A measuring instrument and a measuring method for fissure rate of a rock-soil sample

Abstract

The application discloses a kind of geotechnical sample fissure rate measuring instrument and measuring method, measuring instrument includes fixing device, adjusting device, moisture content measuring system, the fixing device includes two bases, for geotechnical sample is fixed between two bases;Adjusting device is used to adjust the interval of two bases;Fissure rate measuring system is used to detect the sound wave velocity of ultrasonic wave propagation inside geotechnical sample, the fitting curve of initial fissure rate and sound wave velocity is obtained from sound wave velocity;Again, the correction coefficient of sound wave velocity is obtained based on moisture content data, to replace the sound wave velocity in initial fissure rate with corrected sound wave velocity, and the final sample fissure rate data is obtained.The application can accurately measure the fissure rate of geotechnical sample with different moisture content, can accurately and quickly measure the moisture content of sample, without damaging the sample, light, nimble, easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical testing technology, and relates to an instrument and method for measuring the porosity of geotechnical samples, both indoors and outdoors. Background Technology

[0002] In outdoor testing of soil and rock samples, consistency in sample properties is often necessary to ensure consistency across all test variables. Factors measuring the consistency of sample properties include: porosity, gradation, water content, and void ratio. Rock mass fractures refer to the voids created by the fracturing and deformation of consolidated rock under various stresses. Porosity, as an important quantitative indicator reflecting the degree of rock mass fracture development, is mainly involved in specialized engineering projects such as water conservancy and hydropower projects, mining engineering, geological exploration, geotechnical engineering, and rock slope revegetation.

[0003] Currently, the main methods for measuring fracture ratio outdoors are manual measurements through boreholes, tunnel excavation faces, or rock outcrops. In engineering practice, the line method and the statistical window method are commonly used. The line method involves laying a straight line perpendicular to the most developed fracture at the rock outcrop and measuring the geometric parameters of the fractures intersecting the line. It measures the one-dimensional density of fractures, and the result represents the proportion of fractures per unit length in the direction perpendicular to the fracture strike, i.e., the linear fracture ratio. The statistical window method involves selecting appropriate locations at outcrops with well-developed fractures and arranging rectangular or circular statistical windows. It measures the geometric number of all fracture surfaces that are contained, tangent to, or intersect with this window. It measures the two-dimensional density of fractures, and the result represents the proportion of fracture area contained per unit area of ​​the rock outcrop surface, i.e., the surface fracture ratio. However, the following problems exist: (1) The two measurement methods can only reflect the development of local surface fissures in the rock mass from a one-dimensional or two-dimensional perspective, and cannot reflect the development of internal fissures in the rock mass. It is very likely that some key fissure information will be missed; (2) Only when the fissure surface is orthogonal to the exposed surface will the measured fissure width be equal to the actual fissure width. In the field, the fissure surface is mostly oblique to the exposed surface, and the measured value of the fissure width is larger than the actual value. As the fissure width increases, a large error will occur; (3) The measurement results are highly random. Selecting different locations and different sizes of survey lines or statistical windows will result in different measurement results; (4) The exposed surface of the rock mass in the field is mostly uneven. Due to the exposure conditions and operability, it is difficult to set up survey lines or statistical windows, and the application is greatly limited. Due to the complexity of rock mass fissure development, field exposure conditions and the current level of technology, the three-dimensional density of fissures is a difficult parameter to measure. The commonly used measurement methods at present mainly include borehole method, three-dimensional network simulation technology, and digital photography fissure measurement method based on digital image interpretation and processing. Drilling methods disturb the rock mass and alter the original fracture structure during drilling, resulting in less accurate and objective measurement results. Measurements only reflect the fracture development near the borehole, and results from different borehole locations vary significantly, exhibiting considerable randomness. Furthermore, three-dimensional network simulation techniques based on on-site investigation and statistical analysis of fracture surface parameters, or digital photographic fracture measurement methods based on digital image interpretation, are complex, technically demanding, and costly, making them impractical for engineering applications.

