CN107272073A - A kind of method that application GPR calculates frozen soil relative water content - Google Patents
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Abstract
The invention discloses a kind of method that application GPR calculates frozen soil relative water content, methods described includes：S1：Frozen soil is tested using GPR, measurement data is obtained；S2：The Relative Wave Impedance of frozen soil is calculated, frozen soil layer and melt layer is divided；S3：According to the measurement data of melt layer, the weighted average frequency and instantaneous quality factor of frozen soil melt layer are calculated, and is normalized；S4：Frozen soil relative water content is calculated according to the weighted average frequency after normalization and instantaneous quality factor, the invention provides a kind of method that can easy, quickly calculate frozen soil relative water content, support is provided for engineering construction, with great theory significance and engineering practical value.
Description
Technical Field
The invention relates to the field of calculation of relative water content of frozen soil. And more particularly, to a method for calculating the relative water content of frozen soil using ground penetrating radar.
Background
The Qinghai-Tibet plateau is one of the areas with the widest permafrost area and the largest thickness in the low latitude area in the northern hemisphere, and the freeze-thaw state of the permafrost becomes one of the most important tasks when natural disasters are evaluated. Meanwhile, the frozen soil is degraded due to a change in a thermal equilibrium state caused by road construction. The state of frozen soil is grasped in time, necessary maintenance measures are taken to slow down diseases, axle weight is continuously increased, transportation efficiency is improved, and meanwhile driving safety is guaranteed, so that the method becomes a major problem to be solved urgently at present.
At present, methods for detecting the water content of soil on site mainly include a resistance method, a capacitance method and the like, all of which are that according to the change of the resistivity/permittivity of soil along with the change of the water content, signals collected by a sensor are converted into water content parameters by constructing a mathematical model of resistance/capacitance of two electrodes of the sensor and soil water, and finally, water content indexes are displayed, and multi-point real-time monitoring can be realized by constructing a regional wireless network. However, in the early stage of the above-mentioned field detection, the multiple sensors need to be embedded into the target area in advance, and the depth of the embedded sensors cannot be changed, that is, only the water content of a relatively fixed depth can be detected; in addition, more sensors are required for a larger target area, which increases both the instrument cost and the labor cost, and reduces the detection efficiency.
The ground penetrating radar is an important branch of geophysics, by transmitting broadband short-pulse high-frequency electromagnetic waves to the underground and utilizing the electromagnetic characteristics of different underground media and the reflection principle of boundary surfaces of the different underground media on the electromagnetic waves, underground target bodies are identified, the ground penetrating radar has the advantages of high data precision, short acquisition time, low labor consumption and low detection cost, excavation and ground damage are not needed, and the roadbed detection effect is obvious.
At present, the moisture content of permafrost can be qualitatively judged and read by means of manual experience from ground penetrating radar images, but more accurate moisture content data cannot be given. For the section requiring accurate water content, the drilling and geotechnical experiments can be used for further testing, the cost is high, the efficiency is low, the state of frozen soil is mastered, necessary maintenance measures are taken to slow down the damage, and the driving safety is ensured to be difficult while the axle weight is continuously increased and the transportation efficiency is improved.
Therefore, it is necessary to provide a method capable of accurately calculating the relative water content of frozen soil, simply, conveniently and quickly calculating the relative water content of frozen water, and providing support for engineering construction.
Disclosure of Invention
The invention aims to provide a method for calculating the relative water content of frozen soil by applying a ground penetrating radar so as to accurately calculate the relative water content of the frozen soil by utilizing the electromagnetic wave attribute of the ground penetrating radar.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention discloses a method for calculating the relative water content of frozen soil by applying a ground penetrating radar, which comprises the following steps:
s1: testing the frozen soil by using a ground penetrating radar to obtain measurement data;
s2: calculating the relative wave impedance of the frozen soil, and dividing the frozen soil layer and the melting layer;
s3: calculating the weighted average frequency and the instantaneous quality factor of the frozen soil melting layer according to the measurement data of the melting layer, and performing normalization processing;
s4: and calculating the relative water content of the frozen soil according to the normalized weighted average frequency and the instantaneous quality factor.
