Research On Observation And Calculation Method Of Reinforced Retaining Wall Based On Digital Speckle Technique

Digital Speckle Correlation Method(DSCM)has been put forward since the 18 th century,is widely used in the field of experimental mechanics of materials engineering and medical engineering.In the geotechnical engineering,it focuses on the study of the damage evolution of the rock mass structure,The duration of the experimental observation of the rock and soil creep model is so long that it will lead to the discontinuity of gray scale of image.And the rheological properties of the soil particles can cause the adhesion of small particles and the breaking of the soil mass,which will interfere the result of speckle measurement,this is why the application of digital speckle in the deformation and evolution of the mixed medium soil is not wide.This paper is based on the National Natural Science Foundation Project "the research on the long term working mechanism of the sand and gravel packing in the grid creep".A combination of model test and numerical simulation is adopted.The related program has been compiled a well.The main research contents and results are as follows:1)To compile the numerical speckle correlation program according to the characteristics of geotechnical model test.In this paper,the standard covariance correlation method is used as the correlation coefficient algorithm,and the natural speckle pattern is utilized to test the practicability of this method.The algorithm of mountain climbing and particle swarm optimization are compared through the numerical simulation,and the whole pixel search algorithm is determined based on the efficiency and accuracy.Finally,the accuracy of sub pixel interpolation algorithm is tested by numerical simulation.Namely,the average error of horizontal displacement is about 0.00179 pixel and the average error of the vertical displacement is 0.00187 pixel.The speckle measurement program is applied successfully in the direct sheer test of sandy soil,and the c and ? that we measured are almost as same as their actual value.At the same time,this paper has explored the factors which have impact on the accuracy of direct shear test,such as the different light,different particle size,the use of color sand etc.It has been proved that it will be more stable under good illumination condition and focus.It is found out that the normal lens distortion can be produced when using the common lens measurement,and the code rate will be compressed when the picture is transferred,which will cause imagedistortion and loss of details.2)In this paper,basing on the digital image processing technology,for pictures which are captured when natural light is treated as light resource will be disposed by gray histogram equalization process.The pictures which are captured when artificial light is treated as light resource will be disposed by gray scale segmentation and watershed algorithm.The method has been used in the test of long term drawing and the reinforced retaining wall of sand and gravel packing under long-term load.It shows that Histogram equalization of the gray processing and segmentation processing can enhance grain contrast,and highlight shadow image of pore.Gray segmentation method can be used to highlight the intensity of the gray range and suppress the gray region of interest;The watershed algorithm can be used to extract the target large particles to a great extend as well as to close and fill the pores between the particles,which can reduce the error and time of speckle search.3)Digital speckle program is applied for long term drawing test of reinforced soil band and it shows that the material which is made of both soil and steel bar is not to reinforce the whole soil body directly.Instead,the soil close to steel bar belt will produce a stress concentration belt and where is away from steel bar belt cannot be affected by the additional stress of the soil.