Hydromechanical behavior of unsaturated expansive clay under repetitive loading

Compacted layers of expansive soils are used in different engineering projects,such as subgrades,engineered clay barriers,and buffers for radioactive waste disposal.These layers are exposed to a variety of stresses and wetting conditions during field serviceability.Coupling between hydraulic and mechanical repeated loading provides insight understanding to the induced progressive deformation of expansive clay.This study was conducted to investigate the hydromechanical behavior of unsaturated compacted expansive clay under repeated loadingeunloading(RLU)conditions.Two series of onedimensional(1D)oedometer tests were conducted under controlled matric suction up to 1500 kPa using the axis translation technique(Fredlund soil-water characteristic curve device,SWC-150).The first test series was carried out at different levels of controlled matric suction for non-repeated loading eunloading(NRLU)cycles.RLU cycles were applied in the second test series at different repetitivestress levels and under different levels of matric suction.The results indicated increasing axial wetting strainε_(a)(s),axial swell pressure ss(s),compression index C_(c)(s),and swell index C_(s)(s)with suction reduction.The estimated loadecollapse(LC)curves obtained from NRLU series(LCN)and RLU series(LCR)indicated increasing yield stress sy(s)with increasing suction.This is attributed to the developed apparent cohesion between soil particles,which in turn rigidifies the material response.Applying repetitive loading induced a notable reduction of compression index C_(c)(s)at the same level of suction,whereas swell index C_(s)(s)seems to be independent of repetitive loading.Finally,repetitive loading exceeding initial yield stresses results in plastic hardening and,hence,enlargement of yield stress locus(i.e.LCR curve).

Experimental study on hydro-mechanical coupling behaviours of highly compacted expansive clay

Highly compacted expansive clays have been usually considered as a possible material for sealing and backfill in deep geological disposal of radioactive waste. In this condition, the material is simultaneously subjected to water infiltration from the geological barrier and stresses generated by the swelling of engineered barriers in confined conditions. Its behaviour under hydro-mechanical loading is essential to the safe design of the whole storage system. In the present work, MX80 bentonite, a kind of expansive clay from Wyoming, USA, was studied. After compaction, its dry density was 1.8 Mg/m^3 and its initial suction was 110 MPa. Firstly, the soil was humidified under controlled suction and free-swelling conditions. Significant swelling was observed. Secondly, four values of suction of 110, 39, 9 and 0 MPa were employed to perform isotropic compressive tests at constant suction conditions. That allowed studying the effect of suction on the yield pressure, elastic and plastic compressibility parameters. The results show that the elastic and plastic compressibility parameters increase when the suction decreases. The relationship between these parameters and the logarithm of suction can be linearly correlated. The yield stress drastically decreases upon wetting under free-swelling conditions, from 12 - 18 MPa （at an initial suction of 110 MPa） to 0.2 MPa at saturated state.

Cement and Lime Stabilization Effect on the Evolutivity of an Expansive Overconsolidated Clay

This paper presents and analyzes the results of a series of compaction,fragmentability and damage tests performed on an expansive overconsolidated clay treated with cement and lime.This clay was obtained from the urban site of Sidi-Hadjrès city(wilaya of M'sila,Algeria),where significant damages frequently appears in the road infrastructures,roadway systems and light structures.Tests results obtained show that the geotechnical parameters values deduced from these tests are concordant and confirm the evolutivity of this natural clay treated with composed Portland cement or extinct lime and compacted under optimum Proctor conditions.

Behavior and characteristics of compacted expansive unsaturated bentonite-sand mixture

Limited studies dealt with the expansive unsaturated soils in the case of large-scale model close to the field conditions and therefore, there is much more room for improvement. In this study, expansive （bentonite–sand （B–S） mixture） and non-expansive （kaolin） soils were tested in different water contents and dry unit weights chosen from the compaction curve to examine the effect of water content change on soil properties （swelling pressure, expansion indices, shear strength （soil cohesion） and soil suction） for the small soil samples. Large-scale model was also used to show the effect of water content change on different relations （swelling and suction with elapsed time）. The study reveals that the initial soil conditions （water content and dry unit weight） affect the soil cohesion, suction and swelling, where all these parameters slightly decrease with the increase in soil water content especially on the wet side of optimum water content. The settlement of each soil at failure increases with the increase in soil degrees of saturation since the matric suction reduces the soil ability to deform. The settlement observed in B–S mixture is higher than that in kaolin due to the effect of higher swelling observed in B–S mixture and the huge amount of water absorbed which transformed the soil to highly compressible soil. The matric suction seems to decrease with elapsed time from top to bottom of tensiometers due to the effect of water flowing from top of the specimen. The tensiometer reading at first of the saturation process is lower than that at later period of saturation （for soil sample B–S3, the tensiometer #1 took 3 d to drop from 93 kPa to 80 kPa at early stage, while the same tensiometer took 2 d to drop from 60 kPa to 20 kPa）.

Theory and Practice of Ionic Soil Stabilizer Reinforcing Special Clay

The change in the thickness of water films of special clay particles such as sliding clay, red clay, and expansive clay is an important factor in producing geological disasters and geological environmental damage. In order to reduce the thickness of water films, ionic soil stabilizer （ISS） is used to treat sliding clay, red clay, and expansive clay. Direct shear test of sliding clay and shrinkage, free swell rate, zeta potential, and cation-exchange capacity of red clay and expansive clay are carried out. The results show that as the plastic indexes of special clay soil decrease, the shear strength of sliding clay increases, the shrinkage and free swell rate of red clay and expansive clay decrease, and the thickness of the water film thins after treatment with the ionic soil stabilizer. Therefore, the geological engineering disasters caused by changes in the thickness of water films of special clay can be effectively inhibited.

Comparison of short-term and long-term performances for polymer-stabilized sand and clay

A series of tests were carried out on sulfate rich, high-plasticity clay and poorly-graded natural sand to study the effectiveness of a methylene diphenyl diisocyanate based liquid polymer soil stabilizer in improving the unconfined compressive strength （UCS） of freshly stabilized soils and aged sand specimens. The aged specimens were prepared by exposing the specimens to ultraviolet radiation, freeze-thaw, and wet-dry weathering. The polymer soil stabilizer also mitigated the swelling of the expansive clay. For clay, the observations indicated that the sequence of adding water and liquid polymer had great influence on the gained UGS of stabilized specimens. However, this was shown to be of little importance for sand. Furthermore, sand samples showed incremental gains in UCS when they were submerged in water. This increase was significant for up to 4 days of soaking in water after 4 days of ambient air curing. Conversely, the clay samples lost a large fraction of their UCS when soaked in water; however, their remaining strength was still considerable. The stabilized specimens showed acceptable endurance under weathering action, although sample yellowing due to ultraviolet radiation was evident on the surface of the specimens. Except for moisture susceptibility of the clay specimens, the results of this study suggested the liquid stabilizer could be successfully utilized to provide acceptable strength, durability and mitigated swelling.