Experimental Study On The Strength Properties Of Lime-Treated Expansive Soil Affected By Climate And Environment Factors

In order to study the strength properties of lime-treated expansive soils affected by the change of climate and environment factors, the weak expansive soils from east Nanning which treated by lime are used as research objects, the initial treatment parameters are suggested by summarizing the results of previous studies, the indoor methods are used to simulate the effects of climate and environment factors on soils, and a lot of indoor geotechnical tests are carried out. The main results are as follows:1.A series of indoor geotechnical tests are carried out on lime-treated expansive clay, which to study its physical and mechanic properties, and to contrast the properties of the original expansive clay, the test results show that: its proportion, plasticity index decrease after treatment, its soil category changed from mealy sand into cohesive class; moreover, its maximum dry density decline while its optimum moisture content increase, which presents that the hydro-stability is markedly strengthened. The shear strength index increase while its compression coefficient decrease, it presents that the mechanical properties of lime-treat soils is greatly improved when compared to its original expansive clay. It basically inhibit the swell-shrinkage swell-shrink characteristics of the original expansive soil after treatment, to sum up, it reach the standards of highway embankment fill.2.Triaxial tests on treated specimens which subjected to 0-5 times of wetting-drying cycles are carried out by simulating the process of wetting-drying cycles on treated soil of embankment in natural state, the results show that:the wetting-drying cycles has great effects on the shear strength of lime-treated expansive soil. Its shear strength decrease with the increase of wetting-drying times, of which has great effects on cohesive strength, however, the friction angle has obviously decreased after the first wetting-drying cycle, after which the variation tendency of friction angle has no obvious change, but its change range is small. It is suggested that the growing fissures of soil body caused by wetting-drying cycles is the key cause that lead the decline of soil strength.3. The devices remodeled from variable-head permeameter are used to simulate the leaching effect of rain on soil, a series of tests are carried out on soil specimens subjected to different leaching time. The test results show that the Ca2+ content of lime-treated soil decrease with increase of leaching time, while the shear strength and cohesion decrease with increase of leaching time, the linear shrinkage ratio of soil specimens has tiny increase but finally reach a constant state, however, the free-swell ratio has no obvious change. It is found that limited leaching has great effect on cohesion and shear strength of lime-treated soil but has little on its swell-shrinkage properties. The curing environment of lime-treated soil is changed by the process of leaching, which has weaken the structure of soil body, however, leaching has great effect on Ca2+ content in free water layer, but has little on bound water layer.4. Triaxial tests on specimens of different water content are carried at different temperature, the results present that:the shear strength of lime-treated expansive soil is quite disparity in different humiture environment, which the specimens at the same dry density. The specimens are at the same water content, its shear strength increase with the incline of ambient temperature, the strength of treated soil present obvious heat hardening characteristics; when at the same temperature, the shear strength decrease with the increase of water content. Finally, by contrasting the effects degree of all the factors on strength, it is suggested that the process of wetting-drying cycles has greatest impact on the stability of embankment constructed by treated soils.