Soil Relative Density Research Articles

Development of a soil quality index to evaluate agricultural cropping systems in southern Brazil

Soil quality indexes (SQIs) are tools that can help farmers and decision-makers to adopt management protocols that preserve or even improve soil characteristics. In this context, this research aimed to compare six strategies for calculating a soil quality index with different degrees of complexity, to define the simplest, most effective, and low-cost technological tool for soil quality (SQ) assessment, aiming to contribute to soil sustainability management in agricultural production in Southern Brazil. Sample collection points (CPs) were established at three locations (CP1, CP2, and CP3) under three different land-use systems: native forest (NF), a tillage system (TS), and a no-till system (NTS). Characterization of the SQ was performed based on three datasets: a total dataset (TDS) with 30 indicators, a reduced dataset using multivariate Principal Component Analysis (RDS-PCA), with seven indicators, and a dataset based on Literature and Expert Opinions (LEO-DS) with five indicators, as well as two additional systems, including simple addition (SQI-1, SQI-3, and SQI-5) and weighted addition (SQI-2, SQI-4, and SQI-6). The results indicated that all SQIs efficiently detected soil quality changes in the different systems. Dataset reduction approaches to determine SQI values between different land uses confirmed that the simplest QS integration method (SQI-6) is just as effective as the more complex methods (SQI-1, SQI- 2, SQI-3, SQI-4, and SQI-5). The results indicated that all SQIs efficiently detected soil quality changes in the different systems. Therefore, using SQI weighted with a reduced number of soil indicators (LEO-DS), such as pH, phosphorus (P), Rapid Diagnosis of Soil Structure (RDSS), Relative Soil Density (RD), and Total Organic Carbon (TOC), may be a potential protocol to support the implementation of an effective and low-cost technological tool for soil management in southern Brazil.

Effect of Biologically Induced Cementation via Ureolysis in Stabilization of Silty Soil

As a potential eco-friendly and sustainable method of ground improvement, microbiologically induced carbonate precipitation (MICP) has drawn considerable attention from researchers over the last few years. In this study, Bacillus megaterium, a nonpathogenic microorganism has been used for MICP treatment to enhance the shear strength of the weak silty soil. In the 1st stage of the experiment, bacterial cell density, the concentration of cementation solution, and the relative density of soil were considered as treatment variables. The optimum conditions were derived based on Unconfined Compressive Strength (UCS) and calcium carbonate content of soil samples cured for 7 days and were then applied to a study of ‘curing time’ (0, 4, 7, 15, 21, 30, and 60 days) as a variable, with calcium carbonate content and triaxial tests as measures of optimum curing time. Maximum strength gain for treated samples was observed after 21 days of curing. Beyond this period some strength loss, in the range of 20%, was observed due to the dissolution of precipitated calcite indicating the effectiveness of B. megaterium in the strength improvement of silty soil. SEM and EDS analyses confirmed the formation of CaCO3 and justified the experimental findings.

Interpretation of CPT in unsaturated sands under drained conditions: A numerical study

AbstractA finite difference‐based numerical model simulating the cone penetration process in unsaturated sands is presented. Mohr–Coulomb model (MCM) with simple modifications and Sun model (SM) were implemented to capture the unsaturated sand behaviour. It was shown that the cone tip resistance values resulting from the two models were fairly comparable. Predicted cone tip resistance values in dry, saturated and unsaturated sands using MCM were validated by the results of field and calibration chamber tests. Sensitivity analyses were performed, and the influence of parameters including relative density, mean effective stress and apparent cohesion due to suction on the tip resistance was investigated. Based on a large number of numerical analyses, a simple relationship was suggested to predict the cone tip resistance in dry, saturated and unsaturated sands. The accuracy of the proposed relationship was evaluated by a large database of Cone penetration test (CPT) results performed in various calibration chambers containing different sands. Finally, the applicability of the suggested equation in the estimation of the soil relative density and friction angle from CPT results was shown through useful and practical charts and illustrative examples.

