Plastic behavior of soils and shales due to heating and loading under constant elevated temperature is discussed in terms of a thermoplastic version of the critical state model. Rules for dependence of the yield surface on temperature in the elastic states and at yielding are proposed. The elastic domain is assumed to shrink during heating (thermal softening) and to expand during cooling, when the stress state is elastic. In a plastic state thermal softening occurs simultaneously with the plastic strain hardening. At a constant stress state, thermal softening may entirely be compensated by plastic strain hardening leading to thermal consolidation. Loading and unloading criteria are given to determine whether the soil response is thermoelastic or thermoplastic. As opposed to isothermal plasticity, stress rate excursions inside the current yield surface are admissible plastic processes, when temperature grows, even if strain hardening occurs. Also, outside stress rate excursions at the softening side may generate plastic strain, when cooling occurs. Thermally induced plastic strain rate non‐associativity is discussed as well. Direct and inverse incremental strain‐stress‐temperature relationships are formulated. An analysis of the experimental results of fhermomechanical testing of saturated clays is given in a companion paper.

Experimental results obtained from thermomechanical tests on three clays are analyzed in light of the constitutive equations of soil thermoplasticity presented in a companion paper. Heating and cooling drained tests at constant isotropic stress show a strong dependence of the elastic domain on temperature. Thermal sensitivity of elastic domain was found to be different in overconsolidated and in normally consolidated clays. Thermoplastic strain hardening builds up to compensate for thermal softening in normally consolidated clays at plastic compression during drained heating, if the constant stress is imposed. Triaxial compression tests at constant elevated temperatures show an increase in ductility and a decrease in dilatativity at high temperatures. Undrained heating tests show a significant water pressure buildup. At constant principal stress difference, the water pressure growth leads to an effective stress drop and an eventual failure at the critical state line. A temperature‐rate‐dependent non‐associative plastic flow rule is deduced from the comparison between experiments with drained heating at constant stress and loading at constant elevated temperature. Strength appears to be mildly affected by temperature. It decreases with temperature in overconsolidated clays and possibly increases in some normally consolidated clays.

Leaching of calcareous soils due to dewatering is a problem that needs to be addressed because of the cemented nature of Kuwait soils and the numerous projects that incorporate pumping water from the ground. A laboratory investigation is initiated to understand the process of leaching of cementing salts and to study the factors controlling it. Leaching is found to be directly proportional to both soil density and percentage of fines. The flow rate has an insignificant effect, although brackish water has slightly less leaching capability than distilled water. Throughout the testing program the leaching process became essentially complete after a volume of water equivalent to approximately 3.5 times the pore volume passed through the soil.

Soil liners have traditionally been compacted in the field to a minimum dry weight over a specified range in water content. This approach evolved from the practice for structural fills for which strength and compressibility are of primary concern. With soil liners, hydraulic conductivity is usually of paramount importance. Hence, the approach used to ensure adequate strength and permissible compressibility is not necessarily applicable to the construction of soil liners. Data are presented to show that the water content‐density criteria for compacted soil liners can be formulated in a manner that is different from the approach currently used by many engineers. The recommended approach is based on defining water content‐density requirements for a broad, but representative, range of compactive energy, and relating those requirements to hydraulic conductivity and other relevant factors. A case history illustrates the recommended procedure and its implementation. Hydraulic conductivity measurements were performed on three soils to develop an “acceptable zone” on the compaction curve that was used for quality control during construction. As a result of implementing the recommended procedure, construction operations were significantly accelerated.

A force‐equilibrium model was used to derive a theoretical solution for the lateral capacity of rigid piers embedded in cohesionless and c‐ϕ soil profiles having sloping ground surfaces. A parametric study indicated that the amount of reduction due to the slope presence is dependent on the value of the ground‐surface slope angle θ and the soil‐strength properties. The ultimate resistance‐reduction factor ε is presented as a function of the soil properties and the slope angle θ. The developed slope model is validated using the results of five full‐scale pier‐load tests. The angle μ, which defines the size of the displaced wedge in front of the pier, was assumed equal to ϕ/2 for predictions that both accounted for and ignored the slope presence. In addition, predictions were carried out using angle ft corresponding to minimum‐resistance wedge. Accounting for the slope effect, predicted capacities were within 15‐25% of the measured capacities. On the other hand, predictions made ignoring the presence of the slope overpredicted the measured capacities by as much as 50%.

Shells entered into foundation engineering in the mid‐1950s in different parts of the world. Shell foundations have been used as an alternative to the conventional flat shallow foundations. They can be geometrically shaped in elevation, triangular, cylindrical, parabolic, etc., for continuous footings, and conical, spherical, hyperbolic‐paraboloid, etc., for isolated footings. In the literature no reports can be found in which the geotechnical behavior of shell foundations has been evaluated. This paper presents experimental and theoretical investigations of triangular shell strip footings on sand. The results of this study indicate that these footings provide higher bearing capacity and produce less settlement when compared to conventional flat foundations. The classical bearing capacity theory for flat shallow foundations was extended for triangular shell strip footings, and design charts for the modified bearing capacity coefficients are presented for the triangular case. Although there have been rapid advances in efficiency, reliability, and economy in the fields of construction technology and assembly of precast concrete units, the use of shell foundations is still limited by their economics. However, there is potential for the use of shell foundations as an alternative to the conventional flat foundations in the future.

A durability rating system is developed to assist in the classification of shale that is to be used in compacted embankments. The system is based on the loss of shear strength due to the intrusion of water. Nine different shales are assigned relative durability ratings based on consolidated undrained triaxial shear‐strength tests. Companion tests are performed, one using water as the pore fluid and one using silicon oil. The mathematical difference between the results of the two tests is used to quantify the shear strength loss due to the action of water, and to assign relative durability ratings. The shales are also subjected to five simple index tests that have been previously shown to correlate well with durability. The results of the simple tests are correlated with the results of the shear strength tests through use of multiple regression techniques. Equations are developed in which the durability ratings could be estimated from the results of the simple index tests. The new system is compared to other shale rating systems.

A case history and analysis of a flow slide due to soil liquefaction is presented. The failure was triggered by vibratory tampers conducting a seismic reflection survey on a roadway embankment in Michigan's Upper Penninsula. Postfailure investigations included a survey of construction records, in situ and laboratory tests, and replication of the input ground vibrations to estimate the shearing strains and cyclic stress ratios at critical locations in the embankment. Construction records reveal that the embankment was essentially a loose, cohesionless hydraulic fill. Analysis shows that the maximum shearing strain was $5.5\times {10}^{-2}\%\text{,}$ exceeding the known threshold value for generating excess pore pressures. The estimated cyclic stress ratio of 0.12 and corrected standard penetration test (SPT) W‐values of 1‐4 combined for a clear prescription for liquefaction. Stability analyses indicate that the residual shear strength of the liquefied soil mass was between 170 and 260 psf.

Loading tests on nonuniform sand beds with a clay layer are carried out to make the effect of an interstratified weak layer on the ultimate bearing capacity clear. The tests are done under plane strain conditions using a testing box with an inside size of 0.4 m × 0.3 × 0.06 m, while the friction between soil and walls is minimized. Two results are important in practical application. First, even when the clay layer is underlain five times as deep as the footing width, the presence of the weak layer still plays an important role in determining the ultimate bearing capacity. This suggests that appreciable amount of plastic strain occurs even in a clay layer underlain at that depth, and that the plastic strain tends to lower the stability of the upper sand bed. Second, if the clay layer is thin compared to the footing width, a critical depth exists at which the clay layer exerts the most dangerous effect on the bearing capacity.