CN111680403B - Frozen wall development condition judging and early warning method based on thermo-acoustic coupling algorithm - Google Patents
Frozen wall development condition judging and early warning method based on thermo-acoustic coupling algorithm Download PDFInfo
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Abstract
The invention discloses a freezing wall development condition judging and early warning method based on a thermo-acoustic coupling algorithm, which comprises the steps of establishing an indoor physical test model of two-hole freezing of a water-rich sand layer in a freezing construction preparation stage, and drawing a wave velocity-temperature relation curve; establishing a nonlinear relation expression of wave speed-temperature by utilizing a wave speed-temperature relation curve; obtaining an artificial frozen soil thermo-acoustic coupling algorithm considering phase change; solving and designing the average wave velocity of the development of the freezing wall by using a thermo-acoustic coupling algorithm; calculating quantitative relations between different freezing fronts, non-intersection distances and calculated average wave speeds; and judging and early warning the development condition of the frozen wall by comparing the actual measurement with the calculated frozen frontal surface and the distance of the non-crosslinked ring. And judging and early warning the abnormal development condition of the freezing wall between any two holes by using the standard, and timely processing. The method can realize early forecast, process monitoring and effect evaluation of the condition of the freezing wall intersection.
Description
Technical Field
The invention relates to the technical field of frozen wall development condition detection. In particular to a frozen wall development condition judging and early warning method based on a thermo-acoustic coupling algorithm.
Background
The artificial freezing method is a special stratum reinforcing method for freezing stratum around a structure to be built into a continuous closed frozen body by utilizing an artificial refrigerating technology. The construction method has the advantages of isolating underground water, increasing soil intensity, improving stability, being pollution-free and the like, and has been widely applied to mine construction, subway construction, foundation pit and comprehensive pipe gallery construction. However, when the artificial freezing method is applied to a water-rich sand layer with a large flow rate, the phenomena of no intersection of freezing walls, too slow development of the freezing walls and the like often occur, and serious safety accidents are easily caused. Therefore, grasping the development condition of the freezing wall has important significance for safe construction of the artificial freezing method.
At present, the detection of the development condition of the freezing wall widely applied at home and abroad comprises the following steps: the local frozen wall development condition can be accurately obtained by graph multiplication, an empirical formula method, a numerical simulation method and the like. However, the above three methods are all based on real-time temperature monitoring results in the temperature measuring hole, and the key information such as partial freezing wall windowing, insufficient strength and the like is often ignored in judging the development condition of the freezing wall at a position far away from the temperature measuring hole, so that the application risk of the method in the water-rich sand layer when the groundwater flow speed is more than 5m/d is increased to a certain extent. The early forecast, process monitoring and effect evaluation of the freezing wall intersection condition cannot be realized.
Disclosure of Invention
Therefore, the invention aims to solve the technical problem of providing a frozen wall development condition judging method and an early warning method based on a thermo-acoustic coupling algorithm, which can accurately judge and early warn when the groundwater flow speed is more than 5 m/d.
In order to solve the technical problems, the invention provides the following technical scheme:
A frozen wall development condition judging and early warning method based on a thermo-acoustic coupling algorithm comprises the following steps:
Step 1, in the preparation stage of freezing construction, an indoor physical test model of two-hole freezing of a water-rich sand layer is established, and a wave speed-temperature relation curve is drawn;
step 2, establishing a nonlinear relation expression of wave velocity-temperature by using the wave velocity-temperature relation curve in the step 1;
Step 3, obtaining an artificial frozen soil thermo-acoustic coupling algorithm considering phase change;
Step 4, solving and designing the average wave velocity of the development of the freezing wall by using a thermo-acoustic coupling algorithm;
Step 5, calculating quantitative relations between different freezing fronts, non-intersection circle distances and calculated average wave speeds;
And 6, judging and early warning the development condition of the frozen wall by comparing the actually measured and calculated frozen frontal surface and the non-coil distance.
The method for judging and early warning of the development condition of the frozen wall based on the thermo-acoustic coupling algorithm comprises the following steps of
(1-1) Selecting a soil sample with the same thermodynamic parameters as the soil property detected on site, carrying out a two-hole frozen physical junction model experiment indoors, and carrying out heat preservation around an experiment box by using a polyethylene material;
(1-2) wherein two freezing holes are a freezing hole A and a freezing hole B respectively, and the conditions of brine flow, brine temperature drop gradient, refrigeration system, clear water circulation system and soil body freezing system of the freezing hole A and the freezing hole B are consistent with the conditions of the site;
The thickness of the freezing front surface from the freezing hole A or the freezing hole B is h 1, and the non-intersection distance between the freezing hole A and the freezing hole B is h 2;
(1-3) a detection hole C and a detection hole D disposed at positions parallel to the freezing hole a and the freezing hole B, respectively, for ultrasonic detection;
(1-4) injecting saline into the detection hole C and the detection hole D, the freezing hole A and the freezing hole B, starting up a test cycle, opening end caps of the detection hole C and the detection hole D when the temperature of the saline in the freezing pipe A and the freezing pipe B is between 25 ℃ below zero and 28 ℃ below zero, placing probes into the detection hole C and the detection hole D to a detection position, synchronously lifting the transmitting and receiving probes, ensuring that the transmitting and receiving probes are on the same level, detecting ultrasonic wave velocities in different freezing periods, measuring once every 1-2 hours, and then drawing a wave velocity-temperature relation curve.
