Consolidation Of Soft Soil Research Articles

Coupling effects on class C predictions of soft soil settlements

AbstractIn uncoupled consolidation analysis, settlement and pore water pressure are solved independently, whereas in coupled analysis, they are solved simultaneously to ensure continuity (i.e., the volume change in soil due to compression must equal the water volume change caused by dissipation). This study investigates the coupling effects of soil deformation and pore water pressure dissipation in the back analysis of soft soil settlements. It further evaluates the suitability of both coupled and uncoupled constitutive models with different types of monitoring data, providing practical guidance for selecting consolidation models and achieving reliable long-term predictions. The one-dimensional governing equations for soft soil consolidation, incorporating prefabricated vertical drains and creep deformation, are first reviewed. A case study of a trial embankment in Ballina, New South Wales, Australia, is then used to demonstrate the impact of coupling effects and monitoring data on settlement predictions. The results show that considering coupling effects not only improves long-term settlement predictions but also reduces uncertainties in the updated soil parameters, especially when both settlement and pore water pressure data are used.

Re-examination and analysis of test data on consolidation of soft soils exhibiting creep with different thicknesses

Re-examination and analysis of test data on consolidation of soft soils exhibiting creep with different thicknesses

Analytical modeling and experiments on soft soil consolidation with vacuum preloading‐airbag pressurization

AbstractThis study aims to provide substantial theoretical support for employing vacuum preloading‐airbag pressurization (VP‐AP) to enhance soft soil foundations. By integrating the airbags and prefabricated vertical drains (PVDs) within the analytical framework, the consolidation models are developed to accommodate double smear zones and well resistance. Analytical solutions for various airbag pressurization scenarios are derived under the equal‐strain assumption. A model test is subsequently conducted to investigate the settlement process of soft soil using the VP‐AP method. The validity of the proposed theoretical model is corroborated through comparison with existing analytical solutions and experimental data. The accuracy of the predictive model is further substantiated by the model test results. Lastly, this research offers an in‐depth analysis of soil consolidation behavior under diverse influencing factors. The findings indicate that the VP‐AP method demonstrates superior efficacy over conventional vacuum‐surcharge preloading when the airbag pressure matches the external load pressure. Additionally, an increase in the radius of airbags enhances the soil consolidation efficiency. The analytical model presented in this study elucidates the consolidation mechanisms of the VP‐AP method, with experimental research confirming the efficacy of this approach and the predictive model established herein.

Large strain consolidation of soft soils with partially penetrating PVDs: Analytical solutions incorporating variable well resistance

The large-strain geometric assumptions and nonlinear compressibility and permeability have significant effects on the consolidation of soft soils with high compressibility. However, analytical solutions for large-strain nonlinear consolidation of soft soils with partially penetrating PVDs have been rarely reported in the literature. A double logarithmic model is adopted to describe the nonlinear compressibility and permeability of soft soils with high compressibility, and a large-strain consolidation model for soft soils with partially penetrating PVDs under the condition that the excess pore water pressure at the interface between the improved and unimproved layers is equal is established based on Gibson’s large-strain consolidation theory. The analytical solution for the large-strain nonlinear consolidation model for soft soils with partially penetrating PVDs is obtained. The reliability of the analytical solution obtained in this study is verified by comparing it with the existing solutions under different conditions, and the maximum deviation between the two methods does not exceed 5 %. On this basis, consolidation behaviors of soft soils with partially penetrating PVDs under different conditions were analyzed by extensive calculations. Finally, the proposed analytical solution for the large strain consolidation model is applied to the settlement calculation of the Bachiem Highway Project, which further demonstrates the applicability of the consolidation model.

Effect of Adding Surcharge Load Stress on the Acceleration of Soft Soil Consolidation

Effect of Adding Surcharge Load Stress on the Acceleration of Soft Soil Consolidation

Empirical Analysis of Partially Penetrated Prefabricated Vertical Drains (PVD) on Acceleration Consolidation of Soft Soil

Empirical Analysis of Partially Penetrated Prefabricated Vertical Drains (PVD) on Acceleration Consolidation of Soft Soil

Soft soil foundation treatment of hydraulic fill site based on vibration boosting drainage consolidation method

