Earthen ruins air permeability prediction method based on low-field magnetic resonance relaxation technology

Abstract

The invention relates to a method for predicting the air permeability of earthen ruins based on a low-field magnetic resonance relaxation technology, and belongs to the technical field of cultural relic protection. The problems that an earthen archaeological site air permeability testing method is time-consuming, labor-consuming, poor in applicability, prone to damaging soil and the like are solved. Preparing a rammed earth test piece; carrying out low-field magnetic resonance relaxation test analysis on the rammed earth test piece; testing the gas permeability of the rammed earth test pieces with different water contents; and determining a relation model of the gas permeability and the unsaturated pore structure of the rammed earth test pieces with different water contents. A non-invasive low-field magnetic resonance relaxation testing technology is adopted, an earthen ruin body is not damaged, the pore water distribution in the earthen ruin is tested in an undisturbed mode, the testing efficiency and accuracy are greatly improved, an important model between the unsaturated pore structure of the earthen ruin and the air permeability of the earthen ruin can be built, the evolution trend of the air permeability of the earthen ruin is predicted, and the research and development of the earthen ruin is facilitated. Continuous monitoring of the air permeability of the earthen ruins is achieved, and a scientific basis is provided for protection and restoration of the earthen ruins.

Description

Technical Field

[0001] The invention relates to a method for predicting the air permeability of earthen ruins, in particular to a method for predicting the air permeability of earthen ruins based on low-field magnetic resonance relaxation technology, and belongs to the technical field of cultural relics protection. Background Art

[0002] Due to factors such as natural erosion and human destruction, many properties of earthen sites have been declining and deteriorating, and the protection of earthen sites faces severe challenges. Among them, air permeability is a key factor affecting the stability and durability of earthen sites, and is also an important indicator for evaluating the survival status of earthen sites. Generally speaking, good air permeability is conducive to maintaining the humidity balance inside the earthen site, hindering salt accumulation and microbial growth, and delaying the disintegration and peeling process of the earthen site. Therefore, monitoring the air permeability indicators of earthen sites and assisting in judging the survival status of earthen sites are of great significance to the scientific protection and restoration of earthen sites.

[0003] At present, there are no relevant testing technical standards for the air permeability of earthen sites. Most of the air permeability indicators are obtained through destructive sampling, using gas permeation tests or water vapor diffusion tests. This method is time-consuming and labor-intensive, and has extremely high requirements for the drilling location, shape and size of the specimens. It is also easy to cause irreversible damage to the earthen site itself, further deteriorating its state of existence. As a non-destructive testing technology, low-field magnetic resonance relaxation technology can quickly and accurately characterize the internal pore structure and water distribution of porous media, which helps to construct an important model between the pore water distribution of earthen sites and their air permeability, predict the evolution trend of the air permeability of earthen sites, and realize the continuous monitoring needs of the air permeability of earthen sites.

[0004] Therefore, it is urgent to propose a method for predicting the air permeability of earthen sites based on low-field magnetic resonance relaxation technology to solve the above technical problems. Summary of the invention

[0005] The present invention is to solve the problems of time-consuming and labor-intensive, poor applicability and easy destruction of soil in the test method of air permeability of earthen ruins, and to provide a method for predicting air permeability of earthen ruins based on low-field magnetic resonance relaxation technology. A brief overview of some parts of the present invention is given below to provide a basic understanding of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention, nor is it intended to determine the key or important parts of the present invention or to limit the scope of the present invention.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] The method for predicting the air permeability of earthen ruins based on low-field magnetic resonance relaxation technology includes the following steps:

[0008] S1: Rammed earth specimen preparation;

[0009] S2: Low-field magnetic resonance relaxation test analysis of rammed earth specimens, including test preparation, parameter setting, low-field magnetic resonance relaxation signal acquisition, moisture signal calibration, surface relaxation strength test and pore water distribution determination;

[0010] S3: Test the air permeability of rammed earth specimens with different moisture contents. Use a gas permeability test device to test the gas permeability of rammed earth specimens with different moisture contents.

[0011] S4: Determine the relationship model between gas permeability and unsaturated pore structure of rammed earth specimens with different moisture contents, including pore water distribution translation, unsaturated pore content calculation, model construction and fitting parameter determination.

[0012] Preferably, the preparation of the rammed earth specimen in S1 comprises the following steps:

[0013] S1.1. Determine the soil material used to prepare the rammed earth specimens (stripped soil at any location of the earthen site is optimal); determine the optimal water content of the soil material;

[0014] S1.2. Preparation of rammed earth specimens: including preparation of saturated rammed earth specimens and preparation of unsaturated rammed earth specimens;

[0015] Preparation of saturated rammed earth specimens: Select several soil samples and perform saturation treatment using the capillary saturation method in the geotechnical test method standard GB / T50123. Place the soil samples in a frame saturator, add clean water and soak in water for at least two days and nights to fully saturate the samples.

[0016] Preparation of unsaturated rammed earth specimens (rammed earth specimens with different moisture contents): several soil samples are gradually dried in a desiccator controlled by blue silica gel, and the relative humidity is controlled at about 3%; 8-10 rammed earth specimens with different moisture contents are obtained by gradual drying;

[0017] S1.3. Sealing and placement: Place the prepared rammed earth specimens into a sealed plastic bag and place them for more than 3 days to ensure that the moisture inside the specimen is evenly distributed.

