Research On The Method And Technology Of Direct Testing The Wall Pressure Of Contour Blasting Holes

As a blasting method that can effectively control excavation contour formation and damage disturbance,contour blasting has been widely used in infrastructure construction fields such as mining,transportation,and municipal engineering.The hole wall pressure,as the initial parameter of the explosion load acting on the rock mass,is the overall reflection of the effect of the explosion load and energy on the hole wall surrounding rock,and is one of the key parameters determining the blasting effect.The accurate acquisition of this parameter is of great significance for the scientific and reasonable design of contour blasting,the revelation of blasting mechanism,and the development of related blasting theories.Based on this,this thesis takes the on-site testing environment of contour blasting hole wall pressure as the basic condition,combines theoretical analysis and relevant experiments,and constructs a direct testing system for contour blasting hole wall pressure by revealing the actual force electric response characteristics of sensors and the transmission characteristics of explosion pressure signals.The reliability of the testing system is verified through onsite experiments,and finally,a method and technology for direct testing of contour blasting hole wall pressure are developed.The main research content is as follows:Based on previous research,a preliminary analysis was conducted on the testing environment of contour holes and the loading characteristics of hole wall pressure.The requirements for sensors in contour hole wall pressure testing were clarified,and a brief hole wall pressure direct testing system was constructed with a polyvinylidene fluoride piezoelectric sensor as the core.Based on the on-site environment,identify six key design points that affect the reliability and testing accuracy of the system,including sensor specifications,contact mode between the sensor and the surrounding rock of the hole wall and its piezoelectric characteristics,isolation of explosive heat,nondestructive transmission of test signals,impact of error capacitance on signal output,and parameter requirements for signal acquisition devices;The influence of the contact mode between PVDF and substrate on its piezoelectric performance was studied through SHPB indoor impact tests.It was found that when the lateral frictional resistance is small,the Poisson effect of PET on the outer layer of the sensor causes the sensor to bear lateral tensile stress,resulting in greater piezoelectric output.However,lateral tension causes plastic deformation or even failure of the sensor,so the piezoelectric coefficient no longer remains constant when subjected to impact pressure above 100 MPa.When the friction coefficient is large,the lateral frictional resistance provides it with a lateral constraint,and its piezoelectric output is only 1/3-1/4 of the former.At this time,the sensor is in the elastic deformation stage,and the ratio of the lateral constraint to the axial pressure is constant.At this time,the piezoelectric coefficient can remain unchanged throughout a large pressure range.Overall,when measuring the impact pressure of a sensor,a reasonable contact method should be selected to make the 3-axis pressure conditions clear or stable,so as to maintain stable piezoelectric output performance of the sensor.Contour blasting is accompanied by the release of high-temperature products and strong photothermal radiation.To avoid the impact of the pyroelectric effect of the sensor on the measurement results,the high temperature inside the hole and the direct heat transfer mode of the sensor are first analyzed.It is believed that thermal radiation and heat conduction should be the main factors.Based on this analysis,targeted insulation measures for the sensor are designed: it is composed of high reflectivity aluminum foil and low thermal conductivity PET in series,and its insulation effect is analyzed through a theoretical model.Indoor validation tests show that the structure has good insulation performance.Using a lossy cable transmission model to analyze the high-frequency signal transmission characteristics of coaxial cables,three key parameters that determine the signal transmission loss are identified: cable length,cable type,and signal frequency.Generate corresponding analog signals through signal generators and conduct cable signal transmission simulation tests to study the effects of cable connection methods,cable diameter,and other factors on the transmission characteristics of 10 k Hz～20MHz sinusoidal signals,providing a basis for determining coaxial cables during on-site testing.Research has been conducted on the impact of error capacitance on test results in testing systems,and it has been found that its impact can only be ignored when the parallel resistance is small or the parallel capacitance is large.In other cases,ignoring this parameter will lead to deviation in the test results.The error capacitance mainly consists of two parts.The first is the parasitic capacitance of the testing system,which remains constant during the impact load process.The second is the change in capacitance under the PVDF impact pressure,which is directly proportional to the impact pressure it is subjected to.In addition,a voltage output model based on error capacitance was established to analyze the impact of testing parameters such as sensors,impulse pressure,and circuit components on the output signal.The impact of error capacitance on test results under different testing parameters was quantified,and the signal output deviation caused by error capacitance in two measurement modes was compared.This provides a basis for optimizing the design of testing circuits and selecting circuit components in the testing system.The in-situ test results show that the wall pressure of contour blasting is mainly composed of high loading rate explosive shock waves and explosive gas pressure with long blasting time.The current mode is suitable for the former,but it is difficult to accurately capture explosive gas signals due to noise interference.The charge mode is suitable for testing the entire process of explosive gas and hole wall pressure,but the accuracy of shock wave pressure testing is relatively low compared to the current mode;Under the experimental conditions of this article,the explosive gas pressure plays a dominant role in contour blasting,as it is much greater than the shock wave pressure in various aspects such as peak pressure,action time,and impulse.In addition,the comparison between the experimental results and the corresponding theoretical results indicates the reliability of the direct testing method for hole wall pressure developed in this paper.