Report presented at the international conference "NO-DIG - 2008". Author - M.B. Golota (Spetsstroy-Engineering LLC, Russia, Moscow).
The construction of underground communications in dense buildings of such a rapidly developing metropolis as Moscow is a most difficult engineering task. The rapid development of our company is also due to the fact that in our work we use the latest achievements and developments in the field of underground construction. In addition to the fleet of construction equipment, Spetsstroy-Engineering LLC has at its disposal tunnel boring complexes from Herrenkneht AG: AVND 2500 (project M890 and project M1176), ERV 3600 (project M1179) and ERV 3200; equipment from VMT and Jackcontrol companies.
Similarly, tunnels for mining and civil engineering projects share basic procedures but differ largely in the design approach to permanence due to their different purposes. Many tunnels were planned for temporary use only minimal costs during ore mining, although the growing desire by surface owners for legal protection against subsequent tunnel collapse may cause this to change. In contrast, most public transport tunnels involve prolonged human occupancy and complete protection of adjacent owners, and are more conservatively designed to ensure ongoing safety.
With the acquisition of three shields from Herrenkneht AG, the volume of tunneling work has increased significantly. Objects built recently:
- CL-110 kV “Novobratsevo – Voikovskaya. A tunnel with a diameter of 3 m and a length of 1200 m was built. The soil - water-logged sands - was successfully passed between the gas pipeline and the tunnel for large-diameter communications. Due to the impossibility of moving the tunnel with communications, turns were made in the plan and profile of the route. Shield AVND 2500.
- CL from the Novo-Vnukovo substation. A tunnel with a diameter of 3.6 m and a length of 240 m was built. The soil is clay with silt and peat.
- CL from the Marfino substation A tunnel with a diameter of 3 m and a length of 1340 m was constructed. An interval of 852 m long was successfully completed. The excavation was carried out in the most difficult mining and geological conditions - clay soil with stones in contact with heavily watered sands and peat bogs. Shield AVND 2500.
- KVL-110 kV "Novo-Kuntsevo - Setun". A tunnel with a diameter of 3 m and a length of 1350 m was built. Due to high density soil (clay), the presence of underground communications, it was necessary to make a turn with a radius of 300 m, taking joint solutions with Herrenknecht specialists. Shield AVND 2500.
- CL from the Ochakovo substation to the City-2 substation. A tunnel with a diameter of 4.1 m and a length of 500 m was built. The construction was carried out under the most important federal highway. Shield ERV 3600. 2 tunnels with a diameter of 3 m and a length of 400 m were built. The construction was carried out under the river. Moscow, depth 30 m. 2 tunnels with a diameter of 3 m and a length of 550 m were built.
About the areas of application of the equipment
Heavily fractured and soft rocks
In all tunnels, geological conditions play a dominant role in controlling the suitability of construction methods and practicality various designs. Indeed, the history of tunneling is filled with cases where sudden encounters with unforeseen conditions forced lengthy stoppages for changes in construction methods, design, or both, resulting in significant increases in cost and time.
Main elements of the tunnel
Careful geological analysis is necessary to assess the relative risks at different locations and to reduce uncertainties in soil and water conditions at a selected location. The main factors include, in addition to soils and rocks, initial defects that control the behavior of the rock mass; size of stone block between joints; weak layers and zones, including faults, shear zones, and altered areas weakened by weathering or thermal effects; groundwater, including flow pattern and pressure; plus several special hazards such as fire, gas and earthquake risks.
Not every new technical development or discovery will find its application and place on the market; many remain unnoticed and unclaimed. This cannot be said about a relatively young construction industry such as microtunneling.
The growing level of urbanization every year leads to a rapid increase in the population of cities. Such a huge metropolis as Moscow is no exception. The continuous increase in the capital's population has resulted in incredible land values.
For mountainous areas, the high cost and long time required for deep drilling usually limits their number; but much can be learned from careful aerial and ground surveys, as well as logging and geophysics techniques developed in the petroleum industry. Often the problem is addressed by flexibility with respect to changes in design and construction methods, as well as continuous exploration ahead of the tunnel, carried out in old tunnels by mining a pilot drill in front and now by drilling.