[0018] Preferably, the low-field magnetic resonance relaxation test analysis of rammed earth specimens with different moisture contents in S2 comprises the following steps:

[0019] S2.1. Test preparation: Wrap the saturated rammed earth specimens and rammed earth specimens with different moisture contents tightly with plastic wrap, and then place them in the sample chamber of the low-field magnetic resonance relaxation test equipment;

[0020] S2.2, parameter setting: use CPMG pulse sequence to perform low-field magnetic resonance relaxation test, set the echo interval, number of echoes, waiting time, number of scans, sampling time interval, number of acquisition points and other parameters;

[0021] S2.3. Low-field magnetic resonance relaxation signal acquisition: low-field magnetic resonance relaxation tests are performed on saturated rammed earth specimens and rammed earth specimens with different moisture contents using a CPMG pulse sequence to obtain a pulse echo signal M(τ);

[0022] S2.4, moisture signal calibration: using the same CPMG test method, the concentration of 1%wt, water content of m wb The copper sulfate solution was tested and analyzed by low-field magnetic resonance relaxation to obtain its relaxation signal M wb Since the total relaxation signal is strictly proportional to the water mass, the total pore water content m of the saturated rammed earth specimens and rammed earth specimens with different water contents is calculated. w ;

[0023] S2.5. Surface relaxation strength test: Take another rammed earth specimen and place it at 23% relative humidity until the mass is constant. Use the low-field magnetic resonance relaxation test of the Hahn spin echo sequence to obtain the surface relaxation strength ρ2 of the rammed earth specimen. According to the fast relaxation theory, the transverse relaxation time T of the pore water inside the rammed earth specimen is calculated. 2i Converted to the equivalent radius r of the cylindrical pore of pore water i ;

[0024] S2.6. Determination of pore water distribution: Obtain the equivalent radius r of the i-th group of pore water i Its transverse relaxation time T 2i After the relationship between the pore water transverse relaxation time spectra f of the saturated rammed earth specimens and the rammed earth specimens with different moisture contents is calculated, the pore water transverse relaxation time spectra f i (T 2i ) is converted to pore water distribution f i (r i ).

[0025] Preferably: In S2.2, the echo interval τ e The setting is 60μs, the number of echoes N is 10000, the waiting time is 5s, the number of scans is 512, and the number of acquisition points is 4. Except for the echo interval, the other parameters can be flexibly adjusted to make the signal-to-noise ratio of the obtained relaxation data higher than 150;

[0026] In S2.3, the expression of M(τ) is as follows:

[0027]

[0028] In formula (1), the pore water of saturated rammed earth specimens and rammed earth specimens with different moisture contents are divided into J groups, T 2i is the transverse relaxation time of the pore water in the i-th group (i=1,2,...,J), in seconds, f i is the volume fraction of the pore water in the i-th group, dimensionless, V i is the volume of the pore water in group i, in m3 , V0 is the total volume of all pore water, in m 3 , M0 is the total signal of pore water obtained by using the commonly used multi-exponential inversion algorithm of low-field magnetic resonance relaxation signal, the unit is μV, f i (T 2i ) is the pore water transverse relaxation time spectrum obtained using the multi-exponential inversion algorithm;

[0029] In S2.4, the total pore water content m of saturated rammed earth specimens and rammed earth specimens with different moisture contents w + The expression is as follows:

[0030]

[0031] In S2.5, the fast relaxation theory is the equivalent radius r of the pore water of the i-th group i Its transverse relaxation time T 2i Proportional, the expression is as follows:

[0032] r i =2ρ2T 2i (3).

[0033] Preferably, the model for determining the relationship between the gas permeability and the unsaturated pore structure of rammed earth specimens with different moisture contents in S4 specifically includes:

[0034] S4.1. Pore water distribution translation: Considering the pore shrinkage and swelling of rammed earth specimens with different moisture contents; according to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the pore water content peak value is consistent with the abscissa position corresponding to the pore water peak value of rammed earth specimens with different moisture contents. The modified pore water distribution function of the saturated rammed earth specimen is F i,S (r i ) = f i,S (nr i ), n is the translation factor, representing the influence of shrinkage and swelling;

[0035] S4.2. Calculation of unsaturated pore content with different pore sizes: According to the modified saturated rammed earth specimen pore water distribution F i,S (r i ) and pore water distribution of rammed earth specimens with different moisture contents i (r i ), calculate the corrected unsaturated pore content distribution S i (r i )=F i,S (r i )-f i (r i )

[0036] S4.3. Model construction.

[0037] Preferably: In S4.3, based on Darcy's law and the parallel capillary bundle model, the expression of gas permeability k is as follows:

[0038]

[0039] In formula (4), Q is the total volume flow rate of gas, the unit is m 3 / s; A is the cross-sectional area of ​​the total pore channel, in m 2 ; k is the gas permeability, the unit is m 2 ; μ is the gas viscosity, the unit is Pa·s; That is, the pressure gradient dP on a tiny unit length dl, the unit is Pa / m; Q i is the gas volume flow rate of a single pore, in m 3 / s; A i is the cross-sectional area of ​​a single pore channel, in m 2 ;k i is the gas permeability of a single pore, in m 2 ;

[0040] Rearranging formula (4), we can get:

[0041]

[0042] Gas permeability k, gas apparent permeability k a and the gas intrinsic permeability k int There is the following formula,

[0043]

[0044] In formula (6), P g is the average inlet pressure, in Pa, v is a fitting parameter, in Pa, b is the Klinkenberg coefficient of the gas used, in Pa; when conducting gas permeability tests, the average inlet pressure is higher, b / P g vs. v / P g is approximately equal to "0", at this time, the gas intrinsic permeability k int , gas permeability k and gas apparent permeability k a are equal;

[0045] When gas permeation is dominated by viscous flow,

[0046]

[0047] In formula (7), d is the diameter of the specimen, in m; d iis the diameter of the pore channel at the i-th level, in m;

[0048] When the gas permeability k is equal to the gas intrinsic permeability k int When they are equal, using equations (5) and (7), we can get:

[0049]

[0050] In formula (8), l is the length of the gas permeation channel, which is the length of the specimen in meters; V i is the volume of the pore channel at level i, in m 3 ; V is the total volume of the specimen, in m 3 ; K i (r i ) represents the ratio of the volume of the i-th level pore channel to the total volume of the specimen;

[0051] Considering the actual K i (r i ) and the unsaturated pore content distribution S obtained after translation i (r i ) has a linear relationship,

[0052] K i (r i )=aS i (r i )+b (9)

[0053] Then formula (9) can be transformed into:

[0054]

[0055] Determination of fitting parameters: According to the measured gas permeability values ​​of rammed earth specimens with different moisture contents and the unsaturated pore distribution S after translation i (r i ), using formula (11), the values ​​of a and b in the model are fitted to ensure the correlation coefficient R 2 >0.98; The air permeability prediction method of earthen sites based on low-field magnetic resonance relaxation technology first performs low-field magnetic resonance relaxation test analysis on the earthen sites to be tested, and then predicts the air permeability of the earthen sites to be tested by the air permeability prediction model obtained by the method for constructing the air permeability prediction model of earthen sites based on low-field magnetic resonance relaxation technology.