Reclamation from the sea is a method of expanding urban area, but it also faces the problem of difficult treatment of soft soil foundation by hydraulic reclamation. Therefore, a soft soil consolidation method that combines vibration pressure boosting drainage and piled-load static pressure stacking is now proposed. To verify the effectiveness of this method, a consolidation test based on soft soil samples was designed and conducted in the study. The test results showed that when the sampling height was 240mm, the overall moisture content of the consolidated soil sample was the highest, 44.3%, and the consolidation effect was the worst. When the sampling height was 140mm, the overall moisture content obtained from the test was the lowest, 43.1%, and the consolidation effect was the best. The displacement of corner 2 and center point at the intersection of the preceding and following periods was greater, with values of 37.1 mm and 39.2 mm, respectively. At this point, the displacement of corner 1 was significantly smaller, at 30.9 mm. In the later loading stage, the slope of the vertical displacement curve significantly increased. When the experimental time reached 7000 min, the mixed method designed in this study had a drainage rate of 0.53 ml/min, which was significantly higher than other traditional methods. The experiment outcomes indicated that the method designed in this study had certain application potential for improving the consolidation effect of soft soil foundation in hydraulic fill sites.

Surface Subsidence over a Coastal City Using SBAS-InSAR with Sentinel-1A Data: A Case of Nansha District, China

The loss of life and property in economically developed areas due to geological hazards caused by intense ground subsidence is incalculable. As one of the fastest growing areas in the Guangdong-Hong Kong-Macao Greater Bay Area, the study of ground subsidence in Nansha will help to provide a scientific basis for urban planning and improve the capacity of monitoring and prevention of ground subsidence. The combination of coastal soft soil foundation and urbanization conditions creates a certain risk of land subsidence. We chose Nansha District, the geographical center of the Greater Bay Area, as the study area to analyze its surface subsidence characteristics in recent years. The 20-view Sentinel-1A data and SBAS-InSAR technique were used to monitor the ground subsidence in Nansha from 2017 to 2023. The main rate of ground subsidence in Nansha ranges from −19.4 to 7.7 mm/yr and is distributed in the urban area, along the rivers, in the construction area, and in the reclamation area. As of 4 May 2023, the average ground settlement in Nansha is 10.05 mm and the maximum settlement can be up to 142.45 mm. The 6-year total settlement at all four settlement intensities is greater than 60 mm, with the highest value exceeding 110 mm. The cumulative settlement increases with time, but inverse settlement and no settlement also occur at points where settlement is severe. For settlement caused by soft soil consolidation, it is recommended that drainage pipes be installed to accelerate drainage as a means of stabilizing settlement. For settlement caused by groundwater extraction and additional loads on the road surface, it is recommended to rationally extract groundwater and reinforce the foundation of the road surface with severe settlement.

Coupled creep and nonlinear consolidation of soft soils in disturbed state concept framework

A simplified solution for coupled creep and nonlinear consolidation of soils has been presented based on the disturbed state concept (DSC). The nonlinearity of the problem due to the change of the material properties and thicknesses of the soil layer, and creep was considered in the proposed solution. The state of the soil before primary consolidation was considered as initially relatively intact, and after primary consolidation during the pure creep phase was considered as finally fully adjusted state. The state of the soil during the coupled creep and consolidation process was related to its relatively intact and fully adjusted states using two consolidation and creep state functions that have been derived based on the numerical solution of the problem. Using the consolidation state function, the solutions of Terzaghi’s theory of consolidation in two initial and end of the primary consolidation states were interpolated to achieve the solution of the nonlinear primary consolidation phase. The creep state function was used to implement the effect of the creep deformation during and after the primary consolidation in the settlement calculations. The result of the proposed method was verified by the results of the numerical and approximate methods along with laboratory data in the literature.

Axisymmetric finite strain consolidation model for soft soil consolidation with vertical drains under combined loading considering creep and non-Darcy flow

Vertical drain assisted by vacuum and/or surcharge preloading is an effective method for improvement of soft ground with high water content. A large settlement will occur, and the water flow may deviate from the Darcy's law. The creep is also non-negligible in estimating the long-term settlement of such soft ground. To accurately predict the consolidation process, this study develops an axisymmetric finite strain consolidation model based on Barron's free-strain theory incorporating the creep, radial and vertical flows, non-Darcian flow law, and void ratio-dependent hydraulic conductivity during the consolidation process. First, to mathematically validate the model and highlight the new model's features, the existing model not considering the creep and the non-Darcy flow is also adopted as a reference for comparison based on a benchmark simulation. Then, Rowe cell tests involving non-Darcian flow are simulated by the new model to experimentally validate the predictive performance. Furthermore, the model is applied to simulate the consolidation process of a long-term monitoring embankment to examine the applicability of the model for engineering practice. All results demonstrate that the model is capable of accurately describing the consolidation of soft soils with vertical drains under combined loading with features of creep and non-Darcy flow.