Damage to settlements and lost lands
Japanese engineers became pioneers in overcoming problematic rock and water conditions. Soft soil tunnels are most often used for urban services, for which the need for quick access by passengers or maintenance personnel favors a shallow depth. In many cities this means that the tunnels are above bedrock, making tunneling easier but requiring constant support. The tunnel design in such cases is typically designed to support the entire load of the soil above it, partly because the earthen arch in the soil deteriorates over time, and partly to accommodate changes in load as a result of future building or tunnel construction.
In this regard, the city is growing upward and “underground”.
Underground parking is part of the solution to the problem of lack of free space for development, but not the only one. Relatively large areas can be freed up by moving engineering, transport communications, and power lines underground. One of the ways to implement such grandiose projects is microtunneling.
Soft ground tunnels tend to be circular in shape because the shape gives it greater strength and the ability to adapt to future load changes. In areas of street rights en route, the dominant problem of urban tunneling is the need to avoid intolerable damage to adjacent buildings. While this is rarely a problem with modern skyscrapers, which typically have foundations extending into cliffs and deep basements, often running underneath a tunnel, it can be a deciding factor with mid-rise buildings whose foundations are typically shallow.
When the first microtunneling project was implemented in the mid-90s using equipment from Herrenkneht AG, few could have imagined that this technology would take root so easily and quickly in Russia. And for more than ten years, this technology will help solve complex engineering problems.
There is no doubt that in the near future microtunneling will be relevant and in demand more and more. It is impossible to ignore the plans of the Government of the Russian Federation to reform the housing and communal services and energy sector of both the capital and Russia as a whole. According to various statistics, network engineering in Russian cities they are worn out by 70% or more; About 1000 hectares of land within Moscow alone are under power lines.
In this case, the tunnel engineer must choose between reinforcements or using a tunneling method that is reliable enough to prevent settlement damage. Surface settlement occurs due to loss of soil, i.e. earth that moves into the tunnel in excess of the actual volume of the tunnel. All tunneling methods on soft soils result in a certain amount of lost soil. Some are unavoidable, such as the slow lateral compression of the plastic clay that occurs ahead of the tunnel face as new stresses from the dome train cause the clay to move toward the face before the tunnel reaches its location.
In dense urban areas, the slogan “No Dig” is especially relevant. The incessant life of the metropolis does not make it possible to carry out work on relaying or laying tunnels with stopping traffic on congested roads; construction time should also be reduced as much as possible. All of these factors are a strong argument for attracting increasing investments in microtunnelling. And this is important, since impeccably accurate, high-tech equipment requires considerable investment and professionalism of the personnel serving it.
However, most lost results are the result of poor construction methods and careless workmanship. Therefore, the following highlights reasonably conservative tunneling techniques that give best chance keep the land at an acceptable level by about 1 percent.
The ancient practice of manual extraction is still economical for some conditions and may illustrate specific techniques better than its mechanized counterpart. Examples are prepolation methods and breastfeeding, designed for dangerous mileage situations. Figure 3 shows the main aspects of the process: the header is advanced under the roof of the front boards, which are advanced forward on the crown plus a solid board or breast milk in the title. When worked carefully, the method allows progress with very a small amount losses.
Our company has been fruitfully cooperating with Herrenkneht AG for two years now. The motto of our German partners is especially close and perfectly suits the Russian mentality - “Teamwork Tunneling”. Only a team, when the manufacturer, engineers, and builders are involved in the project, can coordinated work and high results be achieved.
Spetsstroy-Engineering LLC has at its disposal various tunnel boring complexes:
The top board could be removed, the small backpack unearthed, that chest board replaced, and progress continued, working on one board at a time. When punctured, the anterior spaces are discontinuous with spaces between them. Crown rotation still resorts to passing through bad ground; in this case, the studs may consist of forward-guided rails or even steel rods set in holes drilled into crushed rock. In soil that provides a reasonable standing time, modern system support uses steel lining plates placed on the ground and secured in a continuous continuous circle, and in larger tunnels reinforced internally with circular steel ribs.
- AVND 2500 project M890,
- AVND 2500 project M1176,
- ERV 3600 project M1179,
- ERV 3200.