[0056] Preferably, the method further comprises S5, low-field magnetic resonance relaxation test analysis of the earthen ruins to be tested, comprising the following steps:

[0057] S5.1: Low-field magnetic resonance relaxation test of the earthen ruins to be tested: Use a single-sided nuclear magnetic resonance relaxation test instrument to test the earthen ruins to be tested. The test parameters are consistent with those for testing rammed earth specimens.

[0058] S5.2: Low-field magnetic resonance relaxation signal acquisition: Use the CPMG pulse sequence to perform low-field magnetic resonance relaxation tests on soil at different locations of the earthen site to obtain its pulse echo signal M(τ) 测 ;

[0059] S5.3: Determine the moisture distribution of the soil body of the soil site to be tested: Use the fast relaxation theory to calculate the relaxation time spectrum f of the soil body at different parts of the soil site to be tested. i (T 2i ) 测 Converted to pore water distribution f i (r i ) 测 , the surface relaxation strength ρ2 is consistent with that in the test of rammed earth specimens;

[0060] S5.4: Pore water distribution translation: Consider the pore shrinkage and swelling of the soil at different parts of the earthen site to be tested; according to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the peak value of the pore water content is consistent with the abscissa position corresponding to the peak value of the pore water content at different parts of the earthen site to be tested. The modified pore water distribution function of the saturated rammed earth specimen is F i,S (r i ) 测 =f i,S (nr i ) 测 , n is the translation factor, representing the influence of shrinkage and swelling;

[0061] S5.5: Calculation of unsaturated pore content with different pore sizes: According to the modified saturated rammed earth specimen pore water distribution F i,S (r i ) and the pore water distribution of different parts of the soil in the site to be tested i (r i ) 测 , calculate the corrected unsaturated pore content distribution S i (r i ) 测 =F i,S (r i ) 测 -f i (r i ) 测 ;

[0062] S5.6: Calculate the gas permeability of soil at different parts of the earthen site to be tested: According to the distribution of unsaturated pore content S at different parts of the earthen site to be tested i (r i ) 测, and use the fitted formula (10) and the corresponding a and b values ​​to calculate the gas permeability of the soil at different parts of the earthen site to be tested.

[0063] The present invention has the following beneficial effects:

[0064] The present invention adopts non-invasive low-field magnetic resonance relaxation testing technology to non-destructively test the distribution of pore water inside the earthen site in situ, thereby greatly improving the testing efficiency and accuracy. It is helpful to construct an important model between the unsaturated pore structure of the earthen site and its air permeability, predict the evolution trend of the air permeability of the earthen site, realize the continuous monitoring demand for the air permeability of the earthen site, and provide a scientific basis for the protection and restoration of the earthen site. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a schematic flow chart of the method for predicting the air permeability of earthen ruins based on low-field magnetic resonance relaxation technology of the present invention.

[0066] Figure 2 The diagram is a schematic diagram of the moisture distribution and its translation of saturated soil and soil with different moisture contents obtained by testing using the low-field magnetic resonance relaxation technique in the present invention.

[0067] Figure 3 This is a comparison chart of the gas permeability predicted by the fitting model and the measured gas permeability in the present invention.

[0068] in Figure 3 a Prediction results of gas permeability of the original soil of Jinsha Site;

[0069] Figure 3 b Prediction results of gas permeability of saline soil in Jinsha Site. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0071] Specific implementation method 1: Combination Figure 1-3 The present embodiment is described. The present embodiment is a method for predicting the air permeability of earthen sites based on low-field magnetic resonance relaxation technology. The present invention aims at the problems that the existing air permeability test methods of earthen sites are time-consuming and labor-intensive, have poor applicability, and are easy to damage the soil. A model and method for predicting the air permeability of earthen sites based on low-field magnetic resonance relaxation technology are proposed, including the following steps:

[0072] S1: Preparation of rammed earth specimens: select a certain type of soil material and prepare rammed earth specimens with its optimal moisture content. Take one of them to prepare a saturated rammed earth specimen using the capillary saturation method. The other rammed earth specimens are gradually dried in a desiccator controlled by blue silica gel (relative humidity is 3%) to obtain 8 to 10 rammed earth specimens with different moisture contents. Then, seal them in a plastic bag and place them for more than 3 days to ensure that the moisture inside the specimen is evenly distributed;

[0073] S2: Low-field magnetic resonance relaxation test analysis of rammed earth specimens, including test preparation, parameter setting, low-field magnetic resonance relaxation signal acquisition, moisture signal calibration, surface relaxation strength test and pore water distribution determination;

[0074] The low-field magnetic resonance relaxation test analysis of rammed earth specimens with different moisture contents described in S2 includes the following steps:

[0075] S2.1. Test preparation: Wrap the saturated rammed earth specimens and rammed earth specimens with different moisture contents tightly with plastic wrap, and then place them in the sample chamber of the low-field magnetic resonance relaxation test equipment;

[0076] S2.2, parameter setting: use CPMG pulse sequence to perform low-field magnetic resonance relaxation test, set the echo interval, number of echoes, waiting time, number of scans, sampling time interval, number of acquisition points and other parameters;

[0077] Specifically, the echo interval τ e The time interval is set to 60 μs, the number of echoes N is 10000, the waiting time is 5 s, the number of scans is 512, and the number of acquisition points is 4. Except for the echo interval, the other parameters can be flexibly adjusted to make the signal-to-noise ratio of the obtained relaxation data higher than 150.

