Evaluation Of Water-rich Crushed Sandstone Grouting Effect Based On Inversion For Permeability From Acoustic Velocity

As a common adverse geological condition,water-rich crushed sandstone stratum is easy to cause the geological disasters such as water gushing,mud bursting and collapse,which is not conducive to underground construction and foundation construction.Grouting is generally applied to reinforce and stop water in crushed rock stratum.At present,the hydraulic fracturing test is the most common method of grouting water-stop effect,but the test results only represent the average permeability of all strata,it is impossible to obtain the permeability of rock strata at precise depth in this way.Therefore,it is proposed to use the acoustic velocity of acoustic logging to invert the permeability of the stratum,which realizes the point-by-point detection of rock grouting water-stop effect.It is of great practical significance for expanding grouting detection methods and the application of acoustic logging.According to the characteristics of water-rich crushed sandstone,the acoustic velocity-permeability model in water-rich environment is established on the basis of the wave velocity-porosity model and permeability-porosity model in this paper.The relationship between the core acoustic velocity and permeability was compared with the model law by the core acoustic test and permeability test.The influence of pore structure parameters and filling parameters on the theoretical model was discussed by numerical simulation.Finally,the model was developed from theoretical research to engineering application of grouting effect evaluation.The main contents and conclusions of the study are as follows:(1)Based on the Wyllie-Clemenceau formula and the Kozeny-Carman equation,the theoretical model of acoustic velocity-permeability of water-rich sandstone is established with porosity as the medium.By the acoustic test and permeability test of water-rich sandstone core in the foundation grouting project in Hunan Province,it is found that the relationship between acoustic velocity and permeability is consistent with the theoretical model.The model shows that the relationship between acoustic velocity and permeability of rock is nonlinear and negatively correlated.The permeability decreases as a concave function with acoustic velocity,and there is a cut-off point of change rate.And based on the correlation between the exponent to the matrix nature and rock matrix acoustic velocity,the grouting model parameters are modified,and the fitting degree is improved.(2)On the basis of constructing the three-dimensional reconstructed core model with random pore structure,the core acoustic and permeability simulation tests were carried out by changing the parameters such as pore density,cell aperture and grouting filling degree.The correlation law of acoustic velocity and permeability and their change mechanism were analyzed.And it is found the consistency between the correlation law and the model.The influence of pore parameters and filling parameters on the related parameters of wave velocity-permeability function is revealed.(3)According to the acoustic velocity-permeability model,the permeability that is inverted by the acoustic velocity of high-density logging monitoring point is compared with the results of water pressure test,which verifies the reliability of the model in practical engineering application.The permeability index based on calculated permeability is constructed,and the permeability reduction ratio is selected as the permeability improvement index.The evaluation system of grouting effect is established on these indexes.The grouting engineering quality in the case is evaluated accurately by the system.