CN110847132A - Method for preventing ice dam by blasting under ice cover - Google Patents
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Abstract
The invention relates to a method for preventing an ice dam by blasting under an ice cover, which comprises the following steps: selecting blasting time; selecting a blasting area; finding a deep hong line; arranging blast holes; blasting under an ice layer; forming a temperature field around the blasting pit; forming clear flow of the ditch; and forming a large-area ice melting water surface. The invention has the following beneficial effects: according to the method, the traditional mode of arranging the blasting points along the cross section of the river channel is abandoned, the blasting points are arranged along the body line of the main channel of the river channel, the blasting time is selected in a time period when the temperature fluctuates at zero degree, a temperature field for accelerating the dissolution of the ice surface is formed at the downstream after blasting, the problems of ice melting and ice flow conveying after upstream blasting are solved, the ice surface is rapidly dissolved, and the threat of forming an ice dam is relieved.
Description
Technical Field
The invention relates to a method for preventing an ice dam by blasting under an ice cover, which is a hydraulic engineering method for preventing and reducing disasters and is a method for preventing flood disasters caused by ice dam formation.
Background
In alpine regions of China, the ice condition of rivers in winter is severe, and flood disasters of ice dams are easy to occur when the rivers are opened, such as yellow rivers, black dragon rivers and Songhua rivers in China. The ice dam is formed by locally accumulating a large amount of flowing ice in a river channel in the river opening period, once the ice dam is formed, the upstream water level is often close to or exceeds the historical highest flood level in a short period, so that the water level is blocked up and overflows out of a river bank, farmland houses are submerged, and coastal hydraulic buildings and structures are damaged.
The method for preventing and reducing disasters of ice plugs and ice dams can adopt mechanical cleaning, blasting and other modes. Blasting operation to eliminate the flood danger of ice dam is an effective non-engineering measure. The operation of blasting to eliminate the flood risk of the ice dam can be divided into two types: blasting ice-breaking dams and blasting ice-preventing dams, wherein the blasting ice-breaking dams are emergency measures passively adopted under the condition that the ice dams are formed when a river is opened, and the blasting ice-preventing dams are preventive measures actively adopted before the river is opened. The blasting modes include a blasting mode of manually perforating and placing explosives on the ice surface, a mode of aircraft shooting and the like. The plane is low in accuracy and high in cost when the plane is thrown and exploded, and the plane can be used only under the emergency condition that ice plugs and ice dams form serious disaster threats and the ice surface cannot be manually operated. The preventive blasting is low in cost and low in danger of manual operation, and is a desirable mode for anti-icing, disaster relief and disaster reduction departments for many years. However, since the research on ice water thermodynamics is lacked, the blasting method has unsatisfactory effect, cannot effectively prevent the formation of ice dams, needs more explosive, and has too large perforating and charging operations on ice surfaces.
Disclosure of Invention
In order to overcome the problems of the prior art, the invention provides a method for preventing an ice dam by blasting under an ice cover. The method combines ice and hydrothermal dynamics theories with blasting effects, carefully selects blasting time, blasting points, arrangement of blasting holes, distribution of temperature fields and the like, maximizes the blasting effects, and can effectively prevent the formation of ice dams.
