Experimental Embankment Research Articles

A model for one-dimensional consolidation of clayey soils with non-linear viscosity

A model for the one-dimensional consolidation of saturated clayey soils, considering creep, is proposed, based on the consolidation mechanism idealized by Terzaghi (1941). The effective vertical stress is divided into two parts: one corresponding to the “solid” contacts, and other relating to the “viscous” contacts, the void ratio changes being caused by variations solely in the solid portion. Based on experimental evidence, a non-linear viscosity law was adopted, described by a hyperbolic function, in addition to its dependence on the void ratio. The resulting differential equation system is solved through the Finite Difference Method. The main “secondary effects of time” – experimental deviations from the classical Terzaghi (1925) theory – were able to be reproduced using the model, as well as experimental results that support other categories of consolidation models, such as the isotache- and Cα/CC-based models. A good fit was obtained for the results of long-term laboratory tests in clays from different parts of the world that reached the end of secondary consolidation. A good prediction was also reached for the evolution of settlements from the experimental embankment on the soft soils of Lilla Mellosa, monitored since 1947 in Sweden.

Limiting burrowing activity and overland dispersal of the invasive alien red swamp crayfish Procambarus clarkii by sophisticated design of watercourses

Invasive alien crayfish species pose major ecological and hydrological risks globally. The red swamp crayfish (Procambarus clarkii) is one of the most widespread crayfish species worldwide. Its impacts arise from burrowing activities and lead to mobilization of soil nutrients, water safety risks by instability of dikes and erosion of banks. Increased sediment load demands additional dredging of drainage ditches and canals to ensure their water discharge capacity. Sustainable methods for limiting burrowing in banks and dispersal behaviour of crayfish were not yet available. Therefore, a field study was performed to determine whether the number of burrows and overland movement of crayfish were related to a particular bank type. Burrows were counted in three watercourses during a water-level decline. The number of burrows was significantly lower in natural banks than in non-natural and semi-natural banks. The construction of natural-like banks along watercourses may significantly reduce sediment load, erosion and the collapse of banks by burrowing activities of crayfish. An inclination experiment mimicking various types of terrestrial dispersal barriers elucidated that steepness, soil type and vegetation structure of small embankments near watercourses were significant factors for manipulating overland movement of crayfish. Crayfish were taken out of the water for this purpose and placed on small experimental embankments varying in slope and types of vegetation. The lowest frequencies of upward movement were recorded at inclinations of 20° and 30° on bare sandy soil and short and species-poor grassland substrates. This implies that crayfish crawling out of the water will return to the watercourse when encountering such a dispersal barrier. Therefore, a sophisticated design of embankments along watercourses can be a tool to reduce colonization risk of nearby located, hydrologically isolated water bodies with high nature values.

Field investigation on moisture, heat and deformation behaviors and their coupling effects of expressway in warm permafrost regions

Expressways construction in warm permafrost regions is faced with serious permafrost degradation, and expressways stability is closely related to its thermal-hydro-mechanical state. However, the behaviors of moisture, heat and deformation of expressway in warm permafrost regions are not completely clear. In this study, the experimental embankment for the proposed Qinghai-Tibet Expressway built on site is taken as the research object, and the behaviors of moisture, heat and deformation and their coupling effects are studied, and the expressway stability in warm permafrost regions is further discussed. The experimental results show that the permafrost degradation beneath expressway is more serious than that beneath ordinary highway. The moisture distribution is affected by temperature distribution and capillary effect, showing high moisture content in the top and bottom of the embankment and low moisture content in the middle. The expressway presents deformation difference due to the differential degradation of underlying permafrost, and the deformation difference increases with time. The embankment settlement is slow before reaching a new thawing depth, but it develops rapidly after reaching a new thawing depth. Frost heaving occurs in cold season and can counteract the creep of warm permafrost, leaving the embankment in a stable deformation state.

Evaluation of the long-term effect of lime treatment on a silty soil embankment after seven years of atmospheric exposure: Mechanical, physicochemical, and microstructural studies

