Investigation on collapse accident of construction site caused by 8 deaths and 2 injuries in Guizhou Province

 Investigation on collapse accident of construction site caused by 8 deaths and 2 injuries in Guizhou Province

At the scene of the incident, a large amount of backfill can be seen around: Zhao Meng

In two seconds, the two floors are flat.

Looking back to the collapse of the parking lot under construction five days ago, Zhou Ping, a construction worker, was still frightened. At that time, he was busy with the construction of an apartment building under construction in a beautiful square beside the site. Suddenly, he heard a loud noise, and hurriedly put his head out of the window to look forward to it

At about 4:21 p.m. on October 28, the baffle of a parking lot in Midea square of Guiyang collapsed. There were 14 people on duty, 3 of whom escaped by themselves, 1 was rescued quickly, and 10 were trapped and lost. By 3 a.m. on October 29, all 10 missing persons had been found, 8 dead and 2 injured.

As a newly listed real estate enterprise, Midea Real Estate Group Co., Ltd. (hereinafter referred to as Midea real estate) has a wide range of contacts. The Third Construction Engineering Co., Ltd. of China Construction Second Engineering Bureau, which cooperates with Midea Real Estate Group Co., Ltd., also has strong strength and strict control over quality and safety in external publicity. However, this accident has pierced the safety myth of these large companies. In the high-risk construction industry, from construction, survey, design, to construction and supervision, any link that is flawed can bring disaster consequences.

Interface news learned from people close to the accident cause investigation that at present, the preliminary conclusion of the accident cause investigation has been formed, and there may be loopholes in the local design, construction and management of the project; under the pressure of seizing image and progress, when the concrete has not reached the curing age, the fertilizer tank is backfilled, which has become a crushing baffle, resulting in the death of 8 people The last straw.

Remove the formwork if the concrete fails to meet the strength requirements

When Zhou Ping ran down from the 15th floor, many panicked workers had gathered at the scene. The parking lot on the second floor, which was 11 meters high, has collapsed and is flush with the nearby ground. Beside the collapsed roof, a large amount of backfilled soil can be seen, some of which are still wet.

A later tower crane worker was scared to squat on the ground and dare not move. Zhou Ping and her workmates quickly separated her from the scene. At this time, he could still hear the workers under the rubble calling for help, but he could not help. Within ten minutes, the first rescue team arrived at the scene, and many workers helped. Because the exact location of the trapped personnel cannot be determined, the rescue team can only try to open multiple openings in the roof.

By the early morning of the next day, all the 10 trapped people were found, but eight were killed and two were injured and hospitalized. A person who has seen the list of the dead told the interface news that the dead belonged to Sichuan Guocheng Labor Service Co., Ltd. and all of them were Guizhou people.

On the day of the incident, the construction of Midea Plaza Phase I and phase II projects has been suspended, and the scene of the incident has also been blocked by fences. There are regular patrols around by security guards. At the scene of the accident, some people wearing safety helmets were still checking. On the collapsed roof, a dozen holes were left because of rescue, and the steel bars distributed in the holes like cobwebs.

At the gate of the project, the original banner of the construction company has also been removed. A signboard that should have been displayed in a prominent position of the project was removed and hidden in the security room.

The signboard states that the construction unit of the project is the Third Construction Engineering Co., Ltd. of China Construction Second Engineering Bureau, the designer is Guangdong Tianyuan Architectural Design Co., Ltd. and the supervisor is Guizhou Zhengye Engineering Consulting Co., Ltd. The name of the project manager, production manager and safety director is also listed on the information bulletin board. The construction period is 180 days.

People close to the investigation team told interface news that after the accident, the investigation was almost carried out at the same time as the rescue. At about 6 oclock that night, Guizhou Provincial Emergency Management Department organized relevant experts to rush to the site, including the five party responsible principal of Construction Engineering of the construction unit, survey unit, design unit, construction unit and supervision unit of the project, who were all required to go to the site to assist in the investigation.

The accident place is an underground garage under construction. For the convenience of construction, it is usually to excavate a part more than the working surface under excavation, which is called fertilizer tank. After the main construction of the building reaches a certain stage, the fertilizer tank needs to be backfilled, but the backfilling has strict requirements on time and soil quality.