EFFECT OF SOIL DENSITY AND PLUG CHARACTERISTICS ON BEHAVIOR OF SINGLE PIPE PILE EMBEDDED IN COHESIONLESS SOIL AND SUBJECTED TO UPLIFT FORCE

It is a significant issue to analyze and understand the pile’s behavior as well as to predict the piles’ capacity exposed to uplifting load when designing a foundation. Experimental model tests have been conducted for a single pile embedded in cohesionless soil and subjected to uplift force. The experimental tests were performed using open-ended steel pipe piles with circular cross-sectional area an outer diameter of 50 mm in steel soil box (0.5*0.5) with four different height (0.30, 0.50 and two with 0.40 m). The tested piles have been embedment with penetration ratios (PR=L/D) of 10. Three different densities (25%, 50% and 75%) have been used to perform the tests. In addition three tests have been made with relative density of 50% to investigate the function the developed soil column inside the pile (soil plug) during installation. The results revealed that the behavior of single piles depends mainly on soil density and the ultimate pull-out capacity of the pile increases with the increasing of the soil relative density and used the data from this tests to presented formula to estimate the IFR and takes the soil state parameter as a qualitative variable. The results showed also that the removing of plugging soil decreases the pile’s pull-out capacity by about 85%. Whilst, using of closed-end or filled with concrete give higher capacity than that of open-end pipe pile by about 33% and 87% respectively.

Settlement of Shallow Foundation in Dry Sand Under an Earthquake

Seismically induced settlement of buildings with shallow foundations resting on dry sand soils has resulted in severe damage in recent earthquakes. A multi-degree of freedom shaking table and a fixed container were manufactured and used to study the foundation settlement. Series of shaking experiments on the shallow foundation situated in a center of the container and atop of a dry sandy soil has been performed to identify the mechanisms involved to calculate the foundation settlement induced by earthquake shaking. In this research, the important factors are identified, including shaking intensity, the soil relative density, the degree of freedom and the building’s weight. Two relative densities (55 % and 80%) are used and three local magnitudes of earthquakes (5.8, 6.4, and 7.2) (Anza, Jalisco, and Guerrero) respectively with one and two degrees of freedom. The results of the shaking indicated that shallow foundation settlement on the dry sand increases with the increase of the local magnitude of earthquakes and maximum acceleration. In the case of Anza, the percentage decrease in the settlement between the relative density of 55% and 80% for systems (x and xy) is (47% and 42%) respectively. While in the case of Jalisco and Guerrero, the percentage decreases in their settlement and for the same systems is (11% and 57%), (36% and 36%) respectively. The degree of freedom has an impact on the foundation settlement; it is proportional to the degree of freedom. Also, the results show that the settlement decreases when the relative density of sand increases.

Shaking table tests on wall-type gravel and rubber drains as a liquefaction countermeasure in silty sand

In this paper, the seismic performance of wall-type gravel and rubber drains as a liquefaction countermeasure in silty sand has been addressed using a series of 1 g shaking table tests. In these tests, the liquefaction resistance of silty sand was studied by changing soil relative density, silt content, number of walls, and materials of drainage walls. In order to evaluate shear wave propagation, the generation and dissipation of pore water pressure (PWP), and the ground surface settlement, various accelerometers, displacement and PWP transducers were placed. The obtained results indicated that an increase in the relative density and the number of wall-type gravel and rubber drains in liquefiable silty sand reduces the settlement, liquefaction-induced deformations, as well as the excess PWP and eventually improves the liquefaction resistance. Totally, it can be noted that the reinforced silty sand with wall-type gravel drains revealed less excess PWP and settlement than that with wall-type rubber drains.

Centrifuge modeling of normal faulting and underground tunnel in sandy soil deposit

Earthquakes of large magnitudes cause fault ruptures propagation in soil layers and lead to interactions with subsurface and surface structures. The emergence of fault ruptures on or adjacent to the position of existing tunnels cause significant damage to the tunnels. The objective of this paper is to study the interaction of an embedded tunnel within a soil layer and the soil deformations imposed upon by normal faulting. A centrifuge modeling under 80-g acceleration was conducted to investigate the rupture propagation pattern for different relative tunnel positions. Compared with the free field condition, due to tunnel and normal fault rupture interactions, focused on soil relative density and tunnel rigidity in this research, found that they can dramatically modify the rupture path depending on the tunnel position relative to the fault tip. The tunnel diverts the rupture path to its sides. This study presents the normal fault-tunnel interaction with the tunnel axis parallel to the normal fault line, to examine the changes that take place in fault rupture plane locations, the vertical displacement of the ground surface with tunnel presence and the effect of tunnel rigidity and soil density on fault tunnel interaction.

BiLSTM-Based Soil–Structure Interface Modeling

Deep learning (DL) algorithm bidirectional long short-term memory (BiLSTM) neural network is employed to model behaviors of the soil–structure interface in this study, as a pioneer research work to investigate the feasibility of using DL to model interface behaviors. Datasets are collected from 12 constant normal stress and 20 constant normal stiffness sand–structure interface tests. A modeling framework with the integration of BiLSTM is thereafter proposed. The results indicate that the BiLSTM-based model can accurately capture the responses of interface behaviors including volumetric dilatancy and strain hardening on the dense samples and volumetric contraction and strain softening on the loose samples, respectively. The effects of surface roughness, soil relative density, and normal stiffness on the interface behaviors are also investigated using the BiLSTM-based model. The predicted normal stress, shear stress, and normal displacement show good agreement with measured results.

