Bearing capacity of single pile and in-flight T-bar penetration for centrifuge modeling of land subsidence caused by the interaction of high-rise buildings

With an increasing number of high-rise buildings in major cities worldwide, land subsidence induced by the interaction between closely-spaced buildings in soft soil areas has become a major challenge for many researchers. The paper considers the interaction of high-rise buildings by determining the bearing capacity of a single pile in the centrifuge model test. The T-bar penetration test was conducted in flight to measure the shear strength of the soft soil, together with vane shear tests when the model had slowed down. By analyzing the relationship curves between land subsidence and the centrifuge acceleration, the allowable bearing capacity of a single pile for the high-rise building was obtained. It is considered that such analysis is a more appropriate method of determining the pile requirements for groups of adjacent high-rise buildings in soft soil areas.     

爆炸液化场地上堤坝变形的模型试验研究

饱和砂土地基在地震、爆炸等振动荷载作用下易发生液化,从而使堤坝等上部构筑物发生破坏。开展了爆炸液化场地上堤坝变形的大型模型试验,考虑了筑坝材料以及堤坝地基加固措施对堤坝变形和坝身裂缝的影响。试验表明:堤坝沉降主要发生在场地液化后的1~2 h内,该段时间内产生的沉降占7 d时沉降量的84%~87%;掺加了碎石的堤坝比未加碎石的堤坝7 d时沉降量大24%;地基内采用土工格栅+土工布的加固措施能够有效减少堤坝在液化场地上的沉降,比未加固的堤坝沉降减少了10%。堤坝的裂缝主要出现在细骨料筑成的坝段和不同筑坝材料的交界处,沿坝身开展。总结了国内外规范中对于液化地基沉降的计算及预测方法,根据液化地基上浅基础建筑物沉降图表对试验中的堤坝沉降进行了推算,发现实测沉降与推算沉降比较接近。     

沉陷区建筑物损害评价补偿模型的研究

为减少沉陷区建筑物损害引起的补偿纠纷,有必要建立公正科学的补偿体系.通过地表变形指标评价沉陷区建筑物损害程度,将沉陷区建筑物损害评价与补偿工作有机的结合,在综合考虑建筑物所处沉陷区位置和使用时间的基础上,对补偿标准进行修正,形成有区别的补偿标准,对沉陷区建筑物进行科学补偿.形成了从建筑物损害判定到损害补偿的流程体系,建立了沉陷区建筑物裂缝补偿和搬迁补偿模型.为沉陷区建筑物损害补偿工作提供了科学、系统的方法.     

Building damage associated with geotechnical problems in the 2011 Tohoku Pacific Earthquake

An overview of the geotechnical aspects of the building damage due to the 2011 Tohoku Pacific Earthquake is presented, based on field reconnaissance made after the earthquake. It is shown that (1) Extensive soil liquefaction occurred along the coast of Tokyo Bay and around the floodplain of the Tonegawa River. Liquefaction was primarily found within the relatively newly reclaimed area, with numerous sand boils and large ground settlements up to 60 cm, accompanied by the settlement/tilting of wooden and reinforced concrete buildings supported by spread foundations. The extent and the distribution of the damage were significantly affected by the local soil conditions, including the thickness and the age of the reclaimed fills, the depth to the bedrock or the natural site period, and whether remedial measures had been taken against soil liquefaction, as well as the effects of structure–soil–structure interaction. (2) Numerous houses in Sendai's hilly residential areas constructed with the cut-and fill method were badly damaged not only by the simple collapse of retaining walls, but also by slope failures in the fills. It was found that most of the slope failures occurred on earth fills. (3) Several pile-supported buildings tilted and settled not only in the Tohoku region, but also on the Kanto plain, implying damage to pile foundations. Ground subsidence with sand boils around those buildings suggests that soil liquefaction might have played a significant role in intensifying the damage. (4) Within Onagawa and Rikuzen-Takata, several steel and reinforced concrete structures were knocked over by tsunami surges, probably after having suffered damage to their pile foundations. Much of the pile damage was concentrated (a) at the joints between pile caps and the piles themselves and (b) near the pile heads. The buildings suffering such damage were old; apparently their pile foundations were not designed to withstand earthquakes.     

