WO2011058911A1 - 地盤調査方法 - Google Patents
地盤調査方法 Download PDFInfo
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- WO2011058911A1 WO2011058911A1 PCT/JP2010/069508 JP2010069508W WO2011058911A1 WO 2011058911 A1 WO2011058911 A1 WO 2011058911A1 JP 2010069508 W JP2010069508 W JP 2010069508W WO 2011058911 A1 WO2011058911 A1 WO 2011058911A1
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- ground
- attenuation rate
- elastic wave
- velocity
- attenuation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
- G01V1/42—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging using generators in one well and receivers elsewhere or vice versa
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D1/00—Investigation of foundation soil in situ
- E02D1/02—Investigation of foundation soil in situ before construction work
Definitions
- the present invention relates to a ground survey method for visualizing and surveying the ground non-destructively using elastic waves (including acoustic waves), and in particular, the structure inside the ground including concrete structures and rocks, local loosening, and cavities. It relates to a method for visualizing the existence of gravel at once.
- Elastic wave tomography is classified according to a means for generating elastic waves and a layout for propagating elastic waves. Broadly classified from means for generating elastic waves, it is classified into transmitters that generate elastic waves by blasting and mechanically, and transmitters that generate elastic waves using piezoelectric ceramics and magnetostrictive materials that use the piezoelectric and magnetostrictive effects. Is done. Roughly classified by layout, there are reflection and refraction methods that use blasting from the ground surface, and inter-hole tomography methods that use boreholes.
- Patent Document 1 there is a technique shown in Patent Document 1 as a tomography between holes. According to this, not only the elastic wave velocity but also the investigation using the inherent attenuation in the ground (referred to as viscous damping) is applied to the investigation of the ground in the design of substructure and the investigation of underground obstacles. It is possible.
- the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a ground investigation method capable of accurately judging the state of the ground and avoiding erroneous interpretation of the ground.
- the invention according to claim 1 of the present application is a ground survey method for non-destructively visualizing and investigating the ground using elastic waves, wherein a receiver and a transmitter for transmitting the elastic waves are transmitted to a known position of the ground.
- the elastic wave transmitted from the transmitter is transmitted by the transmitter, and the elastic wave propagated through the path in the ground from the transmitter to the receiver is received by the receiver, and the propagated elastic wave is transmitted.
- the invention according to claim 2 of the present application mainly determines the difference in the particle size of the main component of the ground of sand, silt, or clay soil by comparing the state of the ground with the speed threshold with respect to the speed, Furthermore, by comparing the attenuation rate with the attenuation rate threshold value, the difference in the saturated state of the ground from a state containing bubbles or gravel to a state where the ground is tightened is mainly determined.
- the state of the ground is the state of sand, loose sand, or gravel, the state of hard viscous soil or tight sand, and the state of viscous soil containing bubbles or sand containing bubbles. And the state of loose cohesive soil or cohesive soil.
- the ground is concrete or rock
- the presence / absence of a crack in the ground is determined based on the speed threshold value
- the ground constituent medium existing between the cracks is determined based on the attenuation rate threshold value. It was decided to do.
- the invention according to claim 5 of the present application is based on a single carrier frequency obtained by modulating the elastic wave with a pseudo-random signal.
- the attenuation rate and the velocity are obtained by performing a correlation operation between the pseudo-random signal and the received elastic wave.
- the invention according to claim 7 of the present application is such that the transmitter and the receiver are all arranged inside the ground.
- the present invention it is possible to accurately determine the state of the ground and avoid erroneous interpretation of the ground. Specifically, the following is possible.
- the state of the ground can be accurately determined by combining with the velocity of the elastic wave in the ground.
- Schematic which shows the ground investigation apparatus which concerns on 1st Embodiment of this invention.
- Schematic diagram showing the arrangement relationship between the ground, transmitter and receiver Schematic showing that the tomography method determines the speed and attenuation rate for each section of the ground Schematic diagram for explaining main attenuation of elastic wave
- the figure which shows the flowchart when determining the state of a ground from the velocity and attenuation factor of the elastic wave which concerns on 1st Embodiment of this invention.
