RU30362U1 - Permafrost intermediate bridge support - Google Patents

Abstract

1. The intermediate support of the permafrost bridge, including one or more racks located in the ground, which is a hollow element closed from the lower end, the upper part of which rises above the low-water level, and a nozzle plate, into which the upper ends of all the racks are embedded, characterized in that around the uprights there is a platform, which is convex in plan and fortified from erosion, made of soil or other material, with the center of the site coinciding with the center of the support, the average diameter of the site not less than 1 m, and the top level oschadki Nopredelyaetsya of zavisimostiN> H- 0,1 + 0,16t, [m], where H is the level of low-flow water, m; t- average outdoor temperature Grad 2. The intermediate support of the permafrost bridge according to claim 1, characterized in that the dimensions of the site in the plan are determined from the following relationships: d≥ D [m], where D is the average diameter of the frozen zone formed by the support in the talik by the end of the cold season, m; d, d- respectively the maximum and minimum size of the site in the plan, m.

Description

INTERMEDIATE BRIDGE BRIDGE ON PERMANENT FROZEN

The utility model relates to the field of construction, namely to the construction of artificial structures in areas with the spread of permafrost.

The intermediate bridge support on permafrost is known, consisting of pillar racks united from above by a nozzle plate. To freeze or lower the soil temperature, cooling units (thermosiphons) designed by S.I. Gapeev or V.I. Makarov were mounted. (“Recommendations on the use of self-regulating liquid cooling devices on the supports of small and medium bridges in permafrost regions, All-Russian Research Institute of Transport Construction, Moscow, 1987, p. 12, Fig. Sv;). A design flaw is that such a support can only be used on dry land. If there is an ice drift, the cooling units, which are steel pipes with a diameter of up to 20 cm, will be cut off by this ice drift

 19/02

The closest in technical essence and the achieved result to the claimed one is the intermediate support of the permafrost bridge, which includes one or several racks located in the ground, which are a hollow element closed from the bottom, the upper part of which rises above the level of low-water waters, and the slab nozzle, in which is fixed to the upper ends of all racks. (“Recommendations for the design and construction of thermal supports for small and medium-sized bridges in permafrost soils, All-Russian Research Institute of Transport Construction, M., 1987, p. 5, Fig. 16).

The disadvantage of such a support is that if there is a water flow at the location of the support of the support with a depth of more than 0.5 - 1.0 m, a stable melt zone is formed in the upper part of the soil mass, on the one hand, worsening the work of the support on horizontal forces, and on the other, requiring a significant increase in the depth of the pillars for the perception of vertical loads.

The objective of the proposed utility model is to increase the efficiency of using thermal supports for maintaining and strengthening permafrost at the base of bridge supports by combining surface and deep cooling of the base soil.

To achieve a technical result in the intermediate support of the permafrost bridge, which includes one or several racks located in the ground, which are a hollow element closed from the lower end, the upper part of which rises above the level of low-water waters and the slab nozzle in which the upper ends of all the racks are embedded, around the uprights there is a platform that is fortified from erosion and planar, made of soil or other material, the center of the site coinciding with the center of the support, the average diameter dcp of the site not less than 1 m, and the pad top level determined from the dependence NPL

NPP Hj ,, e - 0.1 + 0.16 tg, m, where Nmv is the level of low-water waters, m; te, is the average annual outdoor temperature, deg. Moreover, 4 for the conditions under consideration always has a negative value.

In addition, the dimensions of the site in the plan can be determined from the following relationship:

where D is the average diameter of the frozen zone formed by the thermal support in the talik by the end of the warm season;

dm (v: dfnin - respectively the maximum and minimum size of the site in the plan, m;

The invention is illustrated by drawings, where

in FIG. 1 - shows a General view of the intermediate support on permafrost, a section along the longitudinal axis of the bridge;

in FIG. 2 - a graph of the dependence of changes in the residual temperature in the center of the support by the end of the warm period of the year on the average diameter D of the frozen massif;

in FIG. 3 - presents a graph of the average temperature at a depth of 10m directly below the site on its diameter;

in FIG. 4 is a graph of the average temperature of the soil at the end of the warm period on the ratio.

in FIG. 5 - dependence of soil temperature on the depth of the water flow.

