Polyurethane foam adhesive (PFA), a product resulting from exothermic chemical polymerization reactions between the diisocyanate functional group and polyol monomers, can form a closed cellular structure with high strength and stiffness. In the current study, the effectiveness of PFA in improving the strength and ductility of a well-graded gravelly soil was investigated. Using drained triaxial compression tests on the unimproved and PFA-improved soil as the basis for comparison, the peak strength and residual-state strength of the PFA-improved soil increased significantly (from 1.5 to 7 times and from 1.4 to 5.4 times of that of unimproved soil, respectively) with increasing PFA content (from 2 to 8%) at a confining pressure of 100 kPa. For the scenarios of low confining pressure, the PFA additive resulted in a change in volumetric response from contractive to highly dilative. The residual (or pseudo-critical) state lines (RSLs) for PFA-improved soils were observed to be parallel in the $q\sim p^{\prime }$ and $e\sim p^{\prime }$ planes, with an upward translation with increasing PFA content. Strain-dependent reductions in stiffness were observed to become more pronounced with increases in PFA content and confining pressure. In particular, the brittleness index for the PFA-improved soil (ranging from 0.01 to 0.29) was found to be much lower than that for the lime-cemented soil (ranging from 0.03 to 2.36), indicating that the PFA-improved gravel exhibited much better ductility than similar gravelly soils improved with lime due to the ductile nature of the polymer bonds. From the perspective of ductility, strength, and economy, the optimal PFA content ranges from 4 to 6% (with an optimum value of approximately 5%). Given its ductile response and stress-strain-strength characteristics, PFA-improved gravelly soils could offer a promising alternative for application to high rockfill dams or railway embankments.

This paper proposes a framework for describing the modulus degradation behavior of cement-treated soft clay. The results show that effect of the mix ratio on the modulus degradation behavior can be captured through the unconfined compressive strength only, rather than through two parameters (e.g., void ratio and cement content) as used in existing models. The parameters for describing the modulus degradation behavior can be evaluated directly by appropriate plots of the data without any iteration. Fitted expressions are also given which relate these parameters to the unconfined compressive strength. The effect of the mean effective stress becomes significant when it is higher than the primary yield stress. Similarly, the effect of overconsolidation increases with increasing overconsolidation ratio. Both parameters can be incorporated into the expressions for the reference strain, $\alpha$ , and normalized degraded modulus. These expressions allow the effect of mix ratio, mean effective stress, and overconsolidation to be comprehensively described. Together, the proposed models provide a complete framework for describing the effect of mix ratio, mean effective stress, and overconsolidation on the modulus degradation behavior of cement-treated soil.

The stabilization of slopes by placing piles is one of the most innovative and effective slope reinforcement techniques in the coastal engineering in recent years. Due to the simplicity and efficiency, limit analysis method is the most common approach for assessing the stability of slopes. However, the majority of existing limit analysis methods is limited to slope without the presence of piles. In this technical note, a novel upper-bound limit analysis method was proposed to access the stability of three-dimensional slopes reinforced with piles incorporating the admissible rotational failure mechanism where toe failure, face failure, and base failure were taken into account. The effects of key designing parameters, e.g., pile location, pile spacing, slope angle, slope width on the stability of earth slopes, and geometry of critical slip surface were presented and discussed. The results demonstrate that the proposed approach is more appropriate for assessing the stability of slopes reinforced with piles and can be also utilized in the design of piles stabilizing the unstable slopes.

The strength–dilatancy relationship, which is significantly influenced by the shearing mode, is of great importance in modeling evolution of the mobilized strength and predicting deformations of granular soils. In this paper, the effects of the shearing mode on the strength–dilatancy relation were investigated by performing the multiaxial tests on gravelly soils. It was interestingly found that the gradient of the fitting line for the relationship between the peak–failure friction angle and maximum dilatancy angle increased with increasing the intermediate principal stress ratio b. In particular, for b = 0, the gradient of the fitting line was 0.44 (which was smaller than the Bolton dilatancy index of 0.48). In addition, a strength–dilatancy equation incorporating the effects of shearing mode was proposed for this gravel soil. Thereafter, a general equation between peak friction–failure angle and maximum dilatancy was obtained by using experimental data from the literature and current work for different shearing modes. The two equations were then validated by other independent test data on sands and gravels. It was observed that the general strength–dilatancy equation could well capture the strength–dilatancy relationships on various granular soils, including sands and gravel under different shearing modes.

Accurate determination of soil-water characteristic curve (SWCC) is of immense importance for understanding the mechanical behavior of unsaturated soils. Due to the difficulty and long duration of experimental procedures, it is of great significance to estimate the SWCC by indirect methods. To address this issue, in this article an effective fractal method is proposed for predicting the SWCC based on mercury intrusion porosimeter (MIP) data. Only two characteristic parameters, namely the fractal dimension and air-entry value, are needed in the presented approach. Detailed procedures for determining the parameters are clearly elaborated. Due to the influence of sample size difference on the equivalent connected pore size, a sample scale effect coefficient is proposed to predict air-entry values. The concept of “critical pore size” is introduced to obtain the optimal fractal dimension, which can accurately reflect the fractal behaviour of SWCC samples. By comparisons between predicted and experimental SWCCs, the validation of the proposed method is verified. The comparisons reveal the good agreement between the proposed approach and laboratory experiments.

Seismic compression is the accrual of volumetric strains in unsaturated soils caused by cyclic loading and has caused significant damages to buildings and other structures during earthquakes. To date, the available methods for predicting the severity of seismic compression have mainly been simplified procedures, in which a number of equivalent cycles are used to represent the duration of earthquake loading. Often, however, the number of equivalent cycles is computed inconsistently with the underlying mechanics of seismic compression. This paper proposes a non-simplified procedure for predicting the severity of seismic compression. The procedure is based on a modified version of the Richart-Newmark cumulative damage hypothesis, wherein volumetric strain is used as the damage metric. The proposed model was calibrated using data from 425 constant-amplitude sinusoidal strain-controlled cyclic simple shear tests performed on clean sand and validated using test data from samples subjected to variable-am...