- FIG. 1 Schematic diagram schematically showing the condition of the ground with respect to the velocity and attenuation rate of elastic waves
- the schematic diagram which shows the state of the ground which can be determined from the relationship between the velocity and the attenuation factor of the elastic wave which concerns on 2nd Embodiment of this invention
- the cross-sectional view of the ground obtained from the velocity distribution map and attenuation rate distribution map obtained by actual measurement
- the schematic diagram which shows the state of the ground which can be judged from the graph which plotted the speed and the attenuation factor obtained in FIG.
- the schematic diagram which shows roughly the relationship between the velocity of an elastic wave and the damping factor which concern on 3rd Embodiment of this invention.
- the ground survey device 100 receives a transmitter (SOR) 120 that transmits an elastic wave 102 and a receiver (REC) that receives the elastic wave 102 that has propagated through a path 104 ⁇ / b> A in the ground 104. ) 124 and an analysis device (ANE) 132 that determines the state of the ground 104 between them based on the received elastic wave 102 (received wave). Further, the ground survey device 100 determines a single frequency signal (carrier frequency) and outputs a frequency generator (FNG) 112, and a single frequency signal output from the frequency generator 112 is phase-converted.
- SOR transmitter
- REC receiver
- ANE analysis device
- phase converter (PHC) 114 that is a PRBS signal (described later) that is one of the pseudo-random signals.
- the analysis device 132 can obtain a cross-sectional image of the ground 104 between the receiver 124 and the transmitter 120 from the elastic wave 102 received by the plurality of receivers 124 (how to obtain the cross-sectional image is tomography). Known as the law).
- the ground investigation device 100 can visualize and investigate the ground 104 nondestructively using the elastic wave 102 as an elastic wave tomography device.
- the ground 104 is provided with boring holes 106 extending in the vertical direction on the paper surface at predetermined intervals (two in FIG. 2).
- one transmitter 120 can move at a predetermined interval in the vertical direction and can transmit.
- a plurality of receivers 124 are arranged in the other boring hole 106 (on the right side in FIG. 2) at predetermined intervals in the vertical direction (that is, the transmitter 120 and the receiver 124 are arranged at known positions on the ground 104). Have been). All of the transmitter 120 and the receiver 124 are disposed in the borehole 106 (arranged inside the ground 104). For this reason, compared with the case where either or both are arrange
- the transmitter 120 and the receiver 124 will be described later again.
- the frequency generator (FNG) 112 can digitally output a carrier signal, which is a continuous sine wave signal having an arbitrary frequency (single frequency), as a single frequency signal (carrier frequency). It can be said that the frequency generator 112 includes frequency determining means for selecting and determining a single frequency of the elastic wave 102.
- the frequency determining means can be constituted by a circuit including a CPU, for example.
- the phase converter (PHC) 114 is connected to the frequency generator 112.
- the phase converter 114 phase-converts a single frequency digital signal (single frequency signal) output from the frequency generator 112 with a PRBS code.
- a PRBS signal that is one of the pseudo-random signals is output to the DA converter 116 (that is, the carrier frequency of the PRBS signal becomes a single frequency).
- the PRBS code is a pseudo-random binary sequence (Psudo-Random Binary Sequence) code.
- the PRBS code may be introduced from the outside.
- the DA converter (DAC) 116 is connected to the phase converter 114, converts the signal output from the phase converter 114 from a digital value to an analog value, and outputs the analog value.
- the transmission amplifier (AMP) 118 is connected to the DA converter 116, and amplifies the signal output from the DA converter 116 in an analog manner and outputs the amplified signal.
- a transmitter (SOR) 120 is connected to a transmission amplifier 118, converts an electrical signal output from the transmission amplifier 118 into mechanical vibration, and transmits and outputs an elastic wave 102 as a transmission wave.
- Elastic wave 102 is based on a single carrier frequency modulated into a PRBS signal.
- piezoelectric ceramic is used for the transmitter 120. For this reason, it is possible to stably generate mechanical vibration while being small. Such an effect can be similarly obtained even when a magnetostrictive material is used.
- the receiver (REC) 124 receives the elastic wave 102 that is mechanical vibration propagated from the transmitter 120 through the path 104A in the ground 104 as a received wave and converts it into an electrical signal.
- an underwater microphone called a hydrophone can be used as the receiver 124.