[0004] Existing methods for measuring crack ratio in indoor testing include: First, the immersion method requires the sample to be completely submerged in water, which damages the sample and makes further testing impossible. Second, software is used to process images of the sample surface during crack evolution to extract crack parameters such as total crack length ratio, crack ratio, average width, and fractal dimension. This method only considers the crack propagation on the two-dimensional surface and cannot measure the internal crack ratio, resulting in significant errors. Third, CT scanning technology has uncertainties in delivery time, and the transportation process inevitably causes significant disturbance to the sample, leading to errors in crack ratio measurement. Furthermore, continuous observation is costly and time-consuming; CT instruments are very expensive, with high costs and energy consumption per scan. When considering many influencing factors, multiple test groups are required, significantly increasing experimental costs and making it difficult to guarantee that the required three-dimensional internal information can be obtained from CT scans for each test group and each sample. The fracture surfaces developed in rock masses are characterized by spatial complexity, randomness, and morphological diversity. Due to the limitations of existing measurement techniques, it is difficult to accurately describe the true structural surfaces in rock masses.

[0005] Among existing methods for measuring moisture content, the drying method has an excessively long baking time and is affected by the unevenness of soil types, resulting in inconsistent drying effects. In particular, this method transfers heat from the surface to the interior of the soil, and when encountering soils containing small amounts of organic matter, the moisture cannot be completely evaporated. The calcium carbide pneumatic method requires stable calcium carbide powder and testing equipment, which are currently unsuitable for the instruments used in highway engineering construction control in my country, thus limiting its application. The microwave oven method requires calibration and cannot be used to dry and test moisture content in soils with high organic matter content. Furthermore, none of the above methods allow for immediate measurement of moisture content; this physical parameter is easily altered during transportation, leading to experimental errors. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an instrument for measuring the porosity of soil and rock samples. This instrument can accurately measure the porosity of soil and rock samples with different moisture contents, and can simultaneously and accurately measure the moisture content of the samples without damaging them. It is lightweight, portable, and easy to operate, making it suitable for engineering applications and solving the problems existing in the prior art.

[0007] Another objective of this invention is to provide a method for measuring the porosity of soil and rock samples.

[0008] The technical solution adopted in this invention is an instrument for measuring the porosity of soil and rock samples, comprising:

[0009] A fixing device, comprising two bases for fixing a soil sample between the two bases;

[0010] An adjustment device for adjusting the distance between the two bases;

[0011] A moisture content measurement system is used to detect the internal moisture content data of soil and rock samples.

[0012] The fracture rate measurement system is used to detect the sound wave velocity of ultrasonic waves propagating inside the soil and rock sample, and obtain the fitting curve of the initial fracture rate and the sound wave velocity. Then, based on the water content data, the correction coefficient of the sound wave velocity is obtained, and the corrected sound wave velocity is used to replace the sound wave velocity in the initial fracture rate to obtain the final sample fracture rate data.

[0013] Furthermore, the moisture content measurement system includes a moisture content sensing element, which is a hollow columnar structure made of conductive material. The column of the moisture content sensing element is provided with multiple annular grooves evenly spaced apart. A reverse filter membrane is embedded in the groove, and inorganic salt is laid between the reverse filter membrane and the bottom of the groove to form a moisture sensing unit. The two ends of each moisture sensing unit are connected to an external power source through wires. An ammeter is connected in the circuit to measure the current passing through each moisture sensing unit to obtain the resistivity of each moisture sensing unit. The moisture content is calculated from the resistivity.

[0014] Furthermore, the fracture rate measurement system includes an ultrasonic transmitter, an ultrasonic receiver, and a computer. The ultrasonic transmitter is used to emit ultrasonic waves to the sample; the ultrasonic receiver is used to detect the ultrasonic waves after they pass through the sample; and the computer calculates the sound wave velocity of the ultrasonic waves propagating inside the soil and rock sample based on the detected ultrasonic waves.

[0015] Furthermore, the two bases are a left base and a right base, and cylindrical grooves are provided on the opposite sides of the left base and the right base to match the ends of the soil and rock samples.

