Text | "China Science News" reporter Yang Chen
In late April, Dongchuan in Yunnan Province became lively.
The annual China Dongchuan Mudslide International Automobile Off-Road Race is about to start. In the local hotel, off-road enthusiasts from all over the country have checked in one after another, and cool off-road vehicles are lined up.
Dongchuan is located in the Xiaojiang fault zone, and debris flow activities are frequent in the rainy season, forming a large area of debris flow impact beach in the basin. Avoiding the rainy season, Shock Beach becomes a paradise for adventurers. Over the past 20 years, using the unique geological landform, Dongchuan has created an exclusive cultural tourism business card.
However, in the last century, Dongchuan talked about the "color change" of debris flows, because the annual debris flow outbreak posed a great threat to the life and production of residents.
The reason why we can turn the "disaster crisis" into a "cultural tourism business opportunity" is inseparable from the efforts of the scientific research team of the Chengdu Institute of Mountain Hazards and Environment, Chinese Academy of Sciences (hereinafter referred to as the Chengdu Institute of Mountain Disasters). Over the past 60 years, they have taken root in Dongchuan to observe, research, and prevent debris flows, providing scientific support for the prevention and management of mountain disasters.
In order to better reveal the laws of nature and solve more practical problems, in April this year, a world-class scientific device - "Mountain Disaster Large-scale Dynamics Simulation Experimental Platform" was officially put into operation in Dongchuan.
On the mudslide beach, the riders competed with themselves, and the scientists also challenged the scientific peak.
Large-scale dynamic simulation experimental platform for mountain disasters. Yang Chen/photo
What is world-class?
Jiangjiagou, located in Dongchuan, is a first-class branch ditch in the Xiaojiang River Basin, famous for its 3,000-meter-long and 1,000-meter-wide mudslide impact beach. Every year, there are many debris flow outbreaks in the ditch and the scale is large, and it is known as the "World Debris Flow Natural Museum".
Looking down from the mountainside next to the ditch, everyone is amazed by the magic of nature: the mountain peaks on both sides are like being scraped by knives, exposing smooth and broken rock masses; at the bottom of the ditch, the gray river beach is like a big mouth about to swallow the distance, and the momentum is violent, which contrasts with the green fields on the side more quiet and gentle.
The Dongchuan Debris Flow Observation and Research Station of the Chinese Academy of Sciences (hereinafter referred to as the Dongchuan Station) and the large-scale dynamic simulation experimental platform of mountain disasters are located in Jiangjiagou, backed by Dacacao Mountain, and located on the right side of Daaozigou.
The reason why the experimental platform is located here is mainly due to the considerations of space distribution, geological safety, convenient transportation and economic feasibility of scientific installations. "The proximity to the natural debris flow ditch makes it easy to access the 'original' debris flow particulate matter for experiments. Zhou Gongdan, the project leader of the experimental platform, said.
Dongchuan Station is built on the beach, and the experimental platform is carved along the ridge. The entire plant consists of a top platform (bin, storage platform, control room and top reservoir), a drain and an outlet guard, most notably the 150-metre-long drain. Its net width is 6 meters, the depth of the trough is 4 to 5 meters, and the bottom slope of the drainage channel adopts two slopes, the upper section is 32° and the lower section is 16°.
"The method of trench excavation and the parameters of the above parts are all obtained through rigorous demonstration and calculation in order to serve the experimental objectives and simulate more realistic scenarios. Zhong Wei, deputy director of Dongchuan Station, said that in the experiment, the researchers opened the gate at the top to put materials to simulate the occurrence and development of debris flows. "The length of the drainage channel currently designed can ensure that there is sufficient space for the development of debris flow during the movement and facilitate observation. ”
In addition to debris flows, the experimental platform can also realize the simulation of mountain disasters (chains) such as landslides, flash floods, and dammed lakes. The purpose of the simulation experiment is to understand the formation-initiation process and motion mechanism of disasters more clearly.
The 32° slope area of the drain is mainly used to observe and study the formation process of disasters, while in the 16° slope area, researchers pay attention to the movement process of disasters. The approximately 2,500-square-meter horizontal protective platform connected to the outlet of the drain can be used for research related to the accumulation and impact of mountain disasters, especially for disaster prevention and mitigation engineering and product safety testing.
Compared with the existing debris flow dynamics simulation experimental devices at home and abroad, the experimental platform has achieved an order of magnitude improvement in experimental scale and travel distance.
Compared with similar devices in the world, the experimental platform has the advantages of large-scale, repeatable and controllable experiments, and has three "most" - the largest scale of physical simulation of mountain disasters in the world, the highest degree of automatic monitoring, and the best synchronization of system data collection.
The physical simulation scale, i.e. the maximum capacity that can be loaded into the platform bin is 500 cubic meters. The time from the delivery of the material to the completion of the experiment is only about two minutes. During this period, the dynamic process information can be quickly and accurately captured by the multi-dimensional multi-field and multi-frequency monitoring system integrating sound, light, electricity, magnetism and heat in the leakage tank.
According to Zhou Gongdan, the drain is divided into three observation sections from top to bottom, and each section has the technology of acoustic, optical, electrical, magnetic and thermal fusion. "There are 9 groups of equipment distributed, and each group is equipped with cameras and high-speed cameras from the left, center and right directions, and there are also induction modules buried under the concrete floor at the bottom of the drain. "Under the horizontal shield surface, five sets of substrate sensors are also installed.
The synchronously acquired data is pooled into the data collection room at the top. The distributed fiber optic sensor installed in the device can achieve a sensing speed with millisecond error.
Experimental platform from the perspective of a drone. Zhong Wei/photo
The original intention remains the same
Why build such an experimental platform?
