scholarly journals A Numerical Model to Study the Response of Piles under Lateral Loading in Unsaturated Soils

Geosciences ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 1
Author(s):  
Leonardo Maria Lalicata ◽  
Giada Maria Rotisciani ◽  
Augusto Desideri ◽  
Francesca Casini
Keyword(s):  
Numerical Model ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Water Saturation ◽  
Laboratory Data ◽  
Soil Layer ◽  
Soil Conditions ◽  
Soil Reaction ◽  
Modified Cam Clay ◽  
Pile Interaction

The interaction between a laterally loaded pile and the surrounding soil is typically limited to the shallower soil layer. Often, this zone is above the water table and therefore the interaction takes place under unsaturated conditions. The available evidence is scarce but suggests that unsaturated conditions play a major role on the pile’s response. The actual mechanisms governing the soil–pile interaction under unsaturated soil conditions are not understood entirely, and this paper provides a useful insight on this topic. The analysis is carried out with a fully coupled three-dimensional numerical model, the soil behaviour is simulated with a Modified Cam Clay Model extended to unsaturated conditions. The model accounts for the increase in stiffness and strength of unsaturated soils as well as the volumetric collapse upon wetting. The constitutive model is calibrated on the laboratory data and validated against centrifuge data with satisfying agreement. The results highlight the substantial differences in the soil reaction against the pile depending on different water saturation profiles. The study also shows that the influence of unsaturated conditions on the pile response increases as the pile’s flexibility increases. Comparing the findings with currently available design methods such as the p–y curves, it is found that these do not adequately describe the unsaturated soil reaction against the pile, which opens the door for new research in the field. The proposed numerical model is a promising tool to further investigate the mechanisms underlying the soil–pile interaction under unsaturated soils.

Stress Prediction of Buried Pipes Subjected to Operational Loadings in Unsaturated Soils

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Chamal Randeniya ◽  
Dilan Robert ◽  
Chun-Qing Li
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Three Dimensional ◽  
Soil Condition ◽  
Temporal Variations ◽  
Soil Conditions ◽  
Fe Model ◽  
Fe Method ◽  
Buried Pipes ◽  
Stress Prediction

Abstract Pipelines are used to provide variety of services in modern community and have grown rapidly in past few decades due to growing socio-economic requirements. Most of the water mains are buried in shallow depths where the soil is partially saturated with significant spatial and temporal variations. Even though the behavior of buried pipes in such unsaturated soil condition is substantially different when compared to dry or fully saturated soil, the effect of soil saturations is overlooked in the current pipe stress prediction methods, leading to unrealistic predictions of the pipe stresses. In this study, three-dimensional (3D) finite element (FE) method was employed with advanced constitutive soil models to analyze the behavior of pipes buried in unsaturated soil condition. Having validated the FE model using reported field test data, an analytical model was proposed to predict the maximum stress in buried pipes considering soil saturation effect using a series of 3D FE analyses. Results from the FE analyses reveal that the maximum pipe stress can be significantly different when soil is in unsaturated condition when compared to dry condition. The proposed formula shows a good agreement with the field data and FE results, so that the expression can be used in the prediction of maximum pipe stress when they are buried under realistic (i.e., nondry) soil conditions.

scholarly journals Investigating the Effect of Geocell Changes on Slope Stability in Unsaturated Soil

2020 ◽  
Vol 14 (1) ◽  
pp. 66-75
Author(s):  
Behnam Mehdipour ◽  
Hamid Hashemolhosseini ◽  
Bahram Nadi ◽  
Masoud Mirmohamadsadeghi
Keyword(s):  
Slope Stability ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Bending Strength ◽  
Load Capacity ◽  
Three Dimensional ◽  
Bending Moment ◽  
Soil Conditions ◽  
Vertical Side ◽  
Basic Model

The purpose of this research is to investigate the performance and efficiency of reinforced slope in the stability of geocell layers in unsaturated soil conditions. Slope reinforced with geocell acts like a beam in the soil due to the geocell having a height (three-dimensional). Due to its flexural properties, it has moment of inertia as well as bending strength, which reduces the displacement and increases the safety factor of the slope. Taking into consideration unsaturated conditions of soil contributes a lot to making results close to reality. One of the well-known models among elastoplastic models for modeling unsaturated soils is Barcelona Basic Model, which has been added to the FLAC2D software by codification. Changes in thickness, length and number of geocell layers are remarkably effective on slope stability. The results show that the geocell's reinforcing efficiency depends on the number of layers and depth of its placement. As the depth of the geocell's first layer increases, the lateral and vertical side elevation of the upper part of the slope increases with respect to the elevation. Load capacity increases with increasing geocell length. By increasing the length of the geocell layer, the joint strength, the mobilized tensile strength, and the bending moment are increased. At u/H = 0.2, an increase in the bending momentum of about 20% occurs with increasing geocell thickness. In u/H = 1, the increase in bending momentum is 10.4%. In addition, by increasing the thickness of the geocell, the Value of moment of the inertia increases and, as a result, the amount of geocell reinforcement bending moment increases.

