Earth Embankments Research Articles

Numerical analysis of earth embankments in liquefiable soil and ground improvement mitigation

The security and stability of soil structures is seriously affected by earthquake-induced liquefaction, and many earth embankments located in seismically active areas failed to meet the new seismic design code criteria, introduced following the 2011 off the Pacific coast of Tohoku Earthquake. This paper proposes an appropriate in-situ countermeasure, and the seismic performance of the liquefaction mitigation method by grouting is numerically evaluated. The elastoplastic constitutive model of cyclic mobility (CM) model can present the cyclic shearing and liquefaction properties of cohesionless sand and cohesive clay in embankments, by considering stress-induced anisotropy, over-consolidation, and soil structure. A numerical investigation, based on the water-soil coupled finite element and finite difference (FE-FD) methods is conducted to explain the dynamic behavior of embankment in fully saturated sandy deposits, during an earthquake, and long-term post-consolidation in a consistent manner. Special emphasis is placed on the growth of excess pore water pressure (EPWP), acceleration response, and ground deformation (settlement and lateral spreading) in liquefiable soil during earthquake and post-earthquake consolidation (approximately 50 years). A comparative analysis demonstrates that the implemented countermeasure is effective in reducing co-seismic and post-seismic liquefaction-induced deformation, regardless of whether the top sandy layer on both sides of the embankment is completely liquified during the earthquake loading. However, there is local failure on the embankment slope instead of deep-seated failure in the embankment-soil system when grouting the saturated sandy layer, and appropriate countermeasures should be adopted to protect the slope. Furthermore, the ground strengthening effect is not apparent when the reinforcement thickness exceeds 6 m.

Model Test Study on Dynamic Response of Expressway Plastic-Reinforced Earth Embankment under Earthquake

Aiming at the seismic response of plastic geogrid-reinforced embankments, with Zhounan Expressway as the research engineering background, a self-designed seismic-rainfall coupled slope model test system was designed and used to produce 1 : 20 scale plastic geogrid-reinforced embankments. Moreover, the physical model of the unreinforced embankment under Hanshin wave, Wenchuan wave, Tianjin wave, etc. was also studied to carry out comparative analysis on seismic response and dynamic response on test model. The dynamic characteristics and dynamic response of the embankment model were tested from low to high seismic intensity; the changes of the embankment’s natural frequency, damping ratio, acceleration at the measuring point, and dynamic earth pressure were analyzed; and the main influencing factors and damage to the embankment seismic response feature were discussed herein. The test results showed that the initial natural frequency of the reinforced embankment was 42.4% higher than that of the unreinforced embankment, and its initial damping ratio reduced by 19.4%. The attenuation effect of the natural frequency and damping ratio of the reinforced embankment with the loading history was significantly lower than that of the unreinforced embankment. Embankment reinforcement exhibited a very good inhibitory effect on the PGA amplification effect of the embankment, and the inhibitory effect on the interior of the slope was more significant than that on the slope. Moreover, the type of seismic wave, the amplitude of the seismic wave, and the frequency of the seismic wave significantly influenced the PGA amplification effect of the embankment. The peak dynamic soil pressure of the unreinforced embankment at the same location was significantly greater than that of the reinforced embankment. The two embankment models showed significantly different antivibration damage performance. After the peak acceleration of 2 m s-2 was loaded, no cracks were seen on the surface of the embankment model. When the peak acceleration of 3 m s-2 was loaded, on the slopes of the two embankment models, smaller cracks were observed in the middle and upper parts of the face. When the peak acceleration of 4 m s-2 was loaded, the failure of the unreinforced embankment model was obvious. Large cracks on the top of the slope could reach 16 mm in width, and 27 mm settlement appeared at the top, and the slope was convex. The reinforced embankment model was only on the slope shoulder. Moreover, there were fine cracks on the top, and the slope top settlement was less than 5 mm. The research results provide theoretical support for preventing and controlling the road embankment vibration diseases and improving highway durability design.

Influence of height of earth embankment type windbreak wall on flow field characteristics and catenary wind-induced displacement

This paper aims at ensuring the safety of catenary operation, by considering the flow field characteristics of the specific railway terrain and the wind-induced dispalcement of the catanery contact wires. Combining fluid and structure analyses, the improved delayed detached eddy simulation (IDDES) method based on the κ-ω turbulence model was used to explore the flow field characteristics at the position of the contact wire area before and after the windbreak wall was increased. The finite element analysis method was used to study the wind-induced displacement, and the relationship between the raising height, the wind speed, and the displacement was comprehensively analyzed. The simulation results were verified by field tests. The results showed that after the rasising height was increased by 1 m, the horizontal wind speeds at the contact wire positions above two railway lines were reduced by 94.26% and 95.60%, respectively. With the decrease in the horizontal wind speed, the value of the wind-induced displacement in lateral direction was significantly reduced as well. Moreover, the response of the wind speed on the midpoint was more sensitive than that at the hanging point.

