Mechanical and macro-microscopic failure characteristics of grouted mudstone considering grout dehydration effect

Abstract

The analysis of mechanical behaviors for grouted mudstone is the basis of studying the stability of broken mudstone area in tunnel after grouting. Through a series of grouting, mechanical and microscopic scanning tests, it is found that (1) there exists the grout dehydration effect (GDE) during mudstone grouting; (2) in order to reduce the GDE, a new water-retaining cement-basedgrouting material has been developed, and the unconfined compressive strength (UCS) of grouted specimen injected by the new grouting material was larger than that by original cement-based grouting material; (3) the grouted mudstone specimens mainly show tensile failure and shear failure after the action of axial stress; (4) the grouted specimen under pressure and lateral confinement has structural effect, which enhances with the increase of axial pressure. Astheincreasingof Water/Cement (W/C) ratio of grout, the UCS of grouted specimen decreased, whereas with the increasing in particle size of broken mudstone, the UCS increased; (5) the influence factors have different degrees of influence on the microscopic crack development in grouted specimen, where the W/C ratio has the greatest influence, followed by the particle size, while the overburden pressure has little influence. Moreover, the new water-retaining grouting material can effectively restrain the microscopic crack development. At last, based on the results of mechanical experiments for the grouted mudstone, the grouting reinforcement and stability control of broken mudstone area in tunnel floor were analyzed, the results of which showed that the new water-retaininggrouting material was effective to strengthen the broken mudstone tunnel floor.