According to this person, after preliminary survey, the underground parking lot has only completed the structural construction of three spans (partial four spans), and the basement has not yet been enclosed into the overall structure, in order to seize the image and progress, local backfilling construction has been carried out. In architectural terminology, the distance between the support and the support is called span, the distance between two upright poles is called one span, and the distance between three spans is the distance between four upright poles.

He introduced that under the larger backfill side pressure, the shear wall and column of the basement were broken and overturned as a whole, and the whole basement collapsed. Shear wall, also known as anti wind wall, anti-seismic wall or structural wall, is the wall which mainly bears the horizontal load and vertical load caused by wind load or earthquake, generally made of reinforced concrete.

According to the interface news, there are three reasons for the accident: first, the basement has only completed three spans (partial four spans) structure, and one shear wall construction. When backfilling, the single cantilever of some structures is stressed, and the overall rigidity is insufficient, resulting in the overall fracture of shear wall and column;

Secondly, there are some defects in the design and construction of constraint node. The foundation of the underground parking lot is manual dug pile + pile cap, and there is no ground beam connection between pile caps; the base plate is a 300 mm thick reinforced concrete structure, and there is no concealed beam in the base plate; the basement column spacing is 8.4 meters, while the external shear wall column spacing is 11-12 meters; the external shear wall only has a bearing platform under the attached wall column, there is no strip foundation under the shear wall, and the shear wall is not set on the bearing layer;?

Third, the concrete pouring age of basement structure is about 15 days, but no early strength report of concrete is found on site. According to the specification, the concrete with a span of more than 8 meters can only be removed after its strength reaches 100% of the design strength. However, Guiyang has been in continuous rain and low temperature for the last 15 days, the concrete strength should not meet the requirements of formwork removal.

The investigators found that when the collapse happened, the steel bar had been pulled out from the beam column joint. The investigation team is still in the process of further work on the detailed cause and responsibility division of the accident.

Adjusted parking lot design

According to the public information, Midea Plaza has experienced nine years since it took the land. During this period, developers, constructors and designers also changed.

On August 20, 2010, Yonggui Energy Development Co., Ltd. (hereinafter referred to as Yonggui energy) won the state-owned construction land use right of 2010-05 plot in guanshanhu district with 160 million yuan. The planned land for this plot is commercial, office and hotel land, with an area of 64059.3 square meters (96.09 mu). According to the original design, a commercial complex named Longyu city square will be built here. The designer of the project is Chongqing Bolan Architectural Design Co., Ltd.

In August 2017, Yonggui energy signed a cooperation agreement with Guiyang Midea Real Estate Development Co., Ltd. (hereinafter referred to as Midea real estate). Longyu city square was renamed Midea square and the developer became Guiyang Guolong Real Estate Co., Ltd. The company is jointly owned by Yonggui energy and Midea real estate.

In April 2018, Midea real estate changed its name to Midea southwest Real Estate Development Co., Ltd., with Midea real estate holding 100% of its shares. After Midea took over the project, it made many adjustments on the basis of the original project.

Remarkably, on July 2, 2019, Guiyang natural resources and Planning Bureau published on its official website the announcement before the approval of the administrative examination and approval of the Meidi plaza construction project (T4 building and basement, C2-2 building commercial) in guanshanhu District, which explained the design adjustment of the parking lot. The publicity period is from July 2, 2019 to July 10, 2019.

The announcement shows: in the early stage of design, in order to reduce earth excavation and have little impact on the construction of the base, the underground garage is designed as a mixed arrangement of flat parking spaces and mechanical parking spaces. The basement only has two underground floors, and the total parking number meets the planning requirements. However, after the optimization of the multi round plan, the construction party takes full account of the actual use in the future, cancels the original mechanical parking space and changes it to flat parking, which can greatly improve the parking efficiency. Therefore, during the adjustment of this round, the underground garage will be made one more floor, three underground floors will be made locally, and a mezzanine garage will be added locally over the first underground floor. The total parking number is still 1900, which meets the requirements Planning requirements.

Chongqing Bolan Architectural Design Co., Ltd. responded to the interface news. After the completion of the design of Longyu city square, the contract with Party A has been completed. After that, the project was renamed as Midea square, it has nothing to do with us..