Utilization of Energy By-Products for Ground Structures in Terms of Production Process

The article deals with the utilization of energy by-product (EBP) for further processing. The suitability of EBP for ground structures significantly depends on its production process. Its properties are influenced by brown coal flotation and by the usage of desulphurization methods. A comparison of physical-mechanical properties of different types of EBPs was performed. The main goal was to compile an apparent table of utilization and suitability of EBP for ground structures - road earth bodies, dams, and embankments according to the process of their formation.

Experimental investigation on hole erosion behaviors of chemical stabilizer treated soil

Soil erosion plays a vital role in the performance of hydraulic projections such as earth dams and embankments. To improve the erosion resistance of the soil is crucial for preventing the dam break and assuring the safety of the hydraulic projections. In this study, three chemical stabilizers, i.e., sodium silicate (SS) solution, lignosulfonate (LS) powder, and sodium polyacrylate (PAANa), are used to treat the sandy soil. A set of hole erosion tests to investigate the erosion behaviors in treated and untreated specimens. The experiments collect flux and the mass of eroded particles during the erosion process. These data then yield the relations between hydraulic shear stress and erosion rate. Erosion coefficients, i.e., the critical shear stress (CSS), and the erosion rate index (ERI), are acquired from linearly fitted relation curves between the hydraulic shear stress and the erosion rate. During the erosion experiments, we observe that the erosion continues in untreated specimens and leads to the collapse of the specimens if the experiment is not stopped. On the other hand, erosion in treated specimens stops automatically after a long erosion time, even if the hydraulic gradient is maintained. These results indicate that the stabilizers improve the anti-erosion capability of the soil specimen. The improvement becomes significantly noticeable if the stabilizer content and the curing time increase. Among the three stabilizers tested in the experiments, PAANa performs best in treating the sandy soil since the rate of increase in CSS and ERI reaches 214.4% and 85.4%, respectively, when 1.5% PAANa is added into the specimen. The rates of increase in CSS and ERI are 23.2% and 43.8%, respectively, for the specimens treated with lignosulfonate, given the same other conditions. Based on the results, the choice of the stabilizer is discussed and suggested.

Безопасность шламонакопителей и отстойников с вредными промышленными стоками

To reduce the risk of toxic substances ingression into the soil, ground and surface waters, it is proposed to protect the bed and slope ramps of the earth embankment for sludge collectors (sediment tanks) with reliable waterproofing – soil-concrete. It has been recommended to perform the screen soil compacted layers inclined towards the tail bay at an angle to the structure base surface, what is more, the angle value is determined by the permissible values of filtration flow’s parameters. The proposed technical solution allows increase the reliability of sludge collectors, as well as minimize the risk of an emergency situation as a result of the ingression of toxic effluents into the soil and water.

Mathematical modelling of the mechanical response of earth embankments on piled foundations

Piled foundations are largely employed as settlement reducers in the design of artificial embankments on soft soil strata. The commonly employed design methods are, however, based on simplified approaches not allowing the assessment of average and differential settlements at the top of the embankment. With this objective, the authors introduce a generalised constitutive relationship capable of accounting for irreversibilities stemming from both geometrical evolution and soil yielding. The model derives from the interpretation of the results of a campaign of three-dimensional elastic–plastic finite-difference numerical analyses describing the embankment construction process. Numerous simplifying assumptions (for instance smooth pile shaft, drained conditions) have been employed. Nevertheless, this does not compromise the theoretical value of the proposed approach. From a practical point of view, this model is a useful tool for geotechnical engineers to employ with a displacement-based design perspective.

Damflask reservoir: scour system reservoir safety improvements

Designed by Thomas Hawksley, and completed in 1896, Damflask reservoir was constructed to provide compensation flows to the growing industries downstream in Sheffield. The earth embankment dam incorporates two modified bottom outlets used to release water from the reservoir, each comprising sections of tunnel and pipework together with a series of guard and control valves, to form the reservoir scour system. In 2015, a statutory inspection recommended that improvements were made to comply with modern safety standards and enable the reservoir to be drawn down in a reasonable time, if required in an emergency. This paper provides a brief background to the works at Damflask reservoir and summarises the key technical challenges, which were overcome to improve the existing drawdown facilities; from design development through to construction, commissioning and ongoing operation of the final scheme. It provides an insight into the complex two-year project from the author's perspective as project leader and designer, within the design and build team, commissioned to investigate and undertake the upgrade works.

