Lateral Soil Research Articles

Effect of the proximity of slope and pile shape on lateral capacity of piles in clay slopes

The response of laterally loaded piles installed near the crest of clay slopes is analysed. Three-dimensional finite element analyses are presented for piles at various distances from a slope crest and for different pile shape. The results of these analyses are used to study the variation of the pile displacement, the bending moment of the pile and the soil resistance in relation to pile to slope distance and pile shape. The obtained results show that the proximity of slope significantly affects the lateral load capacity of the piles but not significantly when the piles are placed at 7D (where D is pile diameter) or greater from the slope crest. Furthermore, the lateral soil resistance on the ground surface for circular piles is larger than that for rectangular piles at the same lateral load in level ground. The decrease rate of lateral soil resistance on the ground surface for circular piles gets faster as the slope ratio and load level increase.

Simulating Erosion-Induced Soil and Carbon Delivery From Uplands to Rivers in a Global Land Surface Model.

Global water erosion strongly affects the terrestrial carbon balance. However, this process is currently ignored by most global land surface models (LSMs) that are used to project the responses of terrestrial carbon storage to climate and land use changes. One of the main obstacles to implement erosion processes in LSMs is the high spatial resolution needed to accurately represent the effect of topography on soil erosion and sediment delivery to rivers. In this study, we present an upscaling scheme for including erosion‐induced lateral soil organic carbon (SOC) movements into the ORCHIDEE LSM. This upscaling scheme integrates information from high‐resolution (3″) topographic and soil erodibility data into a LSM forcing file at 0.5° spatial resolution. Evaluation of our model for the Rhine catchment indicates that it reproduces well the observed spatial and temporal (both seasonal and interannual) variations in river runoff and the sediment delivery from uplands to the river network. Although the average annual lateral SOC flux from uplands to the Rhine River network only amounts to 0.5% of the annual net primary production and 0.01% of the total SOC stock in the whole catchment, SOC loss caused by soil erosion over a long period (e.g., thousands of years) has the potential to cause a 12% reduction in the simulated equilibrium SOC stocks. Overall, this study presents a promising approach for including the erosion‐induced lateral carbon flux from the land to aquatic systems into LSMs and highlights the important role of erosion processes in the terrestrial carbon balance.

Experimental studies on the interaction mechanism of landslide stabilizing piles and sandwich-type bedrock

The mechanical properties of stabilizing piles are directly affected by the spatial structure of the bedrock of landslides. To effectively reinforce landslides with a sandwich-type bedrock, the interaction mechanism between manually excavated stabilizing piles and the different types of bedrock must be investigated. The research presents experimental models of manually excavated stabilizing piles for two kinds of sandwich-type bedrock structures, namely hard rock–dominant interlayered bedrock (HDIB) and weak rock–dominant interlayered bedrock (WDIB). Six physical models with different bedrock structure types and dip angles θ were prepared to explore the influence of these two parameters on the pile-bedrock interaction mechanism. The mechanical properties of the pile were investigated based on the monitoring results of the earth pressure distributions against the piles and the bending moment distributions. The embedded section of the pile experiences a rotation subjected to lateral soil movement. The center point of the rotation in the HDIB is at a greater elevation than in the WDIB. The earth pressure in the HDIB appears to increase with dip angle θ but is similar to each other in the WDIB. The pile embedded in the HDIB exhibits flexible behavior, whereas the pile embedded in the WDIB exhibits rigid behavior. With the increase of dip angle θ in the WDIB material, the bending moment steadily rises followed by fluctuation. The maximum bending moment of the embedded section increases with θ. These results provide a basis for improving the design of manually excavated stabilizing piles in sandwich-type bedrock.

Quantifying Variable Importance in Predicting Critical Span Length and Scour Depth for Failure of Onshore River Crossing Pipelines Using ANN

Onshore oil and gas pipelines are often buried beneath the river bed and channel banks. One of the primary reasons for the exposure of buried pipelines is the scouring mechanism that occurs when shear stress induced on riverbed by flowing water exceeds the resistance of channel bed material. Depending on the free spanning length and watercourse flow velocity, the vortex shedding phenomena may cause interactions resulting in a catastrophic pipeline failure. Accurate estimation of parameters that influence critical span length and scour depth become extremely important to maintain the integrity of the pipeline system and optimize its effective service life. This study is aimed at quantifying the relative importance of input variables used in predicting critical span length and scour depth based on the weights obtained from an Artificial Neural Network (ANN). The Artificial Neural Network model is developed by collecting pipeline accident reports from Pipeline and Hazardous Material Safety Administration (PHMSA) database for accidents that occurred due to Vortex Induced Vibration (VIV) loading during flooding in the last 35 years. It is seen that factors such as internal fluid pressure, dynamic lateral and vertical soil stiffness, reduced velocity and age of pipeline have a significant contribution in terms of model weights and help in accurately assessing the pipeline’s vulnerability to failure.