Volume–mass unsaturated soil constitutive model for drying–wetting under isotropic loading–unloading conditions

2011 ◽  
Vol 48 (2) ◽  
pp. 280-313 ◽  
Author(s):  
Hung Q. Pham ◽  
Delwyn G. Fredlund
Keyword(s):  
Constitutive Model ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Research Literature ◽  
Degree Of Saturation ◽  
Soil Conditions ◽  
Constitutive Relationships ◽  
Proposed Model ◽  
Wide Range

A rigorous volume–mass constitutive model is proposed for the representation of drying–wetting under isotropic loading–unloading conditions for unsaturated soils. The proposed model utilizes concepts arising from soil physics and geotechnical engineering research and requires readily obtainable soils data for soil properties. The model can be used to predict void ratio and water content constitutive relationships (and therefore degree of saturation) for a wide range of unsaturated soils. Various stress paths (i.e., loading–unloading and drying–wetting) can be simulated, and hysteresis associated with the soil-water characteristic curve is taken into account. Two closed-form equations for the volume–mass constitutive relationships are presented for soils starting from slurry conditions. A number of test results (i.e., from experimental programs reported in the research literature) were used during the verification of the proposed volume–mass constitutive model. The volume–mass constitutive model captures key unsaturated soil conditions such as air-entry value, water-entry value, and residual conditions. The proposed model appears to satisfactorily predict unsaturated soil behavior for soils ranging from low compressible sands to high compressible clays.

scholarly journals Microbial reduction of iron and porewater biogeochemistry in acidic peatlands

2008 ◽  
Vol 5 (6) ◽  
pp. 1537-1549 ◽  
Author(s):  
K. Küsel ◽  
M. Blöthe ◽  
D. Schulz ◽  
M. Reiche ◽  
H. L. Drake
Keyword(s):  
Water Saturation ◽  
Global Climate ◽  
Soil Layer ◽  
Carbon Mineralization ◽  
Microbial Reduction ◽  
Electron Acceptors ◽  
Soil Conditions ◽  
Soil Layers ◽  
Reduction Of Iron ◽  
Pcr Products

Abstract. Temporal drying of upper soil layers of acidic methanogenic peatlands might divert the flow of reductants from CH4 formation to other electron-accepting processes due to a renewal of alternative electron acceptors. In this study, we evaluated the in situ relevance of Fe(III)-reducing microbial activities in peatlands of a forested catchment that differed in their hydrology. Intermittent seeps reduced sequentially nitrate, Fe(III), and sulfate during periods of water saturation. Due to the acidic soil conditions, released Fe(II) was transported with the groundwater flow and accumulated as Fe(III) in upper soil layers of a lowland fen apparently due to oxidation. Microbial Fe(III) reduction in the upper soil layer accounted for 26.7 and 71.6% of the anaerobic organic carbon mineralization in the intermittent seep and the lowland fen, respectively. In an upland fen not receiving exogenous Fe, Fe(III) reduction contributed only to 6.7%. Fe(II) and acetate accumulated in deeper porewater of the lowland fen with maximum concentrations of 7 and 3 mM, respectively. Both supplemental glucose and acetate stimulated the reduction of Fe(III) indicating that fermentative, incomplete, and complete oxidizers were involved in Fe(II) formation in the acidic fen. Amplification of DNA yielded PCR products specific for Acidiphilium-, Geobacter-, and Geothrix-, but not for Shewanella- or Anaeroromyxobacter-related sequences. Porewater biogeochemistry observed during a 3-year-period suggests that increased drought periods and subsequent intensive rainfalls due to global climate change will further favor Fe(III) and sulfate as alternative electron acceptors due to the storage and enhanced re-oxidation of their reduced compounds in the soil.

scholarly journals A Unified Elastoplastic Model of Unsaturated Soils Considering Capillary Hysteresis

2013 ◽  
Vol 2013 ◽  
pp. 1-15
Author(s):  
Tiantian Ma ◽  
Changfu Wei ◽  
Pan Chen ◽  
Huihui Tian ◽  
De'an Sun
Keyword(s):  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Mechanical Response ◽  
Internal State ◽  
Degree Of Saturation ◽  
State Variables ◽  
Soil Behavior ◽  
Capillary Hysteresis ◽  
Modified Cam Clay