The intermediate support of the permafrost bridge contains one or several hollow posts 1, closed by a stopper 2 from the bottom end, and united by a common rigid plate-nozzle 3 from the top. A platform 5 is laid down at the level of the natural surface 4 of the river bottom in the support area, reinforced from above

, M,

max - 2

d

stone outline 6 or some other way. Level 7 of the upper surface of the site can be located below level 8 of low-water, but, depending on structural and technological considerations, it can be located higher, but not higher, as a rule, level 9 of high waters. Under natural conditions, the temperature field at the end of the warm season is determined by position 10 of the isotherm of the freezing temperature of the soil and position 11 of the isotherm of the calculated temperature, for which the bearing capacity of the pillars is determined 1. After the bridge is erected, the position of these isotherms in the steady state is determined respectively by positions 12 and 13. The isotherm of the freezing temperature of the soil (in non-saline soils, this temperature, for example, for sand is 0 ° C) divides the soils into melt 14 and frozen 15.

The intermediate support of the permafrost bridge works as follows. In the winter period, in that part of the air cavity of the racks 1, which rises above the level of 8 low-water waters (taking into account possible snow cover), the air is cooled by heat transfer through the walls of the rack between the external and internal air in the cavity. Due to the difference in weight, cold air moves to the lower part of the cavity, from where warm air is forced out. Warm air in the upper part of the cavity is cooled again and continuous convective heat transfer begins. At the same time, cooling of the soil adjacent to the uprights begins due to heat exchange between the soil and the lower part of the cavity. As a result, the formation of a frozen zone around the support occurs. In the summer, convection stops and a gradual increase in the temperature of the frozen zone occurs, which reaches a maximum by the end of the warm season. The temperature field at this moment is taken as the calculated one.

The features of the location of the support and the formation of the frozen zone around it are as follows. The support is located in the deep talik zone (thawed soil zone). If possible, the bottom of the pillars is immersed in the upper zone

high-temperature plastic frozen soils, i.e. below level 10. Gradually, a frozen zone cylinder forms around the support. In the summer period, permafrost resorption (dispersion) occurs, and by the time the warm period of the year ends, the isotherms of zero and the calculated temperature gradually tend to the positions of 12 and 13, respectively.

The support work described above relates to a prototype, the disadvantage of which is reduced efficiency. With a small number of racks, which is necessary from the point of view of the structural parameters of the support, the design temperature isotherm does not move from position 11 to position 13, but only slightly bends upward, being below the bottom of the pillars. The position can straighten the device of additional racks, which for the construction of the bridge support from the point of view of the layers, it does not need the support abilities, but create additional cooling. However, at the same time, the economic effect may be lost: it is much easier not to cool the soil with additional stands, but simply to lower the existing ones to a greater depth.

In the new technical solution, an increase in efficiency is achieved by including surface cooling in the operation. The area 5 dumped around the support allows in winter to provide a flow of cold into the ground, which dramatically increases the flow of cold in the winter. The upper part of the base soil is subjected to significant cooling, as a result, by the time the warm season ends, the calculated temperature isotherm remains at a level close enough to the bottom surface, occupying position 13.

Thus, the new technical solution combines the effectiveness of deep cooling of the thermal support and surface cooling of the site. But the total effect is higher than the sum of the effects of the application of these measures separately, since the site, in contact with the thermo supports, provides faster freezing of water and

IMGIUI SMI

soil at the specified contact and thereby faster inclusion of the full-fledged work of the cavity of the rack 1 in the work. If there is no site, then instead of the site soil, rack 1 is contacted with water having a significantly higher heat capacity and hidden heat of phase transition, not to mention the fact that in the absence of a fortified site there is a local erosion at drain 1, which increases the total water depth. In this regard, freezing at the contact with the rack is delayed, which delays the normal convection of air in the cavity of the rack 1.

In the proposed new technical solution for the design of the bridge support, the following parameters should be defined:

diameter of racks 1;

the depth of the racks 1;

number of racks 1;

average diameter of the dcp pad;

position of the upper level 7 of the site.

The diameter of the racks is prescribed based on the experience of such structures. The minimum diameter is 0.5 m, but almost normal operation (convection) can be achieved with a diameter of 1 m or more.

Depth of laying and the number of racks is determined based on the following data. On the one hand, horizontal and vertical loads on the support are calculated; on the other hand, using the thermophysical calculations, the freezing region and its temperature are determined.

The average diameter dcp of the site is determined from the following considerations. Any minimum diameter, for example, 1.5 - 2 m, will provide the site with its positive effect, because it will accelerate the freezing of the active layer and full convection of air in the cavity of the rack. However, the best effect will be achieved when the average diameter of the site

will be equal to the average diameter D of the cylinder freezed by the struts 1 of the support. Then the maximum uniformity of the cold impulse along the height of the support is observed.

