Soil Berm Research Articles

Study on the dynamic embedment variation of shallow embedded submarine pipelines in sand

The clarification of the pipe–soil interaction mechanism is a critical link in the design of the in-situ stability of shallow embedded pipes in subsea areas, and the in-situ embedment of pipelines is an important parameter in the pipe-soil interaction mechanism. A large-scale plane strain model test was performed for a shallow embedded pipeline with horizontal cyclic motion in sand. Additionally, a numerical analysis model that is applicable to multicycle submarine pipe–soil interactions in sand was constructed, which can consider the dynamic change in the pore ratio of sand during the motion of a shallow buried pipeline. The development law of dynamic embedment and factors influencing the pipeline after multiple horizontal cycles were studied. A method for calculating the dynamic embedment of pipelines in sandy soil was proposed. The results reveal that horizontal cyclic movement of the pipe in sandy soil increases the embedment depth, and dynamic embedment rises by 1.09–11.78 times depending on the initial state of the pipeline. Furthermore, a soil berm rises on both sides of the pipe following cycling, and the sand around the pipe is sheared and shrunken, causing a large increase in soil resistance during the horizontal movement of the shallow embedded pipe.

Theoretical framework for predicting accumulation of soil berms and peak sliding resistance for tolerably mobile foundations

Tolerably mobile subsea foundations are designed to slide on the seabed to accommodate flowline thermal expansion and contraction, and are a potential alternative to conventional (fixed) foundations. During the periodic sliding events that occur during operation, soil berms form at the extremities of the foundation footprint. The size of the berm increases throughout the life-cycle of the foundation, leading to increasing peak sliding resistance. This may hinder mobility of the foundation and overstress the pipeline connections that the foundation is designed to support. Equally, the berms may be relied on to reduce sliding and thus minimize settlement of the foundation, which can also overstress pipeline connections. This paper analyses the mechanism leading to berm accumulation and its mobilisation, also addressing periodic remoulding and reconsolidation of the sediment in the berm. A framework is proposed to predict the accumulation of soil berms and the resulting peak sliding resistance, and is validated by eight centrifuge model tests performed on a kaolin clay and a calcareous silt.

The practice of arranging a pit deeper than the level of the soles of the foundations of the surrounding buildings

A rational constructive-technological decision to arrange a fence of a deeper pit for a new building than the depth of laying strip foundations of the surrounding buildings has been substantiated and tested in practice. The decision to arrange the fence was tested based on the results of complex experimental and theoretical studies under the conditions of a wet loess massif. At same time, regulatory restrictions on additional subsidence of these buildings foundations are provided. It has been proven that the additional subsidence of existing objects did not exceed the permissible values according to the norms. This happened due to the arrangement of the pit fence, the phasing of soil extraction in the initial stages under of the soil berm protection. The technology provided for the construction of a pit fence with sheet piling (I-beam No. 30) with a step of 1 m, with timber lagging between them. Then they installed the capping beam, struts, rakers and gradually raised the floor and outer wall of the parking lot of the new building.
 The results of long-term geodetic observations of the foundations deformations of buildings located in the zone of the pit influence of the new building at various construction stages of its enclosure are described.
 Sufficient convergence of the simulation results in the plane condition using the FEM and field studies was determined (the relative error did not exceed 20%). An elastic-plastic soil model of the "basement - foundations of an existing building - pit enclosure" system was used for modeling.
 The article describes examples of the results of FEM modeling of soil massif deformations at various stages of pit fence construction.
 It was determined that during construction the largest horizontal movements of the pit fence vary from 8 to 23 mm in the area of existing buildings.The maximum vertical movements of the bases foundations of these buildings amounted to 10 mm, which does not exceed the permissible values according to the norms.
 Prospects for further research on assessing the level of reliability of the pit enclosure by determining the variability parameters of the components of the system "foundation - foundation of the existing building - pit enclosure" have been determined.

Three-dimensional trenches induced by lateral riser-soil interaction and their influence on the behavior of SCR

Although the lateral oscillation of steel catenary risers (SCRs) contributes to trench production, traditional riser-seabed models cannot simulate the process. This study proposes a modified lateral riser-seabed interaction model and integrates it into the SCR model based on the vector form intrinsic finite element (VFIFE) method to simulate the trench formation process. The effects of the loading history, extra soil berm resistance, and cyclic vertical riser-soil interactions were included in the soil model. A 3D trench could be developed under the cyclic out-of-plane movement of the SCR. The trench formation process, seabed resistance distribution, axial tension, bending moment, and stress range distribution of the SCR were discussed in detail to illustrate the effects of the soil model. Different loading amplitudes and nonlinear soil parameters were chosen to determine their influence on the trench shape and distribution of the horizontal seabed resistance. The developed trenches were then inserted into the fresh SCR model before executing the dynamic analysis, in which only the cyclic heave motion was applied to the hang-off point. The simulation results showed that the trenches produced by cyclic sway motions beneficially influenced the fatigue life of the SCR. However, the effect would differ with the profiles.

