The influence of rock weathering caused by freezing–thawing on stone cultural relics cannot be ignored. For immovable stone cultural relics, different parts under different environmental conditions will be under different freeze–thaw actions and suffer different degrees of damage. In this paper, three typical freeze–thaw cycle tests of sandstone are designed, namely immersion test, capillary action test, and periodic saturation test. The macroscopic and microscopic morphologies of rock samples under different freeze–thaw cycles were analyzed. Weathering indicators such as porosity, water content, wave velocity, and surface hardness were tested, as well as uniaxial compressive strength. The variation law of weathering index and uniaxial compressive strength under different freezing–thawing cycles was obtained, and the quantitative relationship between each index parameter was further analyzed. The results show that under different freezing–thawing conditions, the apparent morphology of rock samples is different, and the trend of weathering indexes is similar, but the rate of change is different. The water content of rock has a great influence on the test results of wave velocity but has little influence on the surface hardness. The function relationship between weathering index and compressive strength under different freezing–thawing modes is similar, but the fitting parameters are different. Finally, the strength and wave velocity damage factors were used to quantitatively evaluate the degree of rock weathering. The results show that the immersion freeze–thaw damage is the highest, the periodic saturated freeze–thaw damage is the second highest, and the capillary freeze–thaw damage is the least highest. This is consistent with the field observation results. The conclusion of this paper can provide reference for the detection of stone cultural relics and provides a scientific basis for the anti-weathering protection of stone cultural relics.
Sandstone in the Longshan Grottoes was the research object of this paper. The sandstone samples were soaked in distilled water, Na2SO4 solution and NaCl solution and subjected to 30 cycles of freeze-thaw testing. The quality, wave velocity, surface hardness, uniaxial compressive strength and other physical indices of rock samples were measured after different numbers of cycles. Combined with the results of mercury injection, scanning electron microscopy and X-ray diffraction, the damage characteristics and damage mechanism of rock samples under the combined action of chemical solution and freeze-thaw cycle were explored and studied. The results showed that the degree of damage of the sandstone samples increased logarithmically with an increase in the number of cycles. The damage degree of the sandstone samples soaked in the Na2SO4 solution was the highest, while the damage degree of the samples soaked in the NaCl solution and distilled water was similar. The difference in damage between the solutions is caused by the combination of frost heave, dissolution and salt crystallization, and the damage process generally occurs from the inside and the outside and is manifested as an increase in the number of macropores and the appearance of new pores. Freezing-thawing and salt erosion are the main reasons for the siltation of sandstone in the Longshan Grottoes.
The seismic response of rock slopes is closely related to the dynamic characteristics of earthquakes. In this study, based on a numerical model of rock slopes with bolt support, the seismic responses of both anchored and unanchored rock slopes under different seismic waves are calculated. The results show that a “cumulative effect” of the relative permanent displacement of the slope is generated during seismic action, and it is found that the permanent displacement of the slope is caused by larger earthquake accelerations. The dynamic responses of an anchored slope are analyzed in terms of the wave type, frequency, amplitude, and duration and are compared with those of an unanchored rock slope. This comparison suggests that the nominal shear strain increases with the amplitude and duration, which decreases as frequency increases. The axial force is directly related to the surrounding rock strain. The maximum axial force of the bolt is near the rock interface, which shows that the structural plane of the slope plays a dominant role in the seismic response. The seismic waves are random, whereas the structural plane of the rock slope is certain. The seismic response characteristics of the slope under different earthquake conditions are similar, and the dynamic stability of the slope can be attributed to the structural analysis of the rock slope.
This paper designed a special-shaped cross-section hollow self-drilling bolt with discharge grooves, in which Mindlin’s solution of displacement was used in the elastic solution of a wholly grouted bolt. Theoretically, the ultimate pulling force and the residual pulling force were analyzed by considering the average distribution assumption of residual stress. The bolts’ performance with 2, 3, and 4 discharge grooves was compared with circular cross-section bolts, which experimental results are consistent with the theoretical results. The ultimate pulling force and the residual pulling force of the special-shaped cross-section bolt improved significantly according to the circular bolt. The bonding properties of special-shaped cross-section bolts present significant difference to circular section bolts. The residual pulling strength was contributed both by the bar-grout and grout-grout frictions. Upgrading the grout strength may further enhance the pulling strength of special-shaped cross-section bolts.
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