SPH Simulations of Real Sea Waves Impacting a Large-Scale Structure

The Pont del Petroli is a dismissed pier in the area of Badalona, Spain, with high historical and social value. This structure was heavily damaged in January 2020 during the storm Gloria that hit southeastern Spain with remarkable strength. The reconstruction of the pier requires the assessment and characterization of the wave loading that determined the structural failure. Therefore, a state-of-the-art Computational Fluid Dynamic (CFD) code was employed herein as an aid for a planned experimental campaign that will be carried out at the Maritime Engineering Laboratory of Universitat Politècnica de Catalunya-BarcelonaTech (LIM/UPC). The numerical model is based on Smoothed Particle Hydrodynamics (SPH) and has been employed to simulate conditions very similar to those that manifested during the storm Gloria. The high computational cost for a full 3-D simulation has been alleviated by means of inlet boundary conditions, allowing wave generation very close to the structure. Numerical results reveal forces higher than the design loads of the pier, including both self-weight and accidental loads. This demonstrates that the main failure mechanism that led to severe structural damage of the pier during the storm is related to the exceeded lateral soil resistance. To the best of the authors’ knowledge, this research represents the first known application of SPH open boundary conditions to model a real-world engineering case.

A multi-isotope model for simulating soil organic carbon cycling in eroding landscapes (WATEM_C v1.0)

Abstract. There is increasing recognition that lateral soil organic carbon (SOC) fluxes due to erosion have imposed an important impact on the global C cycling. Field and experimental studies have been conducted to investigate this topic. It is useful to have a modeling tool that takes into account various soil properties and has flexible resolution and scale options so that it can be widely used to study relevant processes and evaluate the effect of soil erosion on SOC cycling. This study presents a model that is capable of simulating SOC cycling in landscapes that are subjected to erosion. It considers all three C isotopes (12C, 13C and 14C) with flexible time steps and a detailed vertical solution of the soil profile. The model also represents radionuclide cycling in soils that can assist in constraining the lateral and vertical redistribution of soil particles within landscapes. The model gives a three-dimensional representation of soil properties including 137Cs activity, SOC stock, and δ13C and Δ14C values. Using the same C cycling processes in stable, eroding and depositional areas, our model is able to reproduce the observed spatial and vertical patterns of C contents, δ13C values, and Δ14C values. This indicates that at the field scale with a similar C decomposition rate, physical soil redistribution is the main cause of the spatial variability of these C metrics.

RESEARCH OF INFLUENCE OF THE EARTH’S SUBSIDENCE OUTSIDE THE LOADS CONTOUR ON THE STABILITY OF THE HEIGHT POSITION OF THE POINTS OF LOCAL LEVELING NETWORKS

The influence of static loadings of the foundations of structures in the process of soil compaction of the base on the subsidence of the soil surface and the bench outside the loaded contour is considered in the work. The studies were performed on models of rectangular massive foundations using the method of equivalent soil layer, based on the theory of compaction of linear-deforming half-space. Using this method, the values of the average sedimentation of the models of rectangular foundations were calculated, taking into account all components of normal stresses and lateral soil extension. On the basis of the method of angular points of the equivalent layer, the values of subsidence of the soil surface outside the contour of the foundation models are calculated, depending on the distance from the contour of the foundation, the value of the average subsidence of the foundation and its parameters. To determine the areas of the soil surface most sensitive to the perception of static loads, lines of equal settlements of the soil surface outside the contour of the foundation models are constructed. On the basis of theoretical studies, probable magnitudes of sedimentation of soil benchmarks are calculated, depending on the subsidence of the soil surface and the distance from the contour of the foundation. The probable minimum distance from the contour of the structure to the places of laying of initial soil benchmarks is established to ensure the required accuracy of geodetic observations. The results of the conducted researches may find application in the design of geodetic observations of the settlements and deformations of the foundations of engineering structures and the choice of the locations of local level points.