According to the frozen wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm, the distance between the detection hole C and the detection hole D is smaller than 1.5m, and the distance between the upper measuring point and the lower measuring point is 250-600 mm.
The frozen wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm comprises the following steps of:
(2-1) piecewise fitting a wave velocity-temperature variation curve using a linear function to obtain a nonlinear relation expression of wave velocity-temperature, as shown in formula (1):
In the formula (1), c is the wave speed, km/s; t is time, h; a 1、a2、b1、b2、d1、d2 is the coefficient to be determined; t 1、T2、T3、T4 is the temperature inflection point in the temperature curve and is at DEG C;
(2-2) substituting the wave velocity c (T, T) into the formula (1) to obtain acoustic impedance fields at different freezing moments, as shown in the formula (2):
Wherein: Acoustic impedance fields for different freezing times.
The frozen wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm comprises the following steps of:
the method comprises the steps of regarding water-containing artificial frozen soil as a porous medium soil body consisting of a soil framework, ice crystals and unfrozen water, wherein the porous medium soil body is provided with a plurality of acoustic impedance areas;
The homogeneous isotropic aqueous artificial frozen soil following the heat conduction equation can be represented by the following formula:
Wherein: ρ is the density; c p is equivalent volumetric heat capacity, kJ/(kg.K); t is the surface temperature, DEG C; u is the velocity vector of the translational motion of the node, m/s; q is the heat flux of heat conduction, W/m -2;qr is the heat flux of heat radiation, W/m -2; q is a heat source, W/m -3; k is the equivalent thermal conductivity, W/(m.K); the radiation heat exchange is not considered in the freezing process, so q r is taken as 0; simplifying the temperature field problem of an ultrasonic detection horizon into a planar two-dimensional model, and taking 1mm for d z;
The equivalent volume fraction of the model is two parts of the phase change volume fraction from water to ice and the soil body skeleton volume fraction, and the density ρ x, the heat capacity C x and the heat conductivity k x of the C p and the phase change material in the formula (3) are respectively shown as the formula (4), the formula (5), the formula (6) and the formula (7):
Cp＝θgρgCg+θxρxCx (4)；
ρx＝θwρw+θiρi (5)；
Wherein:
kx＝θwkw+θiki； (7)
Wherein: θ g、θw、θi is the volume fraction of the soil body skeleton, water and ice respectively; ρ g、ρw、ρi、ρx is the density of the soil body skeleton, water, ice and phase change material, kg.m -3;Cg、Cx、Cw、Ci is the heat capacity of the soil body skeleton, phase change material, water and ice, kJ/(kg.K); k w、ki、kx is the heat conductivity coefficient of water, ice and phase change material, W/(m.K); wherein the phase transition temperature is 0 ℃, the transition interval from water to ice is 10K, and the phase transition latent heat is 333kJ/kg;
the thermodynamic analysis formula of the artificial frozen soil considering the phase change factor is shown as formula (8):
the artificial freezing thermodynamic analysis is carried out by utilizing the formula (8) to obtain temperature fields of different freezing stages under the normal development condition of the freezing wall, namely the formula (1)
Introducing the temperature field obtained by solving the equation (8) into the equation (1), solving c (T, T), substituting the equation (2), and solvingAs an initial acoustic impedance condition for sound field analysis;
Setting acoustic boundary conditions, selecting cylindrical wave radiation as a sound source excitation source, and selecting single-frequency Rake wavelets as a sound source function, wherein the function expression is as follows:
Wherein, when t is sound, μs; f 0 is the center frequency of the sound source, kHz; t 0 is the period, μs;
The acoustic impedance and sound source boundary condition wave equation described above can be expressed by the following equation:
wherein: p is the independent variable sound pressure, pa; t is time, μs; q m is monopole sound source 1/s 2;
the sound pressure field distribution at different freezing periods can be solved by using the method (10), namely
The method for judging and early warning the development condition of the freezing wall based on the thermo-acoustic coupling algorithm comprises the following steps:
Extracting sound pressure signal propagation curves before and at a certain moment after freezing, comparing time displacement tau corresponding to peak positions of a transmitting signal x (t) and a receiving signal y (t) of the sound pressure signal propagation curves, substituting the time displacement tau into a formula (11), and solving the transmission time R xy (tau) of the signal in a freezing wall;
Then substituting the distance S between the two detection holes and the transmission time R xy (tau) into the formula (12) to solve the average wave velocity V p of different freezing periods under the normal freezing wall development condition;
the method for judging and early warning the development condition of the freezing wall based on the thermo-acoustic coupling algorithm comprises the following steps:
obtaining quantitative relations among a freezing frontal surface h 1, an uncrossing distance h 2 and an average wave velocity V p at any position and time of a freezing region under the normal frozen wall development condition by utilizing a thermo-acoustic coupling algorithm; the quantitative relations among different freezing fronts h 1, non-intersection distances h 2 and calculated average wave speeds V p under normal development conditions of the freezing wall accord with quadratic function relations (13) and (14):
Wherein h 1 is the freezing front distance freezing Kong Houdu mm; h 2 is the distance between two freezing holes without intersecting circles, and mm; f 1、f2、f3、g1、g2、g3 is the coefficient to be determined.