[0078] S2.3. Low-field magnetic resonance relaxation signal acquisition: low-field magnetic resonance relaxation tests are performed on saturated rammed earth specimens and rammed earth specimens with different moisture contents using a CPMG pulse sequence to obtain a pulse echo signal M(τ);

[0079] In S2.3, the expression of M(τ) is as follows:

[0080]

[0081] In formula (1), the pore water of saturated rammed earth specimens and rammed earth specimens with different moisture contents are divided into J groups, T 2i is the transverse relaxation time of the pore water in the i-th group (i=1,2,...,J), in seconds, f i is the volume fraction of the pore water in the i-th group, dimensionless, V i is the volume of the pore water in group i, in m 3 , V0 is the total volume of all pore water, in m 3, M0 is the total signal of pore water obtained by using the commonly used multi-exponential inversion algorithm of low-field magnetic resonance relaxation signal, and the unit is μV., f i (T 2i ) is the pore water transverse relaxation time spectrum obtained using the multi-exponential inversion algorithm;

[0082] S2.4, moisture signal calibration: using the same CPMG test method, the concentration of 1%wt, water content of m wb The copper sulfate solution was tested and analyzed by low-field magnetic resonance relaxation to obtain its relaxation signal M wb Since the total relaxation signal is strictly proportional to the water mass, the total pore water content m of the saturated rammed earth specimens and the rammed earth specimens with different water contents is w The expression is as follows:

[0083]

[0084] S2.5. Surface relaxation strength test: Take another rammed earth specimen and place it at 23% relative humidity until the mass is constant. Use the low-field magnetic resonance relaxation test of the Hahn spin echo sequence to obtain the surface relaxation strength ρ2 of the rammed earth specimen. According to the fast relaxation theory, the transverse relaxation time T of the pore water inside the rammed earth specimen is calculated. 2i Converted to the equivalent radius r of the cylindrical pore of pore water i ;

[0085] In S2.5, the fast relaxation theory is the equivalent radius r of the pore water of the i-th group i Its transverse relaxation time T 2i Proportional, the expression is as follows:

[0086] r i =2ρ2T 2i (3)

[0087] S2.6. Determination of pore water distribution: Obtain the equivalent radius r of the i-th group of pore water i Its transverse relaxation time T 2i After the relationship between the pore water transverse relaxation time spectra f of the saturated rammed earth specimens and the rammed earth specimens with different moisture contents is calculated, the pore water transverse relaxation time spectra f i (T 2i ) is converted to pore water distribution f i (r i );

[0088] S3: Test the air permeability of rammed earth specimens with different moisture contents. Use a gas permeability test device to test the gas permeability of rammed earth specimens with different moisture contents.

[0089] S4: Determine the relationship model between gas permeability and unsaturated pore structure of rammed earth specimens with different moisture contents, including pore water distribution translation, unsaturated pore content calculation, model construction and fitting parameter determination.

[0090] The model for determining the relationship between the gas permeability and the unsaturated pore structure of rammed earth specimens with different moisture contents described in S4 specifically includes:

[0091] S4.1. Pore water distribution translation: Considering the pore shrinkage and swelling of rammed earth specimens with different moisture contents; according to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the pore water content peak value is consistent with the abscissa position corresponding to the pore water peak value of rammed earth specimens with different moisture contents. The modified pore water distribution function of the saturated rammed earth specimen is F i,S (r i ) = f i,S (nr i ), n is the translation factor, representing the influence of shrinkage and swelling;

[0092] S4.2. Calculation of unsaturated pore content with different pore sizes: According to the modified saturated rammed earth specimen pore water distribution F i,S (r i ) and pore water distribution of rammed earth specimens with different moisture contents i (r i ), calculate the corrected unsaturated pore content distribution S i (r i )=F i,S (r i )-f i (r i );

[0093] S4.3. Model construction, based on Darcy's law and parallel capillary bundle model, the expression of gas permeability k is as follows:

[0094]

[0095] In formula (4), Q is the total volume flow rate of gas, the unit is m 3 / s; A is the cross-sectional area of ​​the total pore channel, in m 2 ; k is the gas permeability, the unit is m 2 ; μ is the gas viscosity, the unit is Pa·s; That is, the pressure gradient dP on a tiny unit length dl, the unit is Pa / m; Q i is the gas volume flow rate of a single pore, in m 3 / s; A i is the cross-sectional area of ​​a single pore channel, in m 2 ;ki is the gas permeability of a single pore, in m 2 ;

[0096] Rearranging formula (4), we can get:

[0097]

[0098] Gas permeability k, gas apparent permeability k a and the gas intrinsic permeability k int There is the following formula,

[0099]

[0100] In formula (6), P g is the average inlet pressure, in Pa, v is a fitting parameter, in Pa, b is the Klinkenberg coefficient of the gas used, in Pa; when conducting gas permeability tests, the average inlet pressure is higher, b / P g vs. v / P g is approximately equal to "0", at this time, the gas intrinsic permeability k int , gas permeability k and gas apparent permeability k a are equal;

[0101] When gas permeation is dominated by viscous flow,

[0102]

[0103] In formula (7), d is the diameter of the specimen, in m; d i is the diameter of the pore channel at the i-th level, in m;

[0104] When the gas permeability k is equal to the gas intrinsic permeability k int When they are equal, using equations (5) and (7), we can get:

[0105]

[0106] In formula (8), l is the length of the gas permeation channel, which is the length of the specimen in meters; V i is the volume of the pore channel at level i, in m 3 ; V is the total volume of the specimen, in m 3 ; K i (r i ) represents the ratio of the volume of the i-th level pore channel to the total volume of the specimen;

[0107] Considering the actual K i (r i ) and the unsaturated pore content distribution S obtained after translation i (r i) has a linear relationship,

[0108] K i (r i )=aS i (r i )+b (9)

[0109] Then formula (9) can be transformed into:

[0110]

[0111] Determination of fitting parameters: According to the measured gas permeability values ​​of rammed earth specimens with different moisture contents and the unsaturated pore distribution S after translation i (r i ), using formula (10), the values ​​of a and b in the model are fitted to ensure the correlation coefficient R 2 >0.98; The method for predicting the air permeability of earthen sites based on low-field magnetic resonance relaxation technology firstly performs low-field magnetic resonance relaxation test analysis on the earthen sites to be tested, and then predicts the air permeability of the earthen sites to be tested by using the air permeability prediction model obtained by the method for constructing the air permeability prediction model of earthen sites based on low-field magnetic resonance relaxation technology;

[0112] It also includes S5, low-field magnetic resonance relaxation test analysis of the earthen ruins to be tested, including the following steps:

[0113] S5.1: Low-field magnetic resonance relaxation test of the earthen ruins to be tested: Use a single-sided nuclear magnetic resonance relaxation test instrument to test the earthen ruins to be tested. The test parameters are consistent with those for testing rammed earth specimens.