Preferably, the center frequency of the electromagnetic wave of the ground penetrating radar is 200Mhz, 400Mhz or 1000 Mhz.
Preferably, the ground penetrating radar is matched with a shielding antenna of 100Mhz, 250Mhz, 500Mhz, 1000Mhz or 2000Mhz for use.
Preferably, the measurement data comprises amplitude, phase, frequency and velocity.
Preferably, the relative wave impedance is
In the formula, gammaiIs the reflection coefficient of the reflection intensity of the two frozen soil layers,iandi+1the dielectric constant values of the i-th and i + 1-th layers from the top layer of the frozen earth areiAndi+1is an average value ofiAndi+1the difference between the two or more of the two,i、i+1and delta is in the unit of F/m, and [ integral ] gamma dt is the relative wave impedance.
Preferably, the relative wave impedance is indicative of a change in reflectivity of the subsurface medium caused by thawing of frozen earth.
Preferably, the S3 includes:
s31: according to the measurement data, calculating the weighted average frequency of the melting interface and the melting degree of the frozen soil as
In the formula,for weighted average frequency, in Hz, z (t) is the signal of the sum of the N signal indices in db, an(t) is a constant parameter which is,is the phase of the signal in rad, j is the angular frequency in rad/s;
and carrying out normalization treatment on the obtained product:
in the formula,in order to be a normalized weighted average frequency,is the minimum value of the weighted average frequency,is the maximum value of the weighted average frequency,in Hz;
s32: calculating the instantaneous quality factor of the frozen soil melting layer according to the measurement data as
Where decapy (t) is the ratio of the two instantaneous envelope signal differences, freq (t) is the instantaneous frequency at time t, in Hz, and pi is the circumference;
and carrying out normalization treatment on the obtained product:
in the formula (t)nFor normalized instantaneous figure of merit, (t)minIs the minimum value of the instantaneous figure of merit, (t)maxIs the maximum value of the instantaneous figure of merit.
Preferably, the S4 includes:
s41: averaging the normalized weighted average frequency and instantaneous figure of merit to
Wherein,is the normalized weighted average frequency (t)nIs normalized instantaneous figure of merit;
s42: calculating the relative water content of the frozen soil as
θR＝a+bw+cw2+dw3
Wherein a, b, c and d are coefficients.
Preferably, the relative water content of the frozen earth is related to the melting degree of a melting interface of the frozen earth, the porosity of the frozen earth, the permeability, the rock fracture and the relative dielectric constant value.
The invention has the following beneficial effects:
the method for calculating the relative water content of the frozen soil by applying the ground penetrating radar can effectively improve the efficiency of detecting the water content of the frozen soil, introduces the instantaneous quality factors with high correlation with the porosity, the permeability and the rock fracture of the frozen soil, and establishes the function formula with the direct relation with the relative dielectric constant, so that the relative water content of the frozen soil can be simply and quickly estimated according to the measurement data of the ground penetrating radar. The invention provides a reference for mastering the frozen soil state by applying the invention to engineering practice, and has great theoretical significance and engineering practical value.
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
FIG. 1 is a schematic flow chart of a method for calculating the relative water content of frozen soil by applying a ground penetrating radar;
FIG. 2(a) is a schematic cross-sectional view showing relative wave impedance in an embodiment of the present invention;
FIG. 2(b) shows a schematic cross-sectional view of the inversion of water cut in an embodiment of the invention;
FIG. 3(a) is a schematic cross-sectional view showing inversion of the water cut on the anode side of a berm in an embodiment of the invention;
FIG. 3(b) is a schematic cross-sectional view showing an inversion of water cut content of a shadow cast of an embodiment of the invention;
FIG. 4(a) is a schematic cross-sectional view illustrating inversion of water cut in a subgrade in an embodiment of the invention;
FIG. 4(b) is a schematic cross-sectional view showing an inversion of berm water cut in an embodiment of the present invention;
FIG. 4(c) is a schematic cross-sectional view showing the inversion of the original surface water cut in an embodiment of the invention;
FIG. 5(a) is a schematic cross-sectional view illustrating the inversion of water cut on the hot-bar-free side of a subgrade in an embodiment of the invention;
fig. 5(b) shows a schematic cross-sectional view of the inversion of water cut on the subgrade hot-bar side in an embodiment of the invention.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
As shown in FIG. 1, the invention discloses a method for calculating the relative water content of frozen soil by applying a ground penetrating radar, which comprises the following steps:
s1: and testing the frozen soil by using a ground penetrating radar to obtain measurement data. In order to meet different detection depth requirements, a ground penetrating radar with electromagnetic wave center frequency of 200Mhz, 400Mhz or 1000Mhz can be adopted for field test, and measurement data are collected. The ground penetrating radar is required to be approximately parallel to a road shoulder during working. The measurement data includes amplitude, phase, frequency and velocity. The ground penetrating radar can be matched with a shielding antenna for use, and the frequency of the shielding antenna can be selected from 100Mhz, 250Mhz, 500Mhz, 1000Mhz or 2000 Mhz.