The method for judging and early warning the development condition of the freezing wall based on the thermo-acoustic coupling algorithm comprises the following steps: in the field freezing project, ultrasonic detection of the development condition of the frozen wall is divided into two detection stages: a freezing process stage and a freezing acceptance stage;
Before freezing: the field freeze hole and the test hole should be checked for acceptance prior to ultrasonic testing: 1) Checking whether the pipe is blocked by foreign matters or not, and checking whether the pipe body is cracked, bent or flattened or not; 2) The tubes should be kept substantially parallel, and the degree of non-parallelism should be controlled to be less than 1%; 3) After the pipeline is installed, the upper opening is closed so as not to fall into foreign matters, and the pore canal is blocked; 4) The pipeline is 300-500 mm higher than the ground surface, so that the exposed height is guaranteed to be the same;
Stage of freezing process:
setting a freezing hole A26, a freezing hole A27, a detection hole J1 and a temperature measurement hole T8 on a freezing site;
Ultrasonic detecting the wave velocities v p1 of the freezing hole A26 and the detection hole J1 at the freezing site, substituting the wave velocities into a formula (13) to calculate the actual freezing frontal surface distance H 1 at the site for 7 days/time until the freezing wall reaches a freezing boundary;
Ultrasonic testing at freezing site for v p2, wherein the testing period is the date of the cross ring of the freezing wall, and the date of the cross ring of the freezing wall is 20+ -5 days, and substituting into formula (14) to calculate the distance H of non-cross ring 2
Freezing acceptance stage: synchronously lifting the transmitting and receiving probes to ensure that the transmitting and receiving probes are on the same level; the wave velocities v p1 of the freezing hole a26 and the detection hole J1 were recorded.
The method for judging and early warning the development condition of the freezing wall based on the thermo-acoustic coupling algorithm comprises the following steps of:
Substituting the calculated average wave velocities V p1 and V p2 of the freezing wall under the normal development condition in the algorithm into the detection holes (13) and (14) to obtain a freezing frontal surface position h 1 between the two detection holes under the normal development condition of the freezing wall and a non-ring-crossing distance h 2 between the freezing holes under the normal development condition of the freezing wall; substituting the field detection wave speeds v p1 and v p2 into equations (13) and (14) to obtain a freezing front position H 1 between the field freezing hole A26 and the detection hole J1 and a non-ring-crossing distance H 2 between the field freezing hole A26 and the freezing hole A27;
When the freezing front position H 1 is more than 30% smaller than the freezing front position H 1 under the normal development condition of the freezing wall obtained by the specific heat-sound coupling algorithm at the same freezing time judged by field actual measurement, judging that the detection area is a freezing wall development high risk area;
For the time of designing the intersection of the freezing walls, the field actually measured wave velocity v p2 at a certain position calculates the non-intersection distance H 2 not equal to 0 of the two freezing holes, the non-intersection distance H 2 =0 between the freezing holes at the moment under the normal development condition of the freezing walls obtained by a thermo-acoustic coupling algorithm, and meanwhile, the non-intersection distance H 2 approximately equal to 0 of the two freezing holes at other positions is detected on site, so that the detection area is judged to be the high risk area of the freezing walls.
The frozen wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm,
Abnormal conditions of the developmental high risk area and the "windowed" high risk area are:
(a) Excessive seepage velocity or other geological factors;
(b) The cooling capacity of the nearby freezing holes is insufficient, the freezing holes are blocked, and the flow is small;
(c) The nearby freeze holes are too much deflected.
The possible conditions are checked item by item, and timely remedying and remedying measures are carried out:
If the situation (a) is found, grouting, water shutoff and seepage reduction measures are carried out on the high risk area in time;
if the situation (b) is found, the cooling capacity should be increased in time to dredge the foreign matters in the freezing holes;
if the situation (c) is found, the measures of compensating the freezing holes or increasing the cold quantity should be carried out in time.
The technical scheme of the invention has the following beneficial technical effects:
According to the frozen wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm, provided by the invention, the wave velocity-temperature relation expression can be obtained through ultrasonic detection results of two detection holes which are arranged parallel to the frozen holes. And a thermo-acoustic coupling formula is obtained. After the excitation source is added, solving acoustic parameter curves of different freezing periods under normal development conditions to serve as a freezing wall development condition judgment standard. The calculation accuracy of the on-site detection hole wave velocity is in the range of 89.7% -96.97%, which shows that the result of the calculation of the wave velocity by the thermo-acoustic coupling algorithm can effectively reflect the actual ultrasonic detection condition of engineering. The method can accurately judge the development condition of the frozen wall, particularly in a water-rich sand layer when the flow rate of underground water is more than 5m/d, can timely judge and early warn the development condition of the frozen wall, such as the problems of windowing of the frozen wall in a high-risk area, insufficient strength and the like, has the prediction accuracy of more than 80 percent, reduces the application risk in the water-rich sand layer when the flow rate of underground water is more than 5m/d, and can realize the early prediction, process monitoring and effect evaluation of the cross ring condition of the frozen wall, thereby protecting the construction of freezing engineering.
Drawings
FIG. 1 is a schematic diagram of a development model of a freezing wall between two holes of a water-rich sand layer;
FIG. 2 shows a curve of wave velocity-temperature change of frozen soil in a constant temperature maintenance mode;
FIG. 3 freezes hole, detection hole floor plan (partial);
FIG. 4 comparison of test hole simulation results with actual measurement results
Fig. 5 cloud of temperature field distribution at different freezing moments: (a) is 24d, (b) is 42d, and (c) is 60d;
Fig. 6 cloud of acoustic impedance field distribution at different freezing times: (a) is 24d, (b) is 42d, and (c) is 60d;
fig. 7 is a cloud diagram of sound field distribution at different freezing moments: (a) 24d (400 μs); (b) 24d (500 μs); (c) 24d (600 μs); (d) 60d (400 μs); (e) 60d (500 μs); (f) 60d (600 μs);
FIG. 8 is a comparison of the simulation results of the wave velocity between the detection holes with the actual measurement results;
fig. 9 shows wave velocity curves for different freezing front positions.