Mapping soil properties at multiple depths from disaggregated legacy soil maps in the Brittany region, France

Digital Soil Mapping (DSM) is increasingly needed to improve existing soil information and derive soil property maps at the suitable spatial resolution for sustainable soil landscape management. However, predicting several soil properties while preserving specific pedological process is a great challenge, particularly when only coarse soil information is available over large areas. Spatial disaggregation seems to be an effective technique to extract pedological information by downscaling the original information to produce soil maps at finer resolutions. In a previous study, legacy soil maps of Brittany (France) were disaggregated at a 50 m spatial resolution using the DSMART (Disaggregation and Harmonization of Soil Map Units Through Resampled Classification Trees) algorithm and pedological knowledge. The present study had two main objectives: (i) assess the preservation of the relationships between soil properties when soil properties are estimated at standard depths by applying the equal-area spline method on soil data at pedon scale, and (ii) combine disaggregated soil maps and spline-function results to estimate spatial patterns of nine soil properties for six regular soil-depth intervals down to 200 cm across Brittany, an area of 27,040 km2. To this end, soil properties were first generated for standard soil-depth intervals using spline functions. Then, for mapping soil properties at the six standard depths, weighted mean of each soil attribute was calculated for each grid cell from reference soil-property values of the three most probable predicted soil types. Their associated probabilities of occurrence were used as weights. To assess the ability of spline functions to preserve soil-property relationships, multiple statistical analyses were performed using original and splined soil datasets. Bivariate and multivariate analysis highlighted that spline functions preserved soil-property relationships. Derived digital soil maps showed strong spatial patterns: SOC and silt contents generally decreased with depth, while sand content and coarse fragment percentage consistently increased with depth. In addition, experimental semivariogram analysis of SOC content showed high spatial variability over short distances for all soil-depth intervals except the deepest (100–200 cm), while silt content showed high semivariance for the deepest soil layers. This study can be considered an example of harmonization to common output specifications, which generates a geo-database of quantitative soil properties that describe lateral and vertical soil variation for regular depth intervals. These predictions can be incorporated into environmental models to help decision makers manage landscapes.

Ammonia nitrogen sources and pollution along soil profiles in an in-situ leaching rare earth ore

The ammonium sulphate ((NH4)2SO4) in-situ leaching process is the most widely used extraction technology for weathered crust elution-deposited rare earth ores (WCED-REOs). Highly concentrated (NH4)2SO4, a representative leaching agent, is often used in the leaching process of WCED-REOs. However, this in-situ leaching process causes nitrogen pollution in the soil, surrounding surface and ground water due to the high concentrations of (NH4)2SO4 solutions used as a long term leaching agent. To date, the mechanism behind the variations in ammonia nitrogen (AN) in deep soil profiles is unclear. We conducted vertical and lateral soil sampling and analyzed the collected samples for soil moisture, pH, ammonia forms, and AN contents in soil profiles deeper than 500 cm in an in-situ leaching mining area of Ganzhou, Jiangxi Province, southern China. The results show that primary chemical pollutants in the soil are derived from residual leaching agents with high acidities and concentrations of AN. Twelve years after the mining process was completed, the mean pH values of the tailings in the mining area were 3.90 and 4.87 in its lower reaches. Due to the presence of chemical residues, the AN concentration was 12–40 times higher than that of the raw ore soil before it was mined. The percentages of different ammonium forms in the rare earth tailing soil were 65%, 30%, and 5% for the water-soluble, exchangeable, and fixed ammonium forms, respectively. The results of this study support effective prevention and remediation treatment of environmental problems caused by AN pollution of the soil in WCED-REOs.

Comparative Modal Analysis of Monopile and Jacket Supported Offshore Wind Turbines including Soil-Structure Interaction