Temperature effects on pile–soil interface behaviour in the case of piles in sand

The effects of increased temperature on the stress–strain response of geothermal piles and supporting soil were studied in this work. Geothermal piles with different pile end supports were investigated numerically using the finite-element software Abaqus. A critical-state-based constitutive model (clay and sand model) was adopted for simulating the elasto-plastic thermomechanical behaviour of soil using two user-defined material subroutines (UMAT and UMATHT). In order to understand the additional stresses and strains in piles and soil due to thermal loading of piles, a set of parametric investigations was carried out for different values of the restraint at the pile base, the relative density of the sand, pile length, pile diameter and the coefficient of lateral earth pressure of the soil. An increased coefficient of lateral earth pressure in the soil at the pile–soil interface was observed due to circumferential thermal radial strains over the pile length. Furthermore, the thermal response of the piles and soil was found to depend on the soil's relative density and the magnitude of thermal load experienced by the piles. Cyclic thermal loading resulted in increased axial stresses in the piles.

Dynamic response of the saturated soil–reinforced concrete pile–superstructure interaction under repeated shaking

This study conducted a shaking table test using a centrifuge model to clarify the dynamic response of the saturated soil–reinforced concrete pile–superstructure interaction under conditions of multiple earthquakes. The shaking table test was conducted under a 50-G field with multiple shaking inputs reproducing the mainshock and aftershocks to explore the interactions in terms of differences in relative soil density. The centrifuge test demonstrated the liquefaction of saturated soil during the mainshock and the simultaneous formation of plastic hinges at the pile head and base. However, the gradual compaction of the ground by repeated shaking did not promote the occurrence of liquefaction. Ground compaction caused the shear span ratio of the pile member to decrease and the inertial force acting on the superstructure to increase. It is possible that in the case of low relative soil density, the maximum inertial force during aftershock excitation exceeded that of mainshock excitation.

Analysis of Liquefaction Potential of Coastal Sands Using Laminar Box System

Liquefaction is considered as one of the geotechnical risks caused during an earthquake in a saturated sand deposit. Due to their loose, saturated, and cohesionless nature, the sands in the coastal area are susceptible to liquefaction when subjected to cyclic loading. This effect leads to an alteration of soil structure from a stable to an unstable liquid form. The study of liquefaction in Kerala, which is in earthquake zone III, has not been done much earlier and that would be beneficial because of increasing infrastructural development in these areas. This study presents the development of a laminar soil container for shaking table tests in Kerala, and the response of the excess pore water pressure at various locations of the contained sand. The laboratory investigation is intended to understand the effect of gradation of soil and amplitude of base shaking on the generation of excess pore water pressure at varying relative density of soil (30%, 40% and 50%) but at a constant frequency of shaking (1 Hz). The test results have indicated that soil liquefaction resistance decreases as the amplitude of base shaking increases and the relative density of soil decreases. Also, sand with a lower percentage of finer sand content and larger mean grain size showed higher resistance to liquefaction.

Investigation of the end bearing load in pile group model in dry soil under horizontal excitation

A series of 94 laboratory tests were conducted to measure the response of pile foundation when subjected to dynamic loads. Eight tests were conducted on single pile in dry soil at relative density 30 % (loose) and 50 % (medium); 66 tests on group of piles with different spacings and patterns. All tests were carried out under operating frequencies 0.5, 1 and 2 Hz under horizontal shaking. All tests were achieved with one embedment ratio (L/d = 30). These tests were grouped in three different numbers of piles; 2 piles in row and line patterns, 3 piles and 4 piles; and three pile spacing ratios (s/d = 3, 4 and 5). The results of dry soil indicating the mechanism of dynamic response of piles and soil subjected to dynamic horizontal shaking include the variation and distribution of acceleration with time in different states of soil in addition to the vertical and horizontal displacements, end-bearing load, peak acceleration and the peak velocity of foundation. It was concluded that for a dry soil bed, the acceleration amplitudes increase with frequency for both soil relative densities (loose and medium) and different pile patterns (number; single or group and different spacing ratios s/d). The maximum acceleration in the foundation is lower than in the soil bed for all operating shaking frequencies, pile spacing ratios and soil states. The decreasing of the maximum acceleration recorded in the foundation as compared to that in the soil bed is between 10-100 % for loose and medium state of soil, and the decrease in loose state is more than in medium state. This means that there is damping effect or attenuation of vibration waves. The amplitudes of recorded acceleration in the pile cap are much higher than in the soil bed for single pile and pile group with different pile spacing ratios, also these amplitudes are increasing with increase of shaking frequency and relative density of the soil.