In fact, after Midea real estate took over, its design work was also undertaken by its own holding company. Guangdong Tianyuan Architectural Design Co., Ltd., which has made adjustments to the original design, is 100% controlled by Midea real estate. Many of the 105 projects it has announced to participate in the design are Midea real estates own projects.

An architectural designer told the interface news that due to the change of Party A, the demand was different. The adjustment of the project before construction was a normal phenomenon. Generally, when adjusting the design, safety and fire protection are the key factors to be considered, so it is also necessary to adjust the design in terms of survey, structure, stress, etc. All these works must be completed before construction.

From the perspective of public information, after Midea real estate took over the project in 2017, it changed the project publicity introduction at the project site, suspected of construction signs; a number of interviewed workers also said that they entered the project work at the beginning of 2019. But why did the design adjustment information of the project not be published on the website of Guiyang natural resources and Planning Bureau until July 2, 2019?

On October 30, the interface news asked Guiyang natural resources and planning bureau about the adjustment procedure of Midea plaza design scheme. The other side said that it had transferred the problem to the business department, but did not respond as of the release.

Overtime is the norm

After Midea real estate took over, the Third Construction Engineering Co., Ltd. of China Construction Second Engineering Bureau became the construction unit of the project.

A person from a labor service company told interface news that many labor service companies hope to win the bid and eventually lower the labor price in terms of the strength of the company.

After the project was renamed as Midea Plaza, the construction company also brought a new management system. For this set of management system, some construction personnel call it very standard, safety is often talked about; but others say that because of the tedious process, construction materials are often not in place, which affects the progress of the project and the payment of wages, resulting in the loss of workers, and finally it is normal to catch up with the construction period.

Kanghong entered the site of Midea Plaza in March 2019 and was responsible for leading a steel team. In his impression, the construction company has many problems in management. The most prominent one is that the workers are forced to stop work because the raw materials are not in place. After the raw materials are in place, the construction company asks for rush time to catch up with the delayed work and overtime work, which brings great hidden danger to the safety and quality of the project.

He said that the cutting of steel bars on general projects is carried out on or near the construction site, if it is not suitable, it can be replaced immediately, but the raw material processing points of the third company of China Construction Second Engineering Bureau are far away from the construction site. When it is necessary to replace a piece of steel bar whose size does not meet the standard, it needs to find seven or eight people to sign, and the procedure is quite complicated.

Kanghong told interface news that the main raw materials for construction are arranged by the construction party as a whole, and some auxiliary materials are undertaken by the labor company. Because the main materials can not be supplied in time, the delay of construction period often occurs, but this situation has not been changed. One project manager was replaced and a labor service company quit in the middle of the project because the construction period could not be completed on time and the management was poor. In the later stage, the pressure of the construction party and the labor company is relatively large.

Meteorological data show that ten days before the accident, from October 19 to October 28, only one day was overcast on October 23, and the rest were raining. A number of workers told the interface news that in order to catch up with the construction period, although the rain continued, the backfilling of the fertilizer tank beside the parking lot did not stop completely, they were filling when the rain stopped a little.

The strength and stability of the earth material shall be ensured for the backfill. Generally, the silt, muddy soil and expansive soil shall not be used. The water content of the earth material is generally suitable for holding in groups, falling on the ground and blooming. However, some workers said that many of the backfill soil used in the accident site was previously released from the construction site, mixed with stones and a large amount of water. On the day of the incident, some workers said they saw the backfilled soil some of it was mud.

Kanghong told the interface news that it is usually Party A (the developer) chasing the progress, transmitting the pressure to the construction party, and then the construction party to the labor company, which can only transmit the pressure to the team leaders and workers. In this process, there is almost no bargaining space between labor companies and ordinary workers, basically, you can do what you are told to do..

In his impression, there was a time when the workers had four or five days rest because the steel bars were not in place. As the workers are not living on the construction site, the management is loose, and the loss of personnel is serious, once forced to stop work, some workers will change the construction site or leave; when the raw materials are in place, he often cant call up the original workers, only find temporary workers to work.

Another worker engaged in the construction of secondary structure also said that due to the slow progress of the main structure, the construction of secondary structure is often affected, too much rest time, too busy to get up. After three months at the construction site, he chose to go to another construction site, but his salary during working in Midea square has not been settled up to now.

(at the request of the party concerned, Zhou Ping and Kang Hong are aliases)

Source: editor in charge of interface news: Shi Jianlei