Study On Blasting Control Technology For Shallow-Buried Tunnel With Large Section Underneath Existing Highway

With the rapid development of China's highway and railway construction,the construction of newly built tunnels Underneath the existing roads will be more and more.The safety of existing roads are threatened due to the shallow buried depth and the poor surrounding rock when newly built tunnel been blasted and excavated.It's necessary to consider the real construction conditions to studied out safe and reasonable blasting scheme and design parameters to ensure the safe of the newly built tunnels and existing roads.Taking a new tunnel underneath NO.316 national highway as the research object.In this paper,based on the combination of theoretical analysis,field test and numerical simulation,the blasting control technology of shallow buried cross-section tunnel under the existing road is systematically studied.The main contents and conclusions are as follows:(1)The blasting stress wave in the rock are summarized and analyzed.At the same time,the attention law of PPV(peak partied velocity)of the elastic stress wave in the fully elastic body is deduced,and the theoretical calculation formula of the PPV of the porous blasting particle is modified to reveal the propagation attenuation law of the explosive stress wave.(2)Combined with the actual situation of a new tunnel exit under the 316 state section,through the relevant empirical formula and engineering experience,the parameters such as blasting equipment,cutting form,charge structure,driving footage and other parameters are determined,and the blasting scheme is established.(3)According to the actual terrain,engineering geological condition and construction method,the numerical model was established by using Midas GTS NX software to excavate and excavate the upper left and upper guide holes.The results show that the PPV,stress and displacement of road surface mass meet the requirements of relevant specification.(4)The blasting field test has been compeleted in the process of the new tunnel under NO.316 national highway.The results have showed that the minimum of the relative error between the calculated and the measured values is 1.68%and the average relative error is 12.46%.The calculated is very close to the measured,which shows that the formula proposed in this paper can reflect the influence of blasting vibration on existing roads to a certain extent and the formnla is reasonable and feasible.