[0114] S5.2: Low-field magnetic resonance relaxation signal acquisition: Use the CPMG pulse sequence to perform low-field magnetic resonance relaxation tests on soil at different locations of the earthen site to obtain its pulse echo signal M(τ) 测 ;

[0115] S5.3: Determine the moisture distribution of the soil body of the soil site to be tested: Use the fast relaxation theory to calculate the relaxation time spectrum f of the soil body at different parts of the soil site to be tested. i (T 2i ) 测 Converted to pore water distribution f i (r i ) 测 , the surface relaxation strength ρ2 is consistent with that in the test of rammed earth specimens;

[0116] S5.4: Pore water distribution translation: Consider the pore shrinkage and swelling of the soil in different parts of the earthen site to be tested. According to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the peak value of the pore water content is consistent with the abscissa position corresponding to the peak value of the pore water content in different parts of the earthen site to be tested. The modified pore water distribution of the saturated rammed earth specimen is F i,S (r i ) 测 =f i,S (nr i ) 测 , n is the translation factor, representing the influence of shrinkage and swelling;

[0117] S5.5: Calculation of unsaturated pore content with different pore sizes: According to the modified saturated rammed earth specimen pore water distribution F i,S (r i ) and the pore water distribution of different parts of the soil in the site to be tested i (r i ) 测 , calculate the corrected unsaturated pore content distribution S i (r i ) 测 =F i,S (r i ) 测 -f i (r i ) 测 ;

[0118] S5.6: Calculate the gas permeability of soil at different parts of the earthen site to be tested: According to the distribution of unsaturated pore content S at different parts of the earthen site to be tested i (r i ) 测 , and use the fitted formula (10) and the corresponding a and b values ​​to calculate the gas permeability of the soil at different parts of the earthen site to be tested;

[0119] As a non-destructive testing technology, low-field magnetic resonance relaxation technology can quickly and accurately characterize the internal pore structure and water distribution of porous media, which helps to construct an important model between the pore water distribution and the air permeability of earthen sites, predict the evolution trend of the air permeability of earthen sites, and realize the continuous monitoring demand for the air permeability of earthen sites. In general, based on low-field magnetic resonance relaxation technology, the development of prediction models and methods suitable for the air permeability of earthen sites has important engineering significance and application value in the field of earthen site protection. The air permeability test method of earthen sites of the present invention has high efficiency, good applicability and avoids damage to the soil.

[0120] Embodiment 1:

[0121] Taking the Jinsha Ruins as an example, a prediction model and method for the air permeability of earthen ruins based on low-field magnetic resonance relaxation technology is provided, which is achieved through the following steps:

[0122] like Figure 1 As shown, the prediction model and method of air permeability of earthen sites based on low-field magnetic resonance relaxation technology can be implemented through the following steps:

[0123] S1: Preparation of rammed earth specimens. Select the exfoliated soil from any location of the Jinsha Ruins and prepare rammed earth specimens with its optimal moisture content. The specimen size is Φ50mm×50mm. Take one of them to prepare a saturated rammed earth specimen using the capillary saturation method. The other rammed earth specimens are gradually dried in a silica gel-controlled dryer (relative humidity is 3%). When the mass loss is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% and 9% of the soil mass, the rammed earth specimens are taken out, sealed with a plastic bag and placed for 7 days to ensure that the moisture inside the specimen is evenly distributed;

[0124] S2: Low-field magnetic resonance relaxation test analysis of rammed earth specimens. The low-field magnetic resonance relaxation test analysis of rammed earth specimens with different moisture contents specifically includes:

[0125] S2.1: Test preparation: Wrap the saturated rammed earth specimens and rammed earth specimens with different moisture contents tightly with plastic wrap, and then place them in the sample chamber of the low-field magnetic resonance relaxation test equipment;

[0126] S2.2: Parameter setting: Use the CPMG pulse sequence to perform low-field magnetic resonance relaxation testing, and set parameters such as echo interval, number of echoes, waiting time, number of scans, sampling time interval, and number of acquisition points;

[0127] Using CPMG pulse sequence for testing, the key parameters can be set as follows: echo interval τ e The setting is 60μs, the number of echoes N is 60000, the waiting time is 15s, the number of scans is 300, and the number of acquisition points is 4. Except for the echo interval, the other parameters can be flexibly adjusted to make the signal-to-noise ratio of the obtained relaxation data higher than 200;

[0128] S2.3: Low-field magnetic resonance relaxation signal acquisition: The CPMG pulse sequence is used to perform low-field magnetic resonance relaxation tests on saturated rammed earth specimens and rammed earth specimens with different moisture contents to obtain the pulse echo signal M(τ). The expression of M(τ) is as follows:

[0129]

[0130] In formula (1), the pore water of saturated rammed earth specimens and rammed earth specimens with different moisture contents are divided into J groups, T 2i is the transverse relaxation time of the pore water in the i-th group (i=1,2,...,J), in seconds, fi is the volume fraction of the pore water in the i-th group, dimensionless, V i is the volume of the pore water in group i, in m 3 , V0 is the total volume of all pore water, in m 3 , M0 is the total signal of pore water obtained by using the commonly used multi-exponential inversion algorithm of low-field magnetic resonance relaxation signal, and the unit is μV., f i (T 2i ) is the pore water transverse relaxation time spectrum obtained using the multi-exponential inversion algorithm;

[0131] S2.4: Moisture signal calibration: Using the same CPMG test method, the concentration is 1%wt and the water content is m wb The copper sulfate solution was tested and analyzed by low-field magnetic resonance relaxation to obtain its relaxation signal M wb Since the total relaxation signal is strictly proportional to the water mass, the total pore water content m of the saturated rammed earth specimens and the rammed earth specimens with different water contents is w The expression is as follows:

[0132]

[0133] S2.5: Surface relaxation strength test: Take another rammed earth specimen and place it at 23% relative humidity until the mass is constant. Use the low-field magnetic resonance relaxation test of the Hahn spin echo sequence to obtain the surface relaxation strength ρ2 of the rammed earth specimen. According to the fast relaxation theory, the transverse relaxation time T of the pore water inside the rammed earth specimen is calculated. 2i Converted to the equivalent radius r of the cylindrical pore of pore water i ;

[0134] The fast relaxation theory is the equivalent radius r of the pore water of group i i Its transverse relaxation time T 2i Proportional, the expression is as follows:

[0135] r i =2ρ2T 2i (3)

[0136] S2.6: Determination of pore water distribution: Obtain the equivalent radius r of the i-th group of pore water i Its transverse relaxation time T 2i After the relationship between the pore water transverse relaxation time spectra f of the saturated rammed earth specimens and the rammed earth specimens with different moisture contents is calculated, the pore water transverse relaxation time spectra f i (T 2i ) is converted to pore water distribution f i (r i );

[0137] The model for determining the relationship between the gas permeability and the unsaturated pore structure of rammed earth specimens with different moisture contents described in S4 specifically includes:

[0138] S4.1: Pore water distribution translation: Consider the pore shrinkage and swelling of rammed earth specimens with different moisture contents. According to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the pore water content peak value is consistent with the abscissa position corresponding to the pore water peak value of rammed earth specimens with different moisture contents. The modified pore water distribution function of the saturated rammed earth specimen is F i,S (r i ) = f i,S (nr i ), n is the translation factor, representing the influence of shrinkage and swelling;

[0139] S4.2: Calculation of unsaturated pore content with different pore sizes: According to the modified pore water distribution of saturated rammed earth specimens, F i,S (r i ) and pore water distribution of rammed earth specimens with different moisture contents i (r i ), calculate the corrected unsaturated pore content distribution S i (r i )=F i,S (r i )-f i (r i ),like Figure 2 As shown;

[0140] S4.3: Model construction: Based on Darcy's law and the parallel capillary bundle model, the expression of gas permeability k is considered as follows:

[0141]

[0142] In formula (4), Q is the total volume flow rate of gas, the unit is m 3 / s; A is the cross-sectional area of ​​the total pore channel, in m 2 ; k is the gas permeability, the unit is m 2 ; μ is the gas viscosity, the unit is Pa·s; That is, the pressure gradient dP on a tiny unit length dl, the unit is Pa / m; Q i is the gas volume flow rate of a single pore, in m 3 / s; A i is the cross-sectional area of ​​a single pore channel, in m 2 ;k i is the gas permeability of a single pore, in m 2 .

[0143] Rearranging formula (4), we can get

[0144]

[0145] Gas permeability k, gas apparent permeability k a and the gas intrinsic permeability k int There is the following formula,

[0146]

[0147] In formula (6), P g is the average inlet pressure, in Pa, v is a fitting parameter, in Pa, and b is the Klinkenberg coefficient of the gas used, in Pa. When conducting a gas permeability test, the average inlet pressure is higher, b / P g vs. v / P g is approximately equal to "0", at this time, the gas intrinsic permeability k int , gas permeability k and gas apparent permeability k a Are equal.

[0148] When gas permeation is dominated by viscous flow,

[0149]

[0150] When the gas permeability k is equal to the gas intrinsic permeability k int When they are equal, using equations (5) and (7), we can get

[0151]

[0152] In formula (8), l is the length of the gas permeation channel, which is the length of the specimen in meters; V i is the volume of the pore channel at level i, in m 3 ; V is the total volume of the specimen, in m 3 . K i (r i ) represents the ratio of the volume of the i-th level pore channel to the total volume of the specimen.

[0153] Considering the actual K i (r i ) and the unsaturated pore content distribution S obtained after translation i (r i ) has a linear relationship,

[0154] K i (r i )=aS i (r i )+b (9)

[0155] Then formula (9) can be transformed into

[0156]

[0157] Determination of fitting parameters: According to the measured gas permeability values ​​of rammed earth specimens with different moisture contents and the unsaturated pore distribution S after translation i (r i ), using formula (10), the values ​​of a and b in the model are fitted to ensure the correlation coefficient R 2 >0.98; Figure 3 As shown in the figure, the measured gas permeability of rammed earth specimens with different moisture contents is compared with the gas permeability predicted by their pore water distribution. It can be seen that the model has strong applicability, good stability and extremely high fitting accuracy.

[0158] The method for predicting the air permeability of earthen sites based on low-field magnetic resonance relaxation technology firstly performs low-field magnetic resonance relaxation test analysis on the earthen sites to be tested, and then predicts the air permeability of the earthen sites to be tested by using the air permeability prediction model obtained by the method for constructing the air permeability prediction model of earthen sites based on low-field magnetic resonance relaxation technology;

[0159] The low-field magnetic resonance relaxation test analysis of the earthen ruins to be tested is achieved by the following steps:

[0160] S1a: Low-field magnetic resonance relaxation test of the earthen ruins to be tested: The earthen ruins to be tested are tested using a single-sided nuclear magnetic resonance relaxation test instrument, and the test parameters are consistent with those for testing rammed earth specimens;

[0161] S2a: Low-field magnetic resonance relaxation signal acquisition: The CPMG pulse sequence is used to perform low-field magnetic resonance relaxation tests on soil at different locations of the earthen site to obtain its pulse echo signal M(τ) 测 ;

[0162] S3a: Determination of moisture distribution of the soil body of the soil site to be tested: The relaxation time spectrum of the soil body at different parts of the soil site to be tested is calculated by using the fast relaxation theory. i (T 2i ) 测 Converted to pore water distribution f i (r i ) 测 , the surface relaxation strength ρ2 is consistent with that in the test of rammed earth specimens;