The purpose of the invention is realized as follows: a method of preventing ice dams by blasting under an ice cover, the method comprising the steps of:
and 4, step 4: arranging blast holes: according to the river width, 1-3 rows of blast holes are arranged only near the body line along the flow direction, the longitudinal spacing of the blast holes is larger than the sum of the radiuses of blast pits generated by blasting of adjacent blast holes, and the transverse spacing is larger than the longitudinal spacing;
and 5, blasting under an ice layer: drilling ice holes penetrating through an ice layer at the arrangement positions of the blasting holes, hanging explosives to the bottom of the ice layer by using a rope, and fixing the rope on the ice holes by using a cross bar;
and 7, forming a channel cleaning open flow: the free water surfaces of the blasting pits are communicated with each other to form a ditch cleaning to form a local temperature field, and then, the temperature field of the free water surface of the full section is formed along with the melting of ice covers on two sides of the ditch cleaning;
The invention has the following beneficial effects: according to the method, the traditional mode of arranging the blasting points along the cross section of the river channel is abandoned, the blasting points are arranged along the body line of the main channel of the river channel, the blasting time is selected in a time period when the temperature fluctuates at zero degree, a temperature field for accelerating the dissolution of the ice surface is formed at the downstream after blasting, the problems of ice melting and ice flow conveying after upstream blasting are solved, the ice surface is rapidly dissolved, and the threat of forming an ice dam is relieved. The invention combines the ice, water and thermodynamic theories with the blasting effect, and provides a theory for preventing the ice dam disaster by implementing the iced blasting along a deep body line at the easy point of the ice dam to form a temperature field, which comprises the following steps: selection of blasting time, arrangement of blasting holes, estimation of blasting effect, calculation of influence lengths of water temperature of a temperature field and water temperature under a downstream ice cover and calculation of ice cover melting rate. Research proves that the flow rate outside the gas temperature is an important factor influencing the melting rate of the ice cover around the blasting pit, the speed of melting the ice cover at the downstream is obviously increased due to the tiny increase of the water temperature in the temperature field along with the increase of the flow rate, and the water temperature in the temperature field is in direct proportion to the longitudinal length.
Drawings
The invention is further illustrated by the following figures and examples.
FIG. 1 is a flow chart of a method according to an embodiment of the present invention;
FIG. 2 is a schematic illustration of ice hole and cartridge placement;
FIG. 3 is a schematic plan view of the melting potential of the ice layer in the blasting pit after blasting;
fig. 4 is a schematic diagram of the melting potential of the ice layer in the blasting pit in elevation after blasting.
Detailed Description
Example (b):
the embodiment is a method for preventing an ice dam by blasting under an ice cover, and the method comprises the following steps, wherein the flow is shown in fig. 1:
Studies have shown that blasting within hours of just forming an ice dam breaks the ice dam most effectively. To obtain the maximum blasting effect, the explosive needs to be installed under the ice dam or in places where there are holes or cracks, but this is difficult if one cannot place a person on the ice dam. The ice breaking sequence extends upstream from the toe of the ice dam where the water flow can transport the broken ice mass downstream. The problem is that the water level rises continuously within a few hours of the ice dam just formed, the stability of the ice dam generally cannot meet the requirements of personnel and equipment, and there is a great risk in implementing the ice blasting. There is a great risk in taking an ice blast operation after the ice dam is formed.
In order to avoid the operational risk of the personnel, the present embodiment selects the blasting time at the initial stage of the stable temperature change from negative temperature to positive temperature before the ice dam is formed, because: after the ice blasting, the ice cover around the blasting hole is broken to form a blasting pit, and most of the broken ice after the blasting is accumulated in the blasting pit to form water immersed ice except that part of the broken ice is scattered around the blasting pit like snowflakes. When the temperature after blasting is 0.00And C, the water in the blasting pit is frozen again to form an ice cover, and the crushed ice blocks are frozen together, so that the blasting effect is greatly reduced, therefore, the optimal time for implementing the under-ice blasting is the initial stage of stably converting the air temperature from negative temperature to positive temperature, so that the ice cover in the blasting river reach and downstream can be melted for a long time, and the blasting indirect effect is maximized. For example, drilling operation is carried out several weeks before opening a river, and then the bearing capacity of the ice cover is larger, and the risk that an operator drops into an ice cave is smaller.
The ice dam is prone to be narrowed, bent, shoals, multi-branch river reach, river-crossing buildings and transition areas of water depth from shallow to deep, and when the downstream of the river reach with complete ice covers, ice coming from the upstream can be accumulated in front of the ice covers to form the ice dam.
The riverway of the ice dam easy-to-launch point is generally a compound riverway which can be divided into a main trough and an overflowing beach, the main trough is large in water depth and flow rate, and the overflowing beach is small in water depth and flow rate. In the vicinity of the beach tank interface, the water depth and the flow velocity are changed sharply, the turbulent intensity of water flow is high, and complex transverse secondary flow and spiral flow are formed, so that a great amount of mass exchange and convection heat exchange occur in the beach tank water body.