The long-term effect of lime treatment was evaluated on a 2.5% lime-treated experimental embankment after seven years of atmospheric exposure. The evaluation was done by comparison of (i) the mechanical performance of the field sampled specimens with laboratory cured specimens, and (ii) the physicochemical and microstructural properties of the samples from the lime-treated embankment with specimens obtained from an untreated embankment constructed near to it as a reference embankment.An average Unconfined Compressive Strength (UCS) level of 3.29 MPa was measured in the lime-treated specimens sampled from the core of the embankment. This UCS level was found to be comparable to the UCS of accelerated-cured specimens obtained at a laboratory scale. Thus, such levels of UCS can be expected after long-term in-situ curing. Scanning electron microscope images evidenced the contribution of the formation of cementitious bonding towards such UCS evolution in the lime-treated specimen. The persistence of the lime effect within the core of the embankment was confirmed by the presence of a pH greater than 11. However, a relative decrease in the pH and water content was observed in the upper layer compared to the core of the lime-treated embankment. This indicates that the effect of lime was lost in the upper layer under constant soil-atmosphere interaction and due to the development of vegetation roots. Pore structure observations made by Mercury Intrusion Porosimetry (MIP) and Barrett-Joiner-Halendapore (BJH) methods highlight the formation of smaller pores (diameter < 3000 Å) under lime effect. These smaller pores have contributed towards the evolution of suction in the core-sampled specimens of the lime-treated embankment. This has led to the long-term water retention capacity of the lime-treated soil. BJH was able to detect mesopore-formation (25–500 Å) under the lime effect in a more precise manner compared to MIP. The evolution of mesopores was found to be coincident with the development of strength and specific surface area of the lime-treated soil.

Instrumented load tests and layered elastic theory analysis of a large-scale EPS block embankment

This paper presents the behavioral results of a large-scale experimental EPS block embankment under different test and load conditions. The experimental embankment was designed and constructed to be similar to a road structure of flexible pavement and 22 kg/m3 EPS geofoam blocks supported by a soft soil subgrade. The experimental embankment was subjected to the Benkelman beam test and a load test using a 50,000 kg six-axle tractor semitrailer, and was instrumented with total pressure cells (TPC) to verify the vertical stresses propagated from the surface to the depth. Complementary analyses of both tests were performed by the layered elastic theory (LET). The results of the tests and analyses in the LET showed that using a correctly designed flexible pavement over the EPS blocks generates a structure with adequate performance. As well as in some previous studies, the elastic parameters determined in small samples of the EPS blocks tested in laboratory did not correspond to the behavior observed in field, where large blocks submitted to reduced deformations levels are employed. The conclusion was that LET can be used simply and conveniently as an adequate tool for pavement analysis with the presence of EPS blocks in its structure.

BOTTOM-ASH MIXTURE DEFORMATION PARAMETERS OBTAINED IN LABORATORY AND NATURAL CONDITIONS

In engineering geology and soil mechanics, there are dependencies that allow one to transfer from deformation parameters obtained in the laboratory conditions to that obtained in natural conditions and between parameters obtained during laboratory tests using different methods. These dependencies greatly simplify and facilitate research into the field. However, for bottom-ash mixtures, considered as man-made soil for the embankment construction, the construction of such dependencies has not been previously performed. The aim of this work is to obtain these dependencies and determine the modulus of deformation under triaxial compression, the elastic moduli determined in laboratory conditions on a lever press and experimental tray. The dependencies are also obtained using the plate test method on the experimental embankment and the California bearing ratio in a wide range of density and humidity.It is found that the transfer equations derived earlier for deformation parameters are not suitable for the bottom-ash mixes. Mathematical dependencies are then derived for the deformation parameters of these mixes in different conditions.TheOriginalityandpractical implicationsof this work is the derivation of new dependencies based on experimental data allowing to obtain desired values of these parameters for bottom-ash embankments with higher accuracy than achieved by other authors using mathematical calculations.

Development of Seismoacoustic Method of Quality Control of Placement of Rubble-Clayey Soils in a Dam Body

The results of combined geotechnical and geophysical studies of compacted rubble-clayey soil conducted on an experimental embankment for the purpose of developing a seismoacoustic method of quality control of the placement of this soil in a dam body are presented. Recommendations on determining the soil parameters being inspected are given.

Study on the Compaction Effect Factors of Lime-treated Loess Highway Embankments

This paper presents a study to investigate the effects of water content, lime content and compaction energy on the compaction characteristics of lime-treated loess highway embankments. Laboratory compaction tests were conducted to determine the maximum dry density and optimum water content of loess with different lime Contents (0, 3, 5 and 8%), and to examine the effects of water content, lime content and compaction energy on the value of and . In situ compaction tests were performed to obtain the in situ dry density and the degree of compaction of different lime-treated loess. Experimental embankments with different fill materials (0, 3, 5 and 8% lime treated loess) were compacted by different rollers during in situ tests. The results indicate that increases due to the increase of water content . Once water content exceeds , dry density decreases dramatically. The addition of lime induced the increase of and the decrease of . A higher compaction energy results in a higher value of and a lower value of . The value of achieves it’s maximum value when in situ water content was larger than the value of (+1-2%). The degree of compaction can hardly be achieved to 100% in the field construction of embankments. Higher water content and compaction energy is needed for optimum compaction.