Engineering geological characteristics of the 1998 Adana-Ceyhan earthquake, with particular emphasis on liquefaction phenomena and the role of soil behaviour

 The Adana-Ceyhan earthquake (M_s=6.2) occurred in the southern part of Turkey on 27 June 1998 and resulted in the loss of 145 lives and extensive damage to buildings in Ceyhan town and the settlement areas in its vicinity. Soil liquefaction, ground failure due to lateral spreading and rock falls occurred. The area of Adana is characterised by a large alluvial basin with a delta shape. Most of the basin is filled with Quaternary recent Holocene deposits. The recent rapid deposition of sediments and the very shallow groundwater table throughout the basin create conditions conducive to liquefaction. The results of a preliminary investigation of soil liquefaction caused by the earthquake and liquefaction assessments based on field performance data are presented together with evaluations concerning the likely contribution of the soils to the damage sustained by buildings. The results of the liquefaction susceptibility analysis indicated that the data from the liquefied sites were within the empirical bounds suggested by the field-performance evaluation method. It was also shown that shallow sand layers should have liquefied and the surface disruption observed on the site could be predicted by the bounds used for the relationships between the thickness of liquefiable sediments and the overlying non-liquefiable soil. Site-response analyses based on acceleration response spectra from the actual earthquake's strong motion records revealed that soil behaviour was one of the most significant factors in the damage to buildings caused by the earthquake. Received: 4 January 2000 · Accepted: 28 March 2000     

Changes in chemical composition and engineering properties of gypseous soils through leaching: an example from Mashhad,Iran

Gypseous soils are considered problematic when used as the foundation in civil engineering structures such as roads, buildings and dams, due to their solubility. These soils are resistant and have good engineering properties in their dry state. However, when saturated by rainwater or a rising groundwater table, the soluble minerals are washed out, resulting in the subsidence of the structures built on them. In the recent decades, buildings constructed in the Southern Mashhad Metropolitan Area, Iran, have been widely faced with this problem. Since the changes in chemical composition and engineering properties of these soils are based on the amount of dissolved gypsum, the focus of this study is to characterize the soluble soils of this area and their changes throughout the leaching process. Thirty-eight samples were taken from different locations in the area. Chemical tests were conducted on the samples and the gypsum and sulfate concentration maps were produced based on these results, combined with the previously available data from 511 boreholes drilled in the area. Seven soil samples with different gypsum concentrations were selected for further analysis in four major groups of tests, including hydraulic tests (permeability and solubility), chemical tests (chemical analysis of soils samples and total dissolved solids, calcium hardness and chlorine of the leachate samples), physical tests (grain size analysis, Atterberg limits and specific gravity) and mechanical tests (consolidation and direct shear). Changes in the mentioned parameters were investigated through a 5-day leaching process. The results indicate that extensive dissolution of gypsum and removal of gypsum bonding between soil particles change soil chemical composition and decrease the soil compressibility and strength parameters. Therefore, the structures built in this area are in high risk of subsidence and foundation failure; proper measures should be taken to improve the soil quality before construction.     

A web-based tunneling-induced building/utility damage assessment system: TURISK

Prediction of ground movements and assessment of risk of damage to adjacent buildings/utilities have become an essential part of the planning, design, and construction of a tunneling project in urban environments. A web-based tunneling-induced building/utility damage assessment system, named TURISK, was developed. Currently available first order methods were implemented in TURISK for prediction of tunneling-induced ground movements and assessment of damage to adjacent buildings/utilities. TURISK was written in a server-client internet environment using the Microsoft Visual Basic 6.0 in conjunction with the MapGuide ActiveX Control software. The developed system was then implemented to the Daegu Metro Subway Line 2 construction site. The results demonstrated that the developed web-based building/utility assessment system can be used as an efficient tool in the perspective of tunneling-induced settlement risk management for tunneling projects in urban areas. Practical significance of tunneling-induced settlement risk assessment is also discussed.     

