounding rock.
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