RU2120518C1 - Method for construction of approach embankment to bridge piers on permafrost grounds - Google Patents

Abstract

FIELD: construction; may be used in construction of road embankments in permafrost regions. SUBSTANCE: method consists in that in spring period of the year, a platform is filled with rock or coarse-grained dry frozen ground onto natural base cleaned of snow. Laid on filled layer of ground is calculated layer of compacted snow or ice, and covered with a layer of dry frozen ground. Height of ground fill is determined by reduction of full height h_n of embankment by height of layer of upper ground fill. The required thickness of compacted snow is determined by formula H = 0.0316T/

and value of decrease of ground temperature at depth of 10 m is determined by formula Δt= -52/T, where T is number of degree-months of positive temperatures in summer period: T=

, where t₁ is average monthly positive temperature of outdoor air; n i number of months with positive temperature in summer; h_n is full height of embankment. EFFECT: provision of immediate decrease of temperature of base grounds with winter-spring construction of embankment with frozen ground. 2 dwg

Description

 The invention relates to the construction and can be used in the construction of road embankments in areas of permafrost distribution.

 A known method of summer soil filling during the construction of the subgrade in the conditions of the Polar Tundra, including the filling of the embankment from thawed soils, their subsequent compaction and layout.

 The disadvantage of this method is to increase the temperature of permafrost soils of the bases as a result of the introduced heat pulse into the soil. This does not allow putting the bridge into operation immediately after construction or requires the use of expensive cooling devices.

 The closest in technical essence and the achieved result to the proposed one is a method of winter-spring filling with frozen soil, including filling the embankment with dry frozen ground in winter, followed by compaction and layout of the embankment.

 The disadvantage of this method is that when filling the embankment with soil, it is allowed to use only dry soil, while the introduced cold momentum is insignificant, which does not allow reaching the calculated temperature of the soil of the base immediately after filling.

а о величине понижения температуры грунта на глубине 10 м судят по формуле

где
T - количество градусомесяцев положительных температур в летний период:

t₁ - среднемесячная положительная температура наружного воздуха;
n - количество месяцев в летний период с положительной температурой воздуха;
h_п - полная высота насыпи.The essence of the invention lies in the fact that in the method of erecting the suitable part of the embankment to the bridge supports on permafrost soils, including filling the embankment with dry-frozen soil in the winter-spring period with its subsequent compaction, in spring the body of the embankment is poured to the height of snow h _p -h, then a layer of compacted snow with a thickness of H or ice with a thickness of H / 2 is laid on it, which is covered with a layer of dry frozen soil with a thickness of h, while the required thickness of the layer of compacted snow is determined yut by the formula

and the magnitude of the decrease in soil temperature at a depth of 10 m is judged by the formula

Where
T is the number of degrees of positive temperatures in the summer:

t ₁ - monthly average positive outdoor temperature;
n is the number of months in the summer with positive air temperature;
h _p - full height of the embankment.

 The technical result of the proposed method is to immediately lower the temperature of the soil of the base during winter-spring filling of the embankment with frozen soil.

 The invention is illustrated by drawings, where in FIG. 1 - platform embankment, sprinkled with the proposed method in the spring; in FIG. 2 - the same platform by the end of summer.

 The method of construction of the approaching part of the embankment to the supports of the bridge on permafrost soils is as follows.

In the spring period (March – beginning of April), when the reserve of cold is accumulated in the soil of the base and the soil to be poured has a negative temperature, the site 1 is poured with rocky or coarse-grained dry-frozen soil onto a natural foundation cleared of snow 2. A calculation layer 3 is laid on the ground layer 1 of soil compacted snow or ice, and on top of it cover with a layer of 4 dry-frozen soil. In the summer period, layer 3 of snow or ice begins to melt, its temperature is kept at 0 ^o C. Therefore, if we calculate the thickness H of the snow layer so that it completely melts by the end of the thermal period of the year, then we can assume that on the surface of dumping 1 instead of positive a constant temperature of 0 ^o C is maintained at air temperatures. The height of the layer 1 of the soil of the fill is determined by the decrease in the total height of the embankment h _p by the height h of the layer 4 of the upper soil fill. The height h is 0.2-0.7 m and is selected from the condition of slowing down the melting of layer 3 of snow. It is better if ice is used instead of snow / since the sites are in the zone of the bridge with the presence of a watercourse, freezing is simply technologically possible /. To keep the snow in the lateral direction, filter prisms 5 are arranged that allow water to pass from the melting of the snow layer 3. By the end of the summer, the playground takes on the form depicted in FIG. 2, while the temperature of the soil becomes lower by 0.5-1 ^o C compared with the case when the snow layer does not fit.

