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Principle of Unsaturated Soil Mechanics for Sustainability in Engineering Practice

A special issue of Sustainability (ISSN 2071-1050). This special issue belongs to the section "Soil Conservation and Sustainability".

Deadline for manuscript submissions: 31 October 2024 | Viewed by 6237

Special Issue Editors

School of Civil Engineering, Southeast University, Nanjing 210096, China
Interests: principles of unsaturated soil mechanics: soil–water characteristic curve; hydraulic conductivity of unsaturated soil; shear strength of unsaturated soil; volume change of unsaturated soil; foundation engineering: analysis of the complex foundation system; shallow foundation in unsaturated soil zone; analysis and design of piles in loess soils; retaining structure: design of the retaining wall in unsaturated zone; safety evaluation for the excavation in urban area; program development: development of mini program to calculate the hydro-mechanical properties of unsaturated soil; development of a soil database for geotechnical engineering
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Guest Editor
Department of Civil and Environmental Engineering, School of Engineering and Digital Sciences, Nazarbayev University, Nur-Sultan 010000, Kazakhstan
Interests: sustainable construction; geographical information system; IoT-sensing system; unsaturated soil mechanics; finite element analyses
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Guest Editor
Department of Civil and Environmental Engineering, University of Auckland, Auckland 1010, New Zealand
Interests: unsaturated soil mechanics; expansive soil characterization and treatment; soil improvement; waste upcycling, rainfall-induced slope failure; nature-based solutions; numerical modelling
School of Civil Engineering, Wuhan University, Wuhan 430072, China
Interests: slope stability; soil dynamics; expansive soils; geodisaster prevention; pavement engineering
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Guest Editor
School of Hydraulic and Civil Engineering, Zhengzhou University, Zhengzhou 450001, China
Interests: unsaturated soil; expansive soil; collapsible soil; slope stability; pile foundation

Special Issue Information

Dear Colleagues,

In engineering practice, sustainability is defined by the adaptivity, efficiency and reliability of the design solutions. It is known that most of the soil near the surface of the ground is in an unsaturated condition. The classic saturated soil mechanics are incapable of explaining and describing the engineering behaviours of the soil in unsaturated conditions. The principles of unsaturated soil mechanics have the advantages of solving the practical problems related to the unsaturated soil. These problems are commonly associated with the effect of climatic conditions on the sustainability of an engineering structure. Unsaturated soil mechanics principles are necessary to understand the methodology in maintaining the sustainability in engineering practice. With the inclusion of unsaturated soil mechanics, more precise and unique data for the given soil can be provided to enhance the sustainability of urban living. Improving the foundation and retaining wall designs as well as taking into account all the minor details of the soil features, unsaturated soil mechanics are able to provide greater stability of the building structures and natural constructions. In addition, the implementation of the principles of unsaturated soil mechanics is not only limited to unsaturated soil but it can also be used for the environmental engineering, ground improvement and nuclear waste disposal, etc.

The understanding and implementation of the unsaturated soil mechanics is crucial for theoretical and technological developments.

In some countries, guidelines incorporating the principles of unsaturated soil mechanics are available for practical engineering. All papers related to unsaturated soil mechanics are welcome in this Special Issue.

  • Correlation between soil-water characteristic curve and index properties of soil;
  • Law of water flow through unsaturated soil;
  • Theory of shear strength for the unsaturated soil;
  • Theory of soil volume change of unsaturated soil;
  • Bearing capacity of foundation in unsaturated zone;
  • Retaining wall design in unsaturated zone;
  • Stability analysis of unsaturated soil slope.