Unlike its saturated counterparts, the mechanical behavior of an unsaturated soil depends not only upon its stress history but also upon its hydraulic history. In this paper, a soil-water characteristic relationship which is capable of describing the effect of capillary hysteresis is introduced to characterize the influence of hydraulic history on the skeletal deformation. The capillary hysteresis is viewed as a phenomenon associated with the internal structural rearrangements in unsaturated soils, which can be characterized by using a set of internal state variables. It is shown that both capillary hysteresis and plastic deformation can be consistently addressed in a unified theoretical framework. Within this context, a constitutive model of unsaturated soils is developed by generalizing the modified Cam-Clay model. A hardening function is introduced, in which both the matric suction and the degree of saturation are explicitly included as hardening variables, so that the effect of hydraulic history on the mechanical response can be properly addressed. The proposed model is capable of capturing the main features of the unsaturated soil behavior. The new model has a hierarchical structure, and, depending upon application, it can describe the stress-strain relation and the soil-water characteristics in a coupled or uncoupled manner.

scholarly journals Microbial reduction of iron and porewater biogeochemistry in acidic peatlands

2008 ◽  
Vol 5 (3) ◽  
pp. 2165-2196 ◽  
Author(s):  
K. Küsel ◽  
M. Blöthe ◽  
D. Schulz ◽  
M. Reiche ◽  
H. L. Drake
Keyword(s):  
Water Saturation ◽  
Global Climate ◽  
Soil Layer ◽  
Carbon Mineralization ◽  
Microbial Reduction ◽  
Electron Acceptors ◽  
Soil Conditions ◽  
Soil Layers ◽  
Reduction Of Iron ◽  
Pcr Products

Abstract. Temporal drying of upper soil layers of acidic methanogenic peatlands might divert the flow of reductants from CH4 formation to other electron-accepting processes due to a renewal of alternative electron acceptors. In this study, we evaluated the in situ relevance of Fe(III)-reducing microbial activities in peatlands of a forested catchment that differed in their hydrology. Intermittent seeps reduced sequentially nitrate, Fe(III), and sulfate during periods of water saturation. Due to the acidic soil conditions, released Fe(II) was transported with the groundwater flow and accumulated as Fe(III) in upper soil layers of a lowland fen apparently due to oxidation. Microbial Fe(III) reduction in the upper soil layer accounted for 26.7 and 71.6% of the anaerobic organic carbon mineralization in the intermittent seep and the lowland fen, respectively. In an upland fen not receiving exogenous Fe, Fe(III) reduction contributed only to 6.7%. Fe(II) and acetate accumulated in deeper porewater of the lowland fen with maximum concentrations of 7 and 3 mM, respectively. Both supplemental glucose and acetate stimulated the reduction of Fe(III) indicating that fermentative, incomplete, and complete oxidizers were involved in Fe(II) formation in the acidic fen. Amplification of DNA yielded PCR products specific for Acidiphilium-, Geobacter-, and Geothrix-, but not for Shewanella- or Anaeroromyxobacter-related sequences. Porewater biogeochemistry observed during a 3-year-period suggests that increased drought periods and subsequent intensive rainfalls due to global climate change will further favor Fe(III) and sulfate as alternative electron acceptors due to the storage of their reduced compounds in the soil.

Three-dimensional numerical analysis of geocell-reinforced soft clay beds by considering the actual geometry of geocell pockets

2015 ◽  
Vol 52 (9) ◽  
pp. 1396-1407 ◽  
Author(s):  
A.M. Hegde ◽  
T.G. Sitharam
Keyword(s):  
Numerical Model ◽  
Soft Clay ◽  
Soil Layer ◽  
Three Dimensional ◽  
Honeycomb Structure ◽  
Lagrangian Analysis ◽  
Foundation Soil ◽  
Composite Approach ◽  
Modified Cam Clay ◽  
Actual Geometry

Due to its complex honeycomb structure, the numerical modeling of the geocell has always been a big challenge. Generally, the equivalent composite approach is used to model the geocells. In the equivalent composite approach, the geocell–soil composite is treated as the soil layer with improved strength and stiffness values. Though this approach is very simple, it is unrealistic to model the geocells as the soil layer. This paper presents a more realistic approach of modeling the geocells in three-dimensional (3D) framework by considering the actual curvature of the geocell pocket. A square footing resting on geocell reinforced soft clay bed was modeled using the “fast Lagrangian analysis of continua in 3D” (FLAC3D) finite difference package. Three different material models, namely modified Cam-clay, Mohr–Coulomb, and linear elastic were used to simulate the behaviour of foundation soil, infill soil and the geocell, respectively. It was found that the geocells distribute the load laterally to the wider area below the footing as compared to the unreinforced case. More than 50% reduction in the stress was observed in the clay bed in the presence of geocells. In addition to geocells, two other cases, namely, only geogrid and geocell with additional basal geogrid cases were also simulated. The numerical model was systematically validated with the results of the physical model tests. Using the validated numerical model, parametric studies were conducted to evaluate the influence of various geocell properties on the performance of reinforced clay beds.