Simplified Method for Analysis of Piles Undergoing Lateral Spreading in Liquefied Soils

The analysis of piles subjected to lateral spreading is burdened by the uncertainties associated with the spreading of liquefied soils. Namely, it is very difficult to reliably predict the magnitude and spatial distribution of post-liquefaction ground displacements and also there are uncertainties regarding the stiffness and strength of liquefied soils undergoing lateral spreading. In view of the unknowns involved, there is a need for a sufficiently accurate, yet simple and rational method of analysis that will permit to efficiently evaluate the pile response for various magnitudes of ground displacements and stiffness properties of the spreading soils.In this paper a simple analytical solution is presented for evaluating the pile response to lateral spreading with due consideration of the kinematic mechanism associated with spreading of liquefied soils and the need to estimate the inelastic response and damage to piles. Particular attention is given to the loads arising from a non-liquefied crust layer at the ground surface and to the kinematic effects at the interface between the liquefied layer and underlying non­liquefied layer. A closed-form solution for linear behavior is, first derived based on the classical equation for beam on elastic foundation. The method is then extended over the range of nonlinear behavior using the equivalent linear approach for simplified modeling of the deformational behavior of the pile and soil. Key parameters influencing the pile response and being associated with intrinsic uncertainties are identified and discussed. The proposed method permits to estimate the inelastic response of piles, yet it is a simple analytical solution that requires a few conventional engineering parameters as input. The method is envisioned as a rational tool that will be of practical use in the preliminary assessment of piles and uncertainties involved.     

Seismic performance assessment of masonry infill reinforced concrete buildings in Eastern Canada

In Eastern Canada, most of moment resisting reinforced concrete frames with unreinforced masonry infill (MI-MRF) buildings were constructed between 1915 and 1960. These pre-code structures, in terms of seismic requirements, are considered vulnerable to earthquake due to insufficient ductility and resistance. The goal of this study is to provide a quantitative assessment of their seismic performance using fragility functions. Fragility functions represent the probability of damage that corresponds to a specific seismic intensity measure (e.g. peak ground acceleration at the site). Based on a structural characterisation study on existing buildings in Québec region, a case study three storey–three bay MI-MRF was selected as representative for mid-rise buildings. Pushover analyses were conducted on a nonlinear model of the infill frame to obtain the corresponding lateral load-deformation capacity curve. The nonlinear behaviour of the reinforced concrete beams and columns was modelled with concentrated plastic hinges at members’ ends and a modified strut-and-tie model was used for the infill to account for multiple failure modes. A simplified probabilistic nonlinear static procedure was applied to obtain the seismic demand model at increasing levels of seismic intensity. Fragility functions were then developed using an experiment-based damage model that correlate the extent of damage to the displacement demand. Damage assessment using the developed functions was conducted for an earthquake scenario compatible with the design-level seismic hazard in Quebec City with a 2% and 10% probability of exceedance in 50 years. The developed functions and methodology are particularly useful in probability-based seismic loss assessment and in planning mitigation solutions.     

A step forward towards a comprehensive framework for assessing liquefaction land damage vulnerability: Exploration from historical data

The unprecedented liquefaction-related land damage during earthquakes has highlighted the need to develop a model that better interprets the liquefaction land damage vulnerability (LLDV) when determining whether liquefaction is likely to cause damage at the ground’s surface. This paper presents the development of a novel comprehensive framework based on select case history records of cone penetration tests using a Bayesian belief network (BBN) methodology to assess seismic soil liquefaction and liquefaction land damage potentials in one model. The BBN-based LLDV model is developed by integrating multi-related factors of seismic soil liquefaction and its induced hazards using a machine learning (ML) algorithm-K2 and domain knowledge (DK) data fusion methodology. Compared with the C4.5 decision tree-J48 model, naive Bayesian (NB) classifier, and BBN-K2 ML prediction methods in terms of overall accuracy and the Cohen’s kappa coefficient, the proposed BBN K2 and DK model has a better performance and provides a substitutive novel LLDV framework for characterizing the vulnerability of land to liquefaction-induced damage. The proposed model not only predicts quantitatively the seismic soil liquefaction potential and its ground damage potential probability but can also identify the main reasons and fault-finding state combinations, and the results are likely to assist in decisions on seismic risk mitigation measures for sustainable development. The proposed model is simple to perform in practice and provides a step toward a more sophisticated liquefaction risk assessment modeling. This study also interprets the BBN model sensitivity analysis and most probable explanation of seismic soil liquefied sites based on an engineering point of view.     