Dr. Qian Zhai
Dr. Alfrendo Satyanaga
Dr. Arezoo Rahimi
Dr. Zhong Han
Dr. Yunlong Liu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sustainability is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • sustainability
  • unsaturated soil mechanics
  • soil–water characteristic curve
  • hydraulic conductivity function
  • shear strength function
  • geotechnical design

Published Papers (6 papers)

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Research

15 pages, 3534 KiB  
Article
Determination of the Shear Strength of Unsaturated Loess Samples from Conventional Triaxial Shear Tests Applying Rubber Membrane Correction
by Ruixia He, Ziwen Zhou, Sai Vanapalli and Xuyang Wu
Sustainability 2024, 16(5), 2120; https://doi.org/10.3390/su16052120 - 4 Mar 2024
Viewed by 802
Abstract
The shear strength parameters of loess samples are determined from conventional triaxial shear test results and used in the rational design of sustainable geotechnical infrastructures. However, the rubber membrane that is used in the triaxial shear apparatus for applying the all-around pressure to [...] Read more.
The shear strength parameters of loess samples are determined from conventional triaxial shear test results and used in the rational design of sustainable geotechnical infrastructures. However, the rubber membrane that is used in the triaxial shear apparatus for applying the all-around pressure to the test specimen has a significant influence on the measured shear strength parameters. In this paper, remolded and undisturbed unsaturated loess samples from northwest China are used in a comprehensive testing program to determine the shear strength from triaxial tests and understand the influence of a rubber membrane. The results show that the measured undrained cohesion from unconsolidated undrained triaxial tests on unsaturated soil specimens with and without a rubber membrane are significantly different. In this study, differences in the shear strength with and without a rubber membrane are assessed from shear strength index values that can be determined from undrained cohesion and the internal friction angle derived from conventional triaxial tests. Experimental results suggest that predominant changes arise mainly in the undrained cohesion values. The change rate of shear strength indices values of undisturbed loess shows a strong correlation with its water content; however, it is weak for remolded loess. The correlation coefficient between error and measured values of all shear strength indices is more than 0.8. Empirical correction relationships for triaxial shear tests with a rubber membrane for three different types of loess were established from the investigations. The simple approach used in this study can be used as a reference to apply corrections to the measured undrained cohesion values of unsaturated loess samples from northwest China. Full article
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20 pages, 8065 KiB  
Article
Analytical Modeling of Unsaturated Soil Shear Strength during Water Infiltration for Different Initial Void Ratios
by Daniel Batista Santos, Patrícia Figuereido de Sousa and André Luís Brasil Cavalcante
Sustainability 2024, 16(4), 1394; https://doi.org/10.3390/su16041394 - 7 Feb 2024
Viewed by 833
Abstract
Unsaturated soil mechanics, when applied to determine the soil shear strength, are crucial for accurately evaluating the safety of geotechnical structures affected by seasonal moisture variations. Over the past decades, multiple models have been formulated to predict the behavior of unsaturated soils in [...] Read more.
Unsaturated soil mechanics, when applied to determine the soil shear strength, are crucial for accurately evaluating the safety of geotechnical structures affected by seasonal moisture variations. Over the past decades, multiple models have been formulated to predict the behavior of unsaturated soils in terms of water flow and shear strength individually. Building upon these foundational studies, this research introduces a model that couples an analytical solution for one-dimensional water infiltration with an unsaturated shear strength model. This model further incorporates the impact of void ratio fluctuations on soil properties and state variables related to shear strength. A parametric analysis is conducted to evaluate the effects of the initial void ratio on a representative soil profile during a water infiltration event. The model presented in this paper integrates various concepts from the field of unsaturated soil mechanics and is applicable to any homogeneous soil where expansion/collapse effects are negligible. It demonstrates how shear strength might be underestimated when using a saturated soil approach. Conversely, it may also lead to an overestimation of safety conditions if the soil approaches a saturated or dry state. The proposed model offers a more accurate prediction of unsaturated soil shear strength. It is useful for determining transient safety factors in geotechnical structures. Furthermore, when combined with field-installed instrument monitoring, this model contributes significantly to the functionality, safety, cost-effectiveness, and sustainability of geotechnical structures and projects. Full article