Detailed Description
The freezing wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm in the embodiment is applied to about 58.80m of a north-extension airport section of the Guangzhou rail transit No. three lines, and the local curve section is reinforced by adopting a freezing method.
1. Background: the north-south station of the airport at the north-extension section of Guangzhou urban rail transit No. three is about 58.80m, and the local curve section is reinforced and constructed by adopting a freezing method. The thickness of the covering soil of the tunnel vault of the freezing section is 7.63-8.08 m, the buried depth of the underground water level is about 1.0m, the width of the undercut tunnel is 12.6m, the height is 8.82m, the cross-sectional area reaches 90.279 m2, and the buried depth of the bottom plate is about 16.0m. In order to control frost heaving and thawing and sinking as much as possible and reduce the freezing volume, a vertical and sectional heat preservation freezing method is adopted. Wherein the thickness of the fine sand layer with the embedded depth of 14.0-20.1 m is large, and the water is rich, thus being a water-rich sand layer. The design holes of rows A-B, the row spacing of 180mm, the design holes of rows C-D, the row spacing of 2250mm, and the positive freezing time of 60D.
The ultrasonic sounding holes are arranged near the freezing holes of the A rows, so the freezing holes of the A rows and the C rows are selected for analysis in the embodiment. As shown in FIG. 3, the spacing between the vertical freezing holes of row A is between 1.8 and 1.96m due to the limitation of site construction conditions. Y6-Y11 are freezing holes between A, B rows to prevent shortage of cold. Two ultrasonic detection holes J1 and J2 are arranged near the original temperature measurement hole T8. J1-J2 gauge tube spacing 1470mm, vertical axis is disposed between A25-A26 freeze holes. The ultrasonic wave velocity of different freezing front positions under the condition of frozen soil temperature gradient field is measured. In-situ ultrasonic testing was performed at different freeze periods using a NM-4A nonmetallic ultrasonic probe, respectively (wherein J1-J2 inter-well ultrasonic was measured only during the aggressive freeze period 60 d).
2. An indoor test model is established, which comprises the following steps:
Step 1, in the preparation stage of freezing construction, an indoor physical test model of two-hole freezing of a water-rich sand layer is established, and a wave speed-temperature relation curve is drawn;
(1-1) selecting a soil sample with the same thermodynamic parameters as the soil property detected on site, carrying out a two-hole frozen physical junction model experiment indoors, and carrying out heat preservation around an experiment box by using a polyethylene material; as shown in fig. 1;
The two holes are a freezing hole A and a freezing hole B respectively, and the conditions of the brine flow, the brine temperature drop gradient, the refrigerating system, the clear water circulating system and the soil body freezing system of the freezing hole A and the freezing hole B are consistent with the field conditions, namely, the conditions of about 58.80m of the north-south station-north station interval of the airport of the Guangzhou rail transit No. three-wire north-extension section are consistent with the conditions of the north-south station interval of the airport;
The thickness of the freezing front surface from the freezing hole A or the freezing hole B is h 1, and the non-intersection distance between the freezing hole A and the freezing hole B is h 2;
(1-3) a detection hole C and a detection hole D disposed at positions parallel to the freezing hole a and the freezing hole B, respectively, for ultrasonic detection;
(1-4) injecting saline into the detection hole C and the detection hole D, the freezing hole A and the freezing hole B, starting up a test cycle, opening the end caps of the detection hole C and the detection hole D when the temperature of the saline in the freezing pipe A and the freezing pipe B is minus 25 to minus 28 ℃, placing the probes into the detection hole C and the detection hole D to a detection position, synchronously lifting the transmitting and receiving probes, ensuring that the transmitting and receiving probes are on the same level, detecting the ultrasonic wave velocities in different freezing periods, measuring every 1-2 hours, and then drawing a wave velocity-temperature relation curve, as shown in figure 2. The distance between the detection hole C and the detection hole D is smaller than 1.5m, and the distance between the upper and lower adjacent measuring points is 250-600 mm;
step 2, establishing a nonlinear relation expression of wave velocity-temperature by using the wave velocity-temperature relation curve in the step 1;
the wave velocity-temperature change curve of fig. 2 is fitted in segments by using a linear function, and a nonlinear relation expression of the wave velocity-temperature is obtained.
In the formula (1), c is the wave speed, km/s; t is time, h; a 1、a2、b1、b2、d1、d2 is the coefficient to be determined; t 1、T2、T3、T4 is the temperature inflection point in the temperature curve and is at DEG C;
The non-linear wave velocity-temperature relationship expression fitted by using the constant temperature maintenance mode frozen soil wave velocity-temperature variation curve in fig. 2 is as follows:
(2-2) calculation of temperature field at different freezing stages, i.e., in formula (1) It can be seen from fig. 4 that the variation curves of the simulated temperature data and the measured temperature with time have smaller deviations in the individual sections, but have consistent development trends. The temperature result calculated by the porous medium heat transfer algorithm taking phase change into consideration can effectively reflect the actual engineering situation, and the temperature field distribution cloud images at different freezing moments shown in fig. 5 are obtained.
