| Blasting construction method is mainly used when the open caisson foundation of the bridge in the process of excavation encounters special geological conditions, such as the big boulder, hard soil layer, cementation layer. Controlled loose blasting is a special blasting form. When the open caisson foundation passes through the special geological conditions and sinks to the design elevation by using controlled loose blasting, many problems appear. Especially when the open caisson foundation has already sunk about 10m, and the serious hard glued layer of gravel stone appears, the controlled blasting work is more difficult. This thesis introduces the construction methods and corresponding controlled loose blasting which are used in the extra-long bridge of Hutuo River in Shuohuang Railway line, where the 26 open caisson foundations pass through the land waste cementation layer as deep as 2.2-2.4m. Continuous and multipoint controlled blasting is adopted in special geological condition, such as gravel glued layer, in the process of the open caisson foundation subsidence. The following related to these problems are researched:1. Based on the collection and analysis of the domestic and foreign data, and combined with the past construction experience of controlled blasting, the rational design is made. Through this design, the problems have been solved, such as the design of hole gird parameters, the control of the maximal charge weight, etc. It is also considered: When land waste cementation layer appears during the subsidence of the open caisson, the design of controlled loose blasting is approximately the same as the design of controlled blasting when the geological condition appears in the past, and as the change of the cementation layer in intensity and thickness, the greatest powder quantity in each controlled blasting must be controlled to ensure the integrity of the open caisson.2. By careful analysis to the geological data and combined with the past construction experience of controlled blasting, taial blasting has been down and the design of blasting parameters are adjusted.3. By the design of controlled loose blasting, some blasting parametershave been perfected and adjusted to the large and deep land waste cementation layer. All these works can make controlled loose blasting to meet the demand of the construction. |