Investigations on the sinking process of large pneumatic caissons

AbstractIn order to keep the port of Amsterdam accessible for ocean‐going ships, a new sea lock is under construction at the town of IJmuiden. The new sea lock will replace one of the nearly 100‐year‐old locks and will be the largest sea lock in the world upon completion. In order to prevent vibrations in the vicinity of the old locks and to prevent the need for deep building pits, the gate chambers are constructed as pneumatic caissons. Due to the open U‐shape of the caissons for the gate chambers, they are particularly vulnerable to torsional deformations that can occur during the sinking process, as a result of differential settlements. This was the main reason the contractor OpenIJ (a joint venture of BAM and VolkerWessels) wanted to get a better insight into the behaviour of the soil during the sinking process in order to control the deformations of the caissons during sinking. Together with the Hamburg University of Technology (TUHH) advanced Finite Element calculations were performed using the Abaqus/Explicit model to get a better understanding of the behaviour of the soil under a caisson during failure of the supporting soil berms. With the results and the lessons learned from the Abaqus analyses, additional analyses were made with Plaxis 2D and the Brinch Hansen method in order to support the sinking process. During the sinking process a real‐time monitoring system helped the operators to keep the deformations of the caissons within tolerances. The monitoring results showed that the soil behaved as predicted and both caissons were successfully sunk to their final position.

Stability of Extended Earth Berm for High Landfill

This study presents a stability analysis of an extended berm reinforced by geotextiles, with a steep slope of 1V:1.1H (vertical: horizontal). Finite element (FE) analyses were carried out to explore the failure mechanism and factor of safety (FOS) of the berm, on which the effect of the strength of geotextiles, leachate level, and anti-slide pile arrangement located at the toe of the berm were considered. It was found that: (1) failure surfaces developed along the interface between the new and the existing berms; (2) the FOS decreased as the leachate increased, and an FOS value of 1.42 could be obtained if the leachate level was controlled at a height of 20 m; (3) the tensile force of geotextiles was far lower than the available strength, which suggested that the geotextile had enough of a safety reserve; and (4) one row of longer piles at the toe of the berm performed better than two rows of shorter piles if the total length of piles was the same. The design and analysis of this project can be used as a reference for landfill expansion. Especially for a site condition with limited space, a geosynthetic-reinforced soil (GRS) berm is a safe, reliable and promising alternative.

Features of work of retaining walls made of bored piles in flowing sandy loams

The customers usually try to avoid areas with a high groundwater level in the process of choosing a site for construction. The presence of groundwater significantly increases the cost of construction, if there is necessity of the construction of underground floors. But construction in the conditions of modern megacities is increasingly challenging geotechnical engineers, because of the need not only to build on lands with difficult engineering and geological conditions, and not only to develop reliable foundation`s decisions, but also because of the need to more effectively design the underground spaces with its subsequent operation as underground premises for various purposes.The process of water level reducing is not only technologically complex, but also leads to a changes in the physical and mechanical characteristics of soils, which are difficult to predict.This paper shows the features of numerical modeling of walls in water-saturated soils.The effect of the ability to filter water through walls on the stress-strain state of the system of retaining structures – soil mass is demonstrated.The calculations were performed using numerical modeling, since this approach allows engineers to see (predict) the formation of dangerous processes. Numerical modeling also allows to take into account the change in the physical and mechanical characteristics of the soil during drainage of the pit and take into account the process of water level reduction and the effect of water reduction on the formation of the stress-strain state of the system restraining structures – soil mass.In the framework of design process, there is always appear the opportunity to consider various technical decisions for walls and choose the most effective among those considered.In this paper, the construction of walls with the possibility to use the soil berms to temporarily reduce the free height of walls is considered. In addition, the operation of anchor fasteners in soft (weak) soils is shown. Also, elements of the building frame were used to reduce horizontal movements.It is important to understand that not all measures (the construction decisions) are possible in certain conditions, especially when it is a tight environment of dense urban development.