[0163] S4a: Pore water distribution translation: Consider the pore shrinkage and swelling of the soil in different parts of the earthen site to be tested. According to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the peak value of the pore water content is consistent with the abscissa position corresponding to the peak value of the pore water content in different parts of the earthen site to be tested. The modified pore water distribution of the saturated rammed earth specimen is F i,S (r i) 测 =f i,S (nr i ) 测 , n is the translation factor, representing the influence of shrinkage and swelling;

[0164] S5a: Calculation of unsaturated pore content with different pore sizes: According to the modified pore water distribution of saturated rammed earth specimens, F i,S (r i ) and the pore water distribution of different parts of the soil in the site to be tested i (r i ) 测 , calculate the corrected unsaturated pore content distribution S i (r i ) 测 =F i,S (r i ) 测 -f i (r i ) 测 ;

[0165] S6a: Calculate the gas permeability of soil at different parts of the earthen site to be tested: According to the distribution of unsaturated pore content S at different parts of the earthen site to be tested i (r i ) 测 , and use the fitted formula (10) and the corresponding a and b values ​​to calculate the gas permeability of the soil at different parts of the earthen site to be tested.

[0166] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be arranged and combined, and those skilled in the art can exhaust all possibilities based on the mathematical knowledge of arrangement and combination. Therefore, the present invention will no longer describe the technical solutions after arrangement and combination one by one, but it should be understood that the technical solutions after arrangement and combination have been disclosed by the present invention.

[0167] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting the air permeability of earthen ruins based on low-field magnetic resonance relaxation technology, characterized in that: The following steps are involved: Preparation of rammed earth specimens; Low-field magnetic resonance relaxation test analysis of rammed earth specimens; Air permeability test of rammed earth specimens with different moisture contents; Determine the relationship model between gas permeability and unsaturated pore structure of rammed earth specimens with different moisture contents.

2. The method for predicting air permeability of earthen ruins based on low-field magnetic resonance relaxation technology according to claim 1 is characterized in that: The preparation of rammed earth specimens includes the following steps: S1.

1. Determine the soil material to be used; determine the optimal moisture content of the soil material; S1.

2. Preparation of rammed earth specimens: including preparation of saturated rammed earth specimens and preparation of unsaturated rammed earth specimens; Preparation of saturated rammed earth specimens: Select several soil samples and perform saturation treatment; Preparation of unsaturated rammed earth specimens: Several soil samples were gradually dried in a dryer controlled by blue silica gel; rammed earth specimens with different moisture contents were obtained by gradual drying; S1.

3. Sealing and placement: Place the prepared rammed earth specimens into a sealed plastic bag and place them for more than 3 days to ensure that the moisture inside the specimen is evenly distributed.

3. The method for predicting air permeability of earthen ruins based on low-field magnetic resonance relaxation technology according to claim 2 is characterized in that: The low-field magnetic resonance relaxation test analysis of rammed earth specimens includes the following steps: S2.

1. Test preparation: Wrap the saturated rammed earth specimens and rammed earth specimens with different moisture contents tightly with plastic wrap, and then place them in the sample chamber of the low-field magnetic resonance relaxation test equipment; S2.2, parameter setting: use CPMG pulse sequence to perform low-field magnetic resonance relaxation test, set the echo interval, number of echoes, waiting time, number of scans, sampling time interval, and number of acquisition points; S2.

3. Low-field magnetic resonance relaxation signal acquisition: low-field magnetic resonance relaxation tests are performed on saturated rammed earth specimens and rammed earth specimens with different moisture contents using a CPMG pulse sequence to obtain a pulse echo signal M(τ); S2.4, moisture signal calibration: using the same CPMG test method, the concentration of 1%wt, water content of m wb The copper sulfate solution was tested and analyzed by low-field magnetic resonance relaxation to obtain its relaxation signal M wb Since the total relaxation signal is proportional to the water mass, the total pore water content m of the saturated rammed earth specimens and rammed earth specimens with different water contents is calculated. w ; S2.

5. Surface relaxation strength test: Take another rammed earth specimen and place it at 23% relative humidity until its mass is constant. Use the low-field magnetic resonance relaxation test of the Hahn spin echo sequence to obtain the surface relaxation strength ρ2 of the rammed earth specimen. According to the fast relaxation theory, the transverse relaxation time T of the pore water inside the rammed earth specimen is calculated. 2i Converted to the equivalent radius r of the cylindrical pore of pore water i ; S2.

6. Determination of pore water distribution: Obtain the equivalent radius r of the i-th group of pore water i Its transverse relaxation time T 2i After the relationship between the pore water transverse relaxation time spectra f of the saturated rammed earth specimens and the rammed earth specimens with different moisture contents is calculated, the pore water transverse relaxation time spectra f i (T 2i ) is converted to pore water distribution f i (r i ).

4. The method for predicting air permeability of earthen ruins based on low-field magnetic resonance relaxation technology according to claim 2 is characterized in that: In S2.2, the echo interval τ e The setting is 60μs, the number of echoes N is 10000, the waiting time is 5s, the number of scans is 512, and the number of acquisition points is 4. Except for the echo interval, the other parameters can be flexibly adjusted to make the signal-to-noise ratio of the obtained relaxation data higher than 150; In S2.3, the expression of M(τ) is as follows: In formula (1), the pore water of saturated rammed earth specimens and rammed earth specimens with different moisture contents are divided into J groups, T 2i is the transverse relaxation time of the pore water in the i-th group (i=1,2,...,J), in seconds, f i is the volume fraction of the pore water in the i-th group, dimensionless, V i is the volume of the pore water in group i, in m 3 , V0 is the total volume of all pore water, in m 3 , M0 is the total signal of pore water obtained by using the commonly used multi-exponential inversion algorithm of low-field magnetic resonance relaxation signal, the unit is μV, f i (T 2i ) is the pore water transverse relaxation time spectrum obtained using the multi-exponential inversion algorithm; In S2.4, the total pore water content m of saturated rammed earth specimens and rammed earth specimens with different moisture contents w The expression is as follows: In S2.5, the fast relaxation theory is the equivalent radius r of the pore water of the i-th group i Its transverse relaxation time T 2i Proportional, the expression is as follows: r i =2ρ2T 2i (3)。 5. The method for predicting air permeability of earthen ruins based on low-field magnetic resonance relaxation technology according to claim 4 is characterized in that: The model for determining the relationship between the gas permeability and the unsaturated pore structure of rammed earth specimens with different moisture contents described in S4 includes: S4.

