Abstract：摘要 

基于結(jié)構(gòu)的設(shè)計理念和土木工程建筑業(yè)的原則，機制和上海蓮花河畔景苑七號樓的倒塌不可或缺的主要的原因進(jìn)行了分析各方面，如工程地質(zhì)條件，預(yù)應(yīng)力樁基礎(chǔ)開挖及水位在下降土等南部基坑壓差提議地下室應(yīng)扁型高層住宅建筑和正確的施工程序進(jìn)行設(shè)置，應(yīng)采用............新的設(shè)計Based on structural design concept and civil engineering construction principle, the mechanism and primary reasons for the integral collapse of Shanghai Lotus River Garden No．7 Building are analyzed on various aspects, such as engineering geological conditions, prestressed pile foundation excavation and water level lowering in the south foundation pit and pressure difference of soil, etc. It is proposed that basement shall be set in flat－type high－rise residential buildings and correct construction procedures shall be adopted．…………new design

CE Database subject headings: high－rise residential building; collapse of structure; soft soil; pile foundation
Key words： high－rise residential building; collapse of structure; soft soil; pile foundation
 

Introduction 介紹

6月27日2009年，一個新建的上海蓮花河畔景苑7號住宅樓發(fā)生傾覆造成一人傷亡這是中國建筑行業(yè)數(shù)十年罕見的重大事故見圖1.該建筑的整體傾覆是由引起的各種原因。土木工程應(yīng)進(jìn)一步倒塌建筑物的機理分析，，從事故獲得的經(jīng)驗教訓(xùn)。雖然事故調(diào)查組在上海已經(jīng)放棄了計劃中的大樓整體傾覆的主要原因。它被通知工程地質(zhì)勘察報告，原結(jié)構(gòu)設(shè)計均符合該規(guī)范的要求，在地下室中使用管樁是滿足基本質(zhì)量要求。通過仔細(xì)的分析和反思，并查看各種媒體的分析和評論提議的機制崩潰分析，其原因是現(xiàn)在推翻建設(shè)和經(jīng)驗教訓(xùn)的原因，從繪制。On June 27 of 2009, A newly built Shanghai Lotus river garden NO．7 residential building has happened overturning caused one casualty which is a rare major accident of China's construction industry for decades see in Fig 1. The building's overall overturning was caused by a variety of reasons. Civil engineering should further analysis of the mechanism of collapsed of the building and get experiences and lesson from the accident. Although the accident investigation team in Shanghai has been gave the main reason for the proposed building overall overturn. It is notified that the engineering geological investigation report and the original structure design are accord to the requirement of the specification, pipe piles used in the basement are meet basic quality requirements. By careful analysis and reflection, and review the reasons for the collapse analysis of a variety of media analysis and comment on the proposed mechanism and the reason is now overturning the building and the lessons to be drawn from.

Reasons for the collapse of the building

2.1 The site engineering geological condition
the common engineering geological conditions Shanghai area are: below the surface about 3 ~ 4 m to enter the soft sandy soil, local civil engineering profession called "iron sand" It is a blue sand, but in some places there are yellow. The capacity of the layer is strong when the soil carry little water, but when soil become saturated soil which has no bearing capacity. This layer is divided into several sub-layers which have the same geological condition, The total thickness of the layer is about 17 ~ 18 m relatively distributed throughout the urban area, It should be carefully deal with the foundation in Shanghai when structure encounter the "iron sand" layer. Once the Precipitation and seepage are not get well done, There will be a quick blasting with sand and water. The pressure of water will push water and sad from the foundation, soil erosion serious loss rate outside the foundation, and soon, a few hours after the foundation pit lateral will appear big collapse. Hazards and defects that exist in the Shanghai area of geological engineering, In this special zone Dianpu river banks may be more severe, it is a test of the builders of the wisdom and ability to handle the project.