Analytical solutions for one-dimensional nonlinear large strain consolidation of soft soils with high compressibility under a multi-stage loading

At present, many achievements have been made in the analytical theory of large strain consolidation. However, the consideration of nonlinearity of compression and permeability is not yet sufficient. In this study, a large number of compressibility and permeability test data have been investigated to verify the advantages of log-log relationships in describing nonlinear characteristics of compressibility and permeability of soft soils under both large strain and small strain, and the variation range of parameters in log-log relationships are also presented. Also, based on the log-log relationships, a one-dimensional nonlinear large strain consolidation model of thin soft soil layer is established by considering excess pore pressure as a variable, and the analytical solutions of the consolidation model are obtained under three conditions, respectively. Then, the reliability of analytical solutions is verified by comparing with the results observed in the field and degenerate solution, respectively. Finally, the influence of loading method, final load, compressibility and permeability parameters on consolidation behavior are analyzed. This study provides theoretical supports for the calculation of nonlinear large strain consolidation of actual soft soil layer.

Influence of SiO2 nanoparticles and Fe3O4 solution on the consolidation of geological soft soil

Soft soil is widely distributed in coastal areas and needs to be treated first when used as a foundation. A method of incorporating nano SiO2 particles and nano Fe3O4 solution is proposed to address the consolidation problem of geological soft soil. During the process, nanomaterials are selected and a preparation method for incorporating nanomaterial soil is designed. Subsequently, the experimental device is designed and the main instrument usage methods are specified, resulting in a complete experimental process design. The experimental results showed that in the generation of electron microscope images of soil, the soil mixed with nano SiO2 particles or nano Fe3O4 solution has a denser characterization; In the experiment of current variation in soil, the maximum current of the soil mixed with nano SiO2 particles is 0.1052 A at 72 hours; In the soil drainage test, the maximum total drainage of the soil mixed with nano Fe3O4 material at the end reached 1907 mL; In the soil pH value experiment, the pH value of the soil is higher when the proportion of nano SiO2 material added is 3‰ and the proportion of nano Fe3O4 material added is 2‰. The above results indicate that the geological soft soil consolidation method designed by the research institute incorporating nano SiO2 materials or nano Fe3O4 materials can effectively improve the drainage and mechanical properties of the soil.

Nonlinear analysis for consolidation of soft soils improved by composite piles with stiff core and gravel shell

The implementation of composite piles has emerged as an appealing technology for reinforcing soft ground through fulfilling the requisite bearing capacity and facilitating consolidation. Nonetheless, previous investigations into the consolidation behavior of composite pile-improved ground have neglected the nonlinearity of soil compression and permeability. In this context, the logarithm models of e-lgσ and e-lgk are introduced to establish an analytical model for the nonlinear consolidation of composite ground with composite piles. Based on equal strain assumption and annular equivalent method, detailed solutions under four special loading schemes are then obtained. Additionally, a comprehensive analysis is conducted to assess the influence of various parameters on the nonlinear consolidation behavior of composite ground, and the feasibility of current model is verified by degenerations. The results show that ignoring the nonlinearity will lead to an overestimation of consolidation rate when the soil’s compression indices exceed the permeability indices. Moreover, the consolidation rate of composite ground is inversely proportional to σ¯u/σ¯s0′ and Cc/Ckh(v), while demonstrating a direct proportionality to Ksp, Ksg, and kg/kv0. However, σ¯u/σ¯s0′ mainly influences excess pore water pressure at the upper layer, and the influence of Cc/Ckv on the consolidation rate is limited and can even be ignored in comparison to Cc/Ckh. Finally, the proposed model is successfully applied to an engineering project in situ, where the obtained results exhibit a noteworthy agreement with the measured data.

