Foundation Soil Research Articles

Impact evaluation of polypropylene fibres on the engineering behaviour of Siwalik clay

In the Kashmir region of Pakistan, the presence of Siwalik clays engenders serviceability issues to the infrastructure causing substantial loss of property. In this study, an attempt has been made to address these issues using polypropylene fibres (PPFs) as a sustainable modifier. These fibres were used in five different proportions, namely 0.25, 0.5, 0.75, 1 and 1.25% as partial replacement of base soil to analyse their impact on the engineering behaviour of matrices. Classification, compaction, indirect tensile, unconfined and triaxial compression, swell potential, consolidation and California bearing ratio (CBR) tests were conducted on controlled as well as reinforced-clay samples for comparative analyses. The maximum improvements were observed in unconfined compressive strength (109%), tensile strength (300%), cohesion (13%), friction angle (110%), soaked CBR (800%) and un-soaked CBR (550%). Besides, the reduction in swelling strain by 92% was also recorded corresponding to 1 kPa effective vertical stress. The capital cost analyses showed that PPFs reduced the costs of backfill behind the retaining wall and foundation soil beneath isolated footing by 21 and 44.5%, respectively. Moreover, the modifier had no adverse effect on the aqueous media. Conclusively, PPFs can be used as sustainable modifiers leading to a potential solution for serviceability issues.

Variable diameter pile foundations – advantages and disadvantages

Variable diameter pile foundations can be an efficient foundation solution used for special structures, mainly for the ones with increased heights. For economic efficiency in land use, especially in urban areas, there is a tendency to build very high constructions with very small footprint related to their height, which transmit large loads to the foundation soil. Based on these aspects, it is necessary to consider pile foundations in order to ensure the desired safety and stability requirements. The technologies for piles constructions evolved a lot and a main objective was to better use the interaction between the soil and the pile. From this point a view the paper presents a comparison between the bearing capacities of a constant diameter pile and a variable diameter pile, considering different soil conditions. All the calculations were performed using finite element analyses.

Moment-Based Analysis of Onshore Wind Turbine Generator Foundation–Soil Response

Moment-Based Analysis of Onshore Wind Turbine Generator Foundation–Soil Response

Resistance factors for reliability based-design of geogrid reinforced soil foundations against ultimate and serviceability limit state

In the recent decades, the use of geosynthetics to improve the overall soil’s bearing capacity and settlement behavior under shallow foundations has become a major topic. Despite several studies that have been carried out on Reinforced Soil Foundations (RSF), no design specifications have been set to design RSF against the Ultimate and Serviceability Limit State (ULS and SLS) in any of the established codes. This paper presents the development of resistance factors based on the Load and Resistance Factor design (LRFD) approach against the ULS and SLS for strip footing resting on C−ϕ soils. The resistance factors are developed using a spreadsheet-based reliability model based on the First Order Reliability Method (FORM) to be consistent with the ASCE-7 load factors. The resistance factors are calibrated at a targeted probability failure (Pf) of 0.13499% and 0.00317% for ULS and 2.27%, for SLS. A Finite Element Model (FEM) is developed to validate three analytical solutions to establish the reliability model. The FEM results showed an agreement with the analytical solutions. For ULS the developed resistance factors at Pf= 0.13499% ranged from 0.33 to 0.9 assuming lognormally distributed variables and 0.25 to 0.89 assuming normally distributed variables. The resistance factors against SLS at Pf= 2.27%. ranged from 0.39 to 0.85 considering lognormally distributed variables and 0.35 to 0.83 considering normally distributed variables.