Zhou mentioned that in 2005, Science sorted out 125 of the world's most challenging scientific problems, including turbulence dynamics and the kinematics of particulate materials. This problem is closely related to mountain hazards, which are themselves the most complex particulate materials. "The turbulent dynamics of debris flow is an important direction of dynamics research. It can be said that our research aims at international frontier scientific issues. ”
However, the core of the kinematic research of particulate materials is the scale effect of multiphase media motion, and the results of small-scale physical simulation experiments in indoor laboratories cannot reveal the law of physical and mechanical dynamic evolution of large-scale and large-scale natural prototypes in nature.
"Therefore, we urgently need to upgrade our scientific and technological facilities and experimental platforms to better support basic research. He said that revealing the laws of nature is their original intention.
Indeed, since the establishment of Dongchuan Station in 1961, several generations of scientists have been practicing this original mission. From May to September every year, during the dangerous period of the Jiangjiagou debris flow outbreak, the researchers became retrograde and stationed at the station for a long time.
Chen Shunli, who has worked at the station for 16 years, has a lot to say about this, he has served as a deputy stationmaster, and has worked with many stationmasters. Chen Shunli introduced that when the debris flow occurred, the work on the station was mainly measurement, observation, sampling and recording. The measured data includes flow rate, flow rate, mud level height, etc., and radar velocity, floating, ultrasonic mud level gauge, etc. are the main measurement tools.
In the absence of automated equipment, researchers naturally spend more time and energy, sometimes standing on a sun-exposed beach for half a day, and sometimes staying on a summer night with lightning and thunder.
When the power goes out, the semi-automatic sampling device does not work, so the staff has to carry a tin bucket to the ditch to take samples of the mudslide. "The person in charge of the sample had to tie a rope around his waist and be dragged by the people on the shore. Chen Shunli recalled that in 1989, due to the impact of the mudslide, a scientific researcher was dragged down by a bucket when he bent down to take a sample, and almost got involved in a ditch, and everyone present was scared into a cold sweat.
Relying on the Dongchuan Station, the Chengdu Mountain Institute has accumulated observation data on the formation and development processes of the upper, middle and lower reaches of debris flows, as well as the accumulation and evolution of riverbeds based on years of observation and research. Today, the database has accumulated more than 300 gigabytes, with an average of more than 700 people applying for it every year.
Once the first-hand data is in hand, the researchers analyze and conduct simulation experiments to explore the formation mechanism and dynamic process of mountain disasters. However, the stability and repeatability of small-scale field experiments are insufficient, and the conditions of indoor experimental equipment are limited, so they came up with the idea of building a large-scale debris flow field model experimental field.
Back in 2002, the idea was already in the form of preliminary plans. However, for a long time, due to a series of factors such as economic conditions and land procedures, the promotion of related projects has been more than enough but not enough.
In 2015, the construction of a large-scale dynamics simulation experimental platform for mountain disasters was finally put on the agenda. The experimental platform is deployed by the Chinese Academy of Sciences, jointly developed by the Chengdu Institute of Mountain Sciences, the Hong Kong University of Science and Technology, and the Power Construction Corporation of China, with a design service life of 30 years.
After 8 years of preparation, design, construction, installation and commissioning, the experimental platform was put into trial operation in December 2023 and officially put into operation in April this year. A wish for many years has finally come true.
Researchers at Dongchuan Station took old photos of the sampling site. Courtesy of Chen Shunli
"Standing up to the sky"
"After the experimental platform is built, we will not only publish articles, but also solve problems. At the strategic consultation meeting on disaster prevention and mitigation in April, Cui Peng, an academician of the Chinese Academy of Sciences, as the old stationmaster of Dongchuan Station, put forward the requirements for future research work to "stand up to the sky" and "stand on the ground".
"Dingtian" means making good use of this world-class experimental platform to do cutting-edge research; "Standing on the ground" means that all research work should be ultimately oriented to solving practical problems.
In the past, the scientific research work of Dongchuan Station was also a process of combining with actual needs. Researchers cooperate with the local government of Dongchuan to guide the comprehensive research and prevention of debris flows. Based on years of experience in debris flow observation, experiment and research, they have designed a variety of prevention and control projects and technical means, put forward comprehensive treatment measures of "stabilization, blocking and discharge", and created the "Dongchuan model" of debris flow prevention and control of "combining engineering treatment with biological treatment and treatment with treatment and development".
"The specific measures can be summarized as consolidating soil and stabilizing slopes, holding back sand and storing mud, restricting water and attacking sand, and reclaiming land and opening up fields. Chen Shunli introduced, especially in the downstream of the debris flow, the establishment of the "Dongchuan trough" named after the debris flow drainage channel, effectively the debris flow gradually led to the area of small damage, to achieve the purpose of comprehensive treatment.
With these measures, the threat of disasters has been reduced, the barren beach has become fertile land, and even a new form of cultural tourism has been derived.
In the future, with the blessing of simulation experiments, what will be the development of the "Dongchuan model"?
"It is clear that we have simulated mountain disasters with a near-prototype scale through the newly built experimental platform, which will help to find out the influencing factors and internal laws as soon as possible. Chen Xiaoqing, deputy director of the Chengdu Mountain Institute, pointed out that it is also important to use the experimental platform to test disaster prevention and mitigation projects and products, and establish corresponding safety technical standards. "Let our prevention and control work be targeted and well understood. ”
Chen Xiaoqing said that the new generation of scientific researchers should focus on the construction of ecological civilization and explore in accordance with the concept of "green and sustainable" and "more resilient". "In the past, when various conditions were limited, the predecessors summed up a set of 'Dongchuan model' through decades of practice and laid the foundation. Now that we rely on the experimental platform, we may be able to harvest a new set of 'Dongchuan models' in a shorter period of time. ”