[0016] Furthermore, the adjustment device includes fixed rods. Two fixed rods are fixed around one base near the side of the soil sample. A spiral hole is provided on the other base corresponding to the fixed rods, allowing the fixed rods to extend into the spiral hole. The spiral part of the fixed rods meshes with the two outermost gears of the gear set. The knob is connected to the middle gear in the gear set via a metal shaft. Rotating the knob drives the middle gear in the gear set to rotate synchronously, thereby driving the gears on both sides to rotate. In turn, the two outermost gears rotate, causing the fixed rods to move axially, adjusting the distance between the two bases. To ensure that the two outermost gears rotate in the same direction, the number of gears on both sides differs by one.

[0017] Furthermore, one end of the moisture content sensing element has a conical spiral structure.

[0018] A method for measuring the porosity of a soil and rock sample using an instrument, comprising the following steps:

[0019] S1, Prepare the soil and rock to be tested into a cylindrical sample, and drill a hole along the axial direction at the center of the sample;

[0020] S2, insert the moisture content sensing element into the center of the soil and rock sample, and place one end of the soil and rock sample completely into the groove of the left base;

[0021] S3, align the other end of the soil and rock sample with the groove of the right base, adjust the distance between the right base and the left base so that the end of the soil and rock sample is completely placed in the groove of the right base, and fix the sample.

[0022] S4. After the moisture content sensing element stabilizes, the moisture content w of the soil sample and the sound wave velocity v1 of the ultrasonic wave passing through the soil sample are obtained.

[0023] S5, based on the ultrasonic intensity after passing through the sample, the initial fracture rate is obtained by the existing ultrasonic fracture rate measurement method; the acoustic wave velocity v1 is fitted with the initial fracture rate to obtain a curve that conforms to the distribution law of the initial fracture rate S1.

[0024] S6, based on the influence of water content, obtain the correction coefficient of acoustic wave velocity. Replace the acoustic wave velocity v1 in the initial fracture rate S1 with the corrected acoustic wave velocity to obtain the curve of the final fracture rate.

[0025] Furthermore, in step S5, the initial fracture rate data S1 = 4.8257 / (1 + exp(14.969×(v1-2.1886))), where exp is an exponential function with the natural constant e as the base.

[0026] Furthermore, in step S6, the correction coefficient for the sound wave velocity is k = 0.87227 + 0.00657w.

[0027] Furthermore, in step S6, the corrected acoustic wave velocity v = kv1, and the final fissure ratio S2 = 4.8257 / (1 + exp(14.969 × (v - 2.1886))).

[0028] The beneficial effects of this invention are:

[0029] This invention adds inorganic salts to the moisture-sensing element, which can absorb moisture from the soil sample through a reverse filter membrane and generate conductivity through electrolysis after wetting. The amount of absorbed moisture can reflect the internal moisture content of the soil sample and can be reflected by the resistivity of the conductive element. This overcomes the influence of inorganic salts and fine particles in the material on the conductivity of the material. Furthermore, dividing the moisture-sensing element into multiple segments and taking the average value improves the measurement accuracy.

[0030] This invention establishes three-dimensional curves for moisture content, ultrasonic wave velocity, and fracture ratio. It considers the influence of moisture content on the results of ultrasonic testing of soil and rock samples, reducing errors and improving accuracy. It obtains the relationship between fracture ratio and fracture density of soil and rock samples at different moisture contents. Without damaging the sample structure and properties, it rapidly obtains the moisture content and fracture ratio of indoor and outdoor soil and rock samples, effectively improving the fitting accuracy and making the measured fracture ratio more accurate. The measuring instrument has a simple structure, is easy to operate, has low cost, is simple to manufacture, is easy to assemble and disassemble, and is reusable. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a front view of the entire invention.

[0033] Figure 2 yes Figure 1 The left view.

[0034] Figure 3 yes Figure 1 Top view.

[0035] Figure 4 This is an overall diagram of the moisture content sensing element in an embodiment of the present invention.

[0036] Figure 5 This is a schematic diagram of the structure of the humidity sensing unit in an embodiment of the present invention.

[0037] Figure 6 The three-dimensional curves of moisture content, ultrasonic wave velocity, and fracture rate established in the embodiments of the present invention are shown.

[0038] Figure 7 This is a comparison of the measurement results of the method in this embodiment of the invention with those of the traditional method.

