River Dikes Research Articles

Seismic Performance of a River Dike Improved by Sand Compaction Piles

Sand compaction piling is one of the commonly used countermeasures for earthquake liquefaction hazard of river dikes. This paper presents a case study of the performance of an instrumented dike in northeast Japan that was improved by sand compaction piles and subjected to the 2003 Northern Miyagi Earthquake, with the aim to better understand the effectiveness of this ground improvement method. Simulation has been carried out by means of a fully coupled numerical procedure which employs a sophisticated cyclic elastoplastic constitutive model and the updated Lagrangian algorithm. Comparisons between the field measurements and the computed responses, including the time histories of accelerations and pore-water pressures at different locations, show reasonably good agreement. Numerical simulation has also been made of the same dike but without ground improvement to identify the effects of sand compaction piles in altering the performance of the dike. The study demonstrates that the comprehensive numerical procedure is a promising tool for development of seismic performance-based design of earth structures.

Influence of dike breaches on flood frequency estimation

Many river floodplains and their assets are protected by dikes. In case of extreme flood events, dikes may breach and floodwater may spill over into the dike hinterland. Depending on the specific situation, e.g. time and location of breach, and the capacity of the hinterland to contain the floodwater, dike breaches may lead to significant reductions of flood peaks downstream of breach locations. However, the influence of dike breaches on flood frequency distributions along rivers has not been systematically analysed. In order to quantify this influence, a dynamic–probabilistic model is developed. This model combines simplified flood process modules in a Monte Carlo framework. The simplifications allow for the simulation of a large number of different scenarios, taking into account the main physical processes. By using a Monte Carlo approach, frequency distributions can be derived from the simulations. In this way, process understanding and the characteristics of the river–dike–floodplain system are included in the derivation of flood frequency statements. The dynamic–probabilistic model is applied to the Lower Rhine in Germany and compared to the usually used flood frequency analysis. For extreme floods, the model simulates significant retention effects due to dike breaches, which lead to significant modifications of the flood frequency curve downstream of breach locations. The resulting probabilistic statements are much more realistic than those of the flood frequency approach, since the dynamic–probabilistic model incorporates an important flood process, i.e. dike breaching, that only occurs when a certain threshold is reached. Beyond this point, the behaviour of the flood frequency curve is dominated by this process.

Local Failures of Embankments During Earthquakes

Seismic damage to embankments has sometimes been found to take place at locally-limited spots even though the foundation conditions are almost the same along their axes. A few studies related to this kind of local failure have been conducted, however the reason why local failures of embankments take place is not known. This paper aims to study the influence of the three-dimensional response of embankments on their local failures. A series of shaking table tests were conducted. Test results revealed that local failures occurred despite the fact that the model base was shaken uniformly. It was also found that the interval of local failures depends on the frequency of input motion and the stiffness of the embankments. Thus, an equation to calculate the intervals of local failures was derived, and this was found to agree well with the seismic damage to the Kushiro River Dike.

Liquefaction Analysis of River Dike by Distinct Element Method

Liquefaction Analysis of River Dike by Distinct Element Method

Numerical assessment of the effect of reinforcement on the performance of reinforced soil dikes

A reinforced soil dike with geogrids and metallic bar mats has been proposed as a new construction method to satisfy the environmental conservation of rivers. With this method, it is possible to not only reduce construction period and cost, but also retain or reestablish native vegetation as much as possible on the dike slope. The behavior of the reinforced soil dike, however, has not been investigated extensively. An assessment is therefore needed of the effectiveness of various reinforcement designs for the river dike with geogrids and metallic bar mats. In this paper, the background and objective of this study are first outlined. Then, a numerical method and the analysis procedure are briefly described. Based on a full-scale test, the method is used to examine the effectiveness of proposed reinforcement strategies for a soil river dike. The numerical series include: (1) an unreinforced case, (2) use of metallic bar mats, (3) use of geogrids, and (4) use of both geogrids and metallic bar mats. Analyses are carried out using an elastoplastic finite element method, in which the behavior of sands is described by means of an elastoplastic constitutive model previously developed within the framework of the Matsuoka–Nakai failure criterion. Finally, the effectiveness of the reinforcement for the soil river dike is discussed based on the numerical results.

