Experimental Study On Shear Strength And Deformation Characteristics Of Unsaturated Mu Us Sand

Most present researches of Unsaturated soil mechanics are based on the suction controltest. However, there is a wide gap between the Unsaturated soil mechanics and realengineering problems because of the inefficiency and complexity of the tests. Unsaturated soilengineering problems take place frequently while the geotechnical engineers are unable tocompletely interpret the unsaturated soil character by conventional tests. Therefore it is ofgreat reality and theory meaning to interpret the differences and relations of the unsaturatedsoil character by using two different testing methods.In this thesis, taking Mu Us sand as investigative subject, the deformation and shearstrength characteristics of Mu Us sand are analyzed through the press-panel test, the suctioncontrol and moisture content control tri-axial test. The main research work and creative resultsare summarized as follows.1. To improve the present Ceremic plate extractors, I recommend using electronic pressuregauge to improve the accuracy of the Suction control, using electronic balance and settingevaporation-control group to realize the accurate measurement of moisture in soil samplevariation, establishing a data acquisition system to avoid the error accumulation caused bytesters in recording process.2. In order to make up the defect of Tri-axial apparatus GDS, I recommend using low rangeand high accuracy air vent valve and electronic pressure gauge to realize the accurate controlof low suction, using high accuracy electronic balance and setting evaporation-control groupto realize the accurate measurement of moisture in soil sample variation, using a voltageregulators to greatly decrease the voltage caused discretization of the experimental data.3. With the results from tri-axial and the press-panel test, we concluded that state path effectsthe Mu Us sand. In the wetting path, the value of c increases and has a peak while the value ofφ gradually decreases. In the dehydration path, the value of c decreases and has a peak whilethe value of φ gradually increases. After comparing the shear strength values of different statepath, we know that under the same suction the shear strength obtained in the dehydration pathis higher than the shear strength obtained in the wetting path.4. Tri-axial test results show that saturated Mu Us sand is characterized by strain hardening and compaction. In the wetting path sand the strain softening is obvious while in thedehydration path sand contracting first and then dilating during shearing.5. Based on Duncan-Chang nonlinear model, with the results from Tri-axial tests and thesoil-water characteristic, we can conclude: Duncan-Chang nonlinear model parameter K withmoisture (suction) changing occurs peak (peak value in steep zone of the soil-watercharacteristic curve); Effected by water status path, under the same suction the value of K Inthe dehydration path is higher than in the wetting path; From saturated to dry the value ofmodel parameter n increases. Therefore we know the value of Ei/paof Mu Us sand with thewater content (suction) changing has a peak.