[0039] In the diagram, 1. Left base, 2. Ultrasonic transmitter, 3. Moisture content sensing element, 4. Ultrasonic receiver, 5. Right base, 6. Fixing rod, 7. Spiral part, 8. Knob, 9. Gear set, 10. Moisture sensing unit, 11. Wire, 12. Reverse filter membrane, 13. Inorganic salt. Detailed Implementation

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1,

[0042] An instrument for measuring the porosity of soil and rock samples, such as Figure 1 As shown, it includes a fixing device, a hand-cranked device, a moisture content measurement system, and a crack rate measurement system;

[0043] A fixing device is used to place and fix the soil and rock sample. The soil and rock sample should be pre-treated into a cylindrical shape.

[0044] Adjustment device, used to adjust the distance between the two bases of the fixing device;

[0045] The moisture content detection system includes a moisture content sensing element 3, electrodes, a current detection device, and a display. The conductivity of the moisture content sensing element 3 changes with the moisture content and is used to sense the moisture content of different parts of the sample. The electrodes are used to apply voltage to the two poles of the moisture content sensing element 3. The current detection device is used to detect the magnitude of the current passing through the moisture content sensing element 3.

[0046] The crack rate detection system includes an ultrasonic transmitter 2, an ultrasonic receiver 4, and a microcomputer. The ultrasonic transmitter 2 emits ultrasonic waves to the sample; the ultrasonic receiver 4 detects the ultrasonic wave velocity after passing through the sample; the microcomputer obtains the time t it takes for the sound wave to travel through the sample; the microcomputer records the sound waves emitted by the ultrasonic transmitter 2; and stops recording when the ultrasonic receiver 4 receives the sound waves. The height of the sample is the propagation distance of the ultrasonic wave, from which the corresponding sound wave velocity can be obtained; the crack rate of the sample is calculated and displayed on the screen.

[0047] The fixing device includes a left base 1, a right base 5, and four fixing rods 6. The longitudinal section of both the left base 1 and the right base 5 is a square cuboid, and cylindrical grooves are provided on the opposite sides of the left base 1 and the right base 5. Figure 2 As shown, there are four rotating holes at the four corners of the right side of the left base 1, which are used to connect the fixing rod 6 to the left base 1. The moisture content sensing element 3 is connected to the center of the groove of the left base 1, which is used to measure the moisture content of the sample. The ultrasonic transmitter 2 is located in the center of the left base 1, and the ultrasonic receiver 4 is located in the center of the right base 5. The ultrasonic transmitter 2 is located 1 cm to the left of the groove of the left base 1.

[0048] The left base 1 is a hollow cuboid of polyethylene plastic, measuring 15cm-20cm in length, 15cm-20cm in width, and 5.5cm-7cm in height. There is a columnar groove with a diameter of 10cm-15cm and a depth of 1.5cm in the center of the right side. The four corner holes on the right side of the left base 1 have a diameter of 3mm and a depth of 5cm. The right base 5 is symmetrical to the left base 1, and the two grooves fit together to place the sample, matching the size of the sample.

[0049] like Figure 1 , 3 As shown, the length of the fixing rod 6 is 12cm-17cm, and it is divided into two sections, with the left and right halves being symmetrical in length. The left half is spiral-shaped and is inserted into the spiral hole in the left base 1, while the right half is smooth and cylindrical and is connected to the right base 5.

[0050] The adjustment device includes a knob 8 and a gear set 9, which are located inside the right side of the left base 1 and form a transmission structure. The knob 8 is connected to the helical part 7 of the fixing rod 6 through the gear set 9. The depth of the fixing rod 6 entering the left base 1 is adjusted by the knob 8 to adjust the distance between the left base 1 and the right base 5.

[0051] Knob 8 is located above gear set 9 and is connected to the middle gear in gear set 9 via a metal shaft. When knob 8 is turned, the metal shaft drives the middle gear in gear set 9 to rotate synchronously, thereby driving the gears on both sides to rotate. In turn, the outermost two gears drive the fixed rod 6 to slide forward or backward. To ensure that the outermost two gears rotate in the same direction, the number of gears on the left and right sides must differ by one. There are 8 gear sets in total. Before and after installing the soil and rock sample, gear set 9 is always engaged with the auger 7.

