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1.
One method of mitigating the damaging effects of earthquake-induced liquefaction is to provide rapid dissipation of excess pore pressures by the use of vertical drains through the liquefiable material. Drain systems are currently designed using a chart-based approach. Field experience suggests that the performance of these installations cannot yet be accurately predicted.
In this paper, high quality centrifuge testing is used to help clarify drain behaviour. It will be established, supported by centrifuge test data, that the pore water from a radially expanding zone of soil contributing to drainage through the drains is developed. Naturally, the geometry of this expanding zone changes with time. It will be shown that fluid from deeper strata is drained first, reducing the effectiveness of the drain for near-surface soil layers. It is concluded that these zones are useful in analysing more complicated drain system geometries. 相似文献
2.
Wen-Jong Chang Ellen M. Rathje Kenneth H. Stokoe II Brady R. Cox 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):723
A dynamic full scale testing program was performed to quantitatively assess the effectiveness of prefabricated vertical drains as a liquefaction countermeasure. The testing program involved a new in situ liquefaction testing technique, which uses a large hydraulic vibrator to generate waves propagating through an embedded instrumentation area to measure the coupled soil-pore water response. The effectiveness of prefabricated vertical drains is assessed experimentally by comparing the pore pressure generation, pore pressure dissipation, and settlement from two reconstituted soil specimens; one without a drain in place and the other with a single drain installed. Because the prefabricated drain was installed during the specimen preparation process, no accompanying densification during installation occurred. Therefore, the effect of drainage alone was evaluated. The testing results show that the drainage provided by prefabricated drains can significantly reduce pore pressure generation, accelerate post-shaking pore pressure dissipation, and limit associated settlement. The outcome also shows that the new developed in situ liquefaction testing technique can be an alternative to quantitatively evaluate the effects of various liquefaction remediation techniques. 相似文献
3.
Earthquake induced liquefaction continues to be a major threat to many engineered structures around the world. Analysis of liquefaction becomes particularly difficult for two-dimensional (and 3D) problems such as dam/foundation systems. Predominantly, analyses for such systems are performed utilizing some type of finite element or finite difference procedure. Verification or validation of the analyses relies on very limited field performance data with reduced knowledge of the full scope of system conditions or loading conditions.Research reported in this paper represents a portion of ongoing work to obtain a database of information useful for numerical model calibration and to gain a better understanding of the complex dynamics of liquefying foundations under earth dams. Specifically, a highly instrumented model of an earth dam with clay core founded on a liquefiable foundation subjected to earthquake loading is being studied. Properties of the liquefiable foundation are varied to determine the related effects on the overlying earth dam. In this paper, results from three centrifuge physical models will be presented. The models are identical, with the exception of the location (depth) of a liquefiable layer in the foundation, and are subjected to the same dynamic excitation. Results and discussion related to the significance of the liquefiable layer location within the foundation and damage to the earth dam are presented. 相似文献
4.
Study on wall-type gravel drains as liquefaction countermeasure for underground structures 总被引：1，自引：0，他引：1
R. P. Orense I. Morimoto Y. Yamamoto T. Yumiyama H. Yamamoto K. Sugawara 《Soil Dynamics and Earthquake Engineering》2003,23(1):114
One of the most dramatic causes of damage to engineering structures during earthquakes has been the development of soil liquefaction beneath and around the structures. In order to dissipate the excess pore water pressures near structures, gravel drains are usually employed. In this study, the use of recycled concrete crushed stones as gravel drain materials is addressed. In order to investigate the performance of wall-type gravel drains, two series of shaking table tests were performed. The test results showed that gravel drains, when appropriate grain size distribution is considered, effectively dissipate the excess pore water pressure underneath the structure, and consequently reduce the magnitude of uplift. To supplement the laboratory tests, finite element analyses were also performed. For specified structure, ground and earthquake conditions, there is a critical width of gravel drain at which no uplift of structure will occur. The results of the model tests and the finite element analyses were then employed in developing design charts for determining the critical width of gravel drain to prevent buoyant rise of structure when the surrounding soil mass liquefies. 相似文献
5.