The effect of dike geometry on different resistivity configurations

Geoelectrical profiling with multi-electrode systems has become an important tool for monitoring dike embankments bordering rivers. Profiles running perpendicular to the dike axis are affected by the dike topography, with the amplitude of this effect dependent on the surface geometry and the choice of the electrode configuration. Investigations using seven different electrode configurations have shown that some configurations are less sensitive to the topography than others. The topography correction method (TCM) is an important tool for processing data from measurements at river dikes. This method is generally recommended for flank angles steeper than 10°. The topography effect is calculated by two-dimensional finite element modelling. The resulting synthetic data of a homogeneous dike body are used to apply a topographic correction for each measurement. The topographic effect and correction procedure is demonstrated for synthetic dike data and for a data set from a river dike in Thai Binh province (Vietnam). The topography can be ignored for flank angles less than 25° if an averaged Half-Wenner electrode configuration is used. This configuration has proved to be less affected by undulated topography and the focusing effect of averaging the two data sets provides reliable structural information without the need for time-consuming data inversion.

Multi‐electrode measurements at Thai Binh dikes (Vietnam)

ABSTRACTThe province of Thai Binh is located in the delta of the Red River in Vietnam where an extensive system of river and sea dikes protects the population and infrastructure from flooding in the rainy season. The integrity of the river dikes is affected by a diversity of problems. Importantly, various termite species dig their nests in the dikes causing water leakage. Leakage can also occur near sluices and passages.Geoelectrical multi‐electrode profiling has been applied to locate defects in the dikes. Surveys carried out on several dikes demonstrated that a combined half‐Wenner configuration yields high‐resolution images in which termite nests are indicated by resistive anomalies. Petrophysical investigations of soil samples and density logs yield additional information on the dike material. Elsewhere, imaging surveys confirmed the subsurface extent of a buried sluice structure in the dike body.

Distribution, phenology and demography of sympatric sexual and asexual dandelions (Taraxacum officinale s.l.): geographic parthenogenesis on a small scale

In many plant and animal species, sexual and asexual forms have different geographical distributions (‘geographic parthenogenesis’). The common dandelion Taraxacum officinale s.l.provides a particularly clear example of differing distributions: diploid sexuals are restricted to southern and central Europe, while triploid asexuals occur across Europe. To get a better understanding of the factors underlying this pattern, we studied the distribution and demography of sexuals and asexuals in a mixed population that was located at the northern distribution limit of the sexuals. In this population three adjacent, contrasting microhabitats were found: a foreland and south and north slopes of a river dike. Comparative analyses of the distribution, phenology and demography indicated that sexuals had a stronger preference for the south slope than did asexuals. We therefore propose that the large-scale geographic parthenogenesis in T. officinaleis shaped by an environmental gradient which acts upon the sexuals.

River Dike Deformation Measurement With Airborne SAR

Due to extremely high water levels or extremely dry periods, river dikes can deform and eventually burst. The deformation can be measured with repeat-pass synthetic aperture radar (SAR) interferometry. Two flights (5.5-day interval) with an airborne C-band SAR were carried out to verify a particular case. During the second flight, the dike was deliberately deformed. Interferogram analyses showed that the dike deformed by at most 2 mm on this day, in approximate agreement with tachymeter measurements. Corner reflector analysis showed a deformation of about 1 cm during the 5.5-day interval, in good agreement with ground measurements.

Adaptive Mesh Refinement and Error Estimate for 3-D Seismic Analysis of Liquefiable Soil Considering Large Deformation

Such soil structures as river dikes, high way embankments and earth dams frequently have been damaged during major earth- quakes, often due to liquefaction of embankments and foundation soils. In most cases, unacceptable, large, permanent deformation has occurred due to liquefaction of the supporting, loose, cohesion- less foundation soil. The seismic design of soil structures in these liquefiable soils poses very difficult problems for analysis and design. The possibility of liquefaction necessitates further investi- gation not only experimentally but by numerical analysis. ABSTRACT The focus of this paper is on 3-D adaptive analysis method of liquefiable soil improvement of the approximate quality of nonlinear numerical simulation of the liquefaction process with large deformation. This adaptive tech- nique was applied to the 3-D non-linear FE analysis of liquefiable soil considering large deformation, including the liquefaction phenomenon. The cyclic elasto-plastic model and updated Lagrangian formulation were adopted in the three-dimensional FE analysis. The fission procedure belonging to the h-refinement indicated by the error estimator, a posteriori error estimate procedure depending on L 2 -norm of strain and superconvergent patch recov- ery method, was used. The convergence of this error estimate scheme and the effectiveness of h-adaptive mesh refinement were shown by simple examples. The adaptive FE method was applied to the three-dimensional prac- tical seismic analysis of an embankment constructed on liquefiable soil, and its efficacy demonstrated in detail. Application of the adaptive technique to the nonlinear analysis of saturated soil, including the liquefaction process, is a valuable step in the three-dimensional seismic analysis of liquefaction.