The hydraulic characteristics of the bend are as follows: under the action of the centrifugal force of water flow, the recessed river bank is eroded, and the eroded silt is carried to opposite bank to deposit by means of circular flow and gradually forms a convex bank with arc-shaped slope. The concave bank is usually deep in water and large in flow velocity; the slope of the convex bank is gentle, and the water flow near the bank is slow. In cold winter, bank ice is easy to form at the river closing period of one side of the convex bank, and develops towards the center of the river to narrow the river, and when a large amount of floating ice comes upstream, an ice bridge is formed and becomes the starting point of the ice cover and develops upstream. When the 'Wukaihe' river is opened, the river opening sequence is from upstream to downstream, and the ice cover on the curve is thick and not easy to damage, so that a great amount of water flowing ice is easy to extrude downwards to form an ice dam.
The hydrodynamics of the shoal river is as follows: the bottom slope of the upstream riverway is steeper, the water depth is shallower, the average flow velocity is larger, the width of the shoal river is larger, the water depth is shallow, and the average flow velocity is small. During the closing period, static ice is formed on the water surface with the shoal flow rate less than 0.3m/s, and the closing ice cover is formed under the condition that a large amount of incoming ice floats on the upstream water surface. If the upstream riverway water flow is rapid, the water surface can not be iced in a short time, under the action of cold air, a large amount of ice flowers are generated in water and ice in the water flows to a downstream shoal through the heat exchange between the air and the water surface, and an ice plug is formed below the front edge of the ice cover through submerged accumulation, so that the upstream water level is increased, the flow rate is reduced, and the ice cover develops upstream.
The ice cover is blasted under the ice cover at the ice dam initiation point before the river is opened, and the ice cover or the ice plug of the river section is forced to be melted and eliminated before the river is opened at the upstream, so that the ice dam flood can be prevented.
The present embodiment finds the object of creating a location for a blast hole in a body line. The principle of arranging blast holes on a deep body line is as follows:
the effect of the ice blast can be classified into a direct effect and an indirect effect. The common evaluation indexes of the direct effect are the dosage and the size of the area forming the blasting pit. The indirect effect is that the blasting hole forms the back, owing to the direct contact of water and air appears, has strengthened the heat exchange of blasting hole department water and atmosphere, ice and water, not only makes the interior ice of blasting hole melt, makes the blasting hole ice lid melt with higher speed around the hole in addition, and then makes the free surface of water constantly increase, simultaneously, because melting of ice lid, original ice territory also changes the waters into, and the depth of water increases, and the groove holds the volume and increases, is favorable to opening the river smooth passing through of ice row. The actual blasting result under the ice cover proves that the blasting can not well exert the explosive capacity when the blasting is carried out at a place with shallow water depth, and the direct blasting effect can be improved at a place with larger water depth. The optimum position of the blast hole is determined by analyzing the relation between the thickness melting rate of the ice cover and the air temperature, the water temperature, the flow velocity and the water depth, so as to improve the indirect effect of the ice blasting.
The relationship between the thickness melting rate of the ice cover and the air temperature and water temperature under the condition without the snow cover is
In the formula: h is the thickness of the ice cover, and the unit is m; t is time in units of s; t isWThe water temperature is the unit; the daily average air temperature of the air is expressed in units of ℃; t issThe temperature of the ice cover top; t ismFreezing temperature in units of; rhoiIs the density of ice, pi＝915～917kg/m3；LiLatent heat per unit mass of ice, when water freezes, Li＝3.33×105Latent heat of J/kg is released; h isaiIs the heat exchange coefficient of air and ice, and has a unit of W/m2The method is a parameter comprehensively considering factors such as solar radiation, air temperature and humidity, wind speed, air pressure, cloud, rainfall, snowfall and the like; h iswiIs the heat exchange coefficient of water and ice, and has a unit of W/m2DEG C. According to the existing theory, when the air temperature and the water temperature are both right, the ice cover can be melted up and down.
Coefficient of heat exchange hwiThe relationship with flow velocity and hydraulic radius can be described as:
hwi＝1622U0.8/R0.2(2)
in the formula: u is the water depth average flow velocity along the flow direction, and the unit is m/s; h is the water depth at the transverse coordinate y of the water passing section, and the unit is m; r is the hydraulic radius and is expressed in m. Assuming that the ice cover per unit length of the river channel is the same as the wet circumference of the river bottom, R is 0.5H, and then:
hwi＝1863U0.8/H0.2(3)
flow rate lateral distribution formula for denmark DHI:
U＝αUm(H/Hm)3/2(4)
in the formula: u shapemThe average flow speed of the whole river channel water cross section is expressed in m/s; hmThe average water depth of the water passing section is expressed in m, α is a constant, obviously, the larger the water depth H is, the larger the flow velocity U is on the water passing section of the river channel, and of course, some local deep pits are excluded.