S2: and calculating the relative wave impedance of the frozen soil, and dividing the frozen soil layer and the melting layer.
According to the measurement data of the radar, the relative wave impedance which can indicate the change of the reflectivity of the underground medium caused by the melting of the frozen soil is calculated, the frozen soil layer and the melting layer are divided by using the relative wave impedance, the boundary of the two soil layers is determined, and the later calculation only considers the measurement data of the melting layer, so that the later calculation is more accurate. Wherein the relative wave impedance is
In the formula, gammaiIs a reflection coefficient for quantifying the reflection intensity of two frozen soil layers,i(F/m) andi+1(F/m) is the value of the dielectric constant of the i and i +1 layers, respectively, starting from the top layer of frozen earth, (F/m) isiAndi+1is a mean value ofiAndi+1the difference between ^ γ dt is the relative wave impedance, proportional to the natural logarithm of the dielectric constant.
S3: and calculating the weighted average frequency and the instantaneous quality factor of the frozen soil melting layer according to the measurement data of the melting layer, and performing normalization processing. S3 may include:
s31: based on the measurement data, a weighted average frequency is calculated that is indicative of the frozen soil melt interface and degree of melting
In the formula,z (t) (db) is a signal of the sum of N signal indices, an(t) is a constant parameter which is,(rad) is the phase of the signal and j (rad/s) is the angular frequency.
And carrying out normalization treatment on the obtained product:
in the formula,in order to be a normalized weighted average frequency,is the minimum value of the weighted average frequency,is the maximum of the weighted average frequency.
S32: according to the measurement data, the instantaneous quality factor with high correlation with the porosity, permeability and rock fracture of the frozen soil is calculated, and the method has strong representativeness. The instantaneous figure of merit is
Where decap (t) is the ratio of the two instantaneous envelope signal differences, freq (t) (hz) is the instantaneous frequency at time t, and pi is the circumferential ratio.
And carrying out normalization treatment on the obtained product:
in the formula (t)nFor normalized instantaneous figure of merit, (t)minIs the minimum value of the instantaneous figure of merit, (t)maxIs the maximum value of the instantaneous figure of merit.
S4: and calculating the relative water content of the frozen soil according to the normalized weighted average frequency and the instantaneous quality factor.
S41: averaging the normalized weighted average frequency and instantaneous figure of merit to
S42: calculating the relative water content of the frozen soil as
θR＝a+bw+cw2+dw3
Wherein a, b, c and d are coefficients. In general, the coefficients are general coefficients, calibration coefficients can be used if the monitoring range is small, and the average values of the general coefficients and the calibration coefficients are used if the monitoring range is too large, so as to adapt to actual conditions.
