| In geotechnical engineering,pressure(stress)is a very important parameter,which is an important reference index in geotechnical engineering calculation and structural design;it is also very important in all aspects of the project construction cycle,such as the stress state of the initial support in tunnel construction,which is very helpful to judge its stability and safety.It is the importance of pressure(stress)parameters in geotechnical engineering that determines the development of pressure sensors in geotechnical engineering.The monitoring technology formed by pressure sensor,electronic acquisition and transmission equipment has also been widely studied and applied in various fields.In geotechnical engineering,the stress monitoring based on pressure sensor is also widely used in the stress state monitoring of geotechnical engineering structure,stress state monitoring of rock-soil mass,construction process monitoring,support and reinforcement stress monitoring.These applications are of great significance for the study of stability and safety of engineering.The pressure sensor with superior performance is the basic instrument to provide accurate monitoring data for these monitoring applications,so the research of pressure sensor is particularly prominent.There are many types of traditional pressure sensors,their working principles are different from each other,and they have their own uniqueness.However,most of the traditional pressure sensors are made of rigid materials,especially the internal sensitive elements,which are not flexible.After many times of fatigue loading or large deformation,they are prone to mechanical damage.In view of this,the liquid metal pressure sensor with a certain degree of flexibility was fabricated by PDMS and gallia-based liquid alloy based on the related research results in the field of flexible electronics.And a monitoring system is formed with data acquisition and transmission equipment to carry out remote real-time stress monitoring test in the actual project.The main work of this paper is divided into the following four parts:1.Firstly,we compare the working principle of the traditional pressure sensor,clarify their structural characteristics,and select the appropriate metal shell materials and the materials for making the flexible sensing elements.Secondly,the basic principle of resistance pressure sensor is determined as the basic working principle of liquid metal pressure sensor.The working principle is simple and feasible,and the detection equipment is easy to get.Then,the calculation method of key technical indexes such as repeatability,hysteresis and basic error in pressure sensor is introduced.In the end,the manufacturing technology of liquid metal pressure sensor is introduced.2.The liquid metal pressure sensor is designed,including the design of metal shell and two kinds of sensitive elements(single pressure PDMS chip and multi-purpose PDMS chip).The deflexion of metal shell under pressure is analyzed theoretically,and the manufacturing process of two kinds of PDMS chips is introduced in detail.The resistance change of two kinds of PDMS chips under pressure is also analyzed and the capacitance changes of the multi-purpose PDMS chip under tension is also derived.3.The calibration experiments are carried out,including the calibration of the pressure sensor made by two kinds of PDMS chips,and the calibration experiment when the multipurpose PDMS chip is stretched and bent.Firstly,the instrument needed in the experiment is introduced.Secondly,the calibration data is fitted,and the single variable nonlinear problem is transformed into multi linear problem for analysis,which reduces the workload of data processing.In addition,the experimental results of the two PDMS chips are analyzed.4.The stress monitoring system of geotechnical engineering is formed by using liquid metal pressure sensor,collection device and transmission equipment,and the actual stress monitoring test is carried out.Firstly,the composition and performance of the stress monitoring system are introduced.Secondly,the practical operation of liquid metal pressure sensor is introduced.And then,the contact stress monitoring test between surrounding rock and shotcrete is carried out in the actual tunnel engineering.Finally,the monitoring results are analyzed,and the improvement measures for the problems and deficiencies encountered in the test are put forward.In this paper,the liquid metal pressure sensor is designed,manufactured and calibrated.It forms a stress monitoring system with data acquisition equipment and transmission equipment,and successfully carries out the stress monitoring test in the actual project,which provides valuable experience for the follow-up research and development. |
