| Effect of rain and sunshine in nature cause great damage to the strength of expansive soil;it is important to study the effect of dry-wet cycles on the shear strength of expansive soil,especially under the actual loads.At present,the studies on dry-wet cycles of expansive soil are mainly based on laboratory experiments.There are two kinds of test methods for dry-wet cycles of expansive soil.One was carried out under no loads.The other method used counterpoises on the ring-knife to simulate the vertical loads.However,in order to control the range of dry-wet cycle,it had to remove the vertical loads when the water content was calculated by weighing.The stress state of the sample was different from the engineering practice in the two kinds of methods.Based on the limitation,this paper studied the device for dry-wet cycles under simulated loads,and used the device to carry out the relevant verification tests.The main achievements were as follows:(1)A device,for dry-wet cycles and direct shear tests,which could simulate the real loads was developed.The device used ring-knife to simulate the ambient loads effected by the ambient soil at a certain depth.And the vertical loads of the overlying soil was simulated by lever or counterpoises.After the completion of the wet-dry cycles scheduled,the device could be directly installed in the special shear boxes to carry out the direct shear tests while no disassembling and reducing the disturbance.(2)The water content of samples could be controlled within 1%when the dry-wet cycles had carried out by this device.By changing the length of the lever,the vertical loads could be adjusted flexibly so as to simulate the loads at different depths during the dry-wet cycles of expansive soil.(3)The samples were always under loads when the range of dry-wet cycles had not greater than±5%.The range of water content in the expansive soil wrapping embankment was generally not more than ±5%;our studies could be used as a reference for this engineering case.(4)By the help of this device,there was no unloading during the dry-wet cycles and better simulated the actual loads.The 0 ~ 6 cycles were carried out under 0kPa,5kPa,15 kPa,and 30 kPa,then carried out the unconsolidated quick shear tests and studied how the dry-wet cycles under loads affected shear strength of expansive soil.(5)The numerical values of C and Φ under loads were higher than those without.The cohesion decreased with the increase of dry-wet cycles,and the decreases of cohesion varied under different loads.Compared with the samples that had not experienced dry-wet cycles,the internal friction of samples experienced dry-wet cycles reduced greatly.The internal friction of the samples experienced different cycles fluctuated slightly.(6)The dry-wet cycles caused cracks in the samples and decreases of shear strength.The existence of the ambient loads and vertical loads limited the shrinkage cracks of the soil effectively,and greatly restrained the reduction of shear strength,especially that of cohesion.After dry-wet cycles,the density of the sample changed,and ambient loads and vertical loads played a limiting role in the reduction of the density,which restrained the reduction of shear strength at a certain extent. |
