Investigation of Key Parameters of Rock Cracking Using the Expansion of Vermiculite Materia.

Chi-Hyung Ahn,Jong Hu

doi:10.3390/ma8105351

Abstract

The demand for the development of underground spaces has been sharply increased in lieu of saturated ground spaces because the residents of cities have steadily increased since the 1980s. The traditional widely used excavation methods (i.e., explosion and shield) have caused many problems, such as noise, vibration, extended schedule, and increased costs. The vibration-free (and explosion-free) excavation method has currently attracted attention in the construction site because of the advantage of definitively solving these issues. For such reason, a new excavation method that utilizes the expansion of vermiculite with relatively fewer defects is proposed in this study. In general, vermiculite materials are rapidly expanded in volume when they receive thermal energy. Expansion pressure can be produced by thermal expansion of vermiculite in a steel tube, and measured by laboratory tests. The experimental tests are performed with various influencing parameters in an effort to seek the optimal condition to effectively increase expansion pressure at the same temperature. Then, calibrated expansion pressure is estimated, and compared to each model. After analyzing test results for expansion pressure, it is verified that vermiculite expanded by heat can provide enough internal pressure to break hard rock during tunneling work.

Highlights

The urban area has been rapidly increased in the world, and underground space used for territorial expansion has been excavated instead of ground space that has reached a saturation point
Once typical vermiculite materials undergo temperature change, they are likely to expand their volume. Owing to these unique characteristics, internal expansion pressure in the stainless steel tube is easy to generate by only applying heat to vermiculite mixed with silicon carbide
Calibrated radial displacement was measured through a laboratory experiment performed on stainless steel tubes with various parametric conditions, and expansion pressure was calculated based on mechanical equations for the thin-walled cylindrical pressure vessel

Summary

Introduction

The urban area has been rapidly increased in the world, and underground space used for territorial expansion has been excavated instead of ground space that has reached a saturation point. Despite the many advantages with respect to simple equipment, quick construction, and being economical, the vibration-free excavation method using rock breakage by thermal expansion still remains at the early stage of development when compared to the existing methods. Traditional contact measurement techniques, such as electrical resistance strain gauges and mechanical extensometer, possess a lot of limitations in measuring range and frequency responses, and cannot provide adequate information to address the complexity of dynamic mechanical behavior For these reasons, previous research related to developing new vibration-free excavation methods has faced many difficulties in effectively cracking hard rocks. The excavation method proposed makes good use of simple equipment, low cost materials, as well as easy field application, and minimizes construction costs and labor costs It can mitigate the issues of noise and vibration because there are no explosions. The maximum expansion pressures are compared to each model in a bid to present the optimal use of vermiculite

Vermiculite Expansion

Concluding Remarks