Study On Construction Method Of Firstly Curtain Grouting Before Blasting Excavation On Dam Core Foundation

Curtain grouting is usually the critical work item which constraining the total construction period during the construction of high core earth-rock fill dam in wide and deep valley. To solve the conflict between total construction period and curtain grouting, the method of "firstly grouting then excavation" is proposed. That is to penetrate the riverbed covering layer and weathered layer to complete the deep hole curtain grouting before river closure, and then after that to excavate the riverbed covering layer and weathered layer and pour the bottom slab concrete and complete consolidation grouting, and then re-grouting to strengthen the curtain within blasting affected depth to meet the requirements of design. Due to the quantity of curtain grouting after river closure, especially the quantity of curtain grouting within the riverbed stretch to construct the core, is reduced, the total construction period is shortened.Depth of re-grouting, i.e. the depth affected by blasting work, related to not only the construction period of re-grouting, but also the economic rationality, is the key factor to determine if the method is practicable, so all the study is focused on the depth affected by blasting work. The study method is based on vertical particle vibration, which is tested by hydraulic test, to survey the depth affected by blasting work and determine the depth of re-grouting.It is concluded from the results of experiments that the failure of completed curtain by blasting work is sure, but if the explosives amount, blasting method and shock-absorbing measures are optimized, the blasting affected depth can be controlled within proper limit.The re-grouting depth is studied to be 13.4m, after all the curtain re-grouting is finished, hydraulic test on 13 holes total 58 stretches are made, it is tested that all the water permeability rate≤3Lu, meet the requirements of design.The method of curtain grouting after blasting excavation is firstly adopted by Sinohydro Engineering Bureau 15 Co., Ltd. in foundation treatment of Heihe Dam core, it is proved the said method is practicable and successful, the construction period can be shortened by one year comparing to the traditional construction method, so the method, no matter the construction period, quality or the economic benefit, is a reasonable construction method with advantage.This is a operative study made by the author while solving the real problems of Heihe Project, during the study of MoE courses, large amount of first hand data were collected, analysised and studied and summarized, a series of fruits such as blasting test, system protection, underground particle vibration distribution were achieved, some of the experiments were made firstly in China, and some achievements were made firstly in China, which is valuable to later projects adopting the said method.