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23 pages, 4341 KiB  
Article
Analytical and Finite-Element-Method-Based Analyses of Pile Shaft Capacity Subjected to Rainfall Infiltration
by Gerarldo Davin Aventian, Alfrendo Satyanaga, Aizhan Sagu, Bakytkul Serikbek, Gulnur Pernebekova, Bakhyt Aubakirova, Qian Zhai and Jong Kim
Sustainability 2024, 16(1), 313; https://doi.org/10.3390/su16010313 - 29 Dec 2023
Cited by 3 | Viewed by 941
Abstract
The presence of unsaturated soil is critical in geotechnical engineering since the matric suction may aid in accommodating the pile shaft capacity. The design of piles can be optimized by incorporating unsaturated soil mechanics principles. Hence, the amount of waste materials can be [...] Read more.
The presence of unsaturated soil is critical in geotechnical engineering since the matric suction may aid in accommodating the pile shaft capacity. The design of piles can be optimized by incorporating unsaturated soil mechanics principles. Hence, the amount of waste materials can be reduced, the duration of pile installation can be expedited, and the amount of energy used for casting the pile can be optimized, resulting in more sustainable design and construction of piles. Conventional α, β, and λ methods and modified α, β, and λ methods are the common models that are used for calculating the shaft capacity by incorporating soil–water characteristic curves (SWCCs). However, in our opinion, we feel that the investigation of the influence of seepage infiltration due to rainfall on the shaft capacity of piles, calculated using both analytical means and numerical analysis, has been dealt with inadequately in past studies. The objective of this study is to investigate changes in the shaft pile capacity according to suction changes due to rainwater infiltration for the greater reliability of the pile design, using both analytical and numerical studies with the finite element method (FEM). Sand and kaolin, which are typical components of coarse-grained and fine-grained soil, are used in this study. The laboratory results were incorporated into PLAXIS 3D (Version 22), and a coupled analysis was carried out, utilizing the meteorological conditions in Astana. The results showed that the decreases in matric suction in sand and kaolin are similar after their subjection to rainfall, yet sand produces a higher shaft capacity compared to kaolin. The modified β method offers a higher shaft capacity compared to the other methods due to the effective stress factors being taken into account. The modified α and λ methods are recommended for short piles because they are more sustainable, whilst the modified β method is preferable for long piles. Overall, unsaturated soil conditions should be applied to optimize the foundation design since they generate a higher shaft capacity. Full article
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10 pages, 2113 KiB  
Article
Soil Water Retention and Pore Characteristics of Intact Loess Buried at Different Depths
by Xiaokun Hou, Shengwen Qi and Fangcui Liu
Sustainability 2023, 15(20), 14890; https://doi.org/10.3390/su152014890 - 15 Oct 2023
Cited by 3 | Viewed by 1052
Abstract
Surface water infiltration is a primary factor responsible for engineering challenges and geological disasters on the Loess Plateau of China (LPC). Due to the extensive groundwater in this region, surface water must pass through thick unsaturated zones to recharge the groundwater reservoirs. Exploring [...] Read more.
Surface water infiltration is a primary factor responsible for engineering challenges and geological disasters on the Loess Plateau of China (LPC). Due to the extensive groundwater in this region, surface water must pass through thick unsaturated zones to recharge the groundwater reservoirs. Exploring the unsaturated hydraulic characteristics of loess, especially at varying depths, may significantly contribute to disaster prevention and mitigation and the pursuit of sustainable development in the Loess Plateau. The soil-water characteristic curve (SWCC), intricately linked to the soil’s pore structure, is a critical hydraulic parameter of loess. An exploration well with a depth of 30 m was excavated in the LPC to obtain intact specimens at depths of 5 m, 15 m, and 25 m. Basic physical property tests, SWCC measurements, and particle size distribution (PSD) analyses were conducted. Additionally, the relationship between PSD and SWCC is discussed in this paper. The findings highlight the influence of depth on the dominant pore size and distribution density, both of which decreased with increasing depth. The air occlusion value of the SWCC experienced an increase, and the slope of the SWCC in the transition zone exhibited consistency. These observations underscore the pivotal role played by pore structure in shaping the soil’s water-retention behavior. Furthermore, predictions based on PSD data demonstrated excellent accuracy in replicating the wetting SWCC of loess over a wide suction range (e.g., 10–104 kPa). Full article
