“硬软夹层”条件下深浅结合方形布孔爆破技术试验研究

Experimental Study on Blasting Technology of Square Hole Layout with Deep and Shallow Holes under Condition of Hard and Soft rock Layers

某矿山控制爆破工程要求爆破后粒径小于0.4 m,但该区域为“硬软夹层”地质构造,采用传统爆破方法在孔口堵塞段极易产生大块,爆破质量难以满足要求。为改善爆破质量节约施工成本,借鉴深浅结合方形布孔技术,分别在现场工况的基础上以中间浅孔深度为0 m、4 m、5 m、6 m、7 m开展爆破试验研究。首先采用ANSYS/LS-DYNA有限元软件开展数值模拟试验,建立了上半部采用RHT本构关系的石灰岩模型,下半部采用HJC本构关系的泥灰岩模型,形成“硬软夹层”构造。随后在多组数值试验中初步获取相对较优的中间浅孔深度,分析不同试验条件下岩体损伤分布特征与爆炸有效应力分布规律。由于ANSYS/LS-DYNA并未将爆生气体的作用考虑在内,因此为了得到更准确的实验结论,同时考虑到不宜过度增加爆破炸药消耗,结合项目实际情况,选用4 m、5 m中间浅孔深度进行现场爆破试验。研究结果表明:采用深浅结合方形布孔的措施降低爆破大块率是有效的。采用中间浅孔深度为5 m时,可以降低曲率系数Cc与爆破大块率。技改前平均大块率约为64.4%,技改后0.4 m以上的大块率可降低至38.1%左右,使得爆堆级配达到良好水平。其降低大块率效果优于原爆破方案及4 m中间浅孔方案。

The blasting fragment size of a mine is required to be less than 0.4 m.However,this area has a geological structure consisting of both hard and soft layers,which makes the traditional blasting method easy to produce boulders,and the blasting quality difficult to meet the requirements.In order to conquer the problem and save the construction cost,blasting tests on square hole layout with both deep and shallow holes were carried out with the middle shallow hole depths of 0 m,4 m,5 m,6 m and 7 m.Firstly,ANSYS/LS-DYNA finite element software was used to carry out numerical simulations with a limestone model with RHT constitutive relation in the upper part and a marl model with HJC constitutive relation in the lower part,forming a hard-soft interlayer structure.Then,numerical tests were conducted to initially obtain more optimal middle hole depths,and the distribution characteristics of rock mass damage and the distribution law of blast effective stress under different test conditions were analyzed.Since ANSYS/LS-DYNA does not take the effect of detonation gas into account,the middle shallow hole depths of 4 m and 5 m were selected for on-site blast tests in order to obtain more accurate experimental conclusions and not to excessively increase explosive consumption.The research results show that it is effective to reduce the blasting boulder yield by square hole layout combining deep and shallow holes.When the depth of the middle shallow hole is 5m,the curvature coefficient Cc and the boulder yield can be reduced.Before the technology optimization,the average boulder yield was about 64.4%,and the rate of fragments larger than 0.4m have been reduced to about 38.1%after the technology improvement,making the blast fragmentation to a favorable level.So,the scheme of 5 m shallow holes has a better effect of reducing boulder yield than the original blasting scheme and the scheme of 4 m middle shallow hole.