Substituting formula (4) for formula (3) and removing H to obtain:
hwi＝cwiU0.667(7)
in the formula:for a given water flow profile and constant flow, cwiIs a constant.
Thus, it can be seen that: when the water temperature is positive, the flow speed is in direct proportion to the water depth on the same water passing section of the river channel, and the speed of the reduction of the thickness of the ice cover is increased along with the increase of the flow speed.
Similarly, when a cylindrical coordinate system is adopted, the relationship between the ice melting rate of the sidewall of the blasting pit and the water temperature can be described as follows:
in the formula: r is the distance/m from the side wall at the water depth z to the origin of coordinates; h iswi，zThe heat exchange coefficient of water and ice at the side wall of the blasting pit is in W/m2C, hypothesis; h iswi，zHaving the relationship of equation (7) with the flow rate, then:
hwi,z＝cvβ(9)
wherein v is the flow velocity/m/s near the inner side wall of the blasting pit, and c and β are undetermined coefficients.
For a river channel with a large width-depth ratio, the longitudinal distribution characteristics of the flow velocity under the ice cover are as follows: the flow velocity on the bottom of the ice cover and the river bed is zero, the maximum flow velocity is between the ice cover and the river bed, the maximum flow velocity and the ice cover and the maximum flow velocity and the river bed are approximately logarithmically distributed, therefore, under the condition that the size of the blasting pit is smaller relative to the river width, the higher flow velocity below the ice cover pulls the water flow in the blasting pit to move, the convection exchange of quality and heat is enhanced, the water temperature tends to be uniform, the up-down and left-right circular flow is formed in the pit, and the water facing side is close to the watervGreater than the side of the back water and lower partvIs larger than the upper part. Assuming that the water temperatures in the blasting pit are uniformly mixed, the following equations (8) and (9) can be obtained: when the water temperature is positive, the ice melting rate in the range of the side wall of the blasting pit is increased along with the increase of the water depth, and the melting rate of the water-facing side is higher than that of the water-backing side.
The former explosion for preventing the formation of the ice dam arranges the explosion points on the river channel along a certain cross section line, and the explosion effect is not good. This embodiment cuts a blast hole near a body line.
When the blast hole is located the great place of velocity of flow, the speed that the ice lid melts around the blasting hole is great, and the indirect effect of blasting under ice is great promptly, simultaneously, to same river course cross the water section, the place that the depth of water is big more, the average velocity of flow of depth of water is also big, follows from can important conclusion: the best position of the blast hole is the main trough body line of the riverway ice dam which is easy to be ignited, and the main trough body line is a place with large water depth and flow speed.
The observation of the blasting field shows that the ice cover of the downstream Yangtze river section suddenly disintegrates before the river is opened when the river section is blasted under ice, which shows that the water temperature increased by blasting has a great effect on the melting of the ice cover of the downstream. In order to make the ice blasting preventive ice dams successful and economical to invest, it is desirable to form a temperature field of a certain scale by blasting, eliminating not only the ice cap of the blasting river reach but also the ice cap of the downstream considerable river course. In other words, the ice blasting prevention ice dam considers not only the direct effect of blasting but also the indirect effect of ice, water and thermodynamic actions. Therefore, based on the flowing and heat exchange characteristics of the compound river channel and the melting characteristics of the ice cover around the blasting pit, the following blasting hole arrangement mode can be adopted:
1) several rows of blast holes, for example, 1-3 rows, are arranged in the flow direction only near the body line according to the river width to form a temperature field of a certain scale, and then the mass and heat convection of the main trough and the flood beach are utilized to promote the thawing of the two-sided flood beach and the downstream ice cover;
2) considering the effect of blasting indirect effect, the distance between the blasting holes is preferably larger than the sum of the radiuses of the adjacent blasting pits, and the distance between the adjacent blasting holes along the longitudinal direction is preferably larger than the distance between the adjacent blasting holes.
