Clay Embankment Research Articles

Railway embankment failure trends and monitoring – lessons learned from the Anglia route

UK railways were constructed with little consideration of engineering practice and with climate change and the associated greater frequency of extreme weather events, comes the impact on earthworks stability and risk to public safety. Many embankments on Network Rail’s Anglia route have shown a gradual degradation through their steep upper slopes and progressive failure within predominantly clay embankment material and underlying soft deposits. A regional wholistic view allows identification of common geotechnical trends and risk categorisation to better enable prioritisation of asset management. Understanding when to intervene is crucial and monitoring the behaviour of earthworks is a vital asset management tool to control risk and extend lifespan. To be a wise investment, slope instrumentation must be properly thought out in line with a detailed interrogation of the site and alongside a well-developed conceptual model. Automated monitoring can bring greater control and allow more accurate evaluation of intervention but must be assessed in line with prioritising large areas with limited budgets. Correct targeting of ground investigation and ensuring sufficient and reliable data can optimise mitigation and provide confidence the solution has provided resilience to railway infrastructure.

In-situ water retention monitoring system of an operational dike

The severe droughts in recent decades and the lack of regular flooding have caused considerable fissures to develop on clay embankments. Previous surveys in Hungary have identified the examined dike section as prone to desiccation cracks. It is essential to determine the possible extent of these desiccation cracks, as they degrade the dikes’ resistance against several failure mechanisms. A representative dike cross-section was equipped with a unique water retention monitoring system comprising 17 sensors, including 14 soil moisture and 3 water potential sensors. These devices were validated with laboratory measurements to obtain accurate results. The gravimetric water content (w) ranged from 8.3 % to 31.3 %, and the matric potential was recorded between 0.1 kPa and 2350.7 kPa over one and a half years. The study examined the differences in soil behaviour under pavement and turf cover, identifying common moisture content distribution patterns and areas of the cross-section prone to desiccation cracking. The uniqueness of the monitoring system lies in the fact that it was established in an operational embankment, which regulates the flow of a river. Furthermore, it was instrumented along the Tisza River, which is among Europe’s most significant watercourses. The results may help better understand the moisture content change in clay embankments and the role of the crest pavement in the moisture content distribution.

Field Observation and Settlement Prediction Study of a Soft Soil Embankment under Rolling Dynamic Compaction

Rolling dynamic compaction (RDC) has been found to be useful for compaction soils and is now widely used globally. Because RDC is not often used in soft soils with poor engineering properties, field monitoring was used to study the soft clay embankment responses under RDC conditions in this study. Analysis of the monitoring data revealed that the response of the soil occurred mainly in the first 20 passes. Field monitoring revealed a strong correlation between settlement, horizontal displacement, and pore water pressure. The depth of impact of RDC on the soft soil embankment was between 3 and 3.5 m. Although settlement prediction is an important issue for construction, there is a lack of prediction methods for RDC-induced soil settlement. In this study, we used three different machine learning algorithms: random forest regression (RFR), multilayer perceptron (MLP), and extreme gradient boosting (XGBoost) to predict the total settlement and uneven settlement induced by RDC on the soft soil embankment. The three prediction models were compared, and the predictive accuracy of these models was assessed. This study analyzes and summarizes the effect of RDC application on a soft clay embankment and explores the machine learning method used for settlement prediction based on monitoring data, which provides some methods and ideas for research on the application of RDC on soft soil foundations.

Wall and pillar drains in puddle clay embankment dams

Puddle clay core embankment dams were built prior to the use of rolled clay core dams and comprise a large proportion of UK dams, with the dams relying for their watertightness on the addition of water to (puddle) the clay until it has an undrained shear strength of around 10 kPa, and thus has increased ability to deform without cracking. Such dams sometimes had early forms of unfiltered drains, comprising coarse cobbles, in the downstream shoulder, either to assist construction and/or to lower the phreatic surface and improve the slope stability once the reservoir is in operation. These drains are separate from foundation drains dealing with springs encountered in the foundation excavation and drains to deal with surface runoff. This paper gives examples of such drains in dams constructed between 1863 and 1940. These drains were installed prior to the development of classic filter design rules and tools to analyse seepage. This is important as the drains have no filter, and are thus vulnerable to internal erosion which, if not detected, could lead to failure of the dam. These drains may also be the true root cause of historic incidents at these dams, due to embankment fill materials washing into the drain and creating sinkholes.