1. Pore water distribution translation: Considering the pore shrinkage and swelling of rammed earth specimens with different moisture contents; according to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the pore water content peak value is consistent with the abscissa position corresponding to the pore water peak value of rammed earth specimens with different moisture contents. The modified pore water distribution function of the saturated rammed earth specimen is F i,S (r i ) = f i,S (nr i ), n is the translation factor, representing the influence of shrinkage and swelling; S4.

2. Calculation of unsaturated pore content with different pore sizes: Based on the modified pore water distribution F of the saturated rammed earth specimen i,S (r i ) and pore water distribution of rammed earth specimens with different moisture contents i (r i ), calculate the corrected unsaturated pore content distribution S i (r i )=F i,S (r i )-f i (r i ); S4.

3. Model construction.

6. The method for predicting air permeability of earthen ruins based on low-field magnetic resonance relaxation technology according to claim 5 is characterized in that: In S4.3, based on Darcy's law and the parallel capillary bundle model, the expression of gas permeability k is considered as follows: In formula (4), Q is the total volume flow rate of gas, the unit is m 3 / s; A is the cross-sectional area of ​​the total pore channel, in m 2 ; k is the gas permeability, the unit is m 2 ; μ is the gas viscosity, in Pa·s; That is, the pressure gradient dP on a tiny unit length dl, the unit is Pa / m; Q i is the gas volume flow rate of a single pore, in m 3 / s; A i is the cross-sectional area of ​​a single pore channel, in m 2 ; k i is the gas permeability of a single pore, in m 2 ; Rearranging formula (4), we can get: Gas permeability k, gas apparent permeability k a and the gas intrinsic permeability k int There is the following formula, In formula (6), P g is the average inlet pressure, in Pa, v is a fitting parameter, in Pa, b is the Klinkenberg coefficient of the gas used, in Pa; when conducting gas permeability tests, the average inlet pressure is higher, b / P g vs. v / P g is approximately equal to "0", at this time, the gas intrinsic permeability k int , gas permeability k and gas apparent permeability k a are equal; When gas permeation is dominated by viscous flow, In formula (7), d is the specimen diameter, in m; d i is the diameter of the pore channel at the i-th level, in m; When the gas permeability k is equal to the gas intrinsic permeability k int When they are equal, using equations (5) and (7), we can get: In formula (8), l is the length of the gas permeation channel, which is the length of the specimen in meters; V i is the volume of the pore channel at level i, in m 3 ; V is the total volume of the specimen, in m 3 ; K i (r i ) represents the ratio of the volume of the i-th level pore channel to the total volume of the specimen; Considering the actual K i (r i ) and the unsaturated pore content distribution S obtained after translation i (r i ) has a linear relationship, K i (r i )=aS i (r i )+b (9) Then formula (9) can be transformed into: Determination of fitting parameters: According to the measured gas permeability values ​​of rammed earth specimens with different moisture contents and the unsaturated pore distribution S after translation i (r i ), using formula (10), the values ​​of a and b in the model are fitted to ensure the correlation coefficient R 2 >0.98; The air permeability prediction method of earthen sites based on low-field magnetic resonance relaxation technology first performs low-field magnetic resonance relaxation test analysis on the earthen sites to be tested, and then predicts the air permeability of the earthen sites to be tested by the air permeability prediction model obtained by the method for constructing the air permeability prediction model of earthen sites based on low-field magnetic resonance relaxation technology.

7. The method for predicting air permeability of earthen ruins based on low-field magnetic resonance relaxation technology according to claim 6 is characterized in that: It also includes low-field magnetic resonance relaxation test analysis of the earthen ruins to be tested, including the following steps: S5.1: Low-field magnetic resonance relaxation test of the earthen ruins to be tested: Use a single-sided nuclear magnetic resonance relaxation test instrument to test the earthen ruins to be tested. The test parameters are consistent with those for testing rammed earth specimens. S5.2: Low-field magnetic resonance relaxation signal acquisition: Use the CPMG pulse sequence to perform low-field magnetic resonance relaxation tests on soil at different locations of the earthen site to obtain its pulse echo signal M(τ) 测 ; S5.3: Determine the moisture distribution of the soil body of the soil site to be tested: Use the fast relaxation theory to calculate the relaxation time spectrum f of the soil body at different parts of the soil site to be tested. i (T 2i ) 测 Converted to pore water distribution f i (r i ) 测 , the surface relaxation strength ρ2 is consistent with that in the test of rammed earth specimens; S5.4: Pore water distribution translation: Consider the pore shrinkage and swelling of the soil in different parts of the earthen site to be tested. According to the pore water distribution results measured by low-field magnetic resonance relaxation technology, the pore water distribution function of the saturated rammed earth specimen is translated along the lnr coordinate axis as a whole, so that the abscissa position corresponding to the peak value of the pore water content is consistent with the abscissa position corresponding to the peak value of the pore water content in different parts of the earthen site to be tested. The modified pore water distribution of the saturated rammed earth specimen is F i,S (r i ) 测 =f i,S (nr i ) 测 , n is the translation factor, representing the influence of shrinkage and swelling; S5.5: Calculation of unsaturated pore content with different pore sizes: According to the modified saturated rammed earth specimen pore water distribution F i,S (r i ) and the pore water distribution of different parts of the soil in the site to be tested i (r i ) 测 , calculate the corrected unsaturated pore content distribution S i (r i ) 测 =F i,S (r i ) 测 -f i (r i ) 测 ; S5.6: Calculate the gas permeability of soil at different parts of the earthen site to be tested: According to the distribution of unsaturated pore content S at different parts of the earthen site to be tested i (r i ) 测 , and use the fitted formula (10) and the corresponding a and b values ​​to calculate the gas permeability of the soil at different parts of the earthen site to be tested.

Images