The distance between the blasting pits is to promote the ice layer between the blasting pits to melt, the distance between the two blasting pits is too small, so that the blasting efficiency is lower, and the ice melting speed is influenced if the distance is too large. Generally, the distance between blast pits depends on the temperature rise, which is greater when the temperature rises faster, whereas a smaller distance should be set if the temperature wanders near zero.
And 5, blasting under an ice layer: and (4) cutting ice holes penetrating through the ice layer at the arrangement positions of the blasting holes, hanging the explosive to the bottom of the ice layer by using a rope, and fixing the rope on the ice holes by using a cross bar.
Blasting under an ice layer is to place an explosive 1 in water 3 under an ice layer 2. Ice holes 4 are drilled in the ice layer and the explosive is suspended in the ice holes by a rope 5 and a rail 6, as shown in fig. 2. Research shows that the blasting effect is independent of the type of explosive, so that a cartridge used commonly in engineering can be adopted, and the cartridge is low in price, stable, reliable and relatively safe.
And 7, forming a channel cleaning open flow: the free water surfaces of the blasting pits are communicated with each other to form a ditch cleaning to form a local temperature field, and then, the temperature field of the full-section free water surface is formed along with the melting of ice covers on two sides of the ditch cleaning.
the function of the temperature field:
after the ice blasting is carried out according to the blasting time and the arrangement of the blasting holes, crushed ice in the blasting pit and the surrounding ice covers are firstly melted, then the free water surfaces of the blasting pit are mutually communicated to form a ditch cleaning to form a local temperature field, and then the temperature field of the full-section free water surface is formed along with the melting of the ice covers on the two sides of the ditch cleaning.
And analyzing the relationship between field water temperature and length after the temperature field is formed, the influence length of the field water temperature on the water temperature under the downstream ice cover, the relationship between the thickness of the downstream ice cover and the field water temperature and time and the like. To simplify the problem, assume: 1) the cross section of the water passing is rectangular; 2) the temperature field open flow and the downstream under-ice-cap flow are uniform flows.
Temperature field water temperature versus air temperature and temperature field length relationship:
after the temperature field is formed in the ice blasting river reach, the influence of temperature diffusion is ignored, and then the one-dimensional heat convection equation can be described[14]Is composed of
In the formula: x is the distance in the flow direction/m; u shape1Flow velocity in terms of temperature field/m/s; h1Water depth of temperature field/m; ρ is the density of water, and is generally 1000kg/m3；CpIs the specific heat of water/J/kg ℃, at 0 ℃, Cp＝4217.7J/kg℃；hwaThe heat exchange coefficient h of the water-air interface is a parameter which comprehensively considers factors such as solar radiation, air temperature and humidity, wind speed, air pressure, cloud, rainfall, snowfall and the like, and has heat exchange coefficient h of the air-water interface in North Americawa≈20W/m2℃。
Using the characteristic line method, equation (10) can be rewritten as:
in the formula
The distance of the water flow particle from the temperature field inlet is expressed in m.
In one day, the daily average air temperature is constant, and the equation (11) is obtained by ordinary differentiation:
t＝x/U1(14)
in the formula: t isw0The temperature field inlet water temperature at the moment when t is 0 is given in units of ℃.
For still water, X is 0, and formula (13) indicates that the water temperature increases with time to increase in a natural index. The water in the blasting pit at the initial blasting stage can be considered as still water, the water temperature is rapidly increased along with the increase of the air temperature, but the water in the blasting pit flows under the ice cover along with the reduction of crushed ice, the heat is transferred to the lower part, and the water temperature in the blasting pit is reduced.
When the flow velocity is not zero, the relation between the temperature of the temperature field and the distance X can be obtained by substituting the formula (14) into the formula (13):
when the length of the temperature field is X1Then corresponds to the water temperature
In the formula: t isW1The temperature field outlet water temperature or the downstream ice cover leading edge inflow water temperature is measured in degrees centigrade.
In the general case, X1<104m is hwax1/(ρCpHU) < 1, and formula (16) can be rewritten as:
Tw1-Tw0＝(Ta-Tw0)hwax1/(ρCpH1U1) (17)
under natural environment, the water temperature T below the ice coverW0Very close to TmI.e. TW00 ℃ and therefore important conclusions can be drawn: temperature field outlet water temperature TW1Product T of length of temperature field, air temperature and heat exchange coefficient of water and airahwaX1Proportional to single wide flow H1U1In inverse proportion.