Comprehensive wood dwelling tests for Post‐and‐Beam and Shear‐Wall structures reflecting foundation boundaries

AbstractThis paper focuses on the ultimate state of three‐story wood dwellings with high aspect ratios, which are increasing in Japan's urban areas. Using shaking table test results from the 2019 full‐scale shaking table test, a comprehensive study is conducted on the accuracy of evaluating ultimate state through the story shear failure mode at the first story, the tension fracture mode at the wall base of the first story, and foundation sliding mode on the soil. Methods evaluating the dynamic response behaviors of the building systems are also investigated. In the test, the current Japanese seismic design guidelines were applied, and two Grade‐3 buildings were prepared. One adopted the Post‐and‐Beam structure (A‐building), and the other the Shear‐Wall structure (B‐building). A series of tests planned very different physical boundary conditions surrounding their reinforced concrete (RC) mat foundations. The sills, column bases and wall bases of the upper wood structures were anchored to the RC foundations by steel anchor bolts, according to the current Allowable Stress Design (ASD) requirements. In the first stage, A‐building equipped a Base‐Isolation system, while B‐building represented a generic foundation constructed on a 1.5 m‐height real soil ground by preparing a rigid soil box (Foundation‐Soil system). In the second stage of A‐building and B‐building, the foundation was firmly fixed (Fixed‐Foundation system), and shaking table motions were fully applied to the foundations. The entire test system was setup on the large shaking table facility at E‐Defense, and a series of tests were conducted using JMA‐Kobe motion and JR‐Takatori motion recorded in the 1995 Kobe earthquake as Maximum‐Considered‐Earthquake motions. Confirmed was the change in the structural mechanism due to the upper structural systems and the foundation boundaries. Regarding the upper wood structure performance in the Fixed‐Foundation system, a story shear failure mode was observed at the first story in A‐building, while a tension fracture mode at the base of the first story in B‐building. This difference of failure mode is difficult to determine with ASD. The maximum strength were more than four times higher than the ASD base shear force. Tension fracture capacity at the wall base was mainly enhanced by the presence of the steel anchor bolts. Regarding the foundation performance in Foundation‐Soil system of B‐building, a horizontal displacement up to 240 mm was observed between the foundation and soil when JMA‐Kobe 100% was applied. A response reduction effect was observed in the upper wood structure, similar to the Base‐Isolation system of A‐building. The initial friction and cyclic friction strength capacities between the foundation and soil were quantitatively evaluated considering the horizontal two‐directional sliding. The representative test results were converted to the corresponding SDOF systems based on the first mode response assessment. In the Fixed‐Foundation system, the dynamic response characteristics of the upper wood structures were properly represented using Ibarra‐Medina‐Krawinkler pinching model in the equivalent SDOF system.

Issues and Methods of Restoration of Kyivan Rus Period Foundation Masonry

Analysis of the main problems of the emergency state of the monuments shows that the main problem of disrupting the equilibrium of the statics of the “footing-foundation-structure” system is the uneven subsidence of the foundations, weak foundation soils, moistening of the foundation soils due to the violation or absence of waterproofing. The subsidence of footings and foundations, changes in hydrogeological conditions, the absence of blind areas and disorganized drainage from the basement, ageing of masonry solutions, a decrease in the strength and bearing properties of stone, brick and plinthiform brick lead to an emergency state of stone walls, their deformation, moistening, destruction of masonry, the appearance of cracks. Unique monuments of the Kyivan Rus period have been preserved in Ukraine. Unfortunately, as a result of the Mongol-Tatar invasion and destruction of the period of atheism in the 1930s, only foundations or separate parts of many temples remained, and some temples were rebuilt during the Baroque period. From many unique monuments, only the foundations remained, in some, in addition to the foundations, walls and individual fragments remained. In this case, the main restoration task was the maximum preservation of artefacts – foundations, walls, side-chapels.

A simplified model for energy pile-supported embankment

Energy piles can be used for road de-icing in winter or cooling in summer in the pile-supported embankment. This paper presents a simplified model for energy pile-reinforced foundation beneath the embankment to investigate thermal effects of piles on the performance of the system. By considering thermo-mechanical stress–strain of the pile and foundation soil, thermally-induced pile-soil interaction, and applying stress continuity and settlement continuity at the bottom of the embankment fill and the surface of the underlying soil, the settlements of the piles, the surrounding soil, the embankment fill, and the underlying soil are compatible. This proposed method is validated by comparison with numerical analysis. An increase in temperature will mobilize more friction at both the upper and lower sides of the pile, and will decrease the foundation settlement but increase the load-sharing ratio of the piles. The stiffer surrounding soil provides greater constraint to limit the deformation of the energy pile, causing larger thermal-induced stress of the pile.