Development of new drain method for protection of existing pile foundations from liquefaction effects 总被引：1，自引：0，他引：1
Naoyuki Harada Ikuo Towhata Tadashi Takatsu Shinsuke Tsunoda Vlatko Sesov 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):297-312
Pile foundation as well as other underground structures could be seriously affected by soil liquefaction during strong earthquakes. Damages on pile foundation due to liquefaction can be reduced by implementation of some soil improvement method. Main objective of present study is developing of drain method that can improve the soil in order to mitigate the destructiveness of liquefaction on superstructure supported by pile foundation. Series of shaking table tests were conducted on 2×2 pile foundation and soil model was improved by drains. Configurations of drains around piles, intensity of shaking were one of the parameters that were changing during the tests in order to investigate the response of pile foundation in improved soil condition.Shaking table tests and performed On-site experiment showed the following effects of the new drain method. (1) When the intensity of earthquake motion is 200 gal or less, generation of excess pore water pressure is reduced and the pile bending moment is decreased, (2) when the intensity of earthquake motion is stronger (300 gal or more), drainage effect prevents disappearance of subgrade reaction, and (3) proposed new type of drain can control excess pore water pressure without clogging. 相似文献
6.
7.
This paper presents a procedure to compute the values of degradation factors of p-y curves in the pseudo-static analysis of piles in liquefiable soils. Three-dimensional finite-element model was used for the computation of p and y values using OpenSees computer package. The piles were modeled using beam-column elements and elastic section. The soil continuum was modeled using brick elements and a two-surface plasticity model. By comparing the results of models in two cases of liquefiable and non-liquefiable, values of degradation factors were obtained. Validation of the degradation factors computed was conducted through the centrifuge test results. The simulation results showed a similar trend between degradation factor variation in different densities and sands. With increasing depth, the degradation factor increased. By comparing the results of pseudo-static analysis with the centrifuge test results, it was concluded that the use of the p-y curves with computed degradation factors in liquefiable sand gave reasonable results. 相似文献
8.
Open cut drains are the most frequently used drainage technique in peatlands and are common throughout the world. Land drains increase the drainage density and promote enhanced coupling of hillslope sediment sources with streams. They may be major sources of fine sediment to peatland stream systems but data on drain sediment production in peatlands are rare. Many drains are now being dammed by humans, yet some revegetate naturally. This paper presents a survey of the erosion and natural revegetation of peat drains related to variables such as slope, drainage area and shading. The paper also provides measured comparison of sediment flux from open drains, drains that have been blocked by peat dams, undisturbed subcatchments, and the catchment outlet. Natural infilling of drains was often found to occur on gentle slopes <4°. Drains on slopes <2° were rarely eroded, while drains on slopes >4° were rarely infilled. Nick‐point retreat at the confluence of drains was often observed. Revegetation of drains was uncommon where drains have been cut or incised into the underlying mineral substrate. Where the drain floor was peat‐based, revegetation was much more common. Revegetation of drain floors was affected by overhanging vegetation, which provided shading. Drain floors with less than 60% shading tended to have a greater vegetation cover than drains with 60–90% shading. However, drains that were almost totally shaded (>90%) had the greatest floor vegetation. The intact drains were found to be major sources of suspended sediment within the survey catchments, with 18·3% of the sediment originating from the unblocked drains which drained 7·3% of the area. The winter quarter of the year was more important than other seasons for producing suspended sediment, even though precipitation totals were not greatest during this period. Drains which had been dammed at intervals along their length using peat blocks had very low sediment yields. Even poorly dammed drains, where water could still flow along the full course of the drain, had 54 times less suspended sediment production than unblocked drains. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
9.
The method of conformal mapping is applied to the analysis of transient flow toward parallel periodic drains in a semi-infinite aquifer taking into consideration the non-linear boundary conditions on the free surface. The mapping function is expressed as a power series in time and the seepage domain is mapped onto a domain of an auxiliary complex variable. Mapping is performed in such a manner that the free surface will always remain the real axis. Calculations are carried out for different ratios of drain depth to drain spacing using various drain diameter to depth ratios. 相似文献
10.