Three-dimensional modelling at Clays Lake

This paper looks at the three-dimensional (3D) modelling and the benefits and drawbacks that it has, along with how it has been used on the Clays Lake flood storage reservoir and how it was used to improve the efficiency on-site. Clays Lake is one of three flood storage reservoirs on the Upper Mole, which comply with the requirements of the Reservoirs Act 1975, providing flood protection to Crawley town and Gatwick Airport. The reservoir was constructed on behalf of the Environment Agency and was completed in 2019, along with the issue of the preliminary certificate. The dam is formed of a 12 m high earth embankment with a crest length of 120 m. The reservoir has a storage capacity of 385 000 m3 above the permanent lake level. The flow is controlled by an orifice within the main penstock situated at the inlet structure. The main penstock can be opened to release flow more quickly if required. The outlet culvert is 1.8 m in diameter and has fish brushes installed along the invert to aid with fish passage. The downstream embankment slope contains a grasscrete spillway which is overtopped in a one in 1000 year event.

Target reliability indices for long geotechnical embankment slopes

The target reliability indices of earth embankment slopes were investigated using a proposed segmentation-based method. First, an embankment is equally segmented into multiple embankment sections. The total number of sections is determined based on the potential number of discrete failures along the embankment. Then, for two types of engineering embankment, the series system and the k-out-of-n system are used to model the relationship between section reliability and embankment system reliability. Finally, section target reliability indices are derived based on two embankment reliability requirements, which are described by the design failure ratio (the ratio of the allowed section failure number to the total section number) and system target reliability index. The results indicate that the total embankment length and soil variability significantly affect the section target reliability index, and different section target reliability indices may be required for different embankment projects. These effects were appropriately incorporated into the derivation of a section target reliability index in this work, and design charts are provided. Compared with the series system model, where no section failure is allowed, the k-out-of-n system model can provide more-economical design plans by accepting a small design failure ratio.

Effects of subterranean termite nest architectures on earth embankment seepage and stability

Subterranean termites (Odontotermes formosanus Shiraki) that build nests in the soil matrices of earth embankments may adversely affect the stability of these structures in paddy farming regions of southern China. An adult termite nest comprises a primary chamber, fungus gardens, passageways, and other shelter tubes. These porous architectures enable high hydraulic conductivity and rapid groundwater flow. In this study, we performed a field survey to characterize these termite nest architectures and proposed a simulation method that estimates seepage and associated stability in termite-infested earth embankments. Three types of nest architectures—straight, siphon, and string—were investigated in situ. Groundwater flow and its relationship with earth embankment stability were analyzed using a numerical model based on the two-dimensional Richards equation in the HYDRUS software package. Results indicated that the presence of termite nests affected seepage zone geometry and substantially affected its phreatic line, seepage flux, and global and local stabilities of the earth embankment. In the cases examined here, the presence of termite nests resulted in a maximum factor of safety reduction of 17% along the downstream slope. The local instability zones of earth embankment, resulting from clogged termite nest passageways along the downstream slope, were also assessed.

Analysis of the suction evolution during direct shear test in a silty sand soil

Shear strength of soils is one of the essential parameters for analysing and solving divers geotechnical problems (e.g. the bearing capacity of shallow footings pile foundations, slope stability and earth embankments). In this study, a series of conventional large-scale (300 X 300 mm) direct shear tests were carried out on saturated and constant water content silty sand specimens at ei = 0.6 and 1.0 tested under applied vertical stresses of 100, 200, or 400 kPa to investigate the influence of matric suction on the shear strength characteristics of the tested material. A loading steel cap was modified to allow the direct measurements of the matric suction using two commercial available Equitensiometer suction probes (EQ3). The experimental program indicated that, for both studied void ratios, the obtained shear strength of specimens under constant water content is found to be distinctly greater than those obtained from saturated samples. The results showed that the samples compacted at ei = 1.0 exhibited collapse behaviour during saturation stage, whereas same samples did not show any volume change during stabilisation stage when tested under constant water content condition. The study results also showed that the matric suction reduction during consolidation stage depends on initial void ratio of the tested samples as well as the level of applied vertical stress. Moreover, the matric suction evolution during shearing process of both studied void ratios specimens decreased with increasing the level of applied vertical stress.