The influence of non-linear stress-strain behavior of dense sand on seabed response to ice gouging

Subsea pipelines crossing the Arctic shallow waters are usually threatened by ice scour. A cost-effective solution to physically protect the pipeline against the ice gouging is to bury the pipeline in the seabed. Determining the minimum burial depth to minimize the construction cost and ensure pipeline integrity is a challenging design aspect. This requires proper modeling of the ice keel-soil interaction for an accurate assessment of the subgouge soil deformation and the keel reaction forces in a free field ice gouging analysis. In this study, the ice gouging process in dense sand was simulated by advanced large deformation analyses using Coupled Eulerian-Lagrangian (CEL) approach in ABAQUS/Explicit. A modified Mohr-Coulomb (MMC) model was coded into a simplified user subroutine to incorporate the effect of plastic shear strain accumulation, loading condition, density, and confining pressure on the shear strength parameters of dense sand. The MMC model captured the non-linear pre-peak hardening and post-peak softening of the dense sand that is not modeled by conventional Mohr-Coulomb (MC) model. The existing test results and numerical studies were used to verify the performance of the MMC model in ice gouging analysis. A comprehensive parametric study was conducted to investigate the effect of ice keel configuration and soil model parameters on keel reaction forces, subgouge soil deformations, and the soil berm formations. The proposed model resulted in a more accurate prediction of the seabed response to ice gouging and showed the significance of modeling the strain rate dependency of dense sand in ice gouging analysis. The proposed methodology was found to be a strong but simple framework that can be effectively used in daily engineering practice.

Innovative excavation and support techniques for deep large foundations in soft ground

The Suzhou Taihu New City major underground space development was one of the largest and most complex foundation projects in China. It had a footprint area of 93 000 m2 with a depth of 18 m into soft ground. The complexity was increased further by its proximity to existing sensitive assets, which include a metro station and flood defence structure. These challenges were overcome by using multiple innovative excavation and support techniques, including mini-pits, reserved soil berms, compartmentalised excavations, composite slope stabilisation, the observational method and a ‘time–space effect’.

Shear strength of soil berm during lateral buckling of subsea pipelines

The soil resistance developed during temperature- and pressure-induced large lateral movements of shallowly embedded subsea flowlines is an important input parameter for the structural design process. A major source of uncertainty in calculation of the soil resistance is the undrained shear strength of the soil berm produced as the flowline moves across the seabed, which is affected by the level of remoulding. To investigate the effect of pipeline embedment and displacement amplitude on the shear strength of the berm, a set of centrifuge model tests was conducted on kaolin clay, involving laterally moving pipelines with constant embedments in the range 5%–35% of the pipe diameter. Back-analysis of the test results, using finite element limit analysis, showed that the shear strength of the soil berm is a function of pipe displacement amplitude, pipe embedment, and soil sensitivity. On the basis of these results, we propose that the overall berm undrained shear strength may be determined as a convolution of the shear strengths of its constituent soil elements. Finally, a formula is presented for calculating the shear strength of soil elements within the soil berm, and this is used to back-analyse the overall soil berm resistance from the model tests.

Limit Analysis Method for Evaluating Soil Resistance to Lateral Motions of Pipelines Partially Embedded in a Seafloor

The lateral soil resistance available to pipelines partially embedded in a seafloor is of interest in evaluating pipeline lateral buckling capacity, stability under forces resulting from current loads, or route pullout loads. An upper-bound limit analysis method, including equilibrium requirements in a manner common to lower-bound theories, was used to evaluate lateral soil resistance to pipe displacements. The method is applicable to sand and clay foundations with homogeneous or layered conditions. Comparisons with results from physical tests and other limit analysis and finite-element investigations are presented. The numerical limit analysis procedure was implemented through numerical-computing software. An optimization procedure was used to identify the minimum resistance satisfying the governing objective equations. The seafloor surface geometry may include soil berms or other features. The soil strength may be described by a linear Mohr-Coulomb criterion or a curved criterion representing a varying material friction angle.

Softening and consolidation around seabed pipelines: centrifuge modelling

Solutions for lateral breakout and axial response of submarine pipelines are well established if the undrained shear strength conditions of the soil are known and defined simply (such as uniform or increasing proportionally with depth). In reality, the geometry of the free surface and the distribution of undrained shear strength around a submarine pipeline post-lay are affected by the lay process. This is because of soil berms that form adjacent to the pipe, and remoulding and subsequent reconsolidation of the seabed. The effect of post-lay consolidation on the subsequent lateral and axial response of submarine pipelines has not been previously investigated through physical model testing. This paper presents results from centrifuge model tests describing lateral breakout behaviour of a pipe on soft clay as a function of (a) pipe installation conditions, (b) post-lay pipe weight and (c) consolidation prior to breakout. In addition, the effect of post-lay consolidation on axial pipe response is studied. The experimental results are compared with available numerical and analytical predictions. The results quantify the influence of the installation process, pipe weight and post-installation consolidation on the lateral breakout resistance and trajectory of the pipe and also the axial pipe response, and show how existing prediction methods can capture these effects.