The invention will now be further illustrated by the following specific example in which the relative water content of the frozen earth is
θR＝-5.3+2.92w-0.055w2+0.00043w3
The simulation results of this example are shown in fig. 2(a) to 5 (b). Through the inversion of the relative wave impedance, the physical layering of the underground medium can be clearly imaged. The black arrows in fig. 2(b) indicate that the frozen earth is significantly melted and a significant melting peak occurs at the interface of the roadbed and the original pavement, respectively, from top to bottom. Collapse occurs in the interface inside frozen soil melting in the hot karst development area, the reflection intensity of the layer wave resistance is high, interface floating occurs, the wave resistance of the whole reflection interface is reduced and uniform outside the hot karst development area below the depth of 7 m, and the underground frozen soil is well preserved. Fig. 2(b) shows the relative water content profile, with the relative water content of the formation above the apparent melt interface being greater and greater in the hot melt development zone. Fig. 3(a) and 3(b) show the relative water content of the male and female sides, respectively, with a greater relative water content occurring in both the male side berm and the melted interior relative to the female side. Partial accumulation of the molten water occurs in the inside of the sunny underground medium with larger melting depth, so that the side road base is caused to be subjected to larger hot melting and sedimentation. In order to verify the relative water content distribution characteristics of roadbed, berm and original ground frozen soil ablation. Fig. 4(a), 4(b) and 4(c) show in sequence the relative moisture content distribution profiles of the subgrade, berm and primary ground frozen earth ablations. The water content at the guard way is higher, and the water content in the ice-water mixed frozen soil ablation area is higher. The original ground moisture was primarily concentrated near the full ablation interface. The relative water content inside the complete ablation interface in the roadbed is uniformly distributed and is lower. Fig. 5(a) and 5(b) show the water cut inversion profile moisture distribution characteristics on the hot-wand side and the non-hot-wand side. The moisture distribution of the negative side without the heat stick is more uniform, and the moisture seepage is gathered at the lower part of the perennial ablation interface to form a deeper freeze-thaw interface, so that the influence on a deep ice layer is lower; the water distribution on the hot rod side is not concentrated any more due to the reverse heat transfer effect of the hot rod, and the water is distributed in the whole freezing and thawing surface and influences the lower ice layer.
The method optimizes the substituted value in the empirical formula based on the measurement data acquired by the ground penetrating radar, thereby obtaining the relative water content of the frozen soil with high accuracy. The method comprises the steps of obtaining data of a melting layer by dividing a frozen soil layer and the melting layer, calculating weighted average frequency and instantaneous quality factors, normalizing the weighted average frequency and the instantaneous quality factors respectively, averaging the normalized weighted average frequency and the normalized instantaneous quality factors, and substituting the average frequency and the normalized instantaneous quality factors into a water content empirical formula to calculate the relative water content. In view of the complexity of the relative water content of the frozen soil, the calculation formula of the relative water content of the frozen soil provided by the invention is simple, convenient and quick, has high efficiency, is clear in calculation method and high in relative accuracy, and provides support for engineering construction.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.
Claims (9)
1. A method for calculating relative water content of frozen soil by applying a ground penetrating radar, which is characterized by comprising the following steps:
s1: testing the frozen soil by using a ground penetrating radar to obtain electromagnetic wave measurement data;
s2: calculating the relative wave impedance of the frozen soil, and dividing the frozen soil layer and the melting layer;
s3: calculating the weighted average frequency and the instantaneous quality factor of the frozen soil melting layer according to the electromagnetic wave measurement data of the melting layer, and performing normalization processing;
s4: and calculating the relative water content of the frozen soil according to the normalized weighted average frequency and the instantaneous quality factor.
2. The method of claim 1, wherein the ground penetrating radar has a center frequency of electromagnetic waves of 200Mhz, 400Mhz, or 1000 Mhz.
3. The method of claim 1, wherein the ground penetrating radar is used with a shielded antenna of 100Mhz, 250Mhz, 500Mhz, 1000Mhz, or 2000 Mhz.
