A large-strain model was developed to study the consolidation behavior of soil deposits improved with prefabricated vertical drains and subjected to surcharge and vacuum preloading. The smear effect resulting from the installation of drains was incorporated in the model by taking the average values of permeability and compressibility in the smear zone. The dependence of permeability and compressibility on void ratio and the effects of non-Darcian flow at low hydraulic gradients were also incorporated in the model. The creep effect was also taken into account for secondary consolidation of soft soil deposits. The model was applied to two different embankments located at Suvarnabhumi International Airport, Thailand, and Leneghan, Australia. It was observed that the creep effect led to an additional settlement of 12%-17% after the primary consolidation phase. The study further demonstrated that creep settlements increased with the non-Darcian effect. The difference between surface settlement results with and without the creep effect increased from about 12% to 15% when the non-Darcian parameter (n) increased from 1 to 1.6. However, beyond a threshold value of n >= 1.6, the influence of non-Darcian flow on creep settlement diminished. The value of average and actual effective stresses increased by about 13% and 17%, respectively, when the value of n increased from 1 to 2. However, the impact of n on effective stresses became negligible for values of n >= 2.5. The rate of consolidation decreased approximately by about four times when the permeability ratio ((k) over tilde (u)/(k) over tilde (s)) increased from 1 to 5.

Preloading with vertical drains is a well-proven ground improvement technique suitable for soft clay deposits. This technique involves installing vertical drains that cause soil remolding in the immediate vicinity of its surface, creating a disturbed zone known as the smear zone. This study aims to investigate the impact of overburden stress on the characteristics of the smear zone. Very often, the vertical drains penetrate to depths up to 20 m. In such situations, the soil experiences varying stresses, leading to different responses to the drain-induced soil disturbances. Very few studies have investigated how overburden stress affects the smear zone. Through a series of experiments encompassing vertical and radial consolidation tests, along with vane shear tests, this paper evaluates the variation in shear strength and consolidation properties within the smear zone, simulating different depths. Employing three overburden pressure intensities (25 kPa, 50 kPa, 100 kPa, equivalent to depths of about 4 m, 8 m and 16 m), the study establishes that the remolding effect intensifies with depth. Furthermore, it demonstrates the influential role of the smear zone on the undrained shear strength properties of the improved ground, highlighting its variability based on overburden stress.

This paper presents a consolidation model for stone column-reinforced soft ground subjected to time-dependent loading under free strain condition. Smear effects and three types of loadings, namely, constant loading, ramp loading, and sinusoidal loading, are considered in the developed consolidation model, which is solved by a numerical method based on a partial differential equation solver. The applicability of the proposed consolidation model and the reliability of the numerical method are demonstrated and verified by well-predicting the consolidation behaviors of two practical engineering cases and one laboratory experiment. The verified model and the numerical method are then employed to investigate the effects of smear zone and time-dependent loading on consolidation characteristics of stone column-improved soft ground. The results indicate that the excess pore water pressure undergoes a sharp change at the interface between the smear zone and the undisturbed zone due to smear effects. The smaller the range of the smear zone, the faster the settlement of the composite foundation develops. The faster the loading rate, the faster the dissipation of excess pore water pressure and the faster the settlement develops. In addition, for the foundation subjected to sinusoidal loading, the higher loading frequency results in a larger amplitude corresponding to the excess pore water pressure and a smaller amplitude corresponding to the settlement of the soil.

The combining of electroosmotic, vacuum, and surcharge preloading is an emerging technique for soft foundation treatment. Considering smear effects and free strain, an analytical solution for the radial consolidation of combined electroosmotic, vacuum, and surcharge preloading was derived based on the characteristic function method and Bessel function. The correctness of the proposed solution was verified by comparing with existing solutions and numerical results. On this basis, the influence of smear effects, vacuum pressure, surcharge load, and applied voltage on the consolidation characteristics of soil was further analyzed. The results showed that when the electroosmosis permeability coefficient of the undisturbed zone was greater than that of the smear zone, the excess pore-water pressure at the interface between the smear zone and the undisturbed zone increased in the early stage of consolidation owing to the electroosmotic effect. Vacuum pressure had a great influence on soil consolidation in the smear zone, while applied voltage had a great influence on the consolidation of soil in the undisturbed zone.

Conventionally, drainage boundaries are often assumed to be either perfectly permeable or completely impermeable. However, a more realistic approach considers continuous drainage boundaries. In this context, an analytical solution for double drainage consolidation in vertical drains is derived. The proposed method is evaluated against existing solutions and finite element simulations. The study investigates the impact of drainage capacity, soil nonlinearity, smear effect, and well resistance. The results show that the continuous drainage boundary parameters (i.e., b and c) significantly affect the distribution of excess pore water pressure and the consolidation rate. Increasing b and c allows realistic modeling of drainage capacity variations from impermeable to permeable boundaries. Notably, when b not equal c, the maximum excess pore water pressure plane shifts from the mid-height of the foundation soil, diverging from conventional consolidation theory. Soil nonlinearity (Cc/Ck) and boundary permeability (b and c) jointly affect consolidation. Higher Cc/Ck values correlate with more detrimental consolidation effects. Minimizing disturbance around vertical drains during construction is crucial due to well resistance and smear zone effects, which can significantly slow down consolidation. This study provides an analytical solution considering soil nonlinearity for predicting consolidation in actual engineering scenarios involving vertical drainage trenches.