Development of a Multiphase Numerical Modeling Approach for Hydromechanical Behavior of Clay Embankments Subject to Weather-Driven Deterioration

Clay embankments used for road, rail, and flood defense infrastructure experience a suite of weather-driven deterioration processes that lead to a progressive loss of hydromechanical performance: micro-scale deformation (e.g., aggregation and desiccation), changes in soil-water retention, loss of strength, and macro-scale deformation. The objective of this study was to develop a numerical modeling approach to simulate the construction and long-term, weather-driven hydromechanical behavior of clay embankments. Subroutines within a numerical modeling package were developed to capture deterioration processes: (1) strength reduction due to wet-dry cycles; (2) bimodality of the near-surface hydraulic behavior; (3) soil-water and soil-gas retentivity functions considering void ratio dependency; and (4) hydraulic and gas conductivity functions considering void ratio dependency. Uniquely, the modeling approach was comprehensively validated using laboratory tests and nine years of field measurements from a full-scale embankment. The modeling approach captured the variation of near-surface soil moisture and matric suction over the monitored period in response to weather cycles. Further, the developed model approach could successfully simulate weather-driven deterioration processes in clay embankments. The model predictions manifested the ability of the modeling approach in capturing deterioration features such as irrecoverable increases in void ratio and hydraulic permeability near surface. The developed and validated numerical modeling approach enables forecasting the long-term performance of clay embankments under a range of projected climate conditions.

Combined electrical resistivity tomography and ground penetrating radar to map Eurasian badger (Meles Meles) burrows in clay-rich flood embankments (levees)

Globally, earth embankments are used to protect against flooding. Raised above the surrounding water table, these embankments make ideal habitats for many burrowing animals whose burrows can impact their structural integrity. Ground Penetrating Radar (GPR) is commonly used to identify and map animal burrows and other small cavities. However, the depth of investigation of a GPR survey can be severely limited in saline and clay-rich environments, soil properties commonly associated with flood embankments. In contrast, Electrical Resistivity Tomography (ERT) can image subsurface voids in conductive ground conditions but has been rarely used to image animal burrows. Here we aim to assess the efficacy of ERT and GPR to image two badger burrow networks, called ‘setts’, located in clay embankments on the River Ouse, Yorkshire, UK. The two setts were excavated to validate the geophysical results, and the soil was characterised through logging and geotechnical analysis to develop a ground model of the site. We find that ERT can accurately resolve tunnels down to 1.5 m depth, map the structure of a multi-entrance badger sett and successfully identify the end of the tunnels. This result compares favourably to the GPR surveys, which mapped all but the deepest tunnels, limited by its penetration depth due to clay soils. Our results show that ERT can be used as a primary survey tool for animal burrows in clay-rich environments and can be validated using co-located GPR surveys if penetration depth is sufficient. The implications of this study may allow embankment managers to map burrow networks, assess flood embankment stability, minimise repair costs, and reduce unexpected failures during flood events. Additionally, a better understanding of how, for example, local heterogeneities impact badgers' burrow geometry may be achievable using these geophysical methods, as they provide a non-destructive, repeatable method for imaging setts.