[0052] like Figure 4-5As shown, the moisture content sensing element 3 is a hollow stainless steel columnar structure with a diameter of 1.8mm-2.2mm and a length of 10.5cm-15.5cm. The top has a 0.5cm high, 2mm diameter spiral tip to facilitate insertion into the soil sample. The column of the moisture content sensing element 3 consists of 10 layers, each 1cm-1.5cm long, with a moisture-sensing unit 10 on the right side of each layer. The moisture-sensing unit 10 is a ring-shaped groove on the column of the moisture content sensing element 3, 3mm long and 0.2mm deep. If the moisture-sensing unit 10 is too small, it will not accurately measure the moisture content and will cause errors. If it is too large, it will waste materials, increase costs, and easily damage the moisture content sensing element 3. The bottom of the moisture sensing unit 10 is uniformly distributed with inorganic salt KCl (NaCl, Na2SO3, K2SO3, etc. can also be used because they have good stability during water absorption and dehydration, good water absorption, and moderate price) for moisture sensing and conductivity. The reverse filter membrane 12 is embedded in the hollow cylindrical groove. The groove depth and cross-sectional dimensions are completely consistent with the height and cross-sectional dimensions of the reverse filter membrane. It serves as a channel for water to enter the moisture content sensing element 3 and can filter out particles contained in the water in the soil and rock sample as well as impurities such as inorganic salt 13. The inorganic salt is uniformly distributed on the bottom surface of the hollow cylindrical groove and is in direct contact with the reverse filter membrane 12. It is used to improve the suction of the moisture sensing unit 10 for water in the soil and rock and plays a conductive role in the moisture content sensing element 3 after contacting water. The two ends of the moisture content sensing element 3 are connected to an external power source through wires 11. An ammeter is connected in the circuit. The wires 11 are located inside the hollow cylinder.

[0053] Inorganic salt 13 can absorb moisture from the soil sample through the filter membrane 12 and electrolyzes after becoming wet, thus generating conductivity. The amount of absorbed moisture reflects the internal moisture content of the soil sample and can be reflected by the conductivity of the moisture-sensing unit 10, improving measurement accuracy. Considering the uneven distribution of moisture content within the soil sample, the moisture content sensing element 3 is evenly divided into ten parts to uniformly detect the moisture content at different locations in the soil sample. A galvanometer is used to measure the conductivity of each moisture-sensing unit 10. The wire 11 is located inside the hollow cylinder and connected to the galvanometer to record the current change in each small segment of the moisture-sensing unit 10, obtaining the conductivity of each moisture-sensing unit 10. The resistivity is calculated by a computer, and the moisture content data at the corresponding location is obtained through the relationship between resistivity and moisture content. Finally, the average value of the moisture content measured in each part is taken as the final moisture content, thus measuring the moisture content simultaneously with the crack ratio.

[0054] Some existing technologies use the equivalent resistance method to calculate the material resistance and thus obtain the material's moisture content. This essentially relies on simple calculations to obtain the material's conductivity, neglecting the influence of inorganic salts and fine particles on the material's conductivity, resulting in significant errors. In this invention, an inorganic salt layer 13 is laid on the inner side of a filter membrane 12 located outside the moisture-sensing unit 10. The inorganic salt 13 matrix absorbs moisture from the soil sample, and the moisture content of the soil sample is obtained from the change in conductivity of the inorganic salt 13 after water absorption. This effectively reduces the influence of inorganic salts and fine particles on the conductivity of the soil sample, thereby significantly improving the accuracy of moisture content testing.

[0055] Example 2,

[0056] A method for measuring the porosity of soil and rock samples, specifically comprising the following steps:

[0057] S1. After collecting soil and rock samples in the field, the samples are prepared to be 10 cm high and 10 cm in diameter. A hole with a diameter of 2 mm is drilled in the center of the sample to penetrate the top and bottom of the sample.

[0058] S2, align the cavity in the center of the soil and rock sample with the moisture content sensing element 3, insert the moisture content sensing element 3 into the center of the soil and rock sample, and make the top of the soil and rock sample completely placed into the groove of the left base 1.

