Study On Saturation Testing Method Of Cohesiobless Soil Model Test

Physical simulation test of engineering site is an important technical means to study the occurrence mechanism of earthquake damage and evaluate engineering earthquake damage.Saturated cohesionless soil test,especially liquefaction simulation,is the current project needs and research hotspot.Saturation is a key factor in saturated clay-free model.History of unit tests has shown that there is a consensus in the research field that saturation has a significant impact on the test results of saturated cohesionless soil.Taking liquefaction test as an example,in the range of saturation from 0.98 to 1.00,it reduces by 1%,and the anti-liquefaction cyclic stress ratio can increase by more than 30%.Therefore,the B-value method is developed to control the saturation of the test model,and it has become one of the control standards of current test moulding.The saturation technology of model test mainly refers to unit test,but the analysis shows that the B-value saturation control method commonly used in unit test is not suitable for model test and can not be extended directly to model test.At present,the saturation control method of model test still depends on experience,which is incompatible with the importance of model test and the requirement of quantitative control for prototype simulation.Because the test results lack stability and transverse comparability,it is urgent to establish a saturation control method and standard for geotechnical model test.Based on the urgent need for saturation control method in cohesionless soil model test,this paper aims to explore a reasonable method of model saturation test.The main related research work is as follows:1)The main methods of saturation sample preparation and saturation evaluation in cohesionless soil saturation model tests are summarized.It is pointed out that the saturation control at present mostly depends on experience and the B value standard in unit tests is not suitable for model tests.In order to improve the stability and transverse comparability of model test results,it is urgent to establish a saturation measurement method for cohesionless soil samples suitable for model test.2)On the basis of Boyle-Malliot's theory of physics,a set of testing methods for saturation of cohesionless soil is put forward,and relevant instruments and test error analysis methods are developed for saturation testing of cohesionless soil model.The validity of the saturation testing method is proved by a set of parallel tests and the definition method of comparative saturation.3)By using the proposed saturation test method,the saturation effects of water sinking method(degassing water),vacuum flooding method and vacuum dripping method commonly used in current model tests are compared and studied.It is found that the saturation effect of water sinking method is poor,the upper limit of saturation is about 0.995,which is equivalent to about 0.8 saturation of unit test B value.The saturation of vacuum flooding method and vacuum dripping method is higher,and the upper limit of saturation is about 0.998,which is equivalent to about 0.9 saturation of unit test B value.4)The relationship between sample saturation and immersion time was studied.Based on the comparative test results,it is pointed out that the saturation increases with the increase of immersion time,but the trend slows down gradually,which conforms to the hyperbolic function of time.In the controllable time,the saturation sampling method controls the upper limit of sample saturation.Then two sets of saturation methods for cohesionless soil sample preparation are recommended from two dimensions: fine control and easy to use.One is the refinement method based on vacuum flooding method,and the other is the optimal saturation under the condition of only using water sinking method.