Mitigating embankment frost heave with nano-ZnO in the Arctic

Non-frost susceptible soils (e.g., gravel) are typically used as embankment fill to minimize the frost heave problem on the highways in the Arctic. However, accesses to the non-frost susceptible soils are limited in the remote regions, and the transportation costs for it are very high, thereby resulting that frost susceptible soils have to be used to fill the embankments. In this study, nano-ZnO was added to two types of frost susceptible soils, namely silty clay and clay, to reduce the frost susceptibility of soils and to mitigate the frost heave. Firstly, the unconfined compressive strengths of the soil samples whose the mass ratios of the nano-ZnO to the silty clays were 1.5 wt%, 3.0 wt%, 4.5 wt% and 6.0 wt% were tested. A series of isotropic freezing tests were then conducted to study the temperatures and frost heave deformations of the soil samples with the nano-ZnO of 0.0 wt%, 1.5 wt%, 3.0 wt% and 4.5 wt%, thereby verifying the effectiveness of the nano-ZnO in reducing the frost susceptibility of the soils. The optimal mass percentage of the nano-ZnO was determined by the mechanical and freezing tests. Finally, a clay embankment model with the nano-ZnO of the optimal mass percentage (defined as the nano-ZnO embankment model) during freezing-thawing cycles under various artificial rainfall conditions in the Arctic environment was tested. A clay embankment model without nano-ZnO was the control case, and defined as the control embankment model. Experimental results revealed that 1) with the increased nano-ZnO, the unconfined compressive strengths of the soil samples initially increased and subsequently decreased, and the maximum value corresponded to the mass percentage of 4.5 wt%; 2) the usage of the nano-ZnO can considerably reduce the freezing point and the frost heave deformations of the soil samples; 3) the optimal mass percentage of the nano-ZnO was 4.5 wt%. Compared with the soil sample without the nano-ZnO, the frost heave deformation of the soil sample with the nano-ZnO of 4.5 wt% was reduced by 71.98% and 78.44% using the rapidly cooling and step by step cooling method, respectively; 4) the usage of 4.5 wt% nano-ZnO was reduced the frost heave deformation of the clay embankment model by a maximum value of 74.06% under artificial rainfall, whereas the frost heave deformation of the embankment model reduced by a maximum value of 31.94% without artificial rainfall. Moreover, the mechanisms of the increase in the compressive strength and the decrease in the frost heave were analyzed. This study can provide considerable insights for mitigating the frost heave problems in highways in the Arctic when frost susceptible soil is used as embankment fill.

Analysis of the Effect of Smear Zone on Consolidation Decline in the Tebing Tinggi-Kisaran Toll Road Project (Phase 1) Tebing Tinggi – Indrapura STA 102+700 Toll Road Project with 3D PLAXIS Modeling

Repairing of soft clay Embankment loading method with PVD is a soil improvement system consisting of Embankment loading work, installation PVD, installation PHD, and geotechnical instruments. Preload serves to compress the subgrade. PVD serves to speed up the process of soil compaction. Horizontal drains serves to drain pore water taken from the PVD in a horizontal direction to the outside of the location that improved. Geotechnical instruments function to monitor and record the process and determine the performance of the result improving soil that have been carried out. Embankment loading and PVD (Prefabricated Vertical Drain) are technologies that are often used in the construction world to increase shear strength and speed up consolidation time of soft soils. However, during the installation of PVD using a mandrel it can affected the surrounding soil, causing the soil to become disturbed. The disturbed area is called by Smearzone. Due to the presence of a smear area, analysis and calculations are needed to obtain a consolidation time that is in accordance with field conditions. This analysis aims to compare the decrease of displacement in the settlement plate (SP-124) with modeling in PLAXIS 3D considering using with or without taking into account the effect of the smearzone. The method used in this thesis is the analytical method using Terzaghi theory and the finite element method using PLAXIS 3D. From the results obtained analytically the magnitude of the decrease is 15.252 cm while the results from the PLAXIS 3D analysis without the effect of the smear zone is 15.15 cm and with the effect of the smear zone being, 2 times the dimensions of the mandrel the results obtained are 15.131 cm, 15.133 cm and 15.134 cm, with 3 times the dimensions of the mandrel the results obtained are 15,142 cm, 15,141 cm and 15,14 cm and with 4 times the dimensions of the mandrel the results obtained are 15,144 cm, 15,143 cm and 15,143 cm. The decrease that occurs in the settlement plate 124 in the field is 15.10 cm. So it can be concluded that the calculation of consolidation decrease using analytical theory is relatively close to the decrease in actual results in the field with a percentage difference of 1% decrease. There are differences in settlement due to laboratory data not representing the entire soil layer. Due to the decrease that occurred 15.10 cm, the result of the effect of the smear effect 2 times the mandrel dimension and half of the coefficient of permeability of the original soil with a reduction ratio of 0.2% is the result that is closest to the results of field observations compared to without a smear effect of 0.331%.

