Triaxial Experimental Study On Strength Characteristics Of Expansive Soil In Hefei Area Under Larger Confining Pressure

With the development of the national economic construction and the acceleration of urbanization,the population has migrated to the large and medium-sized cities ceaselessly.Hefei is the capital city of Anhui Province,the Vice Center of the Yangtze River Delta and the country's first high-tech innovation center,has its important strategic position and broad prospects for development.To meet the needs of urban development,the height and density of the building in Hefei increases constantly.Meanwhile,in order to solve the problem of urban traffic congestion,the construction of underground traffic-subway is also carried out in the city.In these projects,soil is often under larger confining pressure.At present,the conventional triaxial test indexes are used to calculate the strength and stability of this kind of soil due to the limitation of the test equipment.This is obviously inconsistent with the stress state of the soil.Therefore,the larger confining pressure triaxial test of expansive soil in Hefei city was carried out,the shear strength indexes were studied through experiment,and corresponding parameters were obtained,which will provide a scientific basis for calculating the strength and stability of the soil under the larger confining pressure condition.(1)According to the maximum confining pressure value of test instrument,the three various conditions can be divided into conventional confining pressure of 100~300kPa,middle confining pressure of 600~800 kPa,large confining pressure of1100~1300 kPa.To ensure the consistency of the test's results,the 280 soil samples were obtained from the same foundation pit,and the number of the effective samples was 225.(2)In this paper,process unconsolidated undrained test(UU),consolidated undrained test(CU),consolidated drainage triaxial test(CD)were performed for three various confining pressure condition,respectively.The results of experiment indicated that the strength of the soil decreased with the increment of confining pressure and showed different attenuate pattern with the change of consolidation and drainage condition,which gradually weakened by unconsolidated undrained(UU),consolidated drainage(CD),consolidated undrained(CU)sequence.(3)The Mohr envelope in different confining pressure state was drawn up according to the failure Mohr circle of triaxial test under the same consolidation and drainageconditions.And do some research about fitting methods.Obtain the basic linear Mohr envelope of Hefei expansive soil under the confining pressure was obtained by carrying out corresponding fitting on these Mohr envelopes.The conclusions of the fitting data indicated that the Mohr envelopes were consisted of parabolic pattern for unconsolidated undrained(UU)and logarithmic twice pattern for consolidated undrained(CU)and consolidated drainage(CD),which will provide some ideas for selecting proper intensity indexes of soil in medium and large confining pressure conditions in Hefei area.