喷射混凝土配合比设计

结合兰新铁路第二双线红山二号隧道围岩情况及开挖后初期支护喷射混凝土施工概况，主要介绍隧道开挖后初期支护用C25合成纤维喷射混凝土性能要求、现场施工原材料的选定、基准配合比计算、试拌拌合物性能、现场试喷强度及回弹率验证等过程为喷射混凝土配合比设计提供参考依据；最终确定可喷性好、早期强度发展快、回弹量小、粉尘浓度低符合环保要求、适合现场施工可喷性强的合成纤维喷射混凝土配合比设计。基于喷射混凝土施工工艺的特殊性，喷射混凝土配合比设计与普通混凝土配合比设计既有相似之处也有其特殊性，在遵守规范规定的前提下应特别重视现场试喷调整、强度验证这一过程，这是喷射混凝土配合比设计的重点和难点。

The Mixture Ratio Design of Shotcrete

With the surrounding rock situation of the Red Hill II Tunnel in the second double Lanxin railway and the general construction situation of the primary support shotcrcte after excavation, those things are presented for the reference of shotcrete mixture ratio design, such as the performance requirements of C25 synthetic fiber shotcrete used in primary support after tunnel excavation, the selection of on-site construction raw materials, the calculation of benchmark proportioning, the performance of trial mixtures, the process of the-spot testing spray strength and resilient rate verification. Finally synthetic fiber shotcrete mixture ratio design suitable for site construction is determined in which the sprayed performance is good, early strength development is quick, springback is small, dust concentration is low to meet the environmental protection requirement. Based on the particularity of shotcrete construction technology, there are both similarities and differences in the shotcrete mixture ratio design and the ordinary concrete mixture ratio design. In compllance with the premise of rules and regulations, the spot testing spray adjustment and strength verification process should be emphasized, which is the keystone and difficulity in the shotcrete mixture design.