где
T - количество градусомесяцев положительных температур наружного воздуха в летний период:

t₁ - среднемесячная положительная температура наружного воздуха;
n - количество месяцев в летний период с положительной температурой воздуха;
h - толщина слоя верхней засыпки сухомерзлого грунта.The thickness H of layer 3 of compacted snow depends on several factors - such as the density of the snow layer, the thickness of layer 4 of the soil fill and the temperature of the outside air - and determine it by the formula

Where
T is the number of degrees of positive outside air temperatures in summer:

t ₁ - monthly average positive outdoor temperature;
n is the number of months in the summer with positive air temperature;
h is the thickness of the layer of the top filling of dry frozen soil.

 The use of known technical solutions did not lead to the desired effect. There was a contradiction, which was overcome by creating a new technical solution, which is proposed in this application for an invention.

 The technical contradiction was as follows. The existing method of winter-spring backfilling with dry-frozen soil allows you to add a slight impulse of cold to the soil. Wet frozen soil during backfilling in the winter-spring period will give a good impulse of cold to the soil of the base, but this soil cannot be laid down, since it cannot be compacted.

 A solution to the technical contradiction is achieved by separation of soil and moisture - a layer of compacted snow or ice is laid on a site poured from dry-frozen soil, and they are still covered with a layer of dry-frozen soil with a thickness of 0.2-0.7 m.

The correctness of the proposed method was checked by thermal engineering calculations. The calculation results were compared with a layer of snow in the dump and without it. From all calculation options, it can be seen that for any values of the initial filling temperature, the presence of a snow layer additionally cools the base soil by an average of 0.5 ^o / for Salekhard conditions /. The depth of thawing in the presence of a layer of snow in the dump is also less than in its absence. After 0.5 years, in the presence of a layer of snow, the entire dumping soil is frozen, while without it most of the dumping soil thaws. After 1.5 years after the construction of the dumping, this difference, although it decreases, remains, amounting to 1 m in some cases. The use of a snow layer for one season / for Salekhard conditions / allows to lower the soil temperature at a depth of 10 m by -1 ^o C. The colder the summer, the lower the effect.

 The effectiveness of using the proposed method of erecting the suitable part of the embankment to the permafrost bridge supports lies in the fact that it allows to reduce the cost of the bridge being built and to accelerate the commissioning of the bridge, since the time, in what sequence the soil is being filled, time the achievement of the operational regime can vary with the same design from six months to ten or more years. And the use of a new progressive design of bridge supports, based on the use of widened platforms in the approaching part of the embankment, which allows lowering the temperature of soils in winter and thereby increasing their bearing capacity avoids the use of expensive cooling units for these purposes.

 The greatest efficiency of the proposed method is achieved when it is used for the construction of the approaching parts of embankments to bridges, where the processes approach one-dimensional.

Claims (1)

A method of erecting the approachable part of the embankment to the bridge supports on permafrost soils, including filling the embankment with dry-frozen soil in the winter-spring period with its subsequent compaction, characterized in that in the spring period the body of the embankment is poured to the height h _n - h, then a layer of compacted snow with a thickness of H or ice with a thickness of H / 2 is laid on it, which is then covered with a layer of dry frozen soil with a thickness of h, and the required thickness of the layer of compacted snow is determined by the formula

and the magnitude of the decrease in soil temperature at a depth of 10 m is judged by the formula

where T is the number of degrees of positive temperatures in the summer period:

t ₁ - monthly average positive outdoor temperature;
n is the number of months in the summer with positive air temperature;
h _n is the full height of the embankment.

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