R. B. Sancio J. D. Bray J. P. Stewart T. L. Youd H. T. Durguno
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nalp R. B. Seed C. Christensen M. B. Baturay T. Karaday&#x;lar 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):1093-1102
Ground failure in Adapazari, Turkey during the 1999 Kocaeli earthquake (Mw=7.4) was severe. In four central downtown districts, where more than 1200 buildings collapsed or were heavily damaged, hundreds of structures tilted and penetrated into the ground due in part to liquefaction and ground softening. Based on a multi-institutional subsurface investigation program, soil conditions along four lines in which ground failure was surveyed after the earthquake are classified into four generalized subsurface site categories. This classification is primarily based on the presence or absence of shallow and intermediate depth liquefiable soils. Observations of ground failure are found to correlate well with site categories that are susceptible to liquefaction according to current state-of-the-art methods without strict adherence to the Chinese criteria. Soils that liquefied were found to meet the liquid limit and liquidity index conditions of the Chinese criteria. However, soils that liquefied did not typically meet the clay-size condition for liquefiable soils by the Chinese criteria. 相似文献
11.
Horizontal and vertical components of earthquake ground motions at liquefiable sites 总被引：1，自引：0，他引：1
Field observations on ground motions from recent earthquakes imply that current knowledge is limited with regard to relating vertical and horizontal motions at liquefiable sites. This paper describes a study with the purpose of clarifying this emerging issue to some extent. A series of numerical analyses is carried out on a liquefiable soil deposit with a verified, fully coupled, nonlinear procedure. It is shown that the transformation of vertical motions in the deposit differs considerably from the transformation of horizontal motions. Both the amplitude and frequency content of the horizontal motions are strongly dependent on the shaking level or the associated nonlinear soil behavior. The transfer function for vertical motions is however likely to be independent of the intensity of input motions; no reduction in the amplitude occurs even in the case of strong shaking. The results are shown to be in consistence with the laboratory observations on shaking table tests and recent field observations that less nonlinearity exists for vertical motions. It is also shown that the possibility exists for using information on spectral ratios between the horizontal and vertical surface motions to quickly identify in situ soil behavior and liquefaction that are not readily covered by conventional field or laboratory experimentation procedures. 相似文献
12.
Cement-mixed piles, as countermeasure against liquefaction of silt and sand ground, can improve the shear strength and bearing capacity of foundation soil, meaning cement-mixed piles are capable of resisting displacement when an earthquake happens. However, investigations of cement-mixed piles by experimental methods such as the shaking table test is few and far between. It is especially true for the seismic performance of cement-mixed piles in liquefiable railway foundations in high seismic intensity regions. To this end, a cross-section of the Yuxi-Mengzi railway was selected as the prototype and studied by the shaking table test in this study. The results showed that composite foundation of cement-mixed piles was not liquefied when the seismic acceleration was lower than 0.30g. In the process of acceleration increasing from 0.30g at 2Hz to 0.60g at 3Hz, the upper middle silt outside slope toe was partly liquefied. The foundation soil under the shoulders and center of subgrade was far from the initial liquefaction criterion during the test. Cement-mixed piles can effectively reduce the embankment settlement and differential settlement. It can be concluded that, the design of cement-mixed piles can ensure the seismic performance of the subgrade, and satisfy the seismic design requirements of the Yuxi-Mengzi railway in areas of VⅢ degrees seismic fortification intensity. 相似文献
13.
Large earthquake-induced displacements of a bridge abutment can occur, when the bridge is built on a floodplain or reclaimed area, i.e., liquefiable ground, and crosses a water channel. Seismic responses of a bridge abutment on liquefiable ground are the consequence of complex interactions between the abutment and surrounding soils. Therefore identification of the factors dominating the abutment response is important for the development of simplified seismic design methods. This paper presents the results of dynamic three-dimensional finite element analyses of bridge abutments adjacent to a river dike, including the effect of liquefaction of the underlying ground using earthquake motions widely used in Japan. The analysis shows that conventional design methods may underestimate the permanent abutment displacements unless the following two items are considered: (1) softening of the soil beneath the liquefiable layer, due to cyclic shearing of the soil surrounding the piles, and (2) the forces acting on the side faces of the abutment. 相似文献
14.