[0059] S3, align the bottom of the soil sample with the groove of the right base 5, align the four fixing rods 6 with the four holes at the four corners of the left base 1, adjust the depth of the fixing rods 6 into the left base 1 by turning the knob 8, thereby adjusting the distance between the left base 1 and the right base 5, and completely place the bottom of the soil sample into the groove of the right base and fix the sample.

[0060] S4. Wait about 10 minutes until the moisture content sensing element 3 stabilizes. Then turn on the measuring device switch (i.e., the switch on the display screen) and read the data on the display screen to obtain the data of the soil and rock sample moisture content w and the wave velocity v1 of the sound wave passing through the soil and rock sample.

[0061] S5, based on the ultrasonic intensity after passing through the sample, the initial fracture rate is obtained by the existing ultrasonic fracture rate measurement method; the data fitting between the acoustic wave velocity v1 and the initial fracture rate is performed, and the curve that best matches the distribution law of the initial fracture rate S1 is: S1=4.8257 / (1 + exp(14.969×(v1-2.1886))), where exp is an exponential function with the natural constant e as the base.

[0062] S6. The natural water content of the rock sample was found to be 8.71% through indoor tests. The relationship between wave velocity and fracture ratio of the rock and soil sample was measured at water contents of 5.2%, 7.2%, 8.71%, 10.6%, and 12.2%. A three-dimensional curve of water content-wave velocity-fracture ratio was established. The wave velocity-fracture ratio curve corresponding to the natural water content was used as the calibration value. By observing the different wave velocities at different water contents under the same fracture ratio, a correction coefficient k (k=0.87227+0.00657w) was obtained. This corrected the wave velocity of the rock sample at different water contents to the wave velocity at the natural water content. The corrected wave velocity is v=kv1. The corrected wave velocity v is used to replace the wave velocity v1 in the initial fracture ratio S1 to obtain the final fracture ratio curve S2, S2=4.8257 / (1 + exp(14.969×(v-2.1886))).

[0063] The initial fracture rate is obtained based on the ultrasonic wave intensity after passing through the sample using existing ultrasonic methods. However, this result is affected by the moisture content, leading to significant measurement errors. Current techniques determine the degree of sample damage by testing the ultrasonic wave velocity V at a specific moisture content and observing changes in this velocity. Relying solely on comparing ultrasonic wave velocities to assess damage is insufficient to accurately reflect the fracture rate due to the influence of moisture content. Furthermore, existing moisture content testing processes can easily damage the sample, affecting the accuracy of testing natural samples. In some existing techniques, the fitting of wave velocity and fracture rate uses linear equations or logarithmic relationships, achieving only a certain level of fitting accuracy in the middle of the curve. However, the fitting is poor for fracture rates at low or high wave velocities, still exhibiting significant errors.

[0064] This invention fully considers the influence of moisture content on the results of ultrasonic testing of soil and rock samples. Using a moisture content sensing element 3 with a specific structure, the moisture content of the sample is measured without damaging its natural state. A three-dimensional curve of moisture content, ultrasonic wave velocity, and fracture rate is then established. (See attached diagram.) Figure 6 The influence of moisture content on the results of ultrasonic testing of soil and rock samples was considered. The relationship between the porosity and the number of cracks in soil and rock samples under different moisture contents was obtained. By correcting the wave velocity with natural moisture content, the error caused by the fluctuation of moisture content was effectively reduced, and the accuracy was improved. The moisture content and porosity of indoor and outdoor soil and rock samples were obtained quickly without damaging the structure and properties of the samples.

[0065] By pre-fabricating soil and rock samples with fracture rates of 1%, 2%, 3%, 4%, and 5% in the laboratory, and considering that the soil and rock samples themselves also contain micropores in addition to the pre-fabricated fractures, the measured porosity is slightly larger than the actual pre-fabricated fracture rate, which is more in line with actual conditions. The method of this invention, compared with traditional methods, shows that... Figure 7 It can be seen that R in the embodiments of the present invention 2=98.3%, traditional method R 2 =90.6%, indicating that the porosity measured in this embodiment of the invention is more accurate. Because traditional methods cannot determine the effect of moisture content on wave velocity, when the local moisture content inside the sample is high, the ultrasonic wave velocity is lower than normal due to the influence of cracks and moisture, thus increasing the calculated porosity and resulting in a larger error compared to the true porosity. Figure 7 The portion where the fracture rate suddenly increases as measured by traditional methods.