Analisis Proses Konsolidasi Dengan PVD Pada Proyek Reklamasi di Samping Tangki CPO Antar Pulau Belawan Berdasarkan Bore Log BH-1

In the planning of civil building, construction problems are often encountered in soft soil types, including low soil carrying capacity and large settlements (settlements) when given a load. Soil improvement is needed to speed up the consolidation settlement time. One method that can be applied to speed up the consolidation settlement time is to use a pre-fabricated vertical drain (PVD) and this preloading method is able to increase the shear strength of soft soils and remove pore water in the soil. This research aims to determine the magnitude of settlement of soft soil consolidation using the 1-dimensional Terzaghi consolidation formula and analysis using the finite element method with PLAXIS 2D modeling, comparing the results of PLAXIS 2D modeling with actual data, the effect of the smear zone effect on the settlement of soil consolidation in the embankment area and to determine the difference in the decrease in preloading methods combined with PVD and preloading without PVD based on point bore log BH-1. From the results of the analysis, it is found that the consolidation settlement by analytical method using the 1-dimensional Terzaghi consolidation formula was 0.858 meters. The amount of settlement that occurs in the consolidation process using PLAXIS 2D modeling taking into account the smear zone effect is 0.786 meters and 0.852 meters without taking into account the smear zone effect. Meanwhile, the actual settlement that occurred in the field based on settlement plate (SP-01) was 0.867 meters and the magnitude of the preloading settlement without PVD was 0.512 meters. It can be concluded that the PVD combination preloading method is proven to accelerate consolidation time, while the improvement with the preloading method alone produces a relatively small decrease.

One-Dimensional Consolidation Properties of Soft Clay under Multi-Stage Loading

The consolidation characteristics of soft clay under multi-stage loading and single-stage loading exhibit significant differences. In order to investigate the consolidation behavior of soft clay under multi-stage loading, one-dimensional oedometer tests were conducted on marine sedimentary soft clay from northern China. The results indicate that the overall time-deformation pattern of multi-stage loading is a cyclic nonlinear extension of that of single-stage loading. The final deformation between multi-stage loading and single-stage loading is approximately equal; however, the consolidation rate of single-stage loading is four times that of multi-stage loading. Furthermore, the coefficient of consolidation (Cv) decreases with increasing stress. Subsequently, the traditional Terzaghi one-dimensional consolidation equation was modified and a consolidation equation suitable for multi-stage loading is proposed in this study. The analysis of engineering applications demonstrates that the traditional theory provides more accurate predictions of consolidation rate and settlement when the load is small. However, when the load is large, the settlement predicted using the Terzaghi one-dimensional consolidation equation may have an error of 0–25% compared to that using the modified equation. The modified Terzaghi one-dimensional consolidation equation provides a more accurate representation of the actual consolidation of soft soil.

Improved Mandrel System for Prefabricated Vertical Drain Installation: A Macro to Micro Analysis

Increasing development of infrastructure in Indonesia has driven the need for effective ground improvement methods to accelerate the consolidation of soft soil, which is estimated to occupy around 10% of the country’s land area. A prefabricated vertical drain combined with vacuum preloading is among the most effective methods for this purpose. However, the prefabricated vertical drain creates a smear zone in the surrounding soil area during installation. This study examines the effectiveness of a newly developed mandrel system in reducing the smear zone during prefabricated vertical drain installation. Large-scale consolidation tests at a macro level and microstructure analysis using scanning electron microscopy at a micro level were employed to investigate the effect of soil water content and shear strength. The results show that the water content and shear strength of the soft soil gradually increased in the inner smear zone and transition zone, while both decreased in the radial distance. Furthermore, the soil structure underwent a transformation in which the particle area and pore area became a closed flake structure, and apparent agglomeration occurred. The test results indicate that the newly developed mandrel system can effectively reduce the smear zone. The macro to micro test results demonstrated that the mandrel system is successful in reducing the smear zone effect.

