The Research Of Application And Regularity Of Pressuremeter Test In Subway Project In Gangdy Plain

At present,more than 10 subway lines will be built in Harbin City.Subway geotechnical surveying is part of the subway construction project,which will cost a large amount of capital in the subway exploration phase.However,when determining the bearing capacity of the foundations in Harbin,the result of pressuremeter test has not been taken inot account.The pressuremeter test has various of advantage such as:easy to operate and measure the deep soil’s geotechnical properties.It’s economical and not limited by groundwater.It has been widely used in geotechnical engineering surveys,so it’s meaningful to grasp the application of pressuremeter test in this region.This paper is based on a certain section of the subway Line 3 of Harbin City.The original experimental data were all obtained from on-site in-situ tests and laboratory tests.This paper have analyzed the result regularity of the pressuremeter test in the Gangdy plain in the first part,and then compared result with the laboratory test’s and the standard penetration test’s and the cone penetratiaon test’s in the second part.Finally,this paper discussed the correction coefficient of the pressuremeter test.The main research conclusions are as follows:（1）In the Upper Pleistocene Harbin Formation(Q₃²hr^al+pl),the1)（the standard value of the bearing capacity of foundation）has a periodicity which is about 5m.During each periodicity,the1)increases firstly and then decreases,and the next cycle is higher than that of the previous cycle.This rule is not obvious in the upper lacustrine of the middle Pleistocene Upper Lake Formation（Q₂²h^l）.Only a few holes have that rule.（2）There are differences between the results of the survey test methods for silty clay in the Gangdy plain.The sequence of the bearing capacity of the foundation is pressuremeter test,laboratory test,standard penetration test,cone penetration test,and specification.（3）After analyzed the experimental data obtained from 14 pressuremeter holes,the mean value of（the plastic load）of the Upper Pleistocene Harbin Formation（5¹5m underground depth）is 350kPa.The mean value ofin the alluvial-diluvial layer（15³0m underground depth）of the Upper Nongshan Formation of the Middle Pleistocene is 700 kPa.The load level during the test of the former is 50kPa⁷0kpa the latter 100 kPa to 140 kPa,which are higher than the general requirement of 25⁵0 kPa or 50¹00 kPa.It shown that the clay layer in the Gangdy plains has good mechanical properties.（4）The trend of the pressuremeter test’s result in the upper Pleistocene Harbin Formation had the same as those of other experimental results.There were a strong correlation between them.This paper proposed a corresponding correlation equations.That were good for the application of the later pressuremeter test.But the correlation in the upper lacustrine of the middle Pleistocene Upper Lake Formation had larger difference.By analyzing the characteristic curves of the pressure vessels,the results shown that the holes’quality,loading level,and loading rate were the key factors which affecting the results of the pressuremeter test.