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22 pages, 12586 KiB  
Article
An Experimental and Numerical Investigation of the Characteristics and Mechanism of Spacing Cracks in Loess Considering the Size Effect
by Xin Wei, Yunru Zhou and Xuanyi Chen
Sustainability 2023, 15(16), 12482; https://doi.org/10.3390/su151612482 - 16 Aug 2023
Viewed by 929
Abstract
Loess is a special soil with high water sensitivity which covers a large area in Northwest China. Cracks are prone to generate in loess under the arid and semiarid climates, which will provide a preferential channel for water and reduce the mechanical properties [...] Read more.
Loess is a special soil with high water sensitivity which covers a large area in Northwest China. Cracks are prone to generate in loess under the arid and semiarid climates, which will provide a preferential channel for water and reduce the mechanical properties of soils. It is of great significance to understand the evolution characteristics and mechanisms of the cracks in loess areas. At present, research on cracks in soils mainly concentrates on the characteristics of different cracking patterns. However, spacing cracks are mostly discussed in materials like rock and concrete rather than soils. The cracking characteristics and mechanisms of spacing cracks in loess are still inadequate. In this research, drying tests of loess are carried out with different sizes of specimens. The parameters of spacing cracks and local strain distributions of the loess samples are obtained via PCAS and DIC methods during desiccation, respectively. The cracking modes, spacing cracking laws like insertion, and the saturation of spacing cracks are revealed. Finally, the size effect on the characteristics of spacing cracks is verified with the discrete element software MatDEM. Full article
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20 pages, 10988 KiB  
Article
The Influence of Overburden Stress and Molding Water Content on the Microstructure of Remolded Loess
by Zhiyu Qi and Zhiqing Li
Sustainability 2023, 15(16), 12401; https://doi.org/10.3390/su151612401 - 15 Aug 2023
Cited by 1 | Viewed by 838
Abstract
This study aims to reveal the mechanisms of the microstructural evolution of remolded loess under different molding water contents and overburden stresses. Utilizing L6 loess from Yan’an, remolded soil specimens were fabricated under various pressures and moisture contents, followed by conducting one-dimensional consolidation [...] Read more.
This study aims to reveal the mechanisms of the microstructural evolution of remolded loess under different molding water contents and overburden stresses. Utilizing L6 loess from Yan’an, remolded soil specimens were fabricated under various pressures and moisture contents, followed by conducting one-dimensional consolidation tests. The macroscopic porosity, pore size distribution curves (PSD), and microstructure of these remolded loess samples were examined. Experimental findings indicate that an increase in molding water content leads to an augmentation in macroscopic pore volume and elongated pore shapes, concurrently exerting substantial influence on the primary pore size and pore volume of both macropores (>0.4 μm) and minipores (0.4–4 μm), with minimal impact on micropores (<0.4 μm). The escalation of overburden stress solely contributes to the reduction in pore size and pore volume of macropores. Variations in the Menger fractal dimension occur only beyond the optimal water content, while overburden stress exhibits a minimal effect on the Menger fractal dimension. Furthermore, remolded loess exhibited a certain yield stress, and when the overburden stress was lower than the yield stress, there was almost no change in various types of pores. Finally, a microstructural evolution model of remolded loess under different molding water contents and overburden stresses was proposed. These findings are expected to provide new insights into the microstructural evolution and deformation mechanisms of loess in high embankment construction sites. Full article
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