Karoo Array Telescope Berm Shielding: Efficient Computational Modeling and Multicopter Measurement

The square kilometer array is planned to be the most sensitive radio telescope of the 21st Century. Electromagnetic site quietness is a critical element in achieving the full science goals. We evaluate the shielding effectiveness of a soil berm at the South African Karoo site. The berm is electrically large and computationally expensive to model. A hybrid GO/MoM model using FEKO is proposed. Simulated data are compared to full-scale multicopter measurements. Broadband antennas are built into the landing structure and their patterns are deembedded during postprocessing. Simulations and measurements over 100–900 MHz (vertically polarized) show that the berm becomes effective from the point where its height reaches ten wavelengths. Shielding effectiveness values in the range of 25 dB are predicted by an approximate perfect electrical conductor ground model; the validity of this approximation is investigated. A simple knife-edge model is shown to provide a useful estimate of likely shielding. The results show that 3-D berm optimization using computational techniques is possible.

RFI shielding effectiveness of a soil berm

ABSTRACTWe investigate the electromagnetic (EM) shielding effectiveness (SE) properties of a berm which was created from soil due to construction works near a sensitive radio astronomy site. For the analysis, the berm is approximated as being located above an infinite perfectly electric conducting (PEC) plane. A two‐dimensional cross‐sectional analysis is shown to be sufficient to investigate the SE, which we compute using a computationally efficient single‐layer boundary integral equation method. To verify the method, we compare our results against those obtained by the commercially available Method of Moments (MoM) code, FEKO. Good agreement is demonstrated. It is observed that the berm provides about 25–30 dB SE at heights lower than 5 m and at distances of up to 50 m from the berm. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:17–21, 2017

Mode localization in lateral buckling of partially embedded submarine pipelines

The partially embedded submarine pipelines might buckle laterally at some segments under high pressure and high temperature (HP/HT) conditions. The buckling pattern localization introduces an extra level of analytical complexity when compared with the periodic buckling pattern. In the presented paper the lateral buckling pipeline is modeled by an axial compressive beam supported by lateral distributing nonlinear springs taking the soil berm effects in the horizontal plane. It is found that the model is governed by a time-independent Swift–Hohenberg equation. Based on John Burke and Edgar Knobloch’s work we conclude preliminarily that the equation will have localized solutions. Besides the qualitative conclusion, by AUTO 07P the localized solutions of the equation are studied in detail. The snakes-and-ladders structure of localized solutions explains the transition of buckling modes in theory. The range of the possible critical axial forces is found out. Meanwhile two critical axial force formulas corresponding to the range ends are presented. Finally a typical submarine pipeline is analyzed as an illustration.

Forage and tree seedling growth in a soil with an encased swine sludge layer

The closure of swine farms requires decommissioning of lagoons that contain large amounts of swine solids (sludge). Sludge is typically transported and land applied to soils. However, in some cases this process could be economically prohibitive and/or unpractical. An alternative idea is to encase sludge with lagoon soil berms after removing overlying effluent, followed by establishment of forages or short-rotation woody crops on the encased sludge. The objective of this study was to investigate growth potential for several forages and tree species into a pure layer of swine sludge. Alfalfa (Meticago sativa), bermudagrass (Cynodon dactylon), switchgrass (Panicum virgatum), green ash (Fraxinus pennsylvanica), black locust (Robinia pseudoacacia), and sycamore (Platanus occidentalis) were established in 40 cm deep pots consisting of a lagoon berm soil overlaying a sludge layer for 12 w followed by analysis of aboveground and belowground biomass production. “New” and “old” sludge was collected from an active 10 year old lagoon and decommissioned 50 year old lagoon, respectively. A control (soil only) was used. Encased sludge treatments increased forage biomass production. Sycamore and green ash were sensitive to new sludge but not old sludge as these species had less biomass production in new sludge than control and showed tissue trace nutrient deficiencies. While both sludge materials contained adequate nutrients, the new sludge had a salt concentration 1.8 times higher than old sludge as indicated by electrical conductivity (12.4 mS). Thus, the forage crops and black locust were able to thrive in new sludge due to their salt tolerance.