The Effect of Moisture and Fine Grain Content on the Resilient Modulus of Sandy Clay Embankment Roadbed

This paper studies the effect of moisture and fine grain content on the resilient modulus of sandy clay embankment roadbed in the Mekong Delta, Vietnam. The study analyzed the grain content of 30 soil samples on the annually flooded routes of the Mekong Delta according to the AASHTO T88-97 standard. The triaxial compression test at room temperature was used to estimate the resilient modulus of the samples belonging to 6 moisture levels. The experiments were conducted using 3 levels of lateral pressure, 0, 21, and 41kPa. Five deflection stress tests of 14, 28, 41, 55, and 69kPa, were conducted for each lateral pressure. The results showed that as the percentage of grains finer than 0.075mm increased, the variation ratio of the resilient modulus also increased. The content of grains finer than 0.075mm was between 54.1%-93%, while the variation ratio of the resilient modulus ranged between 53.7% and 89.1%. Moreover, as the percentage of grains finer than 0.075mm increased, water absorption capacity increased and resilient modulus decreased. As moisture and fine grain content influence the resilient modulus of the roadbed, this study’s results will help to limit and prevent the erosion of sandy clay embanked roadbeds, especially on frequently flooded areas such as the Mekong Delta.

Regression Analysis Following Levenberg - Marquardt Algorithm to Estimate Elastic Modulus of Sandy Clay Embankment

Road design must consider the factors affecting the elastic modulus of the cohesive soil used for the roadbed. Accurate determination of the elastic modulus of the pavement will help calculate properly the deformation of the pavement and prevent the appearance of cracks in the pavement; especially when the roadbed is flooded. This study is based on the laboratory data, using Levenberg-Marquardt algorithm and building a program for regression analysis, proposing the coefficients to estimate the elastic modulus of the roadbed. From the research results obtained, the way to choose the adjustment coefficients has been improved by adding the coefficient µ, the Levenberg-Marquardt algorithm has solved the problem with only 1,351 iterations, proving the simplicity and efficiency to solve the problem of nonlinear minimum squares that sometimes cannot be solved by the Gauss-Newton method. This algorithm is applied to regression analysis of experimental results, adding the values of coefficients a₉ and a₁₀ to propose the values of the remaining coefficients a_n and b_n of the formula Dong-Gyou Kim, MS, 2004 with correlation coefficient R² is 0.8929. As a result, the article proposes the appropriate value of the regression coefficients into the formula to estimate the elastic modulus of the sandy clay embankment according to the humidity and material characteristics of land, instead of using the Benkelman method which is time-consuming, expensive and difficult to implement.

Laboratorium Experimental Of Cantilever Sheet Pile Behaviour On Soft Soil Induced By Strip Load

This study aims to analyze the deflection behavior of the sheet pile through experimental testing and numerical analysis using the Finite Element Method (FEM). The Laboratorium scale test on a Tub with length of 1500 mm, width of 600 mm, and height of 1500 mm, and Steel Plate 3.2 mm with dimensions of 1400 mm x 590 mm was used as a model of the sheet pile wall. The subgrade material is clay soil and embankment material in the form of Sirtu which passes the No. sieve. 40. Physical and mechanical testing of soil and gravel materials is carried out with reference to ASTM standards. The measurement of the value of the strip load (q) and deflection was carried out using a load cell with a capacity of 100 kN and a linear variable differential transformer (LVDT). The deflection of the sheet pile was using was analyzed using Plaxis 8.2 software of the FEM method. The results of laboratory tests show that the pile wall collapses at a load of 74 kN/m2, with a deflection of 24.56 mm, while the FEM analysis shows that the pile wall collapses at a load of 71 kN/m2 with a deflection of 21.29 mm.