Acoustic impedance field calculation for different freezing phases, i.e. solvingAs shown in figure 6 of the drawings,
Substituting the wave velocity c (T, T) into formula (1) to obtain acoustic impedance fields at different freezing moments, as shown in formula (2):
Wherein: Acoustic impedance fields for different freezing times.
Step 3, obtaining an artificial frozen soil thermo-acoustic coupling algorithm considering phase change: sound pressure field distribution at different freezing times (freezing 24d and 60d are examples), i.eA sound field distribution cloud image at different freezing moments as shown in fig. 7;
the method comprises the steps of regarding water-containing artificial frozen soil as a porous medium soil body consisting of a soil framework, ice crystals and unfrozen water, wherein the porous medium soil body is provided with a plurality of acoustic impedance areas;
The homogeneous isotropic aqueous artificial frozen soil following the heat conduction equation can be represented by the following formula:
wherein: ρ is the density; c p is equivalent volumetric heat capacity, kJ/(kg.K); t is the surface temperature, DEG C; u is
So q r is taken as 0; simplifying the temperature field problem of an ultrasonic detection horizon into a planar two-dimensional model, and taking 1mm for d z;
The equivalent volume fraction of the model is two parts of the phase change volume fraction from water to ice and the soil body skeleton volume fraction, and the density ρ x, the heat capacity C x and the heat conductivity k x of the C p and the phase change material in the formula (3) are respectively shown as the formula (4), the formula (5), the formula (6) and the formula (7):
Cp＝θgρgCg+θxρxCx (4)；
ρx＝θwρw+θiρi (5)；
Wherein:
kx＝θwkw+θiki； (7)
Wherein: θ g、θw、θi is the volume fraction of the soil body skeleton, water and ice respectively; ρ g、ρw、ρi、ρx is the density of the soil body skeleton, water, ice and phase change material, kg.m -3;Cg、Cx、Cw、Ci is the heat capacity of the soil body skeleton, phase change material, water and ice, kJ/(kg.K); k w、ki、kx is the heat conductivity coefficient of water, ice and phase change material, W/(m.K); wherein the phase transition temperature is 0 ℃, the transition interval from water to ice is 10K, and the phase transition latent heat is 333kJ/kg;
the thermodynamic analysis formula of the artificial frozen soil considering the phase change factor is shown as formula (8):
the artificial freezing thermodynamic analysis is carried out by utilizing the formula (8) to obtain temperature fields of different freezing stages under the normal development condition of the freezing wall, namely the formula (1)
Introducing the temperature field obtained by solving the equation (8) into the equation (2), (1), solving c (T, T), substituting the equation (2), and solvingAs an initial acoustic impedance condition for sound field analysis;
Setting acoustic boundary conditions, selecting cylindrical wave radiation as a sound source excitation source, and selecting single-frequency Rake wavelets as a sound source function, wherein the function expression is as follows:
Wherein, when t is sound, μs; f 0 is the center frequency of the sound source, kHz; t 0 is the period, μs;
The acoustic impedance and sound source boundary condition wave equation described above can be expressed by the following equation:
wherein: p is the independent variable sound pressure, pa; t is time, μs; q m is monopole sound source 1/s 2;
the sound pressure field distribution at different freezing periods can be solved by using the method (10), namely The sound field distribution cloud at different freezing moments as shown in fig. 7.
Step 4, solving and designing the average wave velocity of the development of the freezing wall by using a thermo-acoustic coupling algorithm;
extracting sound pressure signal propagation curves before and at a certain moment after freezing, comparing time displacement tau corresponding to peak positions of a transmitting signal x (t) and a receiving signal y (t) of the sound pressure signal propagation curves, substituting the time displacement tau into a formula (11), and solving the transmission time R xy (tau) of the signal in a freezing wall;
Then substituting the distance S between the two detection holes and the transmission time R xy (tau) into the formula (12) to solve the average wave velocity V p of different freezing periods under the normal freezing wall development condition;
as shown in FIG. 8, the calculation accuracy of the wave velocity of the J1-J2 detection holes is in the range of 89.7-96.97%, and engineering accuracy is basically met. The result of wave velocity calculation by the thermo-acoustic coupling algorithm is proved to effectively reflect the actual ultrasonic detection condition of engineering.
Step 5, calculating quantitative relations between different freezing fronts, non-intersection circle distances and calculated average wave speeds;
Obtaining quantitative relations among a freezing frontal surface h 1, an uncrossing distance h 2 and an average wave velocity V p at any position and time of a freezing region under the normal frozen wall development condition by utilizing a thermo-acoustic coupling algorithm; the quantitative relationship among different freezing fronts h 1, non-intersection distances h 2 and calculated average wave velocity V p under the normal development condition of the regression freezing wall accords with quadratic function relations (13) and (14):
Wherein h 1 is the freezing front distance freezing Kong Houdu mm; h 2 is the distance between two freezing holes without intersecting circles, and mm; f 1、f2、f3、g1、g2、g3 is the coefficient to be determined.
And (3) calculating quantitative relations among different freezing fronts, non-intersection distances and calculated wave speeds by using the calculation methods of the formula (13) and the formula (14) after the thermo-acoustic coupling algorithm are shown as (15) and (16).
And 6, judging and early warning the development condition of the freezing wall.
