Is it necessary to demolish and rebuild all the adobe houses in Ludian disaster area?

Text/Reporter Wu Weitu/Reporter Gu Xuzhan

Ludian county is located in a remote area, and post-disaster reconstruction is very difficult.

Due to the lack of building materials in poverty-stricken mountainous areas with centralized state assistance, how to transform a large number of adobe houses with poor seismic performance has become a difficult problem.

On September 10, the Bureau of Land and Resources announced that the earthquake-stricken area in Ludian, Yunnan Province is gradually entering the stage of transitional resettlement and recovery and reconstruction.

The epicenter was Longtoushan Town, with high mountains and dangerous roads and scattered villages. This sudden 9-degree earthquake seriously damaged the adobe houses built by local farmers. How to rebuild the disaster area in the most scientific and reasonable way has become the most urgent problem.

Not long ago, Professor Zhou Tiegang from the School of Civil Engineering, An University of Architecture and Technology was ordered by the Ministry of Housing and Urban-Rural Development to inspect the damaged houses in Ludian disaster area and design a reconstruction plan. Zhou Tie Iron and Steel told this reporter that although the magnitude of the Ludian earthquake is not large and the affected area is not large, the reconstruction of the disaster area will become the most difficult project after Wenchuan because it is located in a poverty-stricken mountainous area with centralized national aid.

According to official figures, the "8.03" earthquake in Ludian, with a magnitude of 6.5, caused disasters in Ludian County, Qiaojia County, Zhaoyang District, Yongshan County and Huize County188,400 people, 6 17 people died and12 people were missing.

According to Zhou Tiegang's statistics, most of the collapsed houses were adobe houses built by farmers themselves. Most of the casualties died because of the collapse of adobe houses, and only a few people were injured by rolling stones on the mountain. Adobe houses are the most common rural houses in western China.

Present situation of disaster area

Less than 1% of earthquake-resistant buildings have been rebuilt.

Ludian county is located in Xiaojiang fault zone, which is prone to destructive earthquakes. In the past century, there have been at least 15 earthquakes with magnitude above 6 in this seismic zone. In 2004, the earthquake safety project for rural villagers was launched nationwide. Yunnan Province also started the anti-seismic safety project of rural houses in the year of Wenchuan earthquake.

In order to cope with the shortage of funds brought by the project, Yunnan Province has also put forward a plan of "central and local financial subsidies, overall planning by various departments, social donations and self-financing by the masses" to raise funds for the renovation of dangerous houses through multiple channels. At that time, the goal was to strive that by 2020, the rural houses in the province basically had the ability to resist earthquakes of magnitude 6 or so.

However, the disaster area in Ludian did not wait until this day. According to the materials released by official website of Zhaotong Housing and Construction Bureau, in 20 13 years, the task of rebuilding rural dilapidated houses and earthquake-resistant housing projects in Zhaotong City was 54,000 households, and each household was allocated 5,000 yuan in advance. By the end of last year12, there were 65,438 households, of which 45,594 households had been started in the city, with an operating rate of 84.43%, and 4,266 households had been completed, with a completion rate of only 7.93%. However, the operating rate of Ludian County, the epicentre of the earthquake, was only 59.08%, ranking second from the bottom among all 1 1 counties in Zhaotong. In terms of completion rate, Ludian County is only 0.08%.

Professor Zhou Tiegang told reporters that after his investigation, more than 85% of the houses in the disaster area were adobe houses built by farmers themselves. Because of the extremely bad traffic environment and serious poverty in Ludian, it is very difficult and unrealistic to transform all houses into brick-concrete houses.

Can't afford an earthquake-resistant house

The cost is four times that of adobe houses.

Zhou Tiegang said that according to the general experience, the price of building a brick-concrete structure house with good seismic performance of one square meter in the northwest plain area is around 800 yuan, but in the northwest mountainous area, due to the increase of freight and various labor costs, the cost of such a house will reach RMB ~ 1000/200 yuan per square meter.

Compared with brick-concrete houses, the cost of adobe houses built by farmers is more difficult to count. Some farmers rammed earth to build their own houses during the slack season. "Some houses are still built on the hillside, and it costs at least two or three hundred yuan per square meter."

Located in the southwest mountainous area, the situation in Ludian is more severe than that in the northwest. Lu, a 38-year-old villager in Longquan Village, Longtoushan Town, told reporters that she and her husband had long wanted to rebuild the old house that had been built for more than 20 years, but the government subsidy of 5,000 yuan was far from enough, so they had to go out to work. "A brick sells for 30 cents in Ludian County, and it costs 40 cents in Longtoushan Town. There are only mountain roads in our village, only people camel and motorcycle pull. Plus yellow sand, cement and labor, it takes at least 200,000 yuan to build a decent house. "

A useful attempt

Gypsum adobe houses can resist the intensity of 8 degrees.

Zhou Tiegang has been trying earthquake-resistant houses of various structures in various places for many years. One of the most interesting attempts is the gypsum adobe house built in Kashgar, Xinjiang. All building materials are made from local materials: gypsum, adobe and cotton stalks. Firstly, the soil is compacted into adobe, a few cotton stalks are added in the middle of each adobe to expose the corresponding gaps, and then gypsum is poured into the gaps between adobe.

Zhou Tiegang said that after testing in their laboratory, the seismic performance of gypsum adobe earthquake-resistant houses is quite good, and they can resist strong earthquakes of 8 degrees. On the other hand, the cost per square meter of gypsum adobe house is only 300 yuan, which is only about 1/3 of that of brick-concrete structure earthquake-resistant house.

Zhou Tiegang believes that building a house with gypsum is actually very regional. First, gypsum must be produced locally, so the price of gypsum will be relatively cheap. If it is not produced locally, the price of gypsum will be even more expensive than that of cement. "There is no sign of a large amount of gypsum in Ludian."

Zhou Tiegang said that in addition to gypsum adobe houses, they have been focusing on "modern rammed earth buildings" in the past two years. To put it bluntly, it is to build a solid and high-strength adobe house by scientific methods. Compared with gypsum adobe houses, this kind of houses have no regionality, so they have a wider range of applications.

solution

Adopt a variety of housing structures

However, Zhou Tiegang still believes that although modern rammed earth buildings are highly adaptable, it is still very difficult to promote them in disaster areas. "Adobe materials used in disaster areas are weathered topsoil. When farmers build houses, they collect the topsoil and tamp the soil artificially. This kind of soil contains a lot of organic impurities and its viscosity is very poor, which is also the reason why the local adobe house collapsed in the earthquake. "

After inspecting the disaster area in Ludian, Zhou Tie Iron and Steel submitted a report to the Ministry of Housing and Urban-Rural Development. He mentioned in his report that the situation in Ludian disaster area is very special. Although the magnitude of Ludian earthquake is not large and the affected area is not large, it may be the most difficult reconstruction in all previous earthquakes since Wenchuan earthquake. How to rebuild a large number of adobe houses with poor seismic performance in disaster areas needs the overall planning of decision makers and experts. Zhou Tiegang believes that how to rebuild the disaster area in Ludian needs to be subdivided according to local conditions, and many non-traditional housing structures are needed for construction. There is no need to use only one building structure in earthquake-stricken areas.

(Source: yunnan net)