Bearing capacity and the settlement of foundation on biomodified coastal soil

Construction of the foundation on the marine the soil deposit is susceptible to excessive settlement and the construction of foundation is difficult. Although, the most common practice is to construct the raft foundation in these regions even for the low-rise building, excessive settlement can be observed in several building. So, in the present study, laboratory investigations have been done on the marine soil by modifying it with two different type of biopolymer such as Guar gum and Xanthan gum. The geotechnical properties of the soil modified with 1% and 1.5% biopolymer has been evaluated and the obtained properties has been used for settlement analysis. During the settlement analysis, the foundation soil model has been created as layered soil because the top layer has been replaced by biomodified soil. Several combi-nations have been created by varying the thickness of modified soil layer and the type and percentage of modifying agent. The settlement analysis has been performed in the settle 3D software and the biopolymer modification of soil has been found effective in controlling the foundation settlement.

Finite strain elastic visco-plastic consolidation model for layered soils with vertical drain considering self-weight loading and nonlinear creep

Prefabricated vertical drains (PVDs) combined with vacuum and/or surcharge loading have been widely adopted to improve the strength of soft soils. Precise consolidation analysis is the theoretical basis for the design of preloading method with PVD. Current consolidation theories for layered soils with PVD seldom consider the influence of large strain, nonlinear creep, and self-weight loading simultaneously. This paper, thus, presents a finite strain elastic visco-plastic consolidation model, called RCS-EVP, for radial consolidation of layered soils with PVD. RCS-EVP is developed based on the piecewise-linear method. It takes into account nonlinear creep with limit creep strain, variable boundary conditions, anisotropy of soil hydraulic conductivity, and variable compressibility and hydraulic conductivity during the consolidation under self-weight, time-dependent surcharge and/or vacuum loading. The performance of RCS-EVP is evaluated by comparing with the results from finite element simulations and a laboratory physical model test. The variations of settlement and pore pressure of a soft soil ground improved by vacuum preloading with PVD are estimated using RCS-EVP. The results indicate that RCS-EVP provides good estimates of long-term consolidation of layered soils with PVD under both laboratory and in-situ conditions.

Effect of Footing Shape on the Rocking Behavior of Shallow Foundations

Sources such as wind or severe seismic activity often exert extreme lateral loading onto the shallow foundations supporting high-rise structures such as bridge piers, buildings, shear walls, and wind turbine towers. Such loading conditions may cause the foundation to exhibit nonlinear responses such as uplift and bearing capacity mobilization of the supporting soil (i.e., rocking behavior). Previous numerical and experimental studies suggest that while such inelastic behaviors may engender residual deformations in the soil–foundation system, they offer potential benefits to the overall integrity of structures through dissipating energy and reducing inertia forces transmitted to the superstructure, thereby limiting seismic demand on structural elements. This study investigates the effect of footing shape on the rocking performance of shallow foundations in different subgrade densities and initial vertical factor of safety (FSv). To this end, a series of reduced-scale slow cyclic tests under 1 g condition were conducted using a single degree of freedom (SDOF) structure model. The performance of different footing shapes was studied in terms of moment capacity, recentering ratio, rocking stiffness, damping ratio, and settlement. For three foundations with different length-to-width ratios, the results indicate that increasing the safety factor and length-to-width ratio leads to thinner, S-shaped moment–rotation curves, mainly owing to the enhanced recentering capability and the P-δ effect. Moreover, across all foundation types, the repetition of a limited loading cycles with consistent rotation amplitude does not cause stiffness degradation or moment capacity reduction.

