Abstract
The cement-based grouting materials used for practical purposes in high-geothermal tunnels are inevitably affected by humidity and high temperature, leading to the deterioration of mechanical properties. Based on the characteristics of changing high temperatures and two typical conditions of hot-humid and hot-dry environments in high-geothermal tunnels, many mechanical strength tests were carried out on the grouting material cured under different environmental conditions. The study results indicated that high temperature and low relative humidity were unfavorable to the development of mechanical characteristics of grouting material, but the coupling effect of two factors could improve the strength at early ages and reduce the degradation of long-term strength. As the curing temperature exceeded 56.3 °C, the humidity effect on strength played a more important role in recovering the strength of grouting material damaged by high temperature. Temperature had more significant impact on the relative peak stress while the relative humidity had greater influence on the relative peak strain. A calculation compressive constitutive model was prospered, which considering both temperature and relative humidity. The study results may provide much valuable experimental data and theoretical supporting for the design of compression constitutive of cement-based grouting material in high-geothermal tunnel.
Highlights
Grouting has been widely applied in tunnels, subways, foundation pit of buildings and many other underground constructions [1]
The rock temperature tested in the holes on site is almost always above 40 ◦ C, which has a great influence on the reinforcement effect of grouting material, and poses a potential threat to the long-term safety of bolt-supported
The results indicated that the cementitious anti-washout grouting material (CIS) grout had a high early compressive strength due to the admixture of water glass
Summary
Grouting has been widely applied in tunnels, subways, foundation pit of buildings and many other underground constructions [1]. The experimental results indicated that a high temperature of 20 ◦ C led to a lower uniaxial compressive strength of the grouting body than that found at 8 ◦ C Those findings made great contributions to the study on the impact of temperature on grouting material properties, more and more high-geothermal tunnel project cases are presenting rock temperatures far beyond the previously investigated temperature range. Li et al [18] studied the residual compressive strength of cement-based grouting material by exposing the samples to the temperatures of 150 ◦ C, 350 ◦ C, 550 ◦ C, and the testing results indicated that being exposed to higher temperature results in lower mechanical behaviors. The real environmental conditions in high-geothermal tunnels is far complex, and current studies considering the environmental effect (temperature and humidity) on the mechanical properties of grouting material are limited. The results of this investigation may provide valuable information and theoretical support for grouting technology, numerical models of grouting materials, and the supporting design in high-geothermal tunnel
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