Permeable reactive barriers (PRBs) are a popular technology for passive contaminant remediation in aquifers through installation of reactive materials in the pathway of a plume. Of fundamental importance are the degree of remediation inside the reactor (residence time) and the portion of groundwater intercepted by a PRB (capture width). Based on a two-dimensional conformal mapping approach (previously used in related work), the latter is studied in the present work for drain-and-gate (DG) PRBs, which may possess a collector and a distributor drain (“full” configuration) or a collector drain only (“simple” configuration). Inherent assumptions are a homogeneous unbounded aquifer with a uniform far field, in which highly permeable drains establish constant head boundaries. Solutions for aquifer flow fields in terms of the complex potential are derived, illustrated, and analyzed for doubly symmetric DG configurations and arbitrary reactor hydraulic resistance as well as ambient groundwater flow direction. A series of practitioner-friendly charts for capture width is given to assist in PRB design and optimization without requiring complex mathematics. DG PRBs are identified as more susceptible to flow divergence around the reactor than configurations using impermeable side structures (e.g., funnel-and-gate), and deployment of impermeable walls on drains is seen to mitigate this problem under certain circumstances. 相似文献
15.
可液化场地大直径扩底桩-土动力相互作用p-y曲线研究对扩底桩抗震设计具有重要意义。基于有限差分程序FLAC~(3D),分别建立扩底桩和等直径桩的三维有限差分模型,通过在模型底部输入正弦波,得到可液化场地中不同埋深下扩底桩与等直径桩的桩-土动力相互作用p-y曲线,对两者的动力p-y曲线特征进行对比分析。结果表明:正弦波输入下扩底桩动力p-y曲线多呈倒"S"形,随着埋深增加,动力p-y曲线滞回圈面积及面积增长速度逐渐减小,斜率逐渐增大;扩底桩与等直径桩动力p-y曲线所围成的图形相似,两者动力p-y曲线斜率均随埋深增加逐渐增大,扩底桩动力p-y曲线滞回圈面积及面积增长速度在各埋深处均大于等直径桩,利于能量耗散,抗震性能更好。 相似文献
16.
Sand boiling and liquefaction-induced damage to houses and infrastructures occurred in Minami-Kurihashi, Kuki City, during the 2011 off the Pacific Coast of Tohoku Earthquake, Japan. After the earthquake, extensive site investigations were conducted in the affected areas, including 14 borehole surveys and 43 sounding tests, where Piezo Drive Cone penetrometer, a newly developed test method, was used which could be effectively employed in detecting local change of soil profiles. A filled sandy soil layer existed near the ground surface in the affected areas, which originated from reclamation works using dredged materials to construct housing lots. In addition, a Holocene sandy soil layer existed partly at a depth of about 10–13 m. Though these two layers were evaluated to be potentially liquefiable, the liquefaction-induced damage was observed to concentrate in the areas where the reclamation works had been executed, suggesting that the liquefaction of the reclaimed layer caused such damage. It was deduced that possible liquefaction of the Holocene layer did not contribute to the damage and to the occurrence of sand boiling at the ground surface. As countermeasure against future liquefaction, ground water lowering method has been selected, and in-situ tests and numerical analyses were executed to predict the long-term ground settlement. A subsequent study on detailed design of the selected countermeasure is underway as of June 1, 2015. 相似文献
17.
Diffuse sources of sediment and sediment‐associated nutrients are of increasing environmental concern because of their impacts on receiving water courses. The aim of the research reported here was to monitor the outflow from four field (land) drains at two farms in the English Midlands in order to estimate the quantity of sediment delivered to the local rivers and the most likely sources and processes involved. A multiparameter sediment unmixing model was employed, using environmental magnetic, geochemical and radionuclide tracers in order to determine the most likely origin of sediments transported through the drains. Results demonstrated that there was a generally linear relationship between drainflow sediment loss and drainflow volume and that the majority (>70%) of the sediment exported from the drains was derived from topsoil. Macropore flow through heavily cracked soils is supported by the data to be the most likely means of sediment delivery to the drains. In one catchment, drains contributed over 50% of the annual sediment budget. Spatial and temporal variations in the sources of sediment reaching one drain outlet were investigated in detail. A link between soil moisture deficit (SMD) and the frequency of high‐intensity rainfall events was used to explain the appearance and persistence of a new sediment source in this drain after October 1998. It is concluded that field drains have the potential to be significant conduits of sediment and agrochemicals in a wide variety of environments in the UK. It is also suggested that this potential may increase if projected climate change leads to more intense rainfall events and increases in SMD across a greater area of the UK. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
18.