A freezing process stage and a freezing acceptance stage;
Before freezing: the frozen hole site frozen hole and the detection hole should be checked and accepted before ultrasonic detection: 1) Checking whether the pipe is blocked by foreign matters or not, and checking whether the pipe body is cracked, bent or flattened or not; 2) The tubes should be kept substantially parallel, and the degree of non-parallelism should be controlled to be less than 1%; 3) After the pipeline is installed, the upper opening is closed so as not to fall into foreign matters, and the pore canal is blocked; 4) The pipeline is 300-500 mm higher than the ground surface, so that the exposed height is guaranteed to be the same;
Stage of freezing process: as shown in fig. 3, the freezing holes a26 and a27, the detection hole J1, and the temperature measurement hole T8 are directed;
Ultrasonic detecting the wave velocities v p1 of the freezing hole A26 and the detection hole J1 at the freezing site, substituting the wave velocities into a formula (13) to calculate the actual freezing frontal surface distance H 1 at the site for 7 days/time until the freezing wall reaches a freezing boundary;
Ultrasonic detecting the wave velocity v p2 between any two freezing holes such as A26 and A27 at the freezing site, wherein the detection period is the date of designing the intersection circle of the freezing wall, the date of designing the intersection circle of the freezing wall is 20+/-5 days, and substituting the date into a formula (14) to calculate the non-intersection circle distance H 2;
Freezing acceptance stage: synchronously lifting the transmitting and receiving probes to ensure that the transmitting and receiving probes are on the same level; the wave velocities v p1 of the freezing hole a26 and the detection hole J1 were recorded.
For the conditions that the wave speed is abnormal and the passing time is inconsistent with other detection results at the same level, the geological reasons need to be analyzed in time, the reasons such as holes, groundwater flow speed and the like are checked, and the purpose of early forecasting is achieved. After the detection is finished, the freezing Kong Fengtou cap should be screwed down in time, and the sealing condition of the sealing head cap gasket is checked to prevent the leakage of the brine. The acoustic holes should also be provided with end caps to prevent foreign objects from falling into the holes.
The judging and early warning method in the step 6 is as follows:
Substituting average wave velocities V p1 and V p2 under normal development conditions of the freezing wall in the algorithm into formulas (13) and (14) to obtain a freezing frontal surface position h 1 between two detection holes under normal development conditions of the freezing wall and a non-ring distance h 2 between the two detection holes under normal development conditions of the freezing wall; substituting the field detection wave speeds v p1 and v p2 into equations (13) and (14) to obtain a freezing front position H 1 between the field freezing hole A26 and the detection hole J1 and a non-ring-crossing distance H 2 between the field freezing hole A26 and the freezing hole A27;
When the freezing front position H 1 of the same freezing time judged by field actual measurement is more than 30% smaller than the designed freezing front position H 1, judging the detection area as a freezing wall development high risk area;
For the time of designing the intersection of the freezing walls, the field actually measured wave velocity v p2 at a certain position calculates the non-intersection distance H 2 not equal to 0 of the two freezing holes, the non-intersection distance H 2 =0 between the freezing holes at the moment under the normal development condition of the freezing walls obtained by a thermo-acoustic coupling algorithm, and meanwhile, the non-intersection distance H 2 approximately equal to 0 of the two freezing holes at other positions is checked on site, so that the detection area is judged to be the high risk area of the freezing walls.
Abnormal conditions of the developmental high risk area and the "windowed" high risk area are:
(a) Excessive seepage velocity or other geological factors;
(b) The cooling capacity of the nearby freezing holes is insufficient, the blockage is small, the flow is small, and the like;
(c) The nearby freeze holes are too much deflected.
The possible conditions are checked item by item, and timely remedying and remedying measures are carried out:
If the situation (a) is found, grouting, water shutoff and seepage reduction measures are carried out on the high risk area in time;
if the situation (b) is found, the cooling capacity should be increased in time to dredge the foreign matters in the freezing holes;
If the situation (c) is found, measures such as hole freezing compensation or cold capacity increase should be performed in time.
The freezing front position is judged by using the formula (15) as shown in fig. 9, and the freezing front position H 1 obtained by the field actual measurement is basically consistent with the freezing front position H 1 of the same freezing time under the normal development condition of the freezing wall obtained by the thermo-acoustic coupling algorithm. And judging that the development condition of the freezing wall of the area is good.
And judging the position of the freezing front by using the formula (16), and finding that the non-intersection distance H 2 of all freezing holes is basically 0 when the intersection time of the freezing walls is 24d, so as to prove that no freezing abnormality phenomenon exists between the two freezing holes.
The engineering is also smooth and safe after 2019 construction. Proved by the method, the development condition of the freezing wall can be accurately judged, and the method is used for constructing the protection navigation for the freezing engineering-!
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While the obvious variations or modifications which are extended therefrom remain within the scope of the claims of this patent application.