scholarly journals A comparison between performances of the behavioral models in evaluating load-bearing capacity of piles in fine-grained unsaturated soil

2018 ◽  
Vol 8 (1) ◽  
pp. 233-239
Author(s):  
Omid Bandehzadeh ◽  
Masoud Mirmohammad Sadeghi ◽  
Mohammad Ali Rowshanzamir ◽  
Alborz Hajian Nia
Keyword(s):  
Bearing Capacity ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Load Capacity ◽  
Water Pressure ◽  
Behavioral Models ◽  
Load Bearing Capacity ◽  
Static State ◽  
Load Bearing ◽  
Modified Cam Clay

<p>Virtually all structural piles are installed on the top of groundwater level, and these piles are located on unsaturated soils. In this case, the negative orifice water pressure caused by capillarity significantly influences the mechanical behavior of unsaturated soils. Consequently, structural suction is highly important to load-bearing capacity of loads. In this paper, an evaluation was drawn between the Mohr-Coulomb, modified Cam-Clay, and Barcelona behavioral models using the finite-difference method, and results of studies conducted to estimate load-bearing capacity in the static state were provided. The behavioral model guidelines matched the laboratory models. To estimate soil vividness on the suction level of concern, the water-soil curve (showing suction patterns in relation to moisture) utilized. The general tendencies of settlement gotten by the numerical examination are reliable with pile insert test results. Results suggest that the Barcelona personality model (BBM) yields more realistic estimates of load capacity as it looks at the effect of unsaturated soil suction.</p>

scholarly journals Hydraulic Transients in Viscoelastic Pipeline System with Sudden Cross-Section Changes

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4071
Author(s):  
Michał Kubrak ◽  
Agnieszka Malesińska ◽  
Apoloniusz Kodura ◽  
Kamil Urbanowicz ◽  
Michał Stosiak
Keyword(s):  
Numerical Model ◽  
Cross Section ◽  
Laboratory Data ◽  
Experimental Studies ◽  
Distribution Networks ◽  
Water Hammer ◽  
Fluid Distribution ◽  
Pipeline System ◽  
Hydraulic Transients ◽  
Single Pipe

It is well known that the water hammer phenomenon can lead to pipeline system failures. For this reason, there is an increased need for simulation of hydraulic transients. High-density polyethylene (HDPE) pipes are commonly used in various pressurised pipeline systems. Most studies have only focused on water hammer events in a single pipe. However, typical fluid distribution networks are composed of serially connected pipes with various inner diameters. The present paper aims to investigate the influence of sudden cross-section changes in an HDPE pipeline system on pressure oscillations during the water hammer phenomenon. Numerical and experimental studies have been conducted. In order to include the viscoelastic behaviour of the HDPE pipe wall, the generalised Kelvin–Voigt model was introduced into the continuity equation. Transient equations were numerically solved using the explicit MacCormack method. A numerical model that involves assigning two values of flow velocity to the connection node was used. The aim of the conducted experiments was to record pressure changes downstream of the pipeline system during valve-induced water hammer. In order to validate the numerical model, the simulation results were compared with experimental data. A satisfactory compliance between the results of the numerical calculations and laboratory data was obtained.

Soil Strength Reduction Method Induced by Variation of Water Content

2012 ◽  
Vol 170-173 ◽  
pp. 847-852
Author(s):  
Peng Ming Jiang ◽  
Zhong Lei Yan ◽  
Peng Li
Keyword(s):  
Slope Stability ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Strength Reduction ◽  
Actual State ◽  
Soil Slope ◽  
Simple Method ◽  
The Common ◽  
The Stability

As the complexity of unsaturated soil theory, and it must have a long test period when we study the unsaturated soils, so the conventional design analysis software does not provide such analysis, so we can imagine that such a slope stability analysis does not accurately reflect the actual state of the slope. Based on the known soil moisture content，this paper use the soil water characteristic curve and strength theory of unsaturated soil to calculate the strength reduction parameters of soil which can calculate the stability of the soil slope when using the common calculation method. It is noticeable that this method can be extended and applied if we establish regional databases for this simple method, and these databases can improve the accuracy of the calculation of slope stability.

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