河川堤防で観測された2003年宮城県北部地震の強震記録に基づく堤防の震動性状と地盤特性および地震動の関係

河川堤防で観測された2003年宮城県北部地震の強震記録に基づく堤防の震動性状と地盤特性および地震動の関係

River restoration from a river manager’s point of view.

A number of river restoration projects and flood alleviation projects, which also aim to restore more natural river flood plain processes, have been implemented along the Dutch Rhine branches in the past decade. This has provided some information on their effect on the river's morphology and hydraulics. Incorporating this experience into the design of new schemes is one of the main aims of today's river management. Development of vegetation in the floodplains leads to an increase in hydraulic roughness, especially in the first few years, when species such as Willow develop. Secondary channels and small structures such as bridges in the floodplains may have a considerable morphologic effect. Some projects caused bank erosion which may jeopardize river dikes, plus local erosion around structures like groynes. This points out that insufficient attention had been given to their engineering aspects in the design. Monitoring of both the morphologic effects and the development of vegetation is required in order to know when to take action, to prevent loss of function or to secure flood protection levels. To be able to intervene as early as possible, rules of thumb need to be constructed to determine the hydraulic roughness based on knowledge of the vegetation. By proper interpretation of observed changes in morphology and vegetation, translation of experience into design practice is possible. In this way the river manager gains experience to maximize the restoration potential of flood protection schemes. This paper cannot be seen as a scientific study. Visually observed changes in morphology and vegetation are discussed, as well as practical issues related to the impact of vegetation on flood levels and management of river restoration.

Shake Table Tests on Residual Deformation of Sandy Slopes Due to Cyclic Loading

The evidence of earth structure damages due to earthquakes and the need for study on relatively dense and unsaturated earth structures such as river dikes and road embankments motivated this research work. A series of shake table tests were performed in order to provide the needed experimental data for this study. During the experimental program, two types of soils, i.e. Toyoura sand and a sample from natural deposits of sandy material were used. A rectangular laminar box was mounted over a rigidly fabricated slope and subjected to horizontal shaking. Sweep tests and Swedish sounding tests were also performed in order to measure the material properties. The results of these tests show the effect of different parameters such as amplitude of cyclic loading, number of cycles, initial static shear stress, confining pressure and shear stress history (loading-unloading, over-consolidation and creep time) on shear deformation of unsaturated slopes during and after cyclic loading. The outcomes of the test results are used as a basis to develop a new single degree of freedom model of mass and nonlinear spring over a slope. Stress-strain behavior of the soil is defined as a nonlinear stiffness function of a spring. Time dependent input acceleration is considered as the base excitation and the induced inertia force is superimposed on the initial static shear stress. The numerical solution of the equation of motion of the model predicted the residual deformation of the system at the end of shaking. Several cases were analyzed and compared with the test results.

Analytical solution of a flood wave resulting from dike failure

The occurrence of floods due to failures of river dikes is becoming a major problem for many developing countries. Prior knowledge of flood movement acquired through model simulation can help the planner in formulating an efficient management scheme. Numerical schemes for flow simulation are gaining popularity in this context. However, the implementation of a numerical scheme in this situation generally calls for analytic computation of an initial water surface profile. Several analytical methods with various degrees of sophistication are available for solving the dam break problem. However, an appropriate method of solution is not available for the situation of a dike breach flood where the released water moves in a lateral direction relative to the main stream. Therefore a new characteristic-based analytical solution of flood propagation has been developed for the situation where flood water, being released through an opening in the river dike, moves two-dimensionally over a valley.

Analytical solution of a flood wave resulting from dike failure

The occurrence of floods due to failures of river dikes is becoming a major problem for many developing countries. Prior knowledge of flood movement acquired through model simulation can help the planner in formulating an efficient management scheme. Numerical schemes for flow simulation are gaining popularity in this context. However, the implementation of a numerical scheme in this situation generally calls for analytic computation of an initial water surface profile. Several analytical methods with various degrees of sophistication are available for solving the dam break problem. However, an appropriate method of solution is not available for the situation of a dike breach flood where the released water moves in a lateral direction relative to the main stream. Therefore a new characteristic-based analytical solution of flood propagation has been developed for the situation where flood water, being released through an opening in the river dike, moves two-dimensionally over a valley.

