Using the example of objects located in the Sochi mountain cluster and in the Trans-Baikal Territory, a wide range of technical solutions used for engineering protection against mudflows is given.
*The report was read out by Chief Designer of GEOIZOL Project Pavel Alexandrov at the IV International Scientific and Practical Conference «Engineering Protection of Territories, Buildings and Structures» on March 22, 2022. You can download the presentation for the report here.
Chief Designer of GEOIZOL Project Pavel Aleksandrov
The danger of mudflow processes is obvious — their development near settlements, economic and infrastructure facilities is fraught not only with serious economic losses, but also threatens human life and health.
The relevance of the implementation of anti-mudflow measures increases every year. Protection is required both for developed territories and areas for which mudflows were not previously typical. The activation of mudflow processes is caused by climate change, the occurrence of natural and man-made emergencies (anomalous precipitation, forest fires), as well as destructive human activity (uncompensated deforestation).
General view of the mudflow-retaining barrier
The first category includes the resorts of the Sochi mountain cluster, where, because of the Olympics, many sports and recreational infrastructure facilities have appeared that require protection. To the second — a section of the Amur federal highway, which was blocked in the summer of 2018 as a result of a mudflow and a landslide caused by it. The article discribes the experience of the company «GEOIZOL Project» in the design of anti-mudflow structures at these sites.
Modern methods of engineering protection against mudflows
Mudflow protection, as a rule, requires an integrated approach, which provides for a combination of various measures, the main of which include:
— planning decisions involving the transfer of objects from the danger zone;
— exclusion of mudflow formation factors by strengthening the channels of watercourses and soil massifs, arranging of anti-erosion protection;
— changing the direction of mudflows by building longitudinal dams and mudflow control structures;
— reduction of mudflow volumes due to the installation of rigid barriers and flexible mudflow-retaining barriers.
The entrance part of the drainage flume overchute, designed to direct mudflows
The experience of the company «GEOIZOL Project» has shown that the installation of traditional anti-mudflow structures, primarily dams, has a number of significant limitations. Their arrangement, as a rule, involves the need to perform a large amount of excavation work. Large-sized dams are not always possible to fit into the boundaries of the existing land allotment. When they are arranged, the natural relief changes. This can cause serious damage to the environment.
Despite the relatively low cost of the solution, the actual cost of constructing a protective dam can significantly exceed the estimated cost in the case when the protected object is far from settlements and quarries for the extraction of inert materials.
When designing engineering protection against mudslides at facilities in Sochi, these limitations led to the search for modern technical solutions. These include flexible mudflow-retaining barriers.
Arranging mudflow-retaining barrier
The barrier consists of a chain mail or high-strength steel mesh stretched between posts and reinforced with steel ropes. The barriers are additionally held by guy ropes equipped with energy-capturing devices that compensate for the dynamic load from the mudflow. For fixing posts and guy ropes, bored-injection ground anchors are used, including the multifunctional geotechnical system GEOIZOL-MP.
Barriers are installed across the calculated mudflow channel to retain the solid part of the runoff, which poses the greatest danger to the protected objects. Constructions are intended for multiple use. Their correct operation: cleaning after each impact of the force of nature and, if necessary, replacing damaged elements (shock-absorbing devices) guarantees the performance of the structure for decades.
Mudflow-retaining barriers
Barriers are delivered partially assembled to the place of installation. Their arranging requires a small amount of ready-mixed concrete. The work can be carried out by a small team of skilled workers using light equipment, which makes it possible to build barriers in hard-to-reach places and does not require the construction of access roads and the deployment of a construction camp.
The disadvantages of this solution include the relatively high cost of flexible mudflow-retaining barriers. However, in some cases, the total costs are lower than in the implementation of traditional solutions. This is due to the high speed and technological of construction and installation works, the possibility of placing the facility on a small area, the installation of barriers with preservation of the ecosystem (without changing the relief and cutting down trees), as well as low operating costs.
Experience in the design and operation of anti-mudflow structures in the Sochi mountain cluster
On the territory of Krasnaya Polyana in Sochi two major projects have been implemented to protect against mudflows.
The first is within the boundaries of the Mountain Tourist Center (GTZ) Gazprom. Surveys have revealed a focus of mudflow formation above the Rudnichny stream. In addition, repeated man-made mudflows caused by construction work on the slope of the Psekhako Ridge were recorded.
The entrance part of the mudflow chute and barrier No. 1 near the pumping station. GTTS «Gazprom», Sochi.
At the first stage, in order to protect the pumping station under construction and the facilities located below on the banks of the Laura River, an open-type mudflow chute was made in the form of a reinforced concrete flume 4.5 wide, 2.5 high and 365 m long. It designed for a mudflow with a volume of 7,500 cubic meters and with a speed at the entrance of more than 6 m / s. During the inter-mudflows period, the facility functions as an artificial stream bed, preserving its natural hydrological regime.
At the second stage, in order to protect the lower cableway station under construction, the Galaktika entertainment center and other recreational infrastructure located near the mouth of the stream, the Rudnichny channel was blocked with a cascade of six flexible mudflow-retaining barriers. Structures with a width of 25 and a height of 6 m are designed for a total volume of 8,800 cubic meters of retained mass.
Mudflow-retaining barrier No. 2 crossing the Rudnichny stream
The complex of measures completely excluded the impact of mudflows on the protected objects. Considering the fact that mudflow phenomena are recorded on this site almost every year, the technical solution has proved its effectiveness in practice. Access roads are organized to the barriers for mechanized clearing of retained solid runoff, which is carried out as they are filled. Structures are designed for the maximum possible loads and have a sufficient strength reserve, which reduces the replacement of consumable elements.