南阳膨胀土地区房屋开裂的原因和治理对策

1977~1978年南阳出现严重干旱,南阳西郊膨胀土地区发生大规模房屋开裂损坏。介绍了房屋开裂损坏的特征,分析了导致房屋损坏的原因,提出了预防和整治措施。     

谈公路工程中特殊土地基的特性及处理方法

对特殊土中湿陷性黄土和液化土的成因、影响因素和处理方法进行了分析和介绍,指出在特殊土地基上修筑建(构)筑物时,必须对其进行地质勘查与评价,以得出的结论为依据,采取相应的治理措施,从而保证公路工程施工和运营安全。     

Model test of stone columns as liquefaction countermeasure in sandy soils

The shaking table model test was conducted to investigate earthquake resistant behavior of stone columns under the intensity of an earthquake resistance of buildings is VIII. The test results show that when acceleration is less than 0.20 g, composite foundation is not liquefied, settlement is also small and pile dislocation is not observed; when acceleration is 0.3g, ground outside embankment’s slope toe is liquefied and ground within stone column composite foundation is not. It is suggesting that reinforcement scale of stone column foundation should be widened properly. The designed stone column composite foundation meets the requirements for seismic resistance.     

Development of building vulnerability functions in subsidence regions from empirical methods

The extraction of ores and minerals by underground mining often causes ground subsidence phenomena. In urban regions, these phenomena may induce small to severe damage to buildings. To evaluate this damage, several empirical and analytical methods have been developed in different countries. However, these methods are difficult to use and compare due to differences in the number of criteria used (from 1 to 12). Furthermore, the results provided by damage evaluation may be significantly different from one method to another. The present paper develops vulnerability functions based on a concept that has been applied in other areas, such as earthquake engineering, and that appears to be a more efficient way to assess building vulnerability in undermined cities. A methodology is described for calculating vulnerability functions in subsidence zones using empirical methods. The first part of the paper focuses on existing empirical methods for damage evaluation, and selected necessary improvements or modifications are justified. The second part focuses on the development of a building typology in subsidence zones and its application in the Lorraine region, where many villages are subject to subsidence problems due to iron-ore mining. The third section describes and discusses the adopted methodology for determining vulnerability and fragility functions or curves. Finally, vulnerability functions are tested and validated with a set of three subsidences that occurred in Lorraine between 1996 and 1999.     

An analytical model for far-field response spectra with soil amplification effects

The seismic shear waves in the far field could be harzadous due to soil amplification. As such, the seismic risk needs to be reassessed for buildings on soft deposits with fundamental periods close to that of the soil. This was tragically demonstrated in the September 1985 Mexican earthquake. This paper proposes an analytical model which uses an accepted geophysical model incorporated with an amplification model to predict the acceleration response spectra for such cases. The proposed analytical model is more reliable than the statistical models which are accurate in areas where there is an abundance of seismic data or when specific influence of local ground condition is not important.     

Behaviour of Pile Group behind a Sheet Pile Quay Wall Subjected to Liquefaction-Induced Large Ground Deformation Observed in Shaking Test in E-Defense Project