Spatial downscaling of SMAP radiometer soil moisture using radar data: Application of machine learning to the SMAPEx and SMAPVEX campaigns

This study developed a random forest approach for downscaling the coarse-resolution (36 km) soil moisture measured by The National Aeronautics and Space Administration (NASA) Soil Moisture Active Passive (SMAP) mission to 1 km spatial resolution, utilizing airborne remotely sensed data (radar backscatter and radiometer retrieved soil moisture), vegetation characteristics (normalized difference vegetation index), soil properties, topography, and ground soil moisture measurements from before the launch of SMAP for training a random forest model. The 36 km SMAP soil moisture product was then downscaled by the trained model to 1 km resolution using the information from SMAP. The downscaled soil moisture was evaluated using airborne retrieved soil moisture observations and ground soil moisture measurements. Considering the airborne retrieved soil moisture as a reference, the results demonstrated that the proposed random forest model could downscale the SMAP radiometer product to 1 km resolution with a correlation coefficient of 0.97, unbiased Root Mean Square Error of 0.048 m3 m−3 and bias of 0.016 m3 m−3. Accordingly, the downscaled soil moisture captured the spatial and temporal heterogeneity and demonstrated the potential of the proposed machine learning model for soil moisture downscaling.

Propagation Behavior of P1-Wave Passing through Fluid-Saturated Porous Continuous Barrier in Layered Saturated Soil

The fluid-saturated porous continuous barrier has a better vibration isolation effect than the single-phase solid continuous barrier, and layer-forming saturated soils will have an impact on the vibration isolation effect of the barriers due to their irregular layer-forming distribution. Based on Biot’s theory of saturated porous media and Snell’s law, a dynamic model of a fluid-saturated porous continuous barrier in layered saturated soil is established in this study. By introducing the potential function and using the continuous boundary condition of the interface between the saturated soil and the barrier, the analytical solution of the inverse transmission amplitude ratio of a P1-wave passing through the fluid-saturated porous continuous barrier in stratified saturated soil is obtained. The rationality of the proposed method is verified by comparing the solution of the P-wave model at the interface between the elastic medium and the saturated coarse particle interlayer. The differences in the propagation characteristics of fluid-saturated porous continuous barriers in layered saturated soils, homogeneous saturated soils, and layered single-phase soils are analyzed via numerical examples, and the influence of changes in the physical and mechanical parameters of the fluid-saturated porous continuous barriers on the reflectance amplitude ratios under the conditions of a layered saturated soil foundation are also analyzed. The results show that the presence of fluid in the stratified saturated soil model changes the trend of the reflection amplitude ratio with the incidence angle. The reflection amplitude ratio of the P2-wave and the SV-wave increases first and then decreases with the increase in the incident angle, while the reflection amplitude ratio of P1-wave decreases first and then increases. Barrier thickness and porosity change the energy distribution relationship at the interface; a relatively thicker barrier thickness and a higher porosity would result in a higher amplitude of barrier reflections.

Seismic behavior of irregular underground structures in saturated sand

Sand liquefaction is one of the leading causes of severe earthquake damage. In this study, shaking table tests were carried out to investigate the dynamic interaction between the saturated sand and the irregular subway stations. In this test, a method for the preparation of a liquefiable foundation based on a flexible sensing chain combined with water sedimentation was proposed. Typical test results were interpreted, including the development and spatial distribution of pore pressure, surface subsidence, acceleration, deformation, and dynamic earth pressure. Results show that the spatial distribution of excess pore water pressure is changed by the irregular underground structure, and the liquefiable soil below the bottom plate of the structure can be divided into I, II, and III areas based on the degree of liquefication. The surface subsidence is significantly related to Arias intensity and is concentrated within the range of 5 %–95 % of the intensity. The structural floating is synchronized with the liquefaction of the saturated sand, and the uneven floating and inclination of the underground structure are remarkable, anti-flotation design of underground structures should take into account differences in section forms. During the liquefaction of saturated sand, the foundation soil has conspicuous lateral deformation, especially in the deep soil layer. The shape of the dynamic earth pressure increments turns from triangular to linear, when the foundation soil changes from non-liquefied to liquefied. Compared with the limiting values of the elastic inter-story drift ratio, the maximum inter-story drift ratio of the structure is smaller. The tensile strain responses on the columns, particularly in the lower layer, are more prominent than those at the slabs and side walls.