A Comparative Case Study on Drainage Consolidation Improvement of Soft Soil under Vacuum Preloading and Surcharge Preloading

Based on an improvement project of soft soil ground in Zhuhai City on the Pearl River Delta, a comparative study on vacuum preloading and surcharge preloading was performed. The ground and stratified settlements, excess pore water pressure, and the degrees of consolidation of soft soil are analyzed, along with the horizontal displacement and soil strength. The results show that surcharge preloading results in smaller secondary consolidation settlements than vacuum preloading. Primary consolidation settlement quickly increases with increasing excess pore water pressure of less than −40 kPa in vacuum preloading, while also increasing between 20 kPa and 25 kPa in surcharge preloading. The sharp increase in the strata permeability coefficient will induce the increase in strata consolidation degree and has little effect on the ground consolidation degree. The surcharge preloading can be given priority to reduce the settlement foundation in the service stage.

Analytical solutions for consolidation of soft soil improved by air‐boosted vacuum preloading considering clogging effect

AbstractAir‐boosted vacuum preloading is a newly emerging soft soil‐improving technology and increasingly draws attention of researchers and engineers. However, few analytical theories are available in the literature to facilitate the design and calculation of it in practice. To fill this gap, an analytical model for the consolidation of soft ground improved by air‐boosted vacuum preloading is proposed based on the assumption of equal volumetric strain and Darcy's law. Moreover, a time‐dependent clogging effect is taken into consideration to describe the gradual reduction in the drainage capacity of prefabricated vertical drains (PVDs) during the consolidation process. In addition, the smear effect is also considered due to the installation of PVDs. An air booster pipe and the surrounding PVDs are introduced into the unit cell for analysis based on the principle of equal cross‐sectional area, and analytical solutions under two typical time‐dependent horizontal loading are then developed. A comparison is made with the existing analytical model of conventional vacuum consolidation, which indicates that air‐boosted vacuum preloading can promote the consolidation of soft soil more effectively than conventional vacuum preloading. Furthermore, the obtained solution under instantaneously loading is used to investigate the influence of several parameters on consolidation behavior. Finally, to verify the accuracy of the analytical model with or without clogging effect, a comparative study is carried out with a field test.

One‐dimensional nonlinear creep consolidation of soft soils with time‐dependent drainage boundary under construction load

AbstractTo further investigate the nonlinear creep properties of soft soils and the effect of variable loading, a one‐dimensional (1D) nonlinear creep consolidation system of soft soils under construction load is established, including time‐dependent drainage (TDD) boundary, elastic‐viscous‐plastic deformation, non‐Darcy flow (NDF), and self‐weight stress. The consolidation problem is presented by virtue of the finite volume method, and the associated calculation program is compiled. The efficiency of the numerical solutions is validated by comparing the degenerated solution against analytical, semi‐analytical, and numerical solutions. Then the influences of construction load and nonlinear creep model parameters on consolidation are studied. The results show that TDD boundary and construction load significantly affect consolidation, and the larger the loading rate and interface parameter, the faster soil's overall dissipation process of excess pore‐water pressure (EPP). Meanwhile, at the earlier consolidation stage, considering the secondary consolidation effect will cause an increase in excess pore‐water pressure (EPP). Prolonging the construction period, decreasing the interface parameter, considering the self‐weight stress, or increasing the non‐Newtonian index will all aggravate this phenomenon. Additionally, the TDD boundary, construction load, and non‐Newtonian index flow (NNIF) are not a determinant for final soil settlement.

Analytical Solutions for One-Dimensional Large-Strain Nonlinear Consolidation of Soft Soils by Considering a Time-Dependent Drainage Boundary

Over the past decades, many advances have occurred for theories on large-strain nonlinear consolidation of soft soils with regard to traditional drainage boundaries, which are completely permeable and impermeable cases and which may not truly reflect the whole process of drainage boundary. Thus, some further considerations related to a time-dependent drainage boundary are adopted in the analysis of soft soil consolidation by incorporating biologarithmic compressibility and permeability models. Also, the analytical solutions are obtained by means of variable substitution and Laplace transform. Additionally, the proposed solution is degenerated and compared with the existing solution and the laboratory tests to validate its correctness and feasibility. Finally, the soil consolidation behavior is analyzed under different values of the interface parameter, nonlinear compressibility and permeability, and external loading. The results indicate that the drainage boundary permeability is largely determined by the interface parameter; the larger the interface parameter, the better the boundary permeability. Besides, the consolidation rate decreases with the increasing value of Ic(α − 2) when the external loading remains constant. While the parameter Ic(α − 2) is a constant value, the consolidation rate varies with the external loading. Therefore, appropriate parameter values are more conducive to the full consolidation of soft soil foundations.