Fig. 1. Collapse of building NO 7
2.2pipe pile foundation construction of Building 
Prestressed pipe is generally smaller in diameter,  but its length is longer in most case so the belong to slender member that easily cause instability problem, single pipe has high vertical bearing capacity, capacity of C80 high strength prestressed pile with 500mm diameter in Shanghai region can get to 2200 kPa or more. But it required the physical surrounding soil to provide good lateral restraint to its full vertical bearing capacity. 

Fig.2. Broken piles
However, in the capsized buildings and broken pile see in Fig 2, soil around the foundation that exposure to rollover can be judged visually more loosely, indicating higher porosity of the soil, the soil was soft , that the construction process probably not on the basis of effective backfill compaction process, soil soaked in the rain from the plastic state to plastic flow state, thus reducing the lateral restraint of upper pile and foundation, excavation unreasonably on the south of the building and high accumulation of soil cause high pressure on the north and lead to the upper part of the pile with the lateral displacement of soil deformation or differential foundation settlement. When the initial formation appeared, the whole eccentric gravity load of the upper structure will further exacerbate this eccentric process, which is called second-order effect of gravity, when such lateral overturning moment more than the rest of the pile, then the bending load capacity will cause pile instability, leading to overturning the whole building . That is why the collapse will happen in the main project basically completed (maximum vertical load at this time) raining ( at this time the soil into plastic flow state , losing the support of the upper part of the pile ) side foundation pit ( this an important reason for the plastic flow state soil will blasting out of foundation when the soil foundation pit will produce an initial lateral direction ) 
2.3The south side of the basement excavation and lethal effects of precipitation on Building 7
After the completion of 12 high-rise residential building in the Lotus riverside, construction side had just started construction of Building 7 on the south side of the outdoor basement, basement which has no horizontal support with excavation depth 4.6m excavation sidewalls take shotcrete slope, the north side away from the pit of Building 7 facades is about 7 ~ 8 m. Construction side began earth excavation foundation and basement floor cushion sidewall slope construction, in order to ensure the normal construction, it is necessary to take measures to reduce the ground water level, so that the soil remains dry when basement excavation and concrete construction. Since the soil is sandy soil , precipitation well point should be set within the surrounding foundation pit, and the basement excavation plane has larger size can be supplemented sump pit in the middle of precipitation in the region to ensure that the depth of the middle area of precipitation.
Since the origin design has no basement, foundation depth of building7 is about 2 m, and precipitation of south basement excavation depth should be 5 m or more , taking into account outdoor underground water table is generally about -1.0 m, then the 7th groundwater level difference between the lower part of the downstairs portion and the foundation pit is about 4 m .When excavation began pumping the well point , the water level of foundation pit decreased, the 7th downstairs and around foundation will have different pressure resulting groundwater level . In the water pressure difference will flow into the foundation pit under the hydrodynamic pressure on the 7th downstairs in the soil water formed thereby . When the cause of water seepage flooding hydrodynamic pressure not less than the density of the soil , the soil particles will be in a suspended state, and together with the seepage of water flowing into the pit which occurred in quicksand phenomenon, phenomenon occurs when sand experience a complete loss of carrying capacity, also cause severe pit slope landslides , foundation downstairs on the 7th will be emptied so that the buildings to sink and tilt. though large sand phenomenon does not appear during the excavation, soil pore water on the 7th will be downstairs in the pit with the pit precipitation and stream flow , resulting in the lower part of the foundation soil became loose, so that the building generates additional settlement . Since the foundation close to the south of the lower Pit Building 7, the falling of water level is more than the north, resulting in additional settlement construction should be larger than the north to the south , and based on the difference will result in additional settlement building is tilted. If the tilt continues, it will lead to instability of pile construction , it is likely to occur south overturning of the whole building .
Excavation of the foundation pit and continuous precipitation south of foundation pit it Building 7 Building 7 caused the soil to the lower pit side wiggle slip, causing the upper part of the pile bent or broken, leading to the formation of the whole building tta http-equiv="Content-Type" content="text/html; charset=gb2312" />

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