[0066] In this study, it was found that the actual relationship between wave velocity and fracture rate is more in line with an "S"-shaped curve. Therefore, fitting with a Slogistical curve can achieve better fitting accuracy at both ends of the curve and better conforms to the nonlinear relationship between wave velocity and fracture rate. This is of great significance for the development of ultrasonic measurement technology for fracture rate and for outdoor detection of fracture rate of rock samples with different water contents under natural conditions, and has higher practical application value.

[0067] In indoor testing, if soil and rock samples are brought back to the laboratory for moisture content and porosity measurements, disturbances during transport may affect the accuracy of porosity measurements, and temperature changes and moisture evaporation can also affect the accuracy of moisture content measurements. Both measuring porosity and moisture content present challenges due to expensive and inconvenient equipment. Existing indoor testing methods, for both porosity and moisture content measurements, mean that samples cannot be reused after measuring a single physical parameter. When measuring multiple parameters, samples must be duplicated and tested separately, increasing uncertainty. Furthermore, field sampling requires collecting more undisturbed soil and rock samples, resulting in significant time waste and poor economic efficiency. In outdoor measurements, the measured porosity in one-dimensional and two-dimensional states deviates from the actual porosity of the soil and rock mass, failing to reflect the internal fracture development of the rock mass, frequently missing crucial information, and involving cumbersome and repetitive operations with high uncontrollability. Traditional methods for measuring three-dimensional fracture rate involve excessive disturbance to the rock mass, resulting in unreliable and subjective measurements. Furthermore, they are cumbersome, require highly skilled personnel, and incur high costs, making them impractical for engineering applications. In contrast, this invention requires only one sample to simultaneously measure the moisture content and fracture rate of soil and rock. This at least doubles the efficiency of traditional methods. When measuring multiple physical parameters, the number of samples taken and prepared can be reduced by half, saving time and improving economic efficiency. The method is simple to operate, easy to learn, and does not require highly skilled personnel. It is also portable, allowing for on-site sampling and measurement, increasing controllability, reducing measurement errors, and facilitating repeated testing. The measuring instrument has a simple structure, low cost, is easy to manufacture, convenient to assemble and disassemble, and is reusable, making it highly suitable for engineering applications.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. An instrument for measuring the porosity of soil and rock samples, characterized in that, include: A fixing device, comprising two bases for fixing a soil sample between the two bases; An adjustment device for adjusting the distance between the two bases; A moisture content measurement system is used to detect the internal moisture content data of soil and rock samples. A fracture rate measurement system is used to detect the acoustic wave velocity propagating inside a soil or rock sample. The initial fracture rate is obtained using existing ultrasonic fracture rate measurement methods. Data fitting of the acoustic wave velocity v1 with the initial fracture rate yields a curve conforming to the distribution law of the initial fracture rate S1: S1 = 4.8257 / (1 + exp(14.969 × (v1 - 2.1886))), where exp is an exponential function with the natural constant e as the base. A three-dimensional curve of water content-wave velocity-fracture rate is established. Using the wave velocity-fracture rate curve corresponding to the natural water content as the calibration value, and considering the different wave velocities at different water contents under the same fracture rate, a correction coefficient k = 0.87227 + 0.00657w is obtained, where w represents the water content of the soil or rock sample. The corrected acoustic wave velocity v = kv1 is used to replace the acoustic wave velocity in the initial fracture rate, resulting in the final sample fracture rate curve: S2. =4.8257 / (1 + exp(14.969×(v-2.1886))); The moisture content measurement system includes a moisture content sensing element (3), which is a hollow columnar structure made of conductive material. The column of the moisture content sensing element (3) is evenly spaced with multiple annular grooves. A reverse filter membrane (12) is embedded in the groove. Inorganic salt is laid between the reverse filter membrane (12) and the bottom of the groove to form a moisture sensing unit (10). The two ends of each moisture sensing unit (10) are connected to an external power source through wires (11). An ammeter is connected in the circuit to measure the current passing through each moisture sensing unit (10) to obtain the conductivity of each moisture sensing unit (10). After converting the current into resistance, the moisture content data of the corresponding position is obtained through the relationship between resistivity and moisture content. Finally, the average value of the moisture content measured in each part is taken as the final moisture content. The moisture content is measured at the same time as the crack rate.