The fleet of equipment of such considerable diameters is unique in its own way. According to statistics, the share of such tunnel boring complexes in Russia accounts for only 5%.
Personnel policy
The underground space of the capital is becoming more and more complex from year to year. In addition to the long-distance metro, the subsoil of Moscow is saturated with even longer communication tunnels various diameters and appointments.
The longest tunnels
Custom earbuds are lightweight and easy to install by hand. The top header moves forward, preceded by a "monkey's drift" in which the wall slab is set, and provides support for the arched ribs, and is also covered as the wall slab is supported by the installation of posts with small cutouts on each side of the lower bench. Since the ribs and lining provide only light support, they are strengthened by installing a concrete lining approximately one day after mining.
If shields with a diameter of up to 1500 mm have already covered many kilometers near Moscow and accumulated enough great experience, then only a few companies have mastered equipment of such a large diameter. Requiring even greater control and professionalism, such tunnel boring systems are in great demand.
Our company’s specialists - engineers, mechanics, operators - have undergone specialized training in working with equipment from Herrenkneht AG and have certificates.
While liner tunnels are more economical than screening tunnels, the risk of soil loss is somewhat higher and requires not only very careful fabrication, but also a thorough study of soil mechanics in advance, a first for Chicago. The risk of losing ground can also be reduced by using a shield with separate pockets from which my workers can work; they can be quickly closed to stop typing. In extremely soft soil, the shield can simply be pushed forward when all its pockets are closed, displacing the soil completely in front; or it can be tucked in with some open pockets through which the soft soil is squeezed out like a sausage, cut into pieces for removal by a conveyor belt.
Our company's personnel policy is aimed at creating a cohesive team capable of making extraordinary engineering and technical decisions and performing tasks of any complexity. The fusion of youth and experience has the best impact on the quality of fulfillment of assigned tasks, and allows us to look with confidence at future development prospects. Our specialists have worked on the construction of the Moscow Ring Road, in the construction of the Third Transport Ring, and in laying kilometers of tunnels.
The first of these methods was used on mud in the Hudson River. The support, mounted inside the tail of the screen, consists of large segments so heavy that they require an electric heater arm to position them when bolted together. Due to its high corrosion resistance, it is the most commonly used material for segments, eliminating the need for secondary concrete lining. Today the lighter segments are occupied. British engineers have developed segments that are popular in Europe.
An inherent problem with the shield method is the two to five inch ring-shaped void left outside the segments as a result of the thickness of the skin plate and the clearance required for segment erection. The movement of soil into this void can result in a loss of up to 5 percent, which is unacceptable in an urban environment. Lost soil is kept at reasonable levels by quickly blowing fine gravel into the void and then injecting cement.
Objects
Construction of the 110 kV cable collector “Novobratsevo - Voikovskaya”:
The excavation depth was about 10 m.
The excavation was carried out in difficult hydrogeological conditions. Thus, the construction of mines and microtunneling was carried out in watered sands of small and medium size, which, under the influence of technogenic factors, lose their structural strength and become fluid. The groundwater level, taking into account its seasonal increase, throughout the entire construction site exceeded the level of the collector and the bottom of the microtunnel.
Kuznetsovsky railway tunnel
Tunnel with soft ground below level groundwater is associated with a constant risk of soil and water entering the tunnel, often resulting in complete loss of the title. One solution is to lower the groundwater level under the bottom of the tunnel before construction begins. This can be achieved by pumping from deep wells in front and from wells in the tunnel. While this promotes tunneling, the drop in groundwater levels increases stress on deeper soil layers. If they are relatively compressible, the result may be major settlement of adjacent buildings on shallow foundations, an extreme example being subsidence of 15 to 20 feet due to overloading.
To localize the influence of groundwater during the construction period, artificial dewatering was provided through deep wells with pumps (installed at the output of the shield, in a dismantling shaft located in the area of local distribution of aquifers).
The excavation was carried out using an AVND 2500 shield. The 1200 m long route was passed in three intervals of 200 m and one interval of about 600 m.