Freezing and Thawing of Enclosing Structures and Foundation Soils Taking into Account the Effects of Solar Energy: Part 2. Problem Statement

Part 1 provides general information about some of the physical properties of water, ice, and snow necessary to understand the non-stationary processes of freezing and thawing of enclosing structures of wet foundation soils. Part 2 presents the physical and mathematical formulation of the problem of freezing of wet soil, the solution of Lyame and Clapeyron, the solution of Stefan, the physical and mathematical formulation of the problem of freezing of the ribbon foundation. The following are considered: description of the process of freezing of a single-layer enclosing structure considering the phase transformations of moisture in the material of the structure according to V.N. Bogoslovsky and the process of freezing of an unlimited plate considering the phase transformations of moisture in the material of the structure according to A.V. Lykov. Mathematical model of non-stationary heat transfer process in wet layered media. Based on the method of small-time intervals, solutions of boundary value problems for frozen and thawed zones in the region of large and small Fourier numbers are given. Prospects for the application of the proposed mathematical models to describe the processes of freezing and enclosing structures and foundation soils are outlined.

Freezing and Thawing of Enclosing Structures and Foundation Soils Taking into Account the Effects of Solar Energy: Part 1. Theoretical Foundations of Freezing Wet Soils

The temperature and humidity state of the foundations and foundations in the climatic conditions of the Russian Federation is decisive in their design,it affects the bearing capacity, operational reliability, and durability of the foundations and the entire building. When designing foundations and foundations, they solve a set of tasks that are subordinated to one idea, so that the soil (base) he carried the load from the building or structure proposed to him, and the foundation structure itself would ensure reliable operation of the building or structure for the entire life cycle, since the foundations belong to permanent structures, and their repair is associated with large material costs. Existing modern calculation methods assume that the heat transfer process is stationary and do not consider real processes – seasonal and daily fluctuations in outdoor air temperature, heating on and off modes, temperature changes in the depth of the soil, wet structures due to accidents of heating plants, the absence (or destruction) of a blind area, etc. Freezing of soils, as a rule, occurs in autumn-winter period, when the soil is saturated with moisture. Thawing of the soil occurs in the spring-summer period. These processes are non-stationary in nature, which is influenced by many factors, including solar radiation. The work is devoted to modelling and calculation of these real processes. The process of freezing and thawing of the foundation soils is influenced by many factors: the composition of the soil, water, ice, snow, solar radiation, fluctuations in outdoor temperature. The paper provides general information about some of the physical properties of water, ice, and snow, necessary for understanding the processes under consideration.

Fast Lagrangian analysis of the short-term bearing capacity of shallow foundations in clays on the basis of the cone penetration test

Based on a numerical modelling of the cone penetration test CPT as well as the vertical response of shallow foundation in saturated clays, derivation of the cone factor Nk led to propose a CPT-based method of computation of the bearing capacity. This study was carried out by launching a detailed parametric study using the software FLAC-2D (Fast Lagrangian Analyses of Continua) based on the finite difference method. The soil material was modeled as a homogeneous elastic-perfectly plastic medium obeying the Mohr-Coulomb criterion, and the effects of the soil rigidity index Ir, the cone-soil interface, and the initial depth of the penetration on the cone factor Nk were investigated leading to an analytical formulation of Nk. After a comparative study with those proposed in the literature, the cone factor Nk was used to derive the bearing capacity factor Kc of a shallow foundation. Compared to current CPT-based methods proposed in the literature, this method reasonably predicts the short-term bearing capacity of shallow foundations in saturated clayey soil.