4. The method of claim 1, wherein the measurement data includes amplitude, phase, frequency, and velocity.
5. The method of claim 1, wherein the relative wave impedance is
<mrow> <msub> <mi>&gamma;</mi> <mi>i</mi> </msub> <mo>=</mo> <mfrac> <mrow> <msqrt> <msub> <mi>&epsiv;</mi> <mi>i</mi> </msub> </msqrt> <mo>-</mo> <msqrt> <msub> <mi>&epsiv;</mi> <mrow> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> </msqrt> </mrow> <mrow> <msqrt> <msub> <mi>&epsiv;</mi> <mi>i</mi> </msub> </msqrt> <mo>+</mo> <msqrt> <msub> <mi>&epsiv;</mi> <mrow> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> </msqrt> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>&Delta;</mi> <mi>&epsiv;</mi> </mrow> <mrow> <mn>2</mn> <mi>&epsiv;</mi> </mrow> </mfrac> </mrow>
<mrow> <mo>&Integral;</mo> <mi>&gamma;</mi> <mi>d</mi> <mi>t</mi> <mo>&ap;</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <mo>&Integral;</mo> <mfrac> <mrow> <mi>&Delta;</mi> <mi>&epsiv;</mi> </mrow> <mrow> <mn>2</mn> <mi>&epsiv;</mi> </mrow> </mfrac> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <mi>l</mi> <mi>n</mi> <mi>&epsiv;</mi> </mrow>
In the formula, gammaiIs the reflection coefficient of the reflection intensity of the two frozen soil layers,iandi+1the dielectric constant values of the i-th and i + 1-th layers from the top layer of the frozen earth areiAndi+1is an average value ofiAndi+1the difference between the two or more of the two,i、i+1the unit of delta is F/m; and [ j ] γ dt is the relative wave impedance.
6. The method of claim 1, wherein the relative wave impedance represents a change in reflectivity of the subsurface medium caused by frozen earth melting.
7. The method according to claim 1, wherein the S3 includes:
s31: according to the measurement data, calculating the weighted average frequency of the melting interface and the melting degree of the frozen soil as
In the formula,is the weighted average frequency in Hz; z (t) is the signal of the sum of N signal indexes, and has the unit of db, an(t) is a constant parameter which is,is the phase of the signal in rad, j is the angular frequency in rad/s;
and carrying out normalization treatment on the obtained product:
in the formula,in order to be a normalized weighted average frequency,is the minimum value of the weighted average frequency,is the maximum value of the weighted average frequency,in Hz;
s32: calculating the instantaneous quality factor of the frozen soil melting layer according to the measurement data as
<mrow> <mi>&delta;</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mrow> <mo>-</mo> <mi>&pi;</mi> <mo>&CenterDot;</mo> <mi>f</mi> <mi>r</mi> <mi>e</mi> <mi>q</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>d</mi> <mi>e</mi> <mi>c</mi> <mi>a</mi> <mi>y</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow>
Where decapy (t) is the ratio of the two instantaneous envelope signal differences, freq (t) is the instantaneous frequency at time t, in Hz, and pi is the circumference;
and carrying out normalization treatment on the obtained product:
<mrow> <mi>&delta;</mi> <msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mi>n</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mi>&delta;</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>-</mo> <mi>&delta;</mi> <msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mi>min</mi> </msub> </mrow> <mrow> <mi>&delta;</mi> <msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> <mo>-</mo> <mi>&delta;</mi> <msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mi>min</mi> </msub> </mrow> </mfrac> </mrow>
in the formula (t)nFor normalized instantaneous figure of merit, (t)minIs the minimum value of the instantaneous figure of merit, (t)maxIs the maximum value of the instantaneous figure of merit.
8. The method according to claim 1, wherein the S4 includes:
s41: averaging the normalized weighted average frequency and instantaneous figure of merit to
Wherein,is the normalized weighted average frequency (t)nIs normalized instantaneous figure of merit;
s42: calculating the relative water content of the frozen soil as
θR＝a+bw+cw2+dw3
Wherein a, b, c and d are coefficients.
9. The method of claim 1, wherein the frozen earth relative water content is related to frozen earth melt interface melting, frozen earth porosity, permeability, rock fracture and relative dielectric constant values.
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Cited By (4)
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| CN109579685A (en) * | 2018-12-17 | 2019-04-05 | 河南中原光电测控技术有限公司 | A kind of frost penetration calculation method and device |
| CN109682853A (en) * | 2019-01-09 | 2019-04-26 | 南京大学 | A kind of frozen soil ice content distribution in-situ measuring method and device based on FBG |
| CN110792425A (en) * | 2019-11-21 | 2020-02-14 | 中国海洋石油集团有限公司 | Method for measuring water content of formation fluid |
| CN110967773A (en) * | 2019-12-23 | 2020-04-07 | 中国煤炭地质总局地球物理勘探研究院 | Method and device for calculating water-rich property in coal seam and electronic equipment |
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