When soil conditions make it undesirable for the groundwater level to drop, outside water pressure may shift inside the tunnel. In larger tunnels, the air pressure is usually set to balance the water pressure at the bottom of the tunnel, causing it to then exceed the smaller water pressure at the head. Since air tends to escape from the top of the tunnel, constant inspection and repair of leaks with straw and dirt is required. Otherwise, a blowout may occur, depressurizing the tunnel and possibly losing the header as soil enters.
Due to the presence of a gas pipeline and a tunnel for large-diameter communications on the route and the impossibility of transferring existing communications, turns were made in the plan and profile of the route. All intervals were completed on time, without delays.
Construction of the 110 kV cable collector “Novo-Kuntsevo – Setun”:
Compressed air significantly increases operating costs, partly because a large compressor unit is required, with redundant equipment to insure against loss of pressure and partly because of the slow movement of workers and crooks through airlocks. However, the dominant factor is the enormous reduction in production time and long decompression times required for people working under the influence of air to prevent the devastating disease known as also encountered by divers.
The excavation depth was about 15 m.
The excavation was carried out not only under existing driveways and green spaces, but also under high-voltage power lines, as well as under the tracks of the Moscow railway Belarusian direction.
An AVND 2500 shield was used. The 1350 m long route was covered in two intervals of about 600 m.
The first interval, 630 m long, had difficult geological conditions. In the thickness of the developed soil of high density loams and clay, there were fragments of the foundation, reinforced concrete structures from demolished buildings and structures.
Due to the density of underground communications, with the help of Herrenkneht AG specialists, a turn with a radius of 300 m was made. The pipe pushing control system made it possible to accurately determine the location of the tunneling machine at any time. The position of the machine is constantly reflected on the control panel screen, allowing the operator to flawlessly control the mining process.
To localize the influence of groundwater during the construction period, artificial water reduction was provided with light wellpoint filters inside the mine.
Construction of a 110 kV cable collector from the Marfino substation:
The excavation depth was 12 m.
An AVND 2500 shield was used. The 1340 m long route was covered in two intervals. One of the intervals was 850 m long. Passing an interval of such length and with a diameter of 2500 mm is unique for Moscow. The well-coordinated work of the Spetsstroy-Engineering LLC team, the impeccable operation of the equipment and assistance from the manufacturer made it possible to complete the interval without delays, accidents or breakdowns.
The most difficult geological conditions - the excavation was carried out in soil consisting of clay with stones in contact with heavily watered sands and peat bogs.
To localize the influence of groundwater during the construction period, artificial dewatering was provided using deep wells with pumps (installed at the input of the shield, in the mines), as well as light wellpoints (reception pit).
Construction of a 110 kV cable collector from the Yashino substation:
The excavation depth was 10 m.
An AVND 2500 shield was used. The 650 m long route passed in difficult hydrogeological conditions, under existing passages and in close proximity to the Moscow Metro tunnels.
Drilling was carried out in water-logged sands of various granulometric compositions, in places with layers of loam, peat and water-saturated sand. The significant excess of groundwater and the heterogeneity of the lithological composition in the excavation area created a number of difficulties in carrying out water reduction.
Construction of a 110 kV cable collector from the Ochakovo - City-2 substation:
The excavation was carried out under the most important route - Kutuzovsky Prospekt - in connection with this Special attention Care was taken to ensure maximum accuracy and the absence of even minimal drawdown.
An ERV 3600 shield with a soil load was used. The route was 500 m.
The excavation depth was 9 m.
The second interval is currently being excavated under the river. Moscow at a depth of 30 meters.
During the construction of all facilities, special attention was paid to ensuring the tightness of the tunnel lining. The build quality of the lining is extremely important factor, which determines the efficiency of the seals, but on the equipment used. The use of double elastomer seals at any of the facilities did not allow us to doubt the versatility and high quality similar technology.
Prospects
The holding of annual international exhibitions, conferences and seminars leaves no doubt about the wide spread of trenchless construction technology and microtunneling in particular throughout the world.
Construction of a modern reliable and sealed tunnel with high speed penetration and quality is possible only by linking the following components:
- complexes corresponding to the ground conditions of construction;
- high quality and precisely installed tunnel lining;
- correct distribution of labor resources;
- precise planning of preliminary work.