Offshore wind turbines (OWTs) have emerged as a reliable source of renewable energy, witnessing massive deployment across the world. While there is a wide range of support foundations for these structures, the monopile and jacket are most utilized so far; their deployment is largely informed by water depths and turbine ratings. However, the recommended water depth ranges are often violated, leading to cross-deployment of the two foundation types. This study first investigates the dynamic implication of this practice to incorporate the findings into future analysis and design of these structures. Detailed finite element (FE) models of Monopile and Jacket supported OWTs are developed in the commercial software, ANSYS. Nonlinear soil springs are used to simulate the soil-structure interactions (SSI) and the group effects of the jacket piles are considered by using the relevant modification factors. Modal analyzes of the fixed and flexible-base cases are carried out, and natural frequencies are chosen as the comparison parameters throughout the study. Second, this study constructs a few-parameters SSI model for the two FE models developed above, which aims to use fewer variables in the FE model updating process without compromising its simulation quality. Maximum lateral soil resistance and soil depths are related using polynomial equations, this replaces the standard nonlinear soil spring model. The numerical results show that for the same turbine rating and total height, jacket supported OWTs generally have higher first-order natural frequencies than the monopile supported OWTs, while the reverse is true for the second-order vibration modes, for both fixed and flexible foundations. This contributes to future design considerations of OWTs. On the other hand, with only two parameters, the proposed SSI model has achieved the same accuracy as that using the standard model with seven parameters. It has the potential to become a new SSI model, especially for the identification of soil properties through the model updating process.

A Centrifuge Modelling and Finite Element Analysis of Laterally Loaded Single Piles in Sand with Focus on P–Y Curves

Centrifuge modelling and finite element analysis are powerful tools of research on the lateral pile/soil interaction. This paper aims at presenting the main results of experimental and numerical analysis of the pile response under monotonic lateral loading in sand. After description of the experimental devices, it focuses on the determination of the load-transfer P-Y curves for rigid and semi-rigid piles embedded in dry dense sand by using the experimental bending moment profiles obtained in centrifuge tests, as well as by a three-dimensional finite element models using ABAQUS Software. The elastic perfectly plastic Mohr-Coulomb constitutive model has been used to describe the soil response, and the surface-to-surface contact method of ABAQUS software has been used to take into account the nonlinear response at soil/pile interface. The analysis methodology has allowed to propose a hyperbolic function as a model to construct P-Y curves for rigid and semi-rigid piles embedded in dry dense sand, this model is governed by two main parameters, which are the initial subgrade reaction modulus, and the lateral soil resistance, the latter has been formulated in terms of Rankine’s passive earth pressure coefficient, the sand dry unit weight, and the pile diameter.

Calculation of Lateral Soil Pressure at the Hydraulic Construction and its Sustainability on the Stone Bed

The engineering method of analysis of pressure of a ground on flat walls is offered at presence of combine strip superficial loading in view of seismic influences. It is recommended to determine a situation of an internal slip surface dividing an elastic zone from area of limiting balance, on the basis of the technical theory of the ultimate stress condition. Proceeding from a situation of an internal and external slip plane, size of strip loading on the fill, the pressure of a ground which is taking place in an ultimate condition, on an internal slip surface of is determined on developed by P. Yakovlev to the specified Coulomb's method [1], and on an internal side of a retaining structure on the basis of the Boussinesq decision. In comparison with the earlier developed way it is offered specified according to the Boussinesq theory a method of definition of pressure transmitted by bed on a ground of the basis and, as a consequence more reasonable definition of safety factor of stability of a structure. Thus, curvilinear normal pressure diagram in a ground under a sole of lay is replaced on isosides trapeziform.

Centrifuge modelling of a tetrapod jacket foundation under lateral cyclic and monotonic loading in soft soil

The tetrapod jacket foundation is one of the most common types of foundations used for offshore structures. Although the static bearing capacity of the jacket foundation is important, a safe design must be taken into consideration for accumulative deformation and stiffness degradation during cycling. To address this, a set of centrifuge model tests of a tetrapod jacket foundation subjected to cyclic and monotonic loading was conducted in kaolin. The test results mainly reveal (i) the influence of loading history on the lateral bearing capacity of the jacket foundation; (ii) the evolution of accumulative deformation of the jacket foundation during cycling; (iii) the stiffness degradation of soil–pile interaction under cyclic loading. Comparing typical “lateral soil resistance”–“pile lateral displacement” (p–y) curve approaches with test results, a hyperbolic tangent p–y curve method is adopted to calculate the soil–pile interaction of the jacket foundation. The values of the p-multipliers of leading-row and trailing-row piles in soft soils are clearly lower than that in sands. Finally, a cyclic p–y curve method related to cycles and embedded depths is developed for the jacket foundation in the hope of providing guidance for the design of the jacket foundation in soft soil.