Reducing Flood Risk using Computer System for Monitoring River Embankments

Abstract In order to learn about the phenomena occurring in flood embankment under the influence of external factors, including the increasing water level in the river during floods, a Computer System for Monitoring River Embankment (ISMOP) was developed using an experimental flood embankment. The project was carried out by a consortium consisting of AGH University of Science and Technology departments (Computer Science, Hydrogeology and Engineering Geology, Geoinformatics and Applied Computer Science and two companies (NEOSENTIO and SWECO Hydroprojekt Kraków) in co-operation with the Czernichów Community Council. An experimental flood embankment was built with two parallel sections with a length of 150 m and a height of 4.5 m, connected by a meandering, creating a reservoir that can be filled with water. For the construction of the embankment, different types of soils were used in all the five sections. Inside the flood embankment 1300 sensors are placed, including sensors for temperature, pore pressure, vertical displacements, as well as inclinometers. Also fiber optic strands, capable of measuring the temperature of the flood embankment on the upstream side, are located inside the experimental embankment [ismop.pl]. Together with the real experiments, numerical modelling using the Itasca Flac 2D 7.0 was performed in order to describe the impact of water pressing on the flood embankment and the impact of increasing and decreasing reservoir water level on the phenomena that occur within the embankment. The results of modelling compared with the real sensor data allowed the evaluation of the current and future state of the embankment. Based on the data measured by the sensors and data received during the numerical modelling, a group of algorithms that allowed detection of anomaly phenomena was developed.

Assessment of the methods for determining net radiation at different time-scales of meteorological variables

When modeling the soil/atmosphere interaction, it is of paramount importance to determine the net radiation flux. There are two common calculation methods for this purpose. Method 1 relies on use of air temperature, while Method 2 relies on use of both air and soil temperatures. Nowadays, there has been no consensus on the application of these two methods. In this study, the half-hourly data of solar radiation recorded at an experimental embankment are used to calculate the net radiation and long-wave radiation at different time-scales (half-hourly, hourly, and daily) using the two methods. The results show that, compared with Method 2 which has been widely adopted in agronomical, geotechnical and geo-environmental applications, Method 1 is more feasible for its simplicity and accuracy at shorter time-scale. Moreover, in case of longer time-scale, daily for instance, less variations of net radiation and long-wave radiation are obtained, suggesting that no detailed soil temperature variations can be obtained. In other words, shorter time-scales are preferred in determining net radiation flux.

Analysis of annual temperature distribution inside the experimental embankment

The aim of this paper is analysis of temperatures distribution inside experimental embankment from August 2015 to September 2016. Analysis was carried out in order to interpretation of the results of the flood experiments performed on the experimental embankment. The reference for year temperature changes in the embankment at various depths was obtained. A simplified model of temperature changes depending on the depth was made. The model parameters which can be used for modelling the temperatures in the embankment during the experiments were estimated.

Analysis of the filtration processes in soil embankment based on numerical modelling and temperature measurements

This paper presents analysis of the filtration processes in experimental soil embankment. The analysis is made during flooding experiments. The analysis is based on numerical modelling and temperature measurements. The measurements were performed on experimental embankment, which size is in scale 1:5 comparing to Polish typical river embankments. This experimental embankment was built in a frame of ISMOP project [1]. It was constructed by the NeoSentio company to investigate the influence of sensors installation for the filtration process and structure stability. The embankment was dry in the beginning of the experiment. The flooding and discharging process took about 8 hours. Filtration of water through the embankment caused changes of the inner temperature, which was measured by thermal sensors inside the embankment. Pore pressure sensors registered changes in water level in embankment. Furthermore, 2D numerical modelling in FLAC 7.0 software was performed. The model reflects the geometric and geotechnical attributes of the real embankment. Comparison between measured and modelled temperatures was performed. The model quite well predicts the time when water reach each sensor. But there is a difference in the rate of fall of water level. Modification the parameters of the model allows to fit the modelled data to measured values.

The determination of model dimension for an embankment to study soil atmosphere interaction with Finite Element Method

In order to study the interaction between soil and atmosphere, Hericourt experimental embankment was instrumented with different equipments for collecting the meteorological data, runoff, soil temperature and volumetric water content, etc. The corresponding water flux and heat flux boundary conditions of the Hydro-thermal coupled model of unsaturated soil can be calculated based on the energy and mass balance. However, in Finite Element Method, a suitable model dimension of experimental embankment needs to be set in advance, which will diminish the effect of bottom and lateral boundaries. Therefore, in this paper, four different dimension models are calculated respectively and compared in two cases with different boundary conditions. For Case 1, top water flux boundary condition is set as infiltration and evaporation happening on the soil surface alternately. In Case 2, top heat flux boundary condition is assumed based on daily solar radiation value. Comparing the results of four model dimensions, temperature and volumetric water content distributions in four dimensions lead nearly consistent results. Therefore, with consideration of computational time and accuracy, dimension 2 or 3 is suggested for Hydro-thermal study of Hericourt embankment case.