Dynamic Response of A Group of Cylindrical Storage Tanks with Baffles Considering the Effect of Soil Foundation

Dynamic Response of A Group of Cylindrical Storage Tanks with Baffles Considering the Effect of Soil Foundation

Evaluating soil setup after open metallic pile driving

After driving a pile, foundation soil is restructured and thus regains part of its resistance. This phenomenon is aptly named soil setup. This paper’s focus is to study said phenomenon on eight open metal piles driven in a soil composed of sand and marl, while basing our findings on data of dynamic PDA tests processed with CAPWAP software. Firstly, dynamic tests performed after driving phase and at subsequent re-driving phases show an increase in both the required number of blows for a 10-centimeter drive and in the static resistance to re-driving. The correlations of these resistances with the predictions of the models of Skov & Denver (1988) and Svinkin & Skov (2000) were not satisfactory (R2 of 0.77 and 0.75 respectively). Noting that the setup is mainly due to the increase in friction, a layer-by-layer analysis is carried out by treating the sand and the marl separately. Attained results fit well the Skov & Denver model and align with the experimental results of Murad (2014), but given the model’s limitations in terms of reference time determination, we develop a new function model potency considering immediate setup. The new model fits our attained results very well (R2 of 0.944 for sand and 0.980 for marl). The final static strength after setup is thus calculated as a function of time based on the power function model and conservative estimates. This approach encourages allowing time for the soil to gradually and naturally scar instead of rushing into immediate and costly measures such as patching.

Shadowing effect of an existing tunnel on the evolution of soil arching: impact of tunnel shape

This study evaluates the shadowing effect of existing tunnels on the evolution of soil arching, focusing on the shape of the tunnel (circular and rectangular) through trapdoor experiments. The displacement and shear strain distributions of ground soil resulting from trapdoor movement were estimated using a digital image correlation technique. The results showed that the shadowing effect of the rectangular tunnel was significantly greater than that of the circular tunnel of the same size. The sand above the tunnel was displaced in a double-groove pattern owing to the presence of the tunnel, and the maximum surface settlement occurred between the tunnel boundary and the trapdoor edge. The circular tunnels exhibited consistently higher maximum surface displacements than that in the rectangular tunnels. The shear strain value of soil was lower for the rectangular tunnel case than that for the circular tunnel case. The rectangular tunnels required lesser trapdoor displacement than that of the circular tunnel to obtain the minimum soil arching ratio. The minimum and ultimate soil arching ratios increased as the burial depth ratio increased for both the tunnel shapes. The maximum stress ratio of the tunnel crown was consistently larger for the circular case than for the rectangular case.

Experimental investigation of seismic performance of segmental tunnel with secondary lining under strong earthquake

To assess the seismic performance of large-diameter tunnels in soil ground with and without secondary lining, large scale shaking table tests with geometrical ratio of 1:15 were conducted. The model tunnels were grouped as a tunnel only with segmental linings (Single lining), a tunnel liner with additional semi-ring secondary lining (Semi-ring), and a tunnel with additional full-ring secondary lining (Full-ring). Transverse excitations input from shaking-table were designated as Shanghai artificial accelerogram with magnitudes from 0.3 to 1.0 g. Measurements were made mainly on the time histories of acceleration responses, cross-sectional deformation, extension/closure at longitudinal joints of segmental linings, and earth pressure on external surface, of the model tunnels. Comparison the seismic responses of the tested models gives the effects of secondary lining as: 1) the distribution of acceleration responses on segmental linings is significantly different in the case of single lining model; 2) dynamic normal earth pressure on the external surface of the segmental linings increase along depth, but in different patterns; 3) the constraint effects of semi-ring secondary lining on extension/closure of longitudinal joints are not significant in the upper half of segmental lining. Furthermore, with the increase of earthquake intensity, the constraint effects of full-ring secondary lining on both cross-sectional deformation and extension/closure of longitudinal joints become more remarkable, compared with those of the semi-ring secondary lining.