The method of constructing a subway tunnel can be open or closed, depending on hydrogeological conditions, the density of underground communications and urban development. In the central areas of the city, as a rule, work is carried out in a closed way. In the peripheral areas of the city, outside the main streets, it is advisable to carry out construction using an open method.
Closed method. With this method of work, tunnels are constructed simultaneously in several areas, which speeds up the construction time. At each site, a mine shaft is laid on the surface above the tunnel axis or close to it and an adit is connected to the tunnel under construction. The excavation of the soil in the tunnel and the lining is carried out from each shaft to the neighboring ones until they meet, i.e., before the cutting of individual sections.
Mountain way tunneling is as follows: the rock is excavated using the drilling and blasting method or with a mechanized tool, after which a temporary fastening of the face and the excavation contour is immediately performed, and then the tunnel lining is erected. In the case of constructing a lining from monolithic concrete or reinforced concrete in the presence of a soil bottom, arrange internal waterproofing with four to six layers of roofing material on bitumen mastic and a 20 cm thick reinforced concrete shell supporting it. This is how sections of considerable length were built on the first stage of the Moscow Metro.
Panel penetration possible in clays, loams, sands, where round tunnels cross section They are usually constructed using a special mechanism - a shield.
The shield is a movable metal support, under the protection of which, in safe conditions, the face is mined, loosened rock is removed and the tunnel lining is constructed. The cross-sectional shape of the shield corresponds to the outer contour of the tunnel lining. Round shields are most common.
There are many varieties tunneling shields, which have become part of the practice of constructing domestic subways.
The shield looks like metal cylinder, consisting of three main parts:
- Support ring made of steel segments;
- Steel knife;
- Shell made of sheet steel.
If the shield is not mechanized, then it does not have any mechanisms for developing the soil. In this case, the shield performs the functions of a mobile support and working scaffolding. When digging a tunnel in hard rocks, they are developed using the drill-and-blast method, and in plastic and loose rocks - with jackhammers and shovels. The loosened rock is removed using loading machines or special devices mounted in the lower cell of the shield.
Mechanized shields are equipped with working bodies of mechanical and hydraulic action. The most widespread are shields with a rotary working body rotating around the longitudinal axis of the tunnel. Shields with working bodies equipped with cutters are also used.
The team of the Moscow Metrostroy has developed a method for excavating shallow tunnels with maximum use of mechanization of the tunneling cycle, which is called the Moscow method.
Moscow way Drilling shallow tunnels involves working in a closed manner. It replaced the previously used open method of work, in which it was necessary to open the earth's surface along the entire length of the tunnel to the depth of its laying and to a width of 10 to 20 m, and therefore the movement of public transport is disrupted, the relocation of city communications is required, etc. The Moscow method provides use of a mechanized shield. The tunneling cycle includes development of the face and extraction of rock from it, loading of rock into trolleys, movement of the shield and all auxiliary equipment behind it, installation of the lining, injection of mortar behind the lining and other work.
When excavating using the Moscow method, the cost of 1 km of a running tunnel is reduced and labor productivity increases significantly compared to open-pit excavation.
Open method. This method of work is used in the construction of shallow tunnels. In this case, the earth's surface is opened - immediately across the entire width of the pit being developed for lining, or in parts - when constructing poplars using the trench method. The lining structure using the trench method is erected in parts. The lining consists of concrete walls, ceiling and tray. The most important and difficult thing in this case is the installation of external adhesive waterproofing.
The most widely used method is to develop a pit immediately to its full cross-section.
At open method First, from the surface of the earth above the future walls of the tunnel, an exploratory trench is dug and I-beam steel piles are driven in at intervals of 1-2 m from each other to a depth of 3-5 m below the tunnel tray. Then, excavators are used to develop a pit, the walls of which, as it deepens, are secured with boards placed behind the flanges of the piles. The piles are secured with metal spacers and struts located above the lining, providing the possibility of mechanized mining and construction of the lining using industrial methods. Where urban development allows, a pit is dug without fastening, and its walls are made at an angle natural slope soil.
The adhesive waterproofing is applied under the tunnel tray on a special concrete preparation, and within the lining of the walls - onto a pre-constructed protective wall made of slabs various materials. The space behind the protective walls is covered with sand.