Analysis of lateral response of existing single pile caused by penetration of adjacent pile in undrained clay

Quantifying the lateral displacement and bending moment of the existing pile caused by the penetration of the adjacent pile are of great engineering significance to ensure the safety and stability of the buildings. In this paper, a two-stage analysis approach for predicting the response of the existing pile due to the penetration of the adjacent pile is presented. First, a simplified model is proposed to determine the free-field lateral soil displacement induced by the pile penetration. This model assumes that the pile penetration process can be regarded as a series of displacement-controlled spherical cavity expansion in semi-infinite soil, and considers the large deformation effect of soil as well as the influence of the existence of the ground surface. The validity and accuracy of the proposed model are verified by comparing with the published results. Subsequently, the p-y curve method is adopted to analyze the nonlinear pile-soil interaction for solving the response of the existing pile induced by the lateral displacement of soil obtained in the first stage. Through a series of parametric investigations, it is indicated that the impact of the penetration of adjacent pile on the response of the existing pile rests with some factors. Finally, some design charts are presented by parametric analysis, which can be used to assess the response of the existing pile caused by the penetration of the adjacent pile in practical engineering.

A unified lateral soil reaction model for monopiles in soft clay considering various length-to-diameter (L/D) ratios

Large-diameter monopiles are the most commonly used foundation to support offshore wind turbines. Early designs usually adopted pile diameters (D) between 4 and 6 m, which is recently extended to 8 m and will target 10 m in the future. It is increasingly evident that the existing design method (i.e., API's p-y model) can significantly under-predict the lateral stiffness and capacity of large-diameter monopiles in soft clay, due to ignoring the soil resistances from base shear and base moment which become more pronounces as L/D reduces. In this study, a two-spring approach is proposed, aiming to predict the lateral behaviour of monopiles with varied L/D ratios in a unified manner. In light of the soil flow mechanisms around monopiles, the pure lateral soil resistance above the rotation point (RP) is quantified using a p-y model, while the resistances below the RP including the base shear and base moment are integrated into a moment-rotation spring (characterized by a MR-θR model) at the RP. It can naturally recover to a p-y model while analyzing flexible piles, where θR= 0 at RP. Formulations of the ‘p-y + MR-θR’ model (including diameter-related p-y and MR-θR models, and the depth of the RP) are proposed based on the results of a series of well-calibrated 3D numerical models. The proposed model has satisfactorily reproduced a number of field and centrifuge test results on laterally loaded monopiles with a wide range of L/D ratios (including flexible, semi-rigid and rigid piles), using a unified set of parameters. Compared to the standard p-y model, the adoption of the proposed ‘p-y + MR-θR’ model is shown to substantially reduce design conservatism.

Assessment of gold mineralisation in Osu–Amuta–Itagunmodi areas, Southwestern Nigeria

Gold is artisanally mined from eluvial deposits within Osu–Amuta–Itagunmodi areas of Ilesa Schist Belt, southwestern Nigeria. Mine site selection and mining operations are done without any understanding of mode of occurrence, compositional characteristics and extent of gold mineralisation. The present study was aimed at determining the host lithologies, extent and associated geochemical features of the gold mineralisation. Fifty rock samples were cut into thin section for examination and analysed using inductively coupled plasma–mass spectrometry (ICP-MS). Forty-eight soil samples collected from Artisanal Gold Mine (AGM) pits to a depth of 5 m (n = 9), and along defined horizontal profile lines from the mine pits (n = 39) were analysed for elemental constituents, and mineralogical compositions in vertical profile samples using ICPMS and X-ray diffraction (XRD) techniques, respectively. The quartz-biotite schist, quartzite, talc-chlorite schist and amphibolite had Au concentration (ppb) that ranged from 1.3 to 14.4 (average 3.95), BDL–0.9 (average 0.63), 0.9–4.6 (average 2.18) and 0.5–2.7 (average 1.56), respectively. Vertical and lateral profile soil samples were Osu: 4.5–7.6 (average 6.17) and 0.9–78.8 (average 8.54); Amuta: 4.1–6.8 (average 5.2) and 2.8–19.8 (average 7.40); and Itagunmodi 3.9–13.2 (average 7.43) and 0.5–14.8 (average 4.33). Evaluation of the horizontal profile soils revealed higher Au concentrations than the artisanal mine workings, indicating additional mineralisation potentials in the study area. Au concentrations were in the order of quartz-biotite schist > talc-chlorite schist > amphibolite >> quartzite, with anomalous concentrations detected in quartz-biotite and talc-chlorite schists. Elevated concentrations also occurred in residual soils overlying quartzite and amphibolite lithologies. Mineralisation is hydrothermal in nature, extends beyond current artisanal mine workings and has potential for further exploration.