A full three‐dimensional model for the estimation of the natural frequencies of an offshore wind turbine in sand

AbstractThe design of an offshore wind turbine (OWT) founded on a monopile foundation is principally based on dimensioning criteria related to its fundamental frequencies. These frequencies must remain outside the excitation frequencies to avoid resonance. For the calculation of the OWT natural frequencies, several studies exist, but few of them simultaneously consider both the real geometrical configuration of the OWT superstructure (tower, blades, and transition piece) and the three‐dimensional (3D) soil domain and its interaction with the monopile foundation. This paper aims at filling this gap. A rigorous 3D finite element method‐based model of a 10 MW DTU OWT installed in sand is developed. The aim is to perform a structural modal analysis of the wind turbine in parked condition. The obtained natural frequencies are compared with those corresponding to other simplified models available in literature for the foundation and the superstructure in the scope of giving an insight about how poorly the existing simplified models can predict the OWT natural frequencies. Finally, a parametric analysis is performed to study the effect of the water depth, the monopile dimensions (diameter, thickness, and embedded depth), the transition piece height, and the sandy soil relative density on the system natural frequencies.

PISA design model for monopiles for offshore wind turbines: application to a marine sand

This paper describes a one-dimensional (1D) computational model for the analysis and design of laterally loaded monopile foundations for offshore wind turbine applications. The model represents the monopile as an embedded beam and specially formulated functions, referred to as soil reaction curves, are employed to represent the various components of soil reaction that are assumed to act on the pile. This design model was an outcome of a recently completed joint industry research project – known as PISA – on the development of new procedures for the design of monopile foundations for offshore wind applications. The overall framework of the model, and an application to a stiff glacial clay till soil, is described in a companion paper by Byrne and co-workers; the current paper describes an alternative formulation that has been developed for soil reaction curves that are applicable to monopiles installed at offshore homogeneous sand sites, for drained loading. The 1D model is calibrated using data from a set of three-dimensional finite-element analyses, conducted over a calibration space comprising pile geometries, loading configurations and soil relative densities that span typical design values. The performance of the model is demonstrated by the analysis of example design cases. The current form of the model is applicable to homogeneous soil and monotonic loading, although extensions to soil layering and cyclic loading are possible.

Seismic behavior of a dolphin-type berth subjected to liquefaction induced lateral spreading: 1g large scale shake table testing and numerical simulations

The effects of liquefaction induced lateral spreading on the piles of a dolphin-type berth were investigated using 1 g large scale shake table testing accompanied by numerical simulations. For this purpose, various aspects of the response of the soil and the pile group to lateral spreading were considered. The results indicated that large bending moments were induced in the piles during lateral spreading and the downslope piles of the group received greater bending moments than the upslope one. The monotonic components of bending moments in the piles were reasonably predicted by the displacement based numerical approach using p-y springs when they were properly tuned for strength reduction in liquefied soil and the pile position in the group. A three dimensional hydro-mechanical finite element analysis was also undertaken in OpenSees which appropriately reproduced the physical model behavior. Lastly, a comprehensive parametric study on the verified finite element model revealed that the relative density of soil and the amplitude of base excitation can profoundly affect the induced bending moments in piles as well as the pile cap displacements while the effect of pile flexibility was comparably smaller in this regard.

Effectiveness of sand compaction piles in improving loose cohesionless soil

This paper investigates the effectiveness of Sand Compaction Pile (SCP) in improving the density characteristics of cohesionless soil. The performance of SCP for different pile spacing, pile arrangement such as triangular and square, and coarseness of bed materials on the degree of soil improvement is studied in a better-controlled laboratory environment rather than more variable field environment. A SCP miniature device and a miniature dynamic cone penetrometer (DCP) were designed and fabricated in the laboratory. Sand beds containing loose cohesionless soil were prepared in a fabricated tank by sand raining from the pre-calibrated height. The SCPs were installed using the miniature device on the sand bed by displacing soil in the lateral direction in order to densify the bed prior to pouring sand in the displacement holes. The data of DCP in terms of penetration index and field density were measured at various depths to obtain correlation parameters between DCP and relative density of soil. This correlation was used to determine the relative density of improved soil beds due to the installation of SCPs. The improved soil condition was measured in terms of a decrease in penetration index or an increase in the relative density of bed materials. Some of the major findings include: the rate of increase of relative density due to installment of SCP is similar irrespective of the coarseness of bed materials; smaller pile spacing compared to an optimum spacing causes insignificant soil improvement; the triangular pattern shows better soil improvement compared to the square pattern for a given pile spacing.