Impacts of two best management practices on Pb weathering and leachability in shooting range soils

This study investigated the impacts of two best management practices (BMPs) recommended by US Environmental Protection Agency on Pb weathering and leachability in shooting range soils. The two BMPs included replacing soil berm with sand berm and periodically removing bullets or shot from a berm. A column experiment corresponding to the first BMP was conducted by mixing the bullets with sand/soil, or placing bullets on the surface of sand/soil. After a 16-18-week incubation under high or low rainfall simulations, total Pb concentrations in sand were lower than that in soil. Total leachable Pb in sand (8.48 and 5.52μg kg(-1)) was also lower than that in soil (60.0 and 30.4μg kg(-1)) when bullets were mixed with sand/soil; however, they were comparable when bullets were placed on the sand/soil surface. These results indicate that lower Pb concentration in the sand than in soil may be attributed to reduced weathering of bullets. Mechanical removal of Pb bullets in the field transferred Pb from large to finer particles, increasing total Pb in the soil (<2mm) from 2,170 to 5,000mg kg(-1). In contrast, mechanical removal of Pb shot effectively reduced the shot in the soil by 86-92%. Thus, we concluded that, while replacing soil berm with sand berm can slow down Pb weathering, it may increase Pb leachability in the long term. Removal of Pb bullets and Pb shot can be effective, but caution needs to be exercised to minimize the adverse impacts, especially in pistol/rifle ranges because of increased total Pb content in the soil.

Numerical simulations of pipe–soil interaction during large lateral movements on clay

The soil resistance during large lateral movements of pipelines across the seabed is an important input to design solutions for the management of thermal and pressure-induced expansions. To investigate this behaviour, a large-deformation finite-element (LDFE) analysis method involving frequent remeshing was employed. The LDFE method allows the changing geometry of the seabed when disturbed by the pipeline to be incorporated. Also, the effects of strain rate and strain-softening on the undrained shear strength of the soil were accounted for. A back-analysis of a centrifuge modelling simulation was first performed, for validation, and then a parametric study varying the pipe weight and initial embedment was undertaken. The results show that a steady state is generally reached at large displacements, reflecting a balance between the growth of a soil berm ahead of the pipe and the softening of the disturbed soil. The initial breakout response matched well with previously established failure envelopes, and a new interpretation has been proposed to capture the large-displacement response. The ‘effective embedment' concept is used to rationalise the influence of the soil berm ahead of the pipe. This leads to simple new relationships for predicting the steady-state residual lateral resistance, which provide more accurate predictions of the LDFE response than previously established solutions. The complete load–displacement response over large movements was also shown to be well fitted by an exponential relationship, albeit for the specific case of lateral movements under constant vertical load.

Runoff Through and Upslope of Contour Switchgrass Hedges

Grass hedges are specialized vegetative buffers effective in trapping sediment, but less is known about their ability to reduce or redirect runoff. Runoff and sediment yield from natural rainfall were measured during 8 yr from 0.1‐ha contour‐planted plots with and without 1‐m‐wide switchgrass (Panicum virgatum L.) hedges at their lower ends. Plots had slope lengths of 22 m with a steepness of 5%, were located on silt loam soils near Holly Springs, MS, and were cropped to conventional‐tillage corn (Zea mays L.). During the first 4 yr of the study, care was taken to conduct tillage is such a way that no soil was thrown into the grass hedge, while during the last 4 yr of the study, primary disk tillage immediately adjacent to the grass hedges created soil berms that acted as low terraces. Hedges reduced the fraction of rainfall that ran off the plots, and hedges with soil berms reduced runoff even more. The runoff curve number (CN) for a 2‐yr return period rainfall event was about 78 for plots with no hedges, 70 for plots with hedges, and 61 for plots with hedges with berms. Without berms, 95% of runoff passed through the hedges. In contrast, with berms most runoff (&gt;85% from runoff events &lt;3 mm d−1; &gt;55% for events &lt;80 mm d−1) flowed upslope of and parallel to the hedges. With or without berms, grass hedges decrease sediment yield by a factor of 0.25 to 0.28.

The mechanism of steady friction between seabed pipelines and clay soils

The large-amplitude lateral soil resistance between an on-bottom pipeline and the seabed is an important design parameter in assessing pipeline behaviour during lateral thermal buckling or under the impact of a submarine slide. This paper describes a series of centrifuge model tests that shed light on the underlying behaviour during large-amplitude lateral pipe movement. It is shown that at large displacements the lateral response is governed predominantly by the passive resistance of the growing berm of soil ahead of the pipe. Using a new analysis of this growing soil berm, based on conservation of volume, the ‘local' embedment of the pipe relative to the top of the idealised soil berm is defined. In this way, the normalised lateral pipe–soil resistance, H/suD, from tests encompassing a range of pipe weights and initial embedments follows a single trend line. This idealisation of the response is more consistent than the usual terminology of a pipe–soil friction factor.