Scale effects of shallow foundation bearing capacity on granular materials were investigated to further evaluate the trend of decreasing bearing capacity factor, Nγ , with increasing footing width, B , observed by other researchers. Model-scale square and circular footing tests ranging in width from 0.025 to 0.914 m were performed on two compacted sands at three relative densities. Results of the model-scale footing tests show that the bearing capacity factor, Nγ , is dependent on the absolute width of the footing for both square and circular footings. Although this phenomenon is well known, the current study used a large range of footing sizes tested on well-graded sands to show that the previously reported modifications to the bearing capacity factor, Nγ , using grain-size and reference footing width do not sufficiently account for the scale effect seen in the test results from this study. It also shows that behavior of most model-scale footing tests cannot be directly correlated to the behavior of full...

Results of laboratory oedometer tests on reconstituted specimens of four clays prepared at different initial water contents, ranging from the liquid limit to 1.75 times the liquid limit, show that the intrinsic compression line may not be “unique” for a given soil. This suggests that the “intrinsic” parameter Iv, which is based on the constants of intrinsic compressibility, e100*, (void ratio corresponding to σv′=100 kPa), and Cc*, (e100*-e1000*), may in fact not be a truly intrinsic parameter of the soil, but is dependent on sample preparation. The positioning of the normalized compression curve in e-log-σv′ space is significantly influenced by the initial remolding water content, therefore resulting in differing values of e100* for a given soil depending on the initial water content. The influence of initial water content was greater for kaolinitic and illitic clay than for montmorillonitic clay. It is hypothesized that the difference in behavior may be attributed to differences in mineralogy. The resul...

Traditional bearing capacity theories for the ultimate capacity of shallow foundations assume that the thickness of the bearing stratum is infinite. The presence of a hard layer within a certain depth below the foundation can significantly influence the unit load supported by the soil. Therefore the original bearing capacity equations should be modified to account for this condition in determining the ultimate bearing capacity. In order to evaluate this phenomenon further, model square and circular footing tests were performed on a bed of well-graded sand. Test beds were prepared at three different relative densities corresponding to loose, medium, and dense conditions: Dr =24 , 57, and 87%, using five different sand layer thicknesses, H ; H∕B values of 0.5, 1, 2, 3, and 4, where B is the footing width. Results of the model scale footing tests show that the bearing capacity factor, Nγ , should be modified up to H∕B=3 , instead of H∕B=1 , as previously suggested. The footing shape factor, sγ , should accou...

This study uses lime and Class C fly ash, an industrial byproduct of electric power production produced from burning lignite and subbituminous coal, to study the plasticity reduction in highly expansive natural clays from Idabel, Oklahoma. This study is important, especially in Oklahoma, because most of the native soils are highly expansive and cause seasonal damage to roadways and structures. The addition of lime or fly ash helps to arrest the shrinkage and swelling behavior of soil. Four soil samples with the same AASHTO classification (A-7-6) were used in this study to show shrinkage variability within a soil group with the addition of lime and Class C fly ash. The plasticity reduction in this study was quantified using the linear shrinkage test. It was found that soils classified within the same AASHTO group had varying shrinkage characteristics. It was also found that both lime and fly ash reduced the linear shrinkage, however, the addition of lime reduced the linear shrinkage to a greater degree than the same percentage of Class C fly ash. Even though it takes much less lime than fly ash to reduce the plasticity of a highly expansive soil, it may be less expensive to utilize fly ash, which is a waste product of electric power production. Lime also has a lower unit weight than fly ash so weight percentage results may be misleading.

Two expansive soils were studied from a microscopic point of view to better understand the physicochemical, mineralogical, and microstructural changes that occur during Class C Fly Ash (CFA) stabilization. These changes were then related to macroscopic mechanical characteristics in order to better understand the mechanisms controlling expansive soil behavior. CFA stabilization achieved similar results as lime by activating cation exchange and pozzolanic reactions, which resulted in flocculation of clay particles and creation of interconnected assemblages. It was found that the CFA stabilization process reduced the plasticity index (PI), clay size fraction (CF), percent of swell (Δh), swell pressure (p_s), and volumetric water contents of the soil water characteristic curves (SWCCs), and increased the unconfined compressive strength (q_u). X-ray diffraction (XRD) analyses showed that there were negligible changes in mineralogy caused by CFA stabilization; however, there were reductions in the total amount of clay minerals. Significant changes in microstructure were revealed, however, as qualified from scanning electron microscopy (SEM) images. The existence of iron-oxide coating was verified by both XRD and energy-dispersive X-ray spectroscopy (EDXS) analyses. The coating resulted in chemically stable aggregates that resisted dispersion with hexametaphosphate. The combined effects of flocculation and coating reduced the water-retention property of the stabilized soils, decreased their swell potential, and increased the soil strength.