Abstract:Clay hardening grouts is much superior to others when it is applied for roadbed enforcements in karst areas, with advantages such as its lower construction costs,simple and practical technology,good properties for intercepting groundwater seepage,and anti-seismic capability. In this paper,a series of grouting simulating tests show that it is feasible to reinforce roadbed horizontally in karst areas. The corresponding formula for making this grouts is obtained. For example,clay hardening grouting is done through seepage in rocks and its unconfined compressive strength (with samples cured up to 28 days) is 0.928 MPa. Its optimum prescription is made up of 5~15% cement,1~5% water glass,1~3% special hardening agent and viscosity of mud is above 30 s. Through its practical applications in Luozhan railway line,a good economic and technically effective technique has been achieved.