Research On 3D Advanced Geological Forecasting Technology For Newly Built Tunnels

The construction of new tunnels is often accompanied by bad geological bodies such as fault fracture zones,weak interlayers,and karst caves,which often cause serious consequences such as delays in construction,economic losses,and even casualties.Therefore,it is important to find out the geological conditions along the tunnel in advance.Seismic wave method advanced prediction technology has a long detection distance,and can accurately and intuitively predict complex geological hazards in front of the palm face.However,due to the complexity of the tunnel space environment,seismic wave method advanced detection still has many problems.In order to improve the precision and accuracy of the advance detection of the seismic wave tunnel,this paper studies through a combination of theoretical analysis,numerical simulation,and field experiments.The main contents and conclusions are as follows:Based on the theory of elastic media,the propagation law of artificial seismic waves in non-uniform media was analyzed.It is found that the initial stress will affect the parameters of seismic waves.The relationship between the change in the pressure gradient of two particles and the seismic signal parameters when an artificial wave passes from the non-prestressed half-space to the prestressed half-space is obtained.Combined with the tunnel 3D seismic survey technology,the advantages and disadvantages of common tunnel advance detection and observation methods were analyzed,and a tunnel directional advance forecast observation system with a bidirectional offset is proposed.By calculating the coverage times of three types of observation methods,9 detectors,12 sources observation system is more suitable for the tunnel environment.Using ANSYS/LS-DYNA to establish a numerical model,the propagation laws of seismic waves under different geological conditions were calculated and analyzed.The calculation results show that soft rock masses are sensitive to seismic wave frequencies,and hard rock masses are not sensitive to seismic wave frequencies;High frequency waves decay fast,low frequency waves decay slowly,and low frequency waves are more penetrating than high frequency waves and can travel longer distances;Seismic waves consume a lot of energy as they pass through weak interlayers;Through frequency spectrum analysis,it is found that the numerical fitting curve of the direct wave main frequency and the bandwidth is attenuated by a power function,and the numerical fitting curve of the main frequency and the bandwidth of the reflected wave is a constant function;By analyzing the three-dimensional model seismic gathers,it is found that various reflected wave information can be clearly distinguished,and the feasibility of the observation system established in this paper is verified..Through field hammering experiments along the Zhang Jihuai railway,the excitation law of artificial seismic waves under different lithological conditions was analyzed.The research results show that the main frequency of hammering earthquakes is mainly concentrated around 125 Hz and 325 Hz.And as the strength of the rock mass increases,the proportion of artificial waves with high frequency components gradually increases.The above research results were applied to the field engineering example.By comparing the prediction results with the actual disclosure,the two basically match,which verifies the reliability and accuracy of the advanced geological prediction of the seismic wave method proposed in this paper.