Length of influence of temperature field water temperature on water temperature under downstream ice cover:
for flow under the ice cover downstream of the temperature field, the one-dimensional thermal convection equation can be described as:
in the formula: u shape2The flow rate/m/s of the ice cover at the downstream of the temperature field; h2The water depth under the ice cover is/m, namely the difference between the elevation of the ice cover bottom and the elevation of the river bottom.
Similar to the foregoing, one can obtain:
suppose X is equal to X2In time, the water temperature under the ice cover is from T due to the heat exchange between the water and the iceW1Decreases to the temperature field inlet water temperature TW0When L is equal to X2--X1The length of the influence of the temperature field water temperature on the downstream water temperature under the ice cover is as follows:
when L is<104m is hwiL/(ρCpH2U2)<<1, the above formula is rewritten as:
handle type (5) substituted type (21)
From formula (22): the greater the field water temperature, the depth of water under the ice cover and the flow velocity, the greater the length L of the influence of the field water temperature on the downstream water temperature under the ice cover.
When taking rho 1000kg/m3And Cp4217.7J/kg ℃, then:
the relation between the thickness of the ice cover at the downstream of the temperature field and the water temperature, the air temperature and the time of the temperature field is as follows:
equation (1) is also suitable for the change of the thickness of the ice cover downstream of the temperature field, and under the condition of no snow cover, the relation of the change of the thickness of the ice cover with the air temperature and the water temperature is as follows:
when getting TS＝TmSubstituting formula (19) for formula (23) yields the formula for the time-dependent change in ice cover thickness at X downstream of the temperature field:
in the formula: second item on the right
The third term Dh on the right for reduced thickness at X due to ice and water heat exchange2＝haiTat/ρiLiIs the reduced thickness at X affected by the heat exchange of air and ice.
The method provided by the embodiment is applied to the disaster prevention and reduction working practice of Heilongjiang, a good effect is obtained, a large amount of detailed experimental data are obtained, and the correctness and the practicability of the method provided by the embodiment are verified through the experimental data.
Finally, it should be noted that the above is only for illustrating the technical solution of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred arrangement, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solution of the present invention (such as the location of blasting rivers, the application of various formulas, the sequence of steps, etc.) without departing from the spirit and scope of the technical solution of the present invention.
Claims (1)
1. A method for preventing ice dams by blasting under ice covers is characterized by comprising the following steps:
step 1, selection of blasting time: the temperature is stably changed from negative temperature to positive temperature in the initial stage;
step 2, selecting a blasting area: selecting river channel narrowing, curve, shoal, multi-branch river reach, river-crossing building and water depth transition region from shallow to deep as blasting region;
step 3, finding a deep body line: finding a deep body line of the river channel on the ice layer by the existing hydrological data or by geological radar detection;
and 4, step 4: arranging blast holes: according to the river width, only arranging a plurality of rows of blast holes, such as 1-3 rows of blast holes, near the body line along the flow direction, wherein the longitudinal spacing of the blast holes is larger than the sum of the radiuses of blast pits generated by blasting adjacent blast holes, and the transverse spacing is larger than the longitudinal spacing;
and 5, blasting under an ice layer: drilling ice holes penetrating through an ice layer at the arrangement positions of the blasting holes, hanging explosives to the bottom of the ice layer by using a rope, and fixing the rope on the ice holes by using a cross bar;
step 6, forming a temperature field around the blasting pit: the crushed ice and the surrounding ice cover in the blasting pit are firstly melted, the melting rate of the water-facing side of the blasting pit is higher than that of the backwater side, and the melted shape is similar to an asymmetric horn shape with a hanging top opening;
and 7, forming a channel cleaning open flow: the free water surfaces of the blasting pits are communicated with each other to form a ditch cleaning to form a local temperature field, and then, the temperature field of the free water surface of the full section is formed along with the melting of ice covers on two sides of the ditch cleaning;
step 8, forming a large-area ice melting water surface: along the river water flow direction, a temperature field is utilized to promote the downstream ice cover to melt in an accelerated manner, so that the blasting effect is maximized.
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