Structural mitigation measures for flood reduction in urban area: A case study of Ciliwung watershed

Flooding is an obstacle for water infrastructure which installed in a river system in Ciliwung, West Java, Indonesia. The climate change triggers unpredictable rainfall which occurs in the watershed, therefore the vulnerability of river and other infrastructures are alarming. The rehabilitation and maintenance strategies are needed to make water infrastructures in the river system obtain lower damage. The research aims to simulate the 2-D HEC-RAS modelling of river system and stability. The result produces the water level of the river even in 1000-year discharge flood. Also, the research proposes the earth embankment dam for flood reduction in the watershed. The dam is designed according to the ideal condition. The simulation of HEC-RAS shows that the river experiences flooding in a certain condition. Besides, the research concludes that designed dam could overcome the flooding problem and suitable strategy for water infrastructure maintenance towards flooding impacts. Further investigation towards soil data for designed dam should be further analyzed to obtain better and comprehensive understanding.

War time damage at two London reservoirs

It is perhaps inevitable that major infrastructure installations become a target during wartime. While the ‘Dambusters raid’ was perhaps the most notable example of the Second World War, damage was also inflicted on a number of British dams during that conflict. The paper describes the experiences at two London water supply reservoirs, the Queen Mary, a large earth embankment storage reservoir and Honor Oak, a brick-arched roof service reservoir. The extent of the damage inflicted is described along with the emergency remedial works undertaken at the time as well as the longer term consequences.

Evaluation of induced trench twin culverts constructed in deep fill

When culverts are installed beneath high embankments, earth loads become excessive and the induced trench construction method is a viable design option to reduce the culvert loads to acceptable levels. However, limited field studies evaluating the performance of induced trench twin culverts are reported in the literature and the practicality and effectiveness of the induced trench construction method (in general) has been subject to recent criticism. This paper describes the performance of twin 3048 mm inside-diameter reinforced concrete culverts constructed with an induced trench beneath 15.3 m of fill. Research instruments and autonomous data acquisition systems were installed during construction to monitor (i) culvert earth pressures, (ii) embankment deformations, and (iii) groundwater elevations in the vicinity of the compressible fill. The experimental observations recorded throughout the construction phase are presented herein; the embankment deformations are indicative of effective positive arching within the induced trench region, and the average earth pressure at the culvert crown was reduced to approximately 48% of the overburden soil pressure. The experimental data are compared with those reported in the literature by others, and the conclusions attained from this study demonstrate the effectiveness of the induced trench construction method.

Runoff Harvesting Site Suitability Analysis for Wildlife in Sub-Desert Regions

Site selection for runoff harvesting at large scales is a very complex task. It requires inclusion and spatial analysis of a multitude of accurately measured parameters in a time-efficient manner. Compared with direct measurements of runoff, which is time consuming and costly, a combination of a Geographic Information System (GIS) and multi-criteria techniques have proven feasible to address this challenge. Although the accuracy of this new approach is lower than the direct method, conducting in-situ measurements over large scales is not feasible due to its financial issues, a lack of sufficient human resources, and time limitations. To achieve this purpose, climatic, topographic, and soil parameters were used to estimate a runoff coefficient and volume for a single event with the 33%-exceedance probability of maximum daily rainfall in the Kavir National Park of Iran. The main challenges ahead of this research have been a) the large area of the park and the inability to directly evaluate site suitability for runoff harvesting, b) the need for a quick and reliable site evaluation to implement water harvesting measures to address water scarcity, and c) the lack of discharge volume data from water streams (as there are no permanent water streams in the site) and the necessity of reliably estimating runoff in different parts of the park to design water harvesting structures which have been addressed by using GIS and a rainfall-runoff model (Soil Conservation Service Curve Number (SCS-CN)). Site suitability was evaluated for the natural territory of two important wildlife species of the park, namely Gazella dorcas and Ovis orientalis, as the main important food sources of an endangered species named Acinonyx jubatus, commonly known as Persian Cheetah. Saving Persian Cheetah from extinction is currently the top priority for the park managers, which is the main factor behind the species chosen for this research. The Analytic Hierarchical Process (AHP) and fuzzy membership functions were employed to assign weights and standardized thematic layers, respectively. The layers were then integrated using the weighted linear combination method (WLC) to obtain the final suitability map. Accordingly, 38% of the area (846 km2) is suitable or highly suitable for runoff harvesting, while 62% (2623 km2) has a very low potential for this purpose. Afterward, 11 suitable locations were identified to collect runoff. The results indicated that suitable catchments are mainly located on the southern slopes of the Mount Siahkouh as the only major elevation in the area. The storage capacity of the earth embankment in each catchment was estimated based on the upstream area of the catchment and runoff volume. Based on the population of the intended wildlife species and their average water requirement, there is a need for 6500 m3 of drinking water annually. In the best-case scenario and under the circumstance of receiving five rainstorm events a year, only 257 m3 is collectible from all runoff harvesting structures, which is only 4% of the total water demand.