Embankment Breach Research: Observed Internal Erosion Processes

HighlightsThis study provides data from internal erosion tests on four intermediate-scale homogeneous embankment dams.Soil properties influence the breach formation process and breach timing.Results showed that observed erosion rates of the internal flow path varied by several orders of magnitude.Quality control of embankment construction can greatly influence breach development.Abstract. Internal erosion and embankment overtopping are the two most common causes of embankment dam and levee failures and incidents. Internal erosion is the removal of soil material by the flow of water through a continuous defect, cavity, or crack within a compacted fill and/or its foundation. Internal erosion initiates from vulnerabilities within the embankment. The embankment soil material plays a key role in both the erosion process and rate of failure, but characterizing soil properties and how they relate to the rate of failure can be challenging. Soil properties such as texture, density, strength, moisture content, and erodibility can vary greatly; thus, it is important to study the effects of these properties on the breach formation process and breach timing. The USDA Agricultural Research Service performed internal erosion breach experiments on four intermediate-scale homogeneous earthen embankments constructed of soils ranging from a silty sand to a lean clay material. The embankments were constructed to a height of 1.3 m, a top width of 1.8 m, and upstream and downstream slopes of 3(H):1(V). The embankment materials were characterized by water content, density, texture, strength, and erodibility. Erodibility was measured using a jet erosion test (JET) apparatus. A 40 mm diameter, continuous steel pipe was placed through each embankment during construction and removed to form an open-ended void through the embankment connected to the upstream reservoir. The removal of the pipe initiated internal erosion. The objectives of the experiments were to observe the development of the internal erosion process over time and to examine the influence of soil properties on the erosion rate, breach timing, geometry of the breach opening, and breach outflow. The rate of erosion and failure observed in these tests varied by several orders of magnitude, with the silty sand embankment eroding most rapidly and the lean clay embankment with a mean moisture content of 18% dry basis at standard compaction eroding the slowest. These observations were indicative of the soil textures. Although the two lean clay embankments were constructed of similar soils, the difference in erosion rates speak to the importance of quality control (e.g., compaction moisture content) during construction. Soil properties including soil texture, erodibility, and compaction moisture content are key predictors of erosion rate and observed failure. Keywords: Breach, Dam failure, Dams, Embankments, Erodibility, Internal erosion, Levees, Overtopping.

Vertical current structure in a macro-tidal, well mixed Sundarban ecosystem, India

The present study reports on the vertical structure of the current profile of the Jharkhali of Sundarban ecosystem. The clay embankments constructed along the Sundarbans for coastal protection are facing severe erosion problem due to tidal current, extreme water levels, storm surges, overtopping and breaches in embankments which lead to widespread flooding. The understanding of the current profile of Sundarban aquatic system with respect to depth of water column is essential for suitable engineering design for embankment. It will be used for conservation of coastal resources and inhabitants of the Sundarbans from the natural disasters. The tidal range during the present study was 6.1 m and 5 tidal constituents viz. M2, S2, K1, O1, and N2 are predominant at Jharkhali. The minimum (114.55 cm/s) and maximum (134.45 cm/s) current speed were observed at bottom and mid depth respectively. The maximum speed at bottom is also due to longitudinal salinity gradients, which may induce larger velocities in the lower part of the water column. The vertical velocity profiles during flood are characterized by a near bed maximum. The maximum speed usually occurs during mid-flood and mid-ebb periods and also varying with moon phase, usually maximum and minimum speed were observed during spring tide and neap tide respectively. This trend is persisting in the entire water column from the surface to bottom. The direction of the current is controlled by orientation of the river channel and adjacent tributaries. In general, water travels towards North and WNW direction during flood tide and E & ESE direction during ebb tide. Interestingly, about 80-degree difference in current direction was noticed between surface and bottom current with clockwise spiral movement.