This paper aims to illustrate a large-scale test on a pile group and a sheet pile quay wall which were subjected to liquefaction-induced large ground deformation. The sheet pile quay wall was displaced laterally and the 2×3 pile group was forced by the flow of liquefied soil. This experiment was conducted in March 2006 at the National Research Institute for Earth Science and Disaster Prevention (NIED), Hyogo Earthquake Engineering Research Center, Japan. Liquefaction-induced lateral spreading was achieved, and soil moved laterally about 1.1 m behind the sheet pile quay wall. Lateral soil displacement was measured by the inclinometers, and results were in close agreement with the directly observed values. Soil lateral displacement and velocity of soil flow decreased as the distance from the quay wall increased toward the landside. Bending strain records were able to explain the damages to the piles, yielding at the top and buckling at the middle height. Lateral force of the liquefied soil exerted on the piles was obtained using earth pressure (EP) sensors and it is shown that rear row piles (close to the quay wall) received larger lateral forces than front row piles (far from the quay wall). This behaviour is explained by the distribution of displacement and velocity of the liquefied soil throughout the shaking. In addition, the lateral soil force was back calculated from strain gauge data and the results are compared with the ones directly measured by the EP sensors. Then, the limitations and advantages of the back-calculation approach are elaborated in this study. Moreover, the time history of lateral soil force showed no correlation with either soil or pile displacements, while it demonstrated a fairly close correlation with the relative velocity until a specific time. This interesting finding would confirm the rate-dependent behaviour of the liquefied soil, though more data from large scale experiments, field testing and centrifuge model tests are needed in this regard.     

Impact of correlation and induced correlation on the estimation of project cost of buildings

Treatment of correlation between variables is necessary for deriving any theoretical distribution of the project cost of buildings. This paper highlights some often ignored theoretical requirements necessary for a rigorous treatment of correlations. The condition for a positive definite correlation matrix is described, along with an analytical procedure and a computer program developed to verify the positive definite condition when correlation coefficients between input variables are estimated using historical data. The analytical procedure and the developed computer program can be used in any application that obtains correlation information from historical data or as subjective judgements to be used in a functional relationship. A new concept called induced correlation is suggested to define and to treat correlation between derived variables that arise from the common (shared) primary variables in their functional forms. A published numerical example is used to highlight the stages where correlation between variables can have an impact on the estimation of moments (estimated expected value and estimated standard deviation) for the project cost of buildings, and to demonstrate the improvement in the estimation of the standard deviation of project cost as a result of treating correlations in risk analysis.     

隧道开挖引起地表位移的数值模拟研究

隧道开挖扰动隧道上覆岩土层,原有的应力平衡状态发生破坏,导致地表发生移动和变形从而对周边建筑物产生影响.以某地铁隧道为例,应用ANSYS计算隧道开挖这一动态过程引起的地表沉降,分析地表沉降对周围环境尤其是建筑物的影响,并提出相应的防御解决措施,以此来减少隧道开挖对建筑物的影响.     

An analysis of the resilience capacity of soils in North China: a study on land subsidence treatment

In order to study treatment measures for the land subsidence caused by deep groundwater overexploitation, we conducted soil compression and rebound tests to analyze the unloading and rebound regularity of deep soil on the fringes of three typical land subsidence regions in North China. Using fuzzy mathematics, we specifically explored the main factors influencing the soil mass unloading resiliency. The results indicated that the ratio between the unloading resilience volume and the loading deformation volume of soil mass in the study areas (referred to as the resilience capacity of soil mass) is between 1.6 and 37.6 %, with an average of 14.7 %. In other words, only about 14.7 % of the land subsidence deformation in the study areas can be restored. The soil masses with different properties in North China all possess elastoplasticity and the resilience capacities of soil can vary from area to area. The sandy soil is not completely elastic but has a certain degree of plasticity; the resilience capacity of soil mass is not a constant, but rather, a variable that changes with the rebound stress value. When the rebounding stress value is determined, the resilience capacity under a smaller unloading stress is larger than that under a larger unloading stress, which demonstrates that earlier land subsidence treatment can result in better effects. Meanwhile, the resilience capacity of soil mass is also enhanced with the increase of rebounding stress, indicating that the closer to the original groundwater level the restored groundwater is, the better the resilience capacity will be. After repeated loading and unloading tests have been conducted under the same stress, the resilience capacity of soil mass will, in most cases, increase to a certain extent. These results can be quite conducive to the treatment of deep groundwater exploitation-induced disasters such as land subsidence.