To determine the required diameter D of the cylinder of the frozen massif, a series of thermophysical calculations was performed for the conditions of Salekhard (south of the Yamal Peninsula). Different initial temperatures / „of the massif were taken at the beginning of the warm period of the year. By the end of the warm period of the year, the temperature in the center of the cylinder increased to tK. In FIG. Figure 2 shows the dependence of the change in the residual temperature in the center of the support (cylinder of frozen soil) on the average diameter D of the frozen zone. From this dependence it follows that with a diameter of up to 10 m the temperature is 4

almost equal to zero. Only with a diameter of 15-20m "can

the temperature of the soil can be practically ensured at which its strength can provide the bearing capacity of the pillars. Thus, the minimum value of dcp should be of the order of 15 - 20 m.

In FIG. Figure 3 shows the dependence of the site performance on its diameter dcp. From this dependence it is seen that a sharp increase in the effectiveness of the site takes place up to a diameter of 60 m, after which the effect of the diameter is significantly reduced. Thus, increasing the diameter of the site significantly increases its effectiveness. But at the same time, another difficulty arises - constraining the opening of the bridge, which, in turn, may require an increase in its length and thereby reduce the effectiveness of the proposed solution. However, a series of calculations was carried out to find out how the technique of reducing the degree of tightness of the bridge opening by extending the platform along the channel can be applied. The graph in FIG. 4 shows that practically without prejudice to the temperature regime, it is possible to go from elliptical from a round in terms of the shape of the site, while the values of maximum and minimum dmm are taken from the condition:

For example, with s / Wed 15 m 20 m, Yu m.

The position of the upper level 7 of the site is determined on the basis of two opposite requirements. The higher the surface of the site, the better snow is blown away in winter in the conditions of the Arctic, which provides the best cold flow into the ground. However, on the other hand, the higher the level of the site, the greater the tightness of the bridge opening and the reduction in the area of the heat exchanger, i.e. parts of racks 1, washed by outside air. This condition requires, on the contrary, to lower the level of the site. In each case, this issue is resolved taking into account local conditions and the specific design of the bridge. The level of the site, however, should be in the range determined by Ntah and Dis. The value of Hmax is determined from the condition that the height of the heat exchanger is practically no less than 2–3 m. The minimum level Hmin is determined from the condition that the layer “5 of water, at its low-water level, be no more than the value at which the water not only has time to freeze over the winter but also to transmit the necessary impulse of cold for the implementation of freezing. To determine this value, thermophysical studies were carried out, the results of which are shown in the graphs of FIG. 5. As a result, the formula was derived: where 4 is the average annual air temperature in the region where

bridge, city Thus, the level of the top of the site is determined from the dependence:

6 0, l + Q, l6t, M, the site size plan can be where the level of low-water waters, m;

And the dimensions of the site in the plan are determined from the following dependencies:

where D is the average diameter of the frozen zone formed by the thermal support in the talik by the end of the warm season, m;

dmax, dmin, respectively, the maximum and minimum dimensions of the site in terms of ji

The effectiveness of the proposed intermediate support lies in the fact that the design of the support, which combines the surface and deep cooling of the soil, allows for quick and effective freezing of the soil base and thereby preserve and strengthen permafrost.

A significant effect can be obtained when two (or more than two) supports are located at a distance of no more than that at which there is a mutual thermal influence. In this case, the temperature

Improves in comparison with a temperature condition at single support.

Authors: / j / V.V. Passek

„..V-OD + OD6,, well,

d ,, Md.

2

min

/%

N.A. Tsukanov

cell.V. Passek

G.M. Poz (L.I. Nevmerzhitskaya

Claims (2)

1. The intermediate support of the permafrost bridge, including one or more racks located in the ground, which is a hollow element closed from the lower end, the upper part of which rises above the low-water level, and a nozzle plate into which the upper ends of all the racks are embedded, characterized in that around the uprights there is a platform, made from soil or other material, which is convex in plan and fortified from erosion, the center of the site coinciding with the center of the support, the average diameter d _{cf of the} site not less than 1 m, and the level top and the platform N _PL is determined from the dependence N _pl > N _mv - 0.1 + 0.16 t _in , [m], where N _mv - low water level, m; t _in - the average annual outdoor temperature, deg. 2. The intermediate support of the permafrost bridge according to claim 1, characterized in that the dimensions of the site in the plan are determined from the following relationships: d _avg ≥ D [m],

where D is the average diameter of the frozen zone formed by the thermal support in the talik by the end of the cold season, m; d _max , d _min - respectively, the maximum and minimum size of the site in the plan, m