No. 1 Gaoping tunnel on YiWan railway passes through T21j limestone. The tunnel is located in verticalcirculating karst zones, with the maximum overburden being 104m. The karsts along the tunnel are extremely developed, with a total of 51 karst caves having been discovered during the construction of the tunnel. By means of analysis on the karst caves discovered during the tunnel construction, the article makes a study on the features of the development of the karsts located in verticalcirculating zones. On basis of the features of the development of the karsts and the characteristics of the engineering structures, the article suggests a karst scale determination standard, recommends some karst treatment measrues and makes an assessment on the effect of the karst treatment.