On the territory of the Alpika-Service mountain climatic resort, mudflow processes are confined to three watercourses — the Sulimovsky, Shumikhinsky and Rzhanoy streams. Accordingly, anti-mudflow protection measures here are divided into three stages.
The greatest danger to the buildings and facilities of the resort came from the Sulimovsky stream. The mudslide passing along its bed threatened sections of the Alpiysky highway, technological passage to the Rosa Khutor resort and the water scoop of the artificial snowmaking system of the Alpika-Service resort.
General view of the Aibga slope. On the left is a cascade of three barriers. In the center — dowel fastening of the slope. To the right is a part of the retaining wall of the Yunost station. «Alpika-Service», Sochi.
As part of the first stage, a decision was made to fix the soil massif within the boundaries of the mudflow basin located above the Sulimovsky stream. To eliminate part of the focus of mudflow formation, dowel fastening of slope sections was performed in combination with a cover system that provides anti-erosion protection.
Taking into account the residual risks, in the stream bed near the Yunost cableway station, a cascade of three mudflow-retaining barriers was made, designed for a total volume of retained mass of up to 8,000 cubic meters. The constructive solution was adopted similarly to that implemented in the GTZ «Gazprom».
Cascade of three mudflow-retaining barriers
Rzhanoy and Shumikhinsky streams have significantly larger areas of mudflow formation centers and calculated parameters of mudflows — more than 37,000 and 32,000 cubic meters. m respectively. Surveys have shown that mudflows descending along these watercourses do not pose a hazard to buildings located at the foot of the slope of the Aibga ridge on the banks of the Mzymta River, but can damage ski slopes.
Considering, the implementation of measures to prevent mudflows and retain solid runoff is recognized as irrational. To protect the ski slopes, the construction of two mudflow chute facilities of a closed-type was adopted.
Mudflow chute of a closed type, built in the bed of the Rzhanoy stream
Mudflow pass in the channel of Rzhany has a flume width of 10, a height of 7.4 and a length of 192 m, which makes it possible to pass the estimated volume of mudflow under the protected object. The box structure is partly made of pile retaining walls, partly in the form of sheet piling with a protective concrete coating. The artificial concrete channel makes it possible to withstand the loads from the mudflow, as well as to ensure the normal regime of the stream during the inter-mudflow period. Mudflow chute in the channel of the Shumikhinsky stream was made in a similar way.
Monitoring the operation of facilities since 2014 has shown the effectiveness of the decisions made, which is confirmed by the complete elimination of the negative impact of mudflows on protected facilities.
Mudflow protection facilities for transport infrastructure
One of the key points in the design of mudflow protection measures for roads and other linear facilities is the need to place structures in a narrow right of way.
GEOIZOL Project successfully managed this task when designing anti-landslide and anti-mudflow measures at km 17 of the federal highway R-297 «Amur» Chita — Khabarovsk in the Trans-Baikal Territory. The construction of the facilities will be carried out as part of the overhaul of the section km 10 — km 20.
A section of the Amur highway after a mudflow
At the end of July 2018, after long downpours, a mudflow came down, destroying part of the slope. As a result, the highway was blocked for almost a week. Surveys have confirmed the risks of recurrence of hazard phenomenon. Three basins have been identified where mudflows can form.
To protect the highway, it is planned to build a flexible mudflow-retaining barrier, as well as to strengthen the channel with the installation of a reinforced soil embankment along the trajectory of the mudflow.
Location plan of mudflow-retaining barrier and reinforced soil embankment
The designed barrier is a mesh structure 10 meters high and 360 meters long. The stability of the structure is provided by a powerful concrete base with a foundation of bored piles with a diameter of 1000 mm and a length of 10 meters, as well as reinforcement with GEOIZOL-MP ground anchors 19.5 meters long.
Mudflow-retaining barrier. Sectional
The construction retains solid runoff that can fill up the track. Due to the permeability, water is squeezed out through the barrier and is directed through the trays to the drainage system of the road. The use of a high-strength mesh with damping elements allows the barrier to take a powerful blow, extinguishing the energy of the water-ground flow, and retain a large amount of mudflow
Visualization of the designed mudflow-retaining barrier
The uniqueness of the designed barrier lies in the fact that it is able to withstand a high load, protecting against mudflows, but at the same time, it has minimal dimensions, which made it possible to place it in the right of way of the road.
3D model of reinforced soil embankment
The second part of the engineering protection project involves the construction of a reinforced soil stepped embankment to restore the relief and exclude the development of slope processes. The embankment is erected on a foundation reinforced with GEOIZOL-MP soil dowels. An artificial channel is arranged in it to prevent water erosion of the structure and the natural ravine located above.
As a result, it should be noted that all the above technical solutions are localized in Russia. Our partners from the company «Geobarrier» organized the production of materials and components necessary for the implementation of various types of retaining barriers and cover systems.
Work division «Pushkin Machine-Building Plant»
The Pushkin Machine-Building Plant (part of the GEOIZOL group of companies) organized the production of the GEOIZOL-MP multifunctional geotechnical system, which is widely used for fastening barriers and cable-mesh systems.
Transportable Drilling Mining Rig
The company also produces small-sized mining drilling rigs used in the installation of ground anchors and dowels.
Modern technologies significantly expand the range of tasks to be solved in the field of engineering protection of the territory. Competent accounting and assessment of possible risks allow you to choose a rational solution that provides the required level of safety at minimal cost. GEOIZOL Project successfully deals with such tasks.
Chief Designer of GEOIZOL Project
Pavel Aleksandrov