Numerical simulation of the moisture migration of unsaturated clay embankments in southern China considering stress state

To determine the moisture contents of unsaturated clay embankments in southern China considering the stress state, 753 moisture data of three existing embankments for about 20 years were measured, and six frequency domain reflectometry sensors were installed in a widened embankment in southern China to monitor the moisture content. The soil water characteristic curve (SWCC) and stress-dependent soil water characteristic curves (SDSWCCs) were determined in the laboratory using a pressure plate apparatus and a stress-dependent parametric equation was established. The finite element model of a typical unsaturated clay embankment in southern China considering the SWCC and SDSWCCs was created. Then, the variation of the moisture contents of the clay embankment was simulated. The results show that the vertical stress has an obvious effect on the moisture distribution in embankments, especially the positions inside embankments where the vertical stress is large and cannot be neglected. The finite element model considering the SDSWCCs, therefore, should be selected when analyzing the moisture filed of embankments in southern China. For the existing clay embankments in southern China, their moisture contents gradually increase from the optimum moisture content to equilibrium values, which is close to the plastic limit and increases by 99% of the optimum moisture content. In addition, the resilient modulus values at different locations of the embankment and that of the whole embankment are reduced by 55 to 62%. And the safety factor of the slope obviously decreases, and its reduction is greater than 60%.

Effect of cushion and cover on moisture distribution in clay embankments in southern China

To achieve durability of the embankment in southern China, a method to control the change of moisture content with the cushion and cover was proposed. A finite element model of cushion and cover considering different materials and thicknesses for a typical embankment was built, and 20 numerical analyses of transient seepage in the embankment were simulated. The results show that the sand cushion effectively blocks the effect of groundwater capillary rise and the minimum thickness of the sand cushion is 75 cm without considering the atmospheric environment. With the combination of sand cushion and clay cover, as the thickness of the clay cover increases, the duration time of the moisture content from the initial to relative equilibrium state increases, but the equilibrium moisture content is the same as that of the original embankment. Besides, with the combination of the sand cushion and sand cover, the moisture content inside the embankment remains the same, which is consistent with the optimum moisture content during construction. The combination of 75 cm sand cushion and 30 cm sand cover is a very effective method to block groundwater and atmospheric environment, and achieve the control of the humidity stability of the embankment in southern China.

Microstructural insight into permeability and water retention property of compacted binary silty clay

The durability of silty clay embankments is partially controlled by the moisture migration, which depends on soil hydraulic properties. This paper presents an experimental study of hydraulic properties of compacted binary silty clay. Specimens with different mixing ratios and dry densities were prepared. Scanning electron microscopy and mercury intrusion porosimetry were used to characterise the microstructure of silty clay. Thereafter, falling-head permeability tests and water retention tests were conducted to study the permeability and water retention property, respectively. The results demonstrate that clay particles are dispersed and show preferred arrangements after compaction when the clay content is 100%. As the clay content decreases, the arrangement of clay particles is gradually disturbed because of the existence of silt particles, causing the formation of large pores around silt particles. When the dry density increases, the pores around silt particles significantly decrease. Moreover, the permeability of silty clay decreases but the water retention capacity increases with increasing clay content and dry density. This is because the silty clay with larger clay content and dry density has fewer large pores, which greatly restrains the flow of water. Both the permeability and water retention property of silty clay can be predicted from pore size distribution parameters.

Determining Shrinkage Cracks Based on the Small-Strain Shear Modulus–Suction Relationship

This research aims to propose the use of spectral analysis of surface wave (SASW) tests along with in-situ suction measurements for non-destructive determination of shrinkage cracks. The underlying principle behind this proposed method is that, while suction and the small-strain shear modulus are positively correlated for intact samples, this is not the case for cracked ground. A series of SASW tests were performed on a clay embankment at different periods, during which the suction, modulus, and shrinkage crack depth varied seasonally. The soil water retention curve (SWRC) of the undisturbed sample collected from the cracked zone was determined, which related the suction-to-moisture content and void ratio of the soil. A free-free resonant frequency (FFR) test in the lab was conducted to determine the small-strain shear modulus (G0) at various moisture contents. The small-strain moduli from the SASW tests on the intact ground were generally higher than those from the FFR tests due to the effect of confining stress. A drop in the small-strain modulus determined using the SASW test was observed as an increase in suction-induced cracks and it relieved the horizontal stress. The crack depth measured in the field was then modelled using a semi-empirical procedure that can be used to predict crack depth relative to suction.