Suction controlled drying and wetting cycle effects on the volumetric behaviour of a lime-treated high plasticity clay

The paper presents some experimental results collected on samples recovered from an experimental embankment obtained by compacting a lime-treated clay. Samples were collected soon after the in situ compaction and they were cured in controlled environmental conditions for at least 18 months. Mercury intrusion porosimetry tests (MIP) were carried out on freeze-dried specimens to characterize the microstructure of the material. In order to assess the durability of the improved material, laboratory tests focused on the effects of cyclic variations of the degree of saturation on the water retention properties and the volumetric behaviour of the stabilized clay. Collected results show that the lime-treated clay undergoes an almost irreversible volumetric behaviour; this irreversible contraction is associated to severe drying processes, while wetting paths do not produce significant volumetric deformations.

Slope Stability Assessment and Evaluation of Remedial Measures Using Limit Equilibrium and Finite Element Approaches

Slope stability is a recurrent theme amongst all branches of civil engineering and is of major significance on large scale infrastructure projects such as highways, railways or canals, where having more cost effective designs becomes a crucial drive on any scheme. The aim of this paper is to numerically back-analyse the stability of an existing experimental embankment built under the supervision of PhD students at UBI, making use of one of the region's most abundant resource, its granitic residual soil, very commonly used in road schemes. This is part of an on-going study of this natural resource, which has begun by undertaking a laboratory geotechnical characterisation of the granitic residual soil in question.To better understand the potential of the residual soil, this paper is primarily focused on the determination of the Margins of Safety using different calculation methods (LEM and FEM), to allow for an expedite assessment of the stability of granitic residual soil slopes, for different soil properties, geometries, applied loads and groundwater conditions. Additionally, this paper also tries to quantify the merits of some of the most common remediation techniques, drawing a comparison between their effectiveness. However, the remedial options discussed and analysed should be perceived as concept ideas as their gain in terms of MoS will likely vary from case to case. Furthermore, the benefits of combining the effects of more than one remedial options has been excluded from this study.The parametric study has made use of one LEM based software (SLOPE/W) and one FEM based software (PLAXIS 2D), which have allowed for some conclusions to be drawn for each set of conditions, in particular due to changes in groundwater levels and applied surcharges at the crest.

Comparison of Soil Water Retention Curves for sandy clay, obtained using different laboratory testing methods

The design of engineering structures is still a challenging task when considering unsaturated soil mechanics behaviour. The present paper focuses on analysing Soil Water Retention Curves (SWRC) for clayey soil samples collected from a purpose built experimental embankment. SWRC determination is crucial when analysing geotechnical parameters of the soil. During the measurements, soil samples were subjected to wetting and drying cycles using a stage procedure (where the process is carried out in stages to allow equalisation) and continuous processes. The methods used for obtaining the suction curves were high suction tensiometer, attached at the bottom of the sample, and pressure plates with suctions applied up to 800 kPa. The study compares laboratory methods on measuring suction for sandy clay samples. It proves that the wetting and drying history have an impact on the hydraulic behaviour of tested material. In order to give a wider picture of soil behaviour it also presents the outputs as a function of matric suction and volumetric and gravimetric water content, and degree of saturation.

Evaluation of empirical methods for estimating potential evaporation values in northeast France

This study presents and discusses the field monitoring of an experimental embankment divided into two symmetrical sections constructed with two different fine-grained soils in the northeast of France. The field instrumentation included detailed monitoring of volumetric water content, matric suction and temperature within the embankment as well as measurements of meteorological data. The field measurements show that the used instrumentation worked well on monitoring the soil responses to the meteorological changes in the two soils. The study also evaluates different empirical methods for estimating potential evaporation (ET) values based on regional meteorological data. The results show a large variability observed on the ET values for the investigated site calculated by empirical methods or equations based on meteorological local date.

