Soft rocks, especially smectite bearing tuffs and mud stones, sometimes cause the serious troubles such as ground pressure, landslide and crumbling of cut slope.
To study preventive methods of the surface deterioration for smectite bearing soft rocks, experiments in laboratory were carried out. In these experiments, four kinds of preventive methods such as a soak method, a wet curing by covering with mat, an ion exchange method and a seal method have been attemped to six samples of soft rocks. In result, it has become clear to be closely related with exchangeable cation composition of smectite and effect of preventive method. All of the methods are effective to Ca-type smectite bearing soft rocks. On the other hand, only the seal method is applicable to Na-type one.
Field test by the seal method was carried out in tunnel consisted of Na-type smectite bearing tuff. The preventive affect using polymer cement or high molecular resin has been ascertained to extend from three to six months. This result indicates that the prevention of deterioration by the seal method is applicable in the case of short term to foundation rock at dam and cut slope etc.