Claims (6)
1. A frozen wall development condition judging and early warning method based on a thermo-acoustic coupling algorithm is characterized by comprising the following steps:
Step 1, in the preparation stage of freezing construction, an indoor physical test model of two-hole freezing of a water-rich sand layer is established, and a wave speed-temperature relation curve is drawn;
step 2, establishing a nonlinear relation expression of wave velocity-temperature by using the wave velocity-temperature relation curve in the step 1;
Step 3, obtaining an artificial frozen soil thermo-acoustic coupling algorithm considering phase change;
Step 4, solving and designing the average wave velocity of the development of the freezing wall by using a thermo-acoustic coupling algorithm;
Step 5, calculating quantitative relations between different freezing fronts, non-intersection circle distances and calculated average wave speeds;
Step 6, judging and early warning the development condition of the freezing wall by comparing the actually measured and calculated freezing fronts and the non-coil distance;
In step 1:
(1-1) selecting a soil sample with the same thermodynamic parameters as the soil property detected on site, carrying out a two-hole freezing physical model experiment indoors, and carrying out heat preservation around an experiment box by using a polyethylene material;
(1-2) wherein two freezing holes are a freezing hole A and a freezing hole B respectively, and the conditions of brine flow, brine temperature drop gradient, refrigeration system, clear water circulation system and soil body freezing system of the freezing hole A and the freezing hole B are consistent with the conditions of the site;
The thickness of the freezing front surface from the freezing hole A or the freezing hole B is h 1, and the non-intersection distance between the freezing hole A and the freezing hole B is h 2;
(1-3) a detection hole C and a detection hole D disposed at positions parallel to the freezing hole a and the freezing hole B, respectively, for ultrasonic detection;
(1-4) injecting saline into the detection holes C and D, the freezing holes A and B, starting up a test cycle, opening end caps of the detection holes C and D after the temperature of the saline in the freezing pipe A and B is between 25 ℃ below zero and 28 ℃ below zero, placing probes into the detection holes C and D to a detection position, synchronously lifting the transmitting and receiving probes, ensuring that the transmitting and receiving probes are on the same level, detecting ultrasonic wave speeds in different freezing periods, measuring every 1-2 hours, and drawing a wave speed-temperature relation curve;
In step (2):
(2-1) piecewise fitting a wave velocity-temperature variation curve using a linear function to obtain a nonlinear relation expression of wave velocity-temperature, as shown in formula (1):
In the formula (1), c is the wave speed, km/s; t is time, h; a 1、a2、b1、b2、d1、d2 is the coefficient to be determined; t 1、T2、T3、T4 is the temperature inflection point in the temperature curve and is at DEG C;
(2-2) substituting the wave velocity c (T, T) into the formula (1) to obtain acoustic impedance fields at different freezing moments, as shown in the formula (2):
Wherein: acoustic impedance fields for different freezing moments; ρ g is the density of the soil skeleton;
In step (3):
the method comprises the steps of regarding water-containing artificial frozen soil as a porous medium soil body consisting of a soil framework, ice crystals and unfrozen water, wherein the porous medium soil body is provided with a plurality of acoustic impedance areas;
The homogeneous isotropic aqueous artificial frozen soil following the heat conduction equation can be represented by the following formula:
Wherein: ρ is the density; c p is equivalent volumetric heat capacity, kJ/(kg.K); t is the surface temperature, DEG C; u is the velocity vector of the translational motion of the node, m/s; q is the heat flux of heat conduction, W/m -2;qr is the heat flux of heat radiation, W/m -2; q is a heat source, W/m -3; k is the equivalent thermal conductivity, W/(m.K); the radiation heat exchange is not considered in the freezing process, so q r is taken as 0; simplifying the temperature field problem of an ultrasonic detection horizon into a planar two-dimensional model, and taking 1mm for d z;
The equivalent volume fraction of the model is two parts of the phase change volume fraction from water to ice and the soil body skeleton volume fraction, and the density ρ x, the heat capacity C x and the heat conductivity k x of the C p and the phase change material in the formula (3) are respectively shown as the formula (4), the formula (5), the formula (6) and the formula (7):
Cp＝θgρgCg+θxρxCx (4)；
ρx＝θwρw+θiρi (5)；
Wherein:
kx＝θwkw+θiki； (7)；
Wherein: θ g、θw、θi、θx is the volume fraction of the soil body skeleton, water, ice and phase change material respectively; ρ g、ρw、ρi、ρx is the density of the soil body skeleton, water, ice and phase change material, kg.m -3;Cg、Cx、Cw、Ci is the heat capacity of the soil body skeleton, phase change material, water and ice, kJ/(kg.K); k w、ki、kx is the heat conductivity coefficient of water, ice and phase change material, W/(m.K); wherein the phase transition temperature is 0 ℃, the transition interval from water to ice is 10K, and the phase transition latent heat is 333kJ/kg;
the thermodynamic analysis formula of the artificial frozen soil considering the phase change factor is shown as formula (8):
the artificial freezing thermodynamic analysis is carried out by utilizing the formula (8) to obtain temperature fields of different freezing stages under the normal development condition of the freezing wall, namely the formula (1)
Introducing the temperature field obtained by solving the equation (8) into the equation (1), solving c (T, T), substituting the equation (2), and solvingAs an initial acoustic impedance condition for sound field analysis;
Setting acoustic boundary conditions, selecting cylindrical wave radiation as a sound source excitation source, and selecting single-frequency Rake wavelets as a sound source function, wherein the function expression is as follows:
Wherein, when t is sound, μs; f 0 is the center frequency of the sound source, kHz; t 0 is the period, μs;
The acoustic impedance and sound source boundary condition wave equation described above can be expressed by the following equation:
wherein: p is the independent variable sound pressure, pa; t is time, μs; q m is monopole sound source 1/s 2;
the sound pressure field distribution at different freezing periods can be solved by using the method (10), namely
In step 4:
Extracting sound pressure signal propagation curves before and at a certain moment after freezing, comparing time displacement tau corresponding to peak positions of a transmitting signal x (t) and a receiving signal y (t) of the sound pressure signal propagation curves, substituting the time displacement tau into a formula (11), and solving the transmission time R xy (tau) of the signal in a freezing wall;
Then substituting the distance S between the two detection holes and the transmission time R xy (tau) into the formula (12) to solve the average wave velocity V p of different freezing periods under the normal freezing wall development condition;
2. The frozen wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm according to claim 1 is characterized in that the distance between the detection hole C and the detection hole D is smaller than 1.5m, and the distance between the upper measuring point and the lower measuring point is 250-600 mm.