Thermal stabilization of duct-ventilated railway embankments in permafrost regions using ripped-rock revetment

Duct-ventilated railway embankment (DVE) is relatively effective at preserving underlying permafrost under the current climatic conditions. To increase its capacity to adapt to climate warming, a ripped-rock revetment was added to the DVE. To evaluate the effectiveness in cooling of different embankment treatments, long-term in-situ soil temperature data were collected from eight experimental embankment sections along the Qinghai–Xizang Railway in the Beiluhe region between 2002 and 2012. Analysis of these soil temperatures shows that the addition of the ripped-rock revetment is effective in improving the cooling capacity of the DVE, enhancing the thermal stability of both the embankment body and the underlying permafrost. Soil temperature in the overall embankment decreases about 0.5–1.0°C, the temperature of the underlying permafrost decrease, the artificial permafrost table is further raised, and average range for cooling effect gets further enlarged under the joint effect of ventilated ducts and ripped-rock revetment. What is more, this cooling effect of embankments with low-positioned ducts is greater than that with high-positioned ducts. Besides, cooling effect is greater for ducts with a diameter of 30cm coupled with ripped-rock revetment than that of 40cm. Another positive outcome of this reinforcement is the greater restriction in the temperature difference between the sunny and shady embankment shoulders, especially for the embankments with low-positioned ducts or with a diameter of 30cm. Therefore, implementation of ripped-rock revetment is recommended for duct-ventilated embankments, particularly for embankments where high-positioned ducts are present.

Experimental Investigation of Soil-Atmosphere Interaction in an Instrumented Embankment Constructed with Two Treated Clays

This paper discusses the field monitoring of an experimental embankment divided into two symmetrical instrumented sections constructed with two clays treated with lime and/or cement in the northeast of France. The soil-atmosphere interaction is investigated in the monitored embankment. The field instrumentation included spatial and temporal changes of the soil suction, moisture, and temperature at predefined locations within the embankment, as well as measurements of meteorological data, collected from April to November 2011. The data show similarities in the suction daily variations trend in the two treated clays. Maximum changes in suction occur near ground surface. Even at the location of -0.75 m from the slope face the interchange of water between the atmosphere and the ground was observed in the daily soil suction measurements. No significant hydrologic response of the soils to rainfall was observed during the period of water deficit. The rainfall events showed a significant effect on the soil suction changes in the initial period of water surplus after a long period of water deficit. The comparison of the period of water deficit observed in the responses of the mean monthly suction and moisture measurements in the treated soils and the one estimated by simple water balance models based on standard meteorological observations in the region indicate that there is an overall qualitative agreement between the modelling and observational results.

Evolution of the properties of lime-treated silty soil in a small experimental embankment

In order to study the evolution of a lime-treated silty soil under in-situ conditions of mixing, laying out, compaction and environment, an experimental dike was built near Rouen, in northwest France; this dike is 25m long, 4m wide at the crest and 1.8m high. While special care was taken to mix the soil and lime very thoroughly, to precisely measure the quantity of water, to compact the soil using a vibrating sheepsfoot roller, the building conditions were those usually used to construct embankments in all other respects. Samples were taken from the dike approximately 1month, 6months and 12months after the completion of the work and underwent triaxial and oedometric testing. To compare the properties of treated soil with those of untreated soil, another smaller “reference” embankment was built nearby under similar conditions with silty soil.Small-strain triaxial tests were performed on unsaturated specimens of treated and untreated soil using an original strain measurement device. The change in axial secant moduli can be described by a power law E=βσ1m, where β is a parameter that depends on curing time and m is nearly constant (m≈0.45).CU and CD large-strain triaxial tests carried out on saturated treated and untreated specimens, consolidated under confining stresses ranging from 10 to 300kPa, showed a definite increase in cohesion as a function of curing time, with nearly unchanged friction angles. The possibility to use a non-linear failure criterion was examined. The compressibility coefficient Ciso, slope of the critical state line (CSL) in the [log(p′), e] coordinate system, is significantly lower in treated than untreated specimens, but its value remains constant whatever the curing time. At the same time, the CSL of the treated specimens is above that of the untreated silt. The brittleness of the material, derived from the peak to residual deviator stress ratio qpeak/qres is the same for treated and untreated specimens and is independent of curing time and confining stress. However, the axial strain corresponding to the peak of CD curves is much higher in untreated than in treated specimens. The permeability of the saturated lime-treated soil (10−9m/s) is the same as that of the untreated soil. The value measured one month after the embankment was constructed, does not change with time or with the confining stress. The results of the present study confirm those of previous studies on laboratory-prepared unsaturated specimens: they have demonstrated the effectiveness of lime-treatment in the much more difficult environment of a real working site and shown that lime-treated samples present a significant gain in their engineering properties, even when saturated, provided that the dosage of lime and water, mixing and compaction conditions are carefully controlled. The new material thus obtained presents lower plasticity, improved workability, increased stiffness and cohesion without any loss of performance in terms of brittleness or permeability.