Effect of haunch on the stresses of box culvert

Culverts are often required under earth embankment to allow for the crossing of a watercourse, like streams, to prevent the road embankment from obstructing the natural waterway. The opening of the culvert is determined based on the waterway required to accommodate the design flood, whereas the thickness of the culvert section is designed based on the loads applied to the culvert. From the previous literature review, it is noted that the effect of haunch on the stresses of the culvert was not studied. Therefore, this research focuses on the impact of using haunches on the economy of the culvert design. This paper studies some design parameters of box culverts, such as the thickness of the haunch, the coefficient of earth pressure, the thickness of box culvert, and depth of fill on the top slab. The objectives show the effect of haunch on the stresses of the box culvert. The study investigated the variation in stresses and the cost comparison made for different width of the box culvert. The percentage reduction in the cost of culvert based on the presence of haunch is presented. At last, several significant conclusions are given based on numerical results as the presence of haunch is the best solution for decreasing the values of stresses from the economic point of view.

Critical state of compacted lateritic soil and palm kernel shell ash for earth embankments

For most treated soils in compacted form for earth embankments, interest had been limited to the maximum stresses they can sustain before failure. This work studied the stress–strain behaviour of a compacted lateritic soil treated with palm kernel shell ash (PKSA) from 0 to 18% at 3% intervals, with a major focus on the critical-state characteristics (beyond the maximum stresses). The lateritic soil was characterised as A-2-6(0) in the American Association of State Highway and Transportation Officials rating and clayey sand (SC) in the Unified Soil Classification System. The PKSA was found to be pozzolanic. The British Standard light energy level of compaction and drained shear test were carried out on the treated soil. The optimum moisture content increased while the maximum dry density reduced with an increase in PKSA content. The PKSA of 0–18% content by weight of the dry soil improved the strength properties of the lateritic soil by 51·43%. The critical-state parameters (λ, Γ and M) of the soil mixtures were found to be in conformity with the usual range for untreated soils.

Numerical Simulation of Flow around a High-Speed Train Subjected to Different Windbreak Walls and Yaw Angles

The prediction of flow around a high-speed train subjected to different windbreak walls and yaw angles has been investigated using steady Shear Stress Transport (SST) k-ω turbulence model at the Reynolds number of 1.0×106 based on the height of the scaled train model. The results show that an effective windbreak wall provide a favourable shielding effect for the train behind it, and force the primary positive pressure on the windward of the train to transfer on the wall. Consequently, the airflow cannot directly act on the train body, and the train is basically in an environment with small negative pressure. The inclined slope (the earth embankment type) windbreak wall shows poor anti-wind performance that should not be used along the new high-speed railways. When designing the windbreak wall, the influences of yaw angles should be taken into account.

Estimating the friction angle of black shale core specimens with hybrid-ANN approaches

Shear strength parameters of rock play a significant role in the design stage of various geotechnical structures such as earth dams, embankments, foundations and tunnels. The direct determination of these parameters in laboratory is time consuming and expensive. Additionally, preparing core specimens with a good-quality is sometimes difficult, especially in weathered and highly fractured rocks. This paper presents an indirect determination of internal friction angle of shale rock specimens through two hybrid neural net based models that combine artificial neural net with genetic algorithm (GA-ANN) and imperialist competitive algorithm (ICA-ANN). In fact, GA and ICA were utilized to improve the efficiency of ANN predictive model via the weights and biases adjustment. To achieve this aim, an extensive experimental program was designed, according to which a series of black shale specimens were characterized using various laboratory tests, including p-wave velocity, Schmidt hammer, point load and triaxial compression. After establishing a proper database for the analysis, simple and multiple regression as well as hybrid intelligent models were developed to predict the internal friction angle of the shale specimens. To compare the obtained results from the models, several performance statistical indices were computed. The results indicated that simple and multiple regression models are not good enough in predicting the internal friction angles. Concluding remark is that the proposed intelligent models are superior in comparison with simple and multiple regression models. Using the coefficient of determination as performance measure, the quality of the developed GA-ANN model was evaluated as 0.917 and 0.909 for training and testing datasets, respectively whereas these values were achieved as 0.960 and 0.956 for the ICA-ANN model. This means that the ICA-ANN model can provide higher performance capacity in estimating the internal friction angles as compared to the GA-ANN. In addition, the results of other performance indices, i.e. variance account for and root mean square error confirmed that the hybrid ICA-ANN predictive model can be introduced as a new technique for predicting the internal friction angle of shale rock specimens in practice.