The present invention provides an impact type high pressure hydraulic excavation device for forming cylindrical hole on soil of tree growing land and a method of forming cylindrical hole using the same, which comprises a jet pipe having its first end connected with a high pressure water source a nozzle connected with a second end of the jet pipe for discharging the high pressure water source and forming a strong water jet and, an impact head, which is detachably assembled on the exterior of the jet head. The center of the impact head is provided with an ejection hole for discharging the strong water jet. The front end of the impact head is provided with a breaking portion for contacting and impacting the soil. The exterior of the impact head is provided with a guiding portion for controlling the diameter of the cylindrical hole on the soil. The impact type nozzle device utilizes the strong water jet to apply the impacting and dissolving force on a target region of the soil, such that the breaking portion may impact the soil in the target region to be rapidly loosened and thus the target region may be formed a cylindrical hole in a depth reaching the hardpan layer of the soil.一種於樹木生育地土壤形成柱狀孔穴之衝擊式高壓水力挖掘裝置及以該裝置形成柱狀孔穴之方法,包含:一噴管,該噴管之第一端連接一高壓水源;一噴頭,連接於該噴管之第二端,用以將高壓水源釋出並形成強力水射流;一衝擊頭,以可組卸之手段組裝於該噴頭外部;該衝擊頭之中心具有一供強力水射流釋出之出射孔,該衝擊頭的前端具有一用以接觸並衝擊土壤之破擊部,該衝擊頭的外部具有一控制土壤之柱狀孔穴直徑之導引部;該衝擊式噴頭裝置以該強力水射流對土壤之一目標區施加一沖激溶解力,以該破擊部撞擊該目標區之土壤使其加速鬆動,據以於該目標區形成一可深達土壤硬盤層之柱狀孔穴。10‧‧‧噴管20‧‧‧噴頭21‧‧‧噴水孔30‧‧‧衝擊頭31‧‧‧出射孔32‧‧‧破擊部321‧‧‧錐狀結構33‧‧‧導引部