Diagnosis and proposal of erosion control downstream of the Park Alfredo Werner Nyffeler, in Maringá - Paraná

The surface runoff role in the urban erosion in Northwest Paraná cities was strengthened by many factors, such as the establishment of the cities often in disaggregated soil areas, vegetation cover removal, soil surface impermeabilization caused by construction and poorly executed embankment areas. In Maringá, Paraná, in a bottom valley located near the park Alfredo Werner Nyffeler, there is an accelerated erosive process, damaging half of the urban drainage pipes, which are located around one meter far from the sidewalk. In that way, it poses a risk to the local population and may lead to a collapse of the drainage structure. Within this context, this work aims to diagnose and identify the possible aspects that caused these issues and to design a gabion wall to stem the significative erosive process occurring in the area. Thus, on-site data survey and laboratory analysis were carried out in order to characterize the soil and, by means of the software GawacWin, a gabion retaining wall in order to use it as a prompt, needed retaining measure was designed. The obtained results showed a lack of awareness by the local population in regard to the solid waste deposition, which accumulates downstream of the park. In addition, the drainage pipes could not cope with the peak flows, causing structural damage, leaks and uncovering the junction box. A silty clay embankment was found in the area, which is an expansive soil, contaminated with rubble and the soil compaction was not properly executed. It was used to level the area for the pipeline passage, contributing to the erosion. A gabion wall, with 6m high and 3m base, showed to be an efficient solution with regard to terrain loads. Furthermore, the price, simple construction and the easy merging with the environment are advantages for the gabion wall, when compared to other structural measures.

The effect of clay water content in the Jet Erosion Test

The understanding of the onset of breaching induced by surface erosion is fundamental to enable definition of the level of protection afforded by embankments and provision of standards for the design of new structures and the upgrading of existing ones. Compacted embankment materials are generally partially saturated due to seasonal variation in the water content. At the onset of the overflow process embankments undergo to a wetting process due to the changes at the outer surface boundary conditions (i.e. overflow). Erosion behaviour is known to be a counterbalance between gravity forces and shear erosion forces. However, as the particle size decreases (i.e. clayey soils), gravitational forces become negligible and electrochemical interaction between particles play a dominant role. Clay microstructure (e.g. particle configuration and inter-particle forces) changes with the hydro-mechanical stresses history. Thus, it is necessary to consider the microstructural changes in particle configuration to understand the influence of microstructure on the macroscopic behaviour of clay during erosion. Upon wetting, clay have a swelling/collapse behaviour. This research presents experimental results on erosion of clay samples compacted at the same initial dry density but with different compaction water content. The influence of different wetting times on erosion is also investigated. We show that for a given as-compacted water content, the longer the wetting stage, and hence the higher the sample water content, the more erodible the samples. Additionally, for samples compacted at the same dry density, the ones compacted on the dry side of optimum are more erodible than samples compacted at the optimum water content, despite the lower water content at formation. We hypothesise that this may be due to the formation of a different initial microstructure in sample on the dry side of optimum (i.e. bi-modal pore size distribution). Our results contribute to the fundamental understanding of time-dependent mechanisms that influence erosion of clay embankments during overflow and, hence, to embankment failure. In addition, these tests show how basic concepts of unsaturated soil mechanics can serve as a guide to ‘design’ the compaction conditions of embankment material.

The Effects of Geosynthetic-Reinforcement on Consolidation Behavior of Soft Clay Embankment under Step Construction

Geosynthetics–reinforced structures are widely used in embankments and walls. This paper presents the simulation of the embankment under load in order to compare the behavior of clay embankment with and without wrapping-facing-geosynthetics-reinforcement using finite element method (FEM) and to analyse the variation of behavior included of displacement and excess pore pressure under the different over-consolidation ratios (OCR). The calculation results show that embankment with higher OCR showing lower displacement compare to embankment with lower OCR. However, OCR isn’t very sensitive to the dissipation of excess pore pressure. Geosynthetics-reinforcements could reduce the displacement of embankment and accelerate dissipation of excess pore pressure after construction and surcharge. Gravel, geosynthetics-reinforcement and clay soil are properly combined, clayey soil is expected to be useful as embankment material.