A numerical investigation of bedrock groundwater recharge and exfiltration on soil mantled hillslopes

AbstractHere we use Richards Equation models of variably saturated soil and bedrock groundwater flow to investigate first‐order patterns of the coupling between soil and bedrock flow systems. We utilize a Monte Carlo sensitivity analysis to identify important hillslope parameters controlling bedrock recharge and then model the transient response of bedrock and soil flow to seasonal precipitation. Our results suggest that hillslopes can be divided into three conceptual zones of groundwater interaction, (a) the zone of lateral unsaturated soil moisture accumulation (upper portion of hillslope), (b) the zone of soil saturation and bedrock recharge (middle of hillslope) and (c) the zone of saturated‐soil lateral flow and bedrock groundwater exfiltration (bottom of hillslope). Zones of groundwater interaction expand upslope during periods of precipitation and drain downslope during dry periods. The amount of water partitioned to the bedrock groundwater system a can be predicted by the ratio of bedrock to soil saturated hydraulic conductivity across a variety of hillslope configurations. Our modelled processes are qualitatively consistent with observations of shallow subsurface saturation and groundwater fluctuation on hillslopes studied in our two experimental watersheds and support a conceptual model of tightly coupled shallow and deep subsurface circulation where groundwater recharge and discharge continuously stores and releases water from longer residence time storage.

Investigations of seismic response to an irregular-section subway station structure located in a soft clay site

In this study, shaking table tests were performed to investigate the dynamic interaction of a silty-clay soil with an irregular-section subway station. During the tests, a shape acceleration array (SAA) was used to measure the lateral deformation of the model soil, and a non-contact dynamic displacement testing method was applied to visualize and digitalize the seismic damage process of the station structure. Typical test results, including the dynamic earth pressure, seismic settlement, deformation, and acceleration of different levels of the structure, were interpreted. The results indicated that the movement of the subway station was more controlled by the surrounding silty-clay soil in terms of phase and amplitude. SAA can effectively measure the soil deformation, and the relationship between the relative lateral displacement and soil depth can be well fitted in a cosine function, especially when subjected to strong earthquakes. Seismic settlement is significantly linked to Arias intensity, and the subway station experienced significant uneven settlement, resulting in soil-structure separation in the vertical direction. The multi-story irregular-section subway station deforms in a shear mode. The maximum inter-story drift ratio was approximately 1/171. The components in the lower layers of the shallow-buried subway station structure, particularly in the central columns, underwent cumulative damage. Hence, more robust forms of structural members and the ductility of central columns should be carefully considered in the seismic design of subway station structures.

On the Response of Polyethylene Pipes to Lateral Ground Movements: Insights from Finite-Discrete Element Analysis

The current knowledge of the behaviour of polyethylene pipes subjected to lateral soil movement is limited and the commonly used design equations were initially developed for steel pipes. In this study, an attempt has been made to understand the soil–structure interaction using a three-dimensional finite-discrete (FE-DE) element model of a medium density polyethylene (MDPE) pipe buried in dense sand and subjected to lateral soil movement. The soil particles are modelled using discrete elements, while the pipe is modelled using finite elements and interface elements are introduced to transfer the forces between the two domains. Validation is performed using experimental data. This study shows that, when a pipe section experiences lateral movement induced by two symmetrically applied loads, the pipe will resist the imposed lateral forces by bending. Particle displacement patterns show that passive wedges develop locally close to the applied loads and the remaining pipe sections experience negligible deformation. Furthermore, it is found that the current expressions used to estimate the ultimate lateral soil force on buried pipes in granular soil, which is generally developed for rigid steel pipes, should be used with caution as they may overestimate the soil load on flexible MDPE pipes.

K0determination using improved experimental technique

Lateral soil pressures under at-rest conditions are commonly estimated as K0times vertical normal pressure, where K0is obtained from generally accepted empirical formulae, related to the soil's friction angle and the stress history. Results of a programme of laterally, rigidly confined, vertical compression and unloading tests on sand and clay are presented, in which two significant experimental techniques were employed: (a) lateral pressures were measured using null pressure gauges, preventing gauge diaphragm deflection; (b) side-wall friction was measured, and minimised using special friction reduction measures. Comparative tests in which one or both of these measures were not employed indicate the significant errors induced in both the vertical and the horizontal pressures used for K0determination. The bank of experimental data, which formed the basis for the commonly accepted empirical formulae, did not take account of these issues, and they are shown to be inconsistent with values measured in the present study.