2. The instrument for measuring the porosity of soil and rock samples according to claim 1, characterized in that, The fracture rate measurement system includes an ultrasonic transmitter (2), an ultrasonic receiver (4), and a computer. The ultrasonic transmitter (2) is used to emit ultrasonic waves to the sample; the ultrasonic receiver (4) is used to detect the ultrasonic waves after they pass through the sample; the computer obtains the time t of the sound wave passing through the soil sample, and calculates the sound wave velocity of the ultrasonic wave propagating inside the soil sample in combination with the height of the sample.

3. The instrument for measuring the porosity of soil and rock samples according to claim 1, characterized in that, The two bases are left base (1) and right base (5), respectively. The opposite sides of the left base (1) and right base (5) are provided with cylindrical grooves that match the ends of the soil and rock samples.

4. The instrument for measuring the porosity of a soil and rock sample according to claim 1, characterized in that, The adjustment device includes a fixed rod (6). Two fixed rods (6) are fixed around one base near the side of the soil sample. The other base has a spiral hole at the position corresponding to the fixed rod (6). The fixed rod (6) can extend into the spiral hole. The spiral part (7) of the fixed rod (6) is connected to the two outermost gears of the gear set (9). The knob (8) is connected to the middle gear in the gear set (9) through a metal shaft. Rotating the knob (8) drives the middle gear in the gear set (9) to rotate synchronously, thereby driving the gears on both sides to rotate. Then, the two outermost gears drive the fixed rod (6) to move axially, adjusting the distance between the two bases. To ensure that the two outermost gears rotate in the same direction, the number of gears on both sides differs by one.

5. The instrument for measuring the porosity of soil and rock samples according to claim 1, characterized in that, One end of the moisture content sensing element (3) has a conical spiral structure.

6. A method for measuring the porosity of a soil and rock sample using an instrument as described in claim 3, characterized in that, Includes the following steps: S1, Prepare the soil and rock to be tested into a cylindrical sample, and drill a hole along the axial direction at the center of the sample; S2, insert the moisture content sensing element (3) into the center of the soil sample, and place one end of the soil sample completely into the groove of the left base (1); S3, align the other end of the soil and rock sample with the groove of the right base (5), adjust the distance between the right base (5) and the left base (1) so that the end of the soil and rock sample is completely placed in the groove of the right base (5) and the sample is fixed. S4. After the water content sensing element (3) stabilizes, the water content w of the soil sample and the sound wave velocity v1 of the ultrasonic wave passing through the soil sample are obtained. S5, based on the ultrasonic intensity after passing through the sample, the initial fracture rate is obtained by the existing ultrasonic measurement method; the acoustic wave velocity v1 is fitted with the initial fracture rate to obtain a curve that conforms to the distribution law of the initial fracture rate S1. S6, based on the influence of water content, obtain the correction coefficient of acoustic wave velocity. Replace the acoustic wave velocity v1 in the initial fracture rate S1 with the corrected acoustic wave velocity to obtain the curve of the final fracture rate.

7. The method for measuring the porosity of a rock and soil sample according to claim 6, characterized in that, In step S5, the curve that conforms to the initial fracture rate distribution law is: S1=4.8257 / (1 + exp(14.969×(v1-2.1886))), where exp is an exponential function with the natural constant e as the base.

8. The method for measuring the porosity of a soil and rock sample according to claim 7, characterized in that, In step S6, the correction coefficient for the sound wave velocity is k = 0.87227 + 0.00657w.

9. The method for measuring the porosity of a soil and rock sample using an instrument according to claim 8, characterized in that, In step S6, the corrected acoustic wave velocity v = kv1, and the final fissure ratio S2 = 4.8257 / (1 + exp(14.969×(v-2.1886))).

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