Load-settlement Behavior of Steel Piles in Different Sandy Soil Configurations

In the case where a shallow foundation does not satisfy with design requirements alone, the addition of a pile may be suitable to improve the performance of the foundation design. The lack of in-situ data and the complexity of the issues caused by lagging in the research area of pile foundations are notable. In this study, different types of piles were used under the same geometric conditions to determine the load-settlement relationships with various sandy soil relative densities. The ultimate pile capacity for each selected pile is obtained from a modified California Bearing Ratio (CBR) machine to be suitable for axial pile loading. Based on the results, the values of Qu for close-ended square pile were increased by 15.2, 19.3, and 9.1 % for different pile lengths of 100, 150, and 200 mm in comparison with the H-pile. At the same time, the open-ended square pile had a lower capacity in comparison with closed-ended square pile tested in medium sand. Also, in the dense sand, the values of Qu for close-ended square pile were increased by 49.7, 47.8, and 69.6% for the same pile length in comparison with the H-pile. Notably, sand's density has a significant effect on the ultimate load capacity for different types of piles.

Liquefaction study of soils in unified model and liquefaction potential evaluation of compacted sand

Owing to their specific sedimentary or weathering formation history, most soils confronted in civil engineering can be categorised into clayey and sandy soils. In view of the great mechanical difference, particularly the distinct liquefaction resistance, then precisely simulate the mechanical and liquefaction characteristics of different type soils become an important research issue in seismic design of civil engineering structures. Considering soil turns into overconsolidated state once experiences stress unloading, and which affects the mechanical and liquefaction characteristics in turn. Based on the classical Cam-clay model, with the introducing of subloading surface concept, the subloading surface Cam-clay model provide an unified constitutive model in the numerical simulation of different type soils. Based on the comprehensive parametric studies of state variables evolution and anti-liquefaction capability of soil conducted in this paper, we creatively unified the relationship between OCR and relative density of soil that widely adopted in the liquefaction resistance evaluation of sandy soil, and our test results shows high correlation between these two parameters. These findings provide a solid theoretic support and guidance for the dynamic compaction method that widely adopted in anti-liquefaction design.

Application of Grey Taguchi Method to optimize the internal erosion parameters of stabilized soil

Surface erosion and sub-surface erosion play a major role in the failure of the water-retained structures. The main aim of the present work is to optimize the erosion parameters of the stabilized soil simultaneously during internal erosion of the soil stabilized with a bio polymer-Xanthan gum by Taguchi-based grey relational analysis. In this study, three parameters namely Xanthan gum content, relative density of soil, hole diameter and inlet pressure each of the three levels was considered to know their erosion parameters on the stabilized soil. Taguchi’s L9 orthogonal array was considered to perform the hole erosion experiments. Based on the results obtained from the hole erosion test, grey relational grades were calculated. Moreover, ANOVA was carried out on the three responses namely erosion rate, critical hydraulic stress and final hole diameter to know the influencing factors on the aforementioned responses. SEM analysis was carried out on treated samples to know their bonding behaviour among soil particles.

Numerical Modeling of Unfavorable CFA Pile Drilling Conditions

Drilling and installation of deep foundations typically alter and affect surrounding soils and subsequently affect the adjacent structures. Possible effects on the adjacent structures due to the installation of driven piles have been thoroughly investigated in the literature. However, little attention has been given to other pile installation techniques such as continuous flight auger (CFA). In this paper, unfavorable CFA drilling conditions are discussed and investigated using three-dimensional (3D) finite element analyses. The induced settlements around the piles are calculated to assess the possible adverse effects on surrounding structures. The numerical models are validated using laboratory physical modeling of unfavorable soil drilling conditions reported in the literature. The analyses showed that unfavorable drilling conditions might have a major effect on adjacent structures up to two times the pile length. Parametric numerical modeling has also been conducted to study the influence of different parameters such as soil shear strength parameters, pile length, pile diameter, and soil permeability on the deformation adjacent to CFA pile during construction. The results revealed that soil relative density and permeability have a significant influence on the calculated surface settlement. Finally, several pile group drilling scenarios were investigated to gain insight into the optimum scenario for pile drilling. The analyses show that alternating between drilling piles near the structure and those far from it, may significantly reduce the surface settlement during pile construction.