3. The frozen wall development condition judgment and early warning method based on the thermo-acoustic coupling algorithm according to claim 1, wherein in step 5:
Obtaining quantitative relations among a freezing frontal surface h 1, an uncrossing distance h 2 and an average wave velocity V p at any position of a freezing region under the normal frozen wall development condition by utilizing a thermo-acoustic coupling algorithm; the quantitative relationship among different freezing fronts h 1, non-intersection distances h 2 and calculated average wave velocity V p under the normal development condition of the regression freezing wall accords with quadratic function relations (13) and (14):
Wherein h 1 is the freezing front distance freezing Kong Houdu mm; h 2 is the distance between two freezing holes without intersecting circles, and mm; f 1、f2、f3、g1、g2、g3 is the coefficient to be determined.
4. The frozen wall development condition judgment and early warning method based on the thermo-acoustic coupling algorithm according to claim 3, wherein in step 6: in the field freezing project, ultrasonic detection of the development condition of the frozen wall is divided into two detection stages: a freezing process stage and a freezing acceptance stage;
Before freezing: the field freezing hole and the detection hole should be checked and accepted before ultrasonic detection: 1) Checking whether the pipe is blocked by foreign matters or not, and checking whether the pipe body is cracked, bent or flattened or not; 2) The tubes should be kept parallel, and the non-parallelism should be controlled to be less than 1%; 3) After the pipeline is installed, the upper opening is closed so as not to fall into foreign matters, and the pore canal is blocked; 4) The pipeline is 300-500 mm higher than the ground surface, so that the exposed height is guaranteed to be the same;
Stage of freezing process:
setting a freezing hole A26, a freezing hole A27, a detection hole J1 and a temperature measurement hole T8 on a freezing site;
Ultrasonic detecting the wave velocities v p1 of the freezing hole A26 and the detection hole J1 at the freezing site, substituting the wave velocities into a formula (13) to calculate the actual freezing frontal surface distance H 1 at the site for 7 days/time until the freezing wall reaches a freezing boundary;
Ultrasonic detecting the wave velocity v p2 between any two freezing holes A26 and A27 at the freezing site, wherein the detection period is the date of designing the intersection circle of the freezing wall, the date of designing the intersection circle of the freezing wall is 20+/-5 days, and substituting the date into a formula (14) to calculate the non-intersection circle distance H 2;
Freezing acceptance stage: synchronously lifting the transmitting and receiving probes to ensure that the transmitting and receiving probes are on the same level; the wave velocities v p1 of the freezing hole a26 and the detection hole J1 were recorded.
5. The frozen wall development condition judging and early warning method based on the thermo-acoustic coupling algorithm according to claim 4, characterized in that,
The judging and early warning method in the step 6 is as follows:
substituting average wave velocities V p1 and V p2 under normal development conditions of the freezing wall in the algorithm into formulas (13) and (14) to obtain a freezing frontal surface position h 1 between two detection holes under normal development conditions of the freezing wall and a non-ring distance h 2 between the two detection holes under normal development conditions of the freezing wall; substituting the field detection wave speeds v p1 and v p2 into equations (13) and (14) to obtain a freezing front position H 1 between the field freezing hole A26 and the detection hole J1 and a non-ring-crossing distance H 2 between the field freezing hole A26 and the freezing hole A27;
When the freezing front position H 1 is more than 30% smaller than the freezing front position H 1 under the normal development condition of the freezing wall obtained by the specific heat-sound coupling algorithm at the same freezing time judged by field actual measurement, judging that the detection area is a freezing wall development high risk area;
For the time of designing the intersection of the freezing walls, the field actually measured wave velocity v p2 at a certain position calculates the non-intersection distance H 2 not equal to 0 of the two freezing holes, the non-intersection distance H 2 =0 between the freezing holes at the moment under the normal development condition of the freezing walls obtained by a thermo-acoustic coupling algorithm, and meanwhile, the non-intersection distance H 2 approximately equal to 0 of the two freezing holes at other positions is detected on site, so that the detection area is judged to be the high risk area of the freezing walls.
6. The method for judging and pre-warning the development condition of the freezing wall based on the thermo-acoustic coupling algorithm according to claim 5, wherein,
Abnormal conditions of the developmental high risk area and the "windowed" high risk area are:
(a) Excessive seepage velocity or other geological factors;
(b) The cooling capacity of the nearby freezing holes is insufficient, the freezing holes are blocked, and the flow is small;
(c) The nearby freezing holes are too much deflected;
The possible conditions are checked item by item, and the remedy is carried out in time, and the remedy measures are as follows:
If the situation (a) is found, grouting, water shutoff and seepage reduction measures are carried out on the high risk area in time;
if the situation (b) is found, the cooling capacity should be increased in time to dredge the foreign matters in the freezing holes;
if the situation (c) is found, the measures of compensating the freezing holes or increasing the cold quantity should be carried out in time.
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