Analytical solution of a flood wave resulting from dike failure

The occurrence of floods due to failures of river dikes is becoming a major problem for many developing countries. Prior knowledge of flood movement acquired through model simulation can help the planner in formulating an efficient management scheme. Numerical schemes for flow simulation are gaining popularity in this context. However, the implementation of a numerical scheme in this situation generally calls for analytic computation of an initial water surface profile. Several analytical methods with various degrees of sophistication are available for solving the dam break problem. However, an appropriate method of solution is not available for the situation of a dike breach flood where the released water moves in a lateral direction relative to the main stream. Therefore a new characteristic-based analytical solution of flood propagation has been developed for the situation where flood water, being released through an opening in the river dike, moves two-dimensionally over a valley.

Effective stress analyses of liquefaction-induced deformation in river dikes

A series of effective stress analyses is carried out on the seismic performance of river dikes based on the case histories during the 1993 Hokkaido-Nansei-oki and 1995 Hyogoken-Nambu earthquakes in Japan. Seven case histories selected for the analyses involve a crest settlement ranging from none to 2.7 m in the dikes 3–6 m high with evidence of liquefaction at foundation soil. The effective stress model used is based on a multiple shear mechanism and was developed by one of the authors. The soil parameters are evaluated based on the site investigation and laboratory test results. The results of the analyses are basically consistent with the observed performance of the river dikes. In particular, the effective stress model shows a reasonable capability to reproduce the varying degree of settlements depending on the geotechnical conditions of foundation soils beneath the dikes. The analyses also indicate that the effect of a cohesive soil layer mixed with the liquefiable sand layers beneath the dikes can be a primary factor for reducing the liquefaction-induced deformation of dikes.

Effects of remedial measures for mitigating embankment settlement due to foundation liquefaction

In Japan, after the Hyogoken-nambu earthquake remedial measures have often been constructed for river dikes supported on liquefiable sand beds. In this study a series of dynamic centrifuge tests was conducted to assess seismic performances of embankments with and without countermeasures and to provide a basis for establishing conventional methods to evaluate crest settlement. Three types of countermeasures used in the current practice in Japan (the solidification by the deep mixing method, the densification by the sand compaction piles and the sheet pile enclosure) were tested. It was observed that the excess pore pressure under the embankment toes tends to be higher for models with countermeasures than benchmark models without countermeasures. The horizontal displacement constraint imposed by the remedial zone is considered to be responsible for this. It was also found that the countermeasure techniques could reduce lateral deformation of the liquefied foundation sand and shear deformation of the embankment significantly, however, some embankment crest settlement was inevitable. The higher excess pore pressure under the embankment due to the existence of the remedial countermeasures resulting in an increase in contractive volume change of sand under embankment was responsible for the inevitable crest settlement. It is concluded that displacement predictions of the remediation zone as well as a volumetric strain of the liquefied sand beneath the embankment are key aspects to assess crest settlements.

RESTORATION WORKS OF SEISMICALLY DAMAGED RIVER DIKES USING REMEDIAL TREATMENT OF LIQUEFIABLE LAYER

本稿では, 近年発生した3例の震災で基礎地盤が液状化した堤防復旧において実施した調査方法, 被災メカニズムの推定, 再度災害防止のための基礎地盤改良工事の設計・施工について述べ, この理解を助けるために堤防築造と設計に関する歴史的経緯や技術基準類の改定経緯にも言及した.従来, 地震により被災した堤防の復旧は原形復旧が原則であった. 地盤改良を併用した復旧が行われたのは釧路沖地震による復旧が国内初であった. 後に, これらの実績も参考としつつ, 必要な区間を限って堤防の築造に耐震計算を導入することが河川砂防技術基準 (案) に明記されることとなった.

Use of Embedded Walls for Mitigation of Liquefaction-Induced Displacement in Slopes and Embankments

The effects of large displacement and deformation of liquefied subsoil during earthquakes have been seriously discussed in recent years. Although mitigative measures to prevent the onset of liquefaction are desirable, it is important from an economical viewpoint that there is a level of allowable displacement and deformation below which the induced ground movement does not cause serious problems to concerned facilities. That deformation is also acceptable that can be repaired within a reasonably short period of time. The present paper briefly examines the recent experience of a river dike during the 1995 Kobe earthquake and suggests that several measures, inclusive of an embedded sheet pile wall, are able to mitigate the displacement to an acceptable level. Then the study presents the results of small shaking table tests in which displacement of a liquefied slope was mitigated by an embedded wall made of either a sheet pile or compacted sand. The study proceeds to the development of an analytical method by which the mitigative effects of embedded walls are evaluated. The proposed method is so simple that a closed-form solution is available for simplified situations. Example studies were made of several situations.