Upon completion of the work, the metal piles are removed. After the ceiling is erected, a waterproofing layer is also glued onto it, the protective layer is covered, and the pit is covered with earth.
IN last years Tunnel lining sections are constructed primarily from prefabricated reinforced concrete blocks, which significantly reduces construction time. However, the presence of four to six elements in a lining section requires labor-intensive work on cementing joints between blocks, installing glued waterproofing at the work site, etc. These disadvantages are eliminated by the use of prestressed reinforced concrete linings from ready-made sections.
When constructing shallow tunnels and their location under buildings or in the immediate vicinity of them, a device is provided supporting structures, strengthening soils or constructing enclosing walls, as well as measures to reduce vibration and noise from passing trains.
Cracks may appear in tunnel structures due to temperature fluctuations and shrinkage of concrete, uneven settlement of heterogeneous soil. To prevent the occurrence of such cracks, vertical cuts are made in the structure, called temperature-shrinkage or expansion joints. The distance between such seams, depending on the design of the finish, can be 20; 40; 50 and 60 m.
Special methods of work. Such methods are used in particularly difficult engineering and geological conditions, when conventional mining methods cannot be used.
When digging tunnels located below the groundwater level, it is always necessary to combat the flooding of the faces. The following methods are used artificial drainage And consolidation of rocks:
- water reduction;
- freezing;
- chemical fixation;
- cementation;
- bituminization;
- installation of anti-filtration jumpers.
Way freezing does not require removal of water from the pores of the rock. The rock is fixed by freezing, which occurs when a special solution circulates through pipes (columns) installed in freezing wells drilled along a certain contour. The solution (refrigerant) is supplied by refrigeration units.
As a result, a contour of an ice-hydrogen mass is formed near the future excavation, which has sufficient strength and is completely waterproof. This method is used when excavating inclined passages of escalators, tunnels and stations in the most unfavorable hydrogeological conditions. The disadvantages of this method include the susceptibility of some rocks to heaving during freezing and precipitation during thawing, complexity preparatory work, the duration of the process itself and the high cost of freezing.
The rock is secured by freezing and water lowering only for the period of construction of the underground structure; after the construction of all structures and their waterproofing, the rock thaws to its original state and the rock and hydrostatic pressure are transferred to the lining of the structure.
Chemical fixation rocks are carried out by silicatization and resinization. Silication involves the sequential injection of aqueous solutions into the pores of the rock - first liquid glass (sodium silicate), and then calcium chloride. As a result chemical reaction a gelatinous mass is formed, which hardens and binds rock particles into a monolith with high mechanical strength and waterproof. Resinization consists of injecting solutions of synthetic resins with hardener additives. The high cost of this material limits its use.
Cementation consists of filling pores, cracks and voids in the rock cement mortar, displacing water under pressure. When groundwater is highly aggressive, cementation is difficult to carry out; In addition, not all breeds lend themselves well to fixation using this method.
Bituminization consists in filling cracks and voids in the rock mass with molten hot bitumen, which displaces water and hardens to form a monolith. For the same purpose, a fine bitumen emulsion is sometimes injected into the rock; This method is called cold bitumenization.
The rock is saturated with bitumen or a special emulsion through wells into which columns are lowered steel pipes using special equipment.
Installation of anti-filtration jumpers. Such jumpers - sheet piling- are solid walls outside the excavation contour, constructed before the start of earthworks. They are built from piles immersed in the ground close to each other. They can be made of wood, metal and other materials. Such protection of workings from groundwater can be arranged quickly and provides a complete guarantee of work safety.
Tunneling under compressed air. In water-bearing unstable rocks, tunneling can also be done under compressed air ( caisson method). Before the start of caisson work in the tunnel, at a distance of 40-50 m from the face, a sluice airtight reinforced concrete or steel partition is constructed, dividing the tunnel into two zones: a normal pressure zone and work area(from the bottom to the partition), called a caisson, where increased pressure is created (compared to atmospheric pressure), feeding compressed air from the compressor station. The face can be developed using any of the methods described above. Due to the increased air pressure in the caisson, which exceeds hydrostatic pressure, water is pushed out of the face and working area.