Millen Maxim Viana da Fonseca Antonio Quintero Julieth Ferreira Cristiana Oztoprak Sadik Oser Cihan Bozbey Ilknur Aysal Namik Kosič Mirko Logar Janko 《Bulletin of Earthquake Engineering》2021,19(10):3987-4012
The seismic behaviour of a building on a liquefiable deposit is a complex interaction which involves quantifying both shaking induced damage and permanent ground deformation-related damage. In this paper the key parameters that influence both surface shaking and foundation settlements have been identified as the depth, thickness and liquefaction resistance of an equivalent liquefiable layer. These parameters can be used to develop an ‘equivalent soil profile’ that is analogous to the equivalent single degree-of-freedom that reduces the complexity of the dynamic response of a building into comparable and easily understood quantities. The equivalent soil profile is quantified independent of the seismic hazard, making it compatible with performance based design and assessment frameworks such that the building and soil profile can be directly assessed at different levels of seismic hazard. Several numerical studies are presented that demonstrate the influence of these key parameters on the ground surface shaking and foundation settlement. A set of criteria are proposed for classifying soil profiles into 22 different soil classes for regional loss assessment. An algorithm was developed for automatically fitting the equivalent soil profile to a cone penetration test trace and issues with the fitting are discussed. Field reconnaissance was undertaken to collect additional data to support existing datasets on the performance of buildings in Adapazari, during the 1999 Kocaeli, Turkey, earthquake (Mw = 7.4). The field case history data was used to investigate the correlation between the depth, thickness and liquefaction resistance of an equivalent liquefiable layer, on the extent of foundation permanent deformation. The case history data showed that in general a shallow, thick and weak liquefiable layer near the surface results in significant settlement but a lack of data for buildings on non-liquefiable deposits and the additional complexities involved with real buildings and soil deposits, meant that the trends observed in the idealised numerical models could not identified in the field case history data set.
相似文献19.
Damage of embankments during earthquakes is widely attributed to the liquefaction of foundation soil. Previous studies have investigated the dynamic response of embankments by mainly considering uniform sand foundation and a single earthquake event. However, the foundation of an embankment consists of many sublayers of soil from liquefiable sand to relatively impermeable layer, and during earthquakes a mainshock may trigger numerous aftershocks within a short time which may have the potential to cause additional damage to soil structures. Accordingly, the investigation of liquefaction-induced deformation of earthen embankments on various liquefiable foundation conditions under mainshock–aftershock sequential ground motions is carried out by a series of dynamic centrifuge tests in this study. The liquefiable foundation includes uniform sand profile, continuous layered soil profile, and non-homogeneous soil profiles. Effects of various foundation conditions on embankment deformations are compared and analyzed. From the test results, it is found that the embankment resting on non-homogeneous soil deposits suffer more damage compared to the uniform sand foundation of same relative density. The test results also suggest that the sequential ground motions have a significant effect on the accumulated deformation of embankment. 相似文献
20.
Using controlled liquefaction, a seismic isolation technique is introduced by which a large area with dozens of structures can be seismically isolated. The proposed Large Scale Seismic Isolation (LSSI) is in many ways similar to conventional base isolations. The required bearing is provided by a fully undrained pre-saturated liquefiable layer which has substantial vertical stiffness/capacity and minimal lateral stiffness. Moreover, required energy dissipation would be provided through material damping and Biot flow-induced damping within the liquefied layer. LSSI consists of a thick nonliquefiable crust layer and an underlying engineered pre-saturated liquefiable layer bounded by two impermeable thin clay layers. The liquefiable layer should be designed to trigger liquefaction as soon as possible within the early seconds of a design level seismic event. Adopting the energy-based GMP liquefaction theory, optimum gradation of the liquefiable layer is also investigated. It turned out that LSSI would effectively reduce acceleration response spectrum within short to medium periods. Contribution of the proposed LSSI is more pronounced in the case of stronger ground motions such as near field events as well as ground motions with longer return periods. 相似文献