- the reception filter (RCF) 126 is connected to the receiver 124 and removes, for example, traffic noise and construction noise generated on the ground 104 from the signal received by the receiver 124. For this reason, by selecting an appropriate noise filter, the reception filter 126 can extremely reduce the influence of those noises. Note that the reception filter 126 may include a variable amplifier as necessary.
- the AD converter (ADC) 128 is connected to the reception filter 126 and converts a signal that has passed through the reception filter 126 from an analog value to a digital value.
- the data recorder (DTR) 130 is connected to the AD converter 128 and records the signal output from the AD converter 128.
- the analysis device (ANE) 132 is connected to the phase converter 114 and the data recorder 130, and recorded in the data recorder 130 and the PRBS signal (pseudorandom signal) related to the transmission wave output from the phase converter 114.
- the correlation value with the signal by the received wave is calculated.
- the arrival time of the elastic wave 102 to the receiver 124 can be accurately measured.
- the velocity V of the elastic wave 102 (here, P wave velocity) can be obtained.
- the attenuation rate D can be accurately obtained from the ratio of the amplitude intensity of the received wave to the amplitude intensity of the initial transmission of the elastic wave 102 using the correlation value.
- the sound pressure (amplitude intensity) of the transmitted wave is AWi (dB)
- the sound pressure of the received wave is AWo (dB)
- the distance between the transmitter 120 and the receiver 124 is L (m)
- the acoustic wave 102 Let the carrier frequency be f (kHz).
- the attenuation amount AT (dB) and the attenuation rate D (dB / kHz / m) can be expressed as Expressions (1) and (2), respectively.
- AT (dB) AWi (dB) ⁇ AWo (dB) (1)
- D (dB / m) AT (dB) / f (kHz) / L (m) (2)
- the analysis device 132 stores a speed threshold value Vsh and an attenuation rate threshold value Dsh provided for each of the obtained velocity V and attenuation rate D. Then, the analysis device 132 compares the velocity V (including a velocity Vij described later) and the attenuation factor D (including an attenuation factor Dij described later) with respect to the velocity threshold Vsh and the attenuation rate threshold Dsh, and details of the state of the ground 104 Determination (described later) can be performed. The determination result is plotted on a cross-sectional image or a velocity-attenuation rate graph by a monitor or printer (not shown) attached to the analysis device 132. Alternatively, the determination result is stored as electronic data in the analysis device 132.
- the analysis device 132 uses the data (the speed V and the attenuation rate D) obtained at the predetermined positions of the receivers 124 corresponding to the predetermined positions of the boring holes 106 of the transmitter 120 to use the boring holes.
- the speed Vij and the attenuation rate Dij can be obtained.
- the analysis device 132 can determine the state of the path 104A configured by the section Aij in the ground 104 with a high S / N ratio using the pulse compression technique based on the correlation calculation.
- the attenuation AT in the ground is displayed as the sum of distance attenuation, viscosity attenuation, transmission attenuation, and scattering attenuation, as shown in Equation (3).
- Attenuation distance attenuation + viscous attenuation + transmission attenuation + scattering attenuation (3)
- Viscous damping is damping caused by friction between the soil particles SP and the water W because the vibrations of the soil particles SP and the water W do not match when the elastic wave passes (FIG. 4A).
- Viscous damping can be calculated by wave theory in a porous medium, Biot 1955, etc. For example, when a carrier frequency of 1 kHz to 20 kHz is used, the viscosity attenuation increases as the particle size increases in the completely saturated ground 104, that is, the viscosity attenuation increases in sand and decreases in viscous soil. According to the wave theory in the porous medium, the viscous damping is not easily affected by the looseness of the ground.
- Transmission attenuation is attenuation caused by conversion into thermal energy when an elastic wave enters and transmits (transmission from density D1 to D2) into substances having different densities (FIG. 4B). Transmission attenuation occurs at the boundary of the formation, etc., and increases when passing through a portion with a small density such as bubbles (hereinafter, including gas) in the ground. Scattering attenuation is attenuation caused by reflection or scattering when elastic waves are incident on substances having different densities (FIG. 4C). Scattering attenuation occurs when an object larger than 1 ⁇ 4 to 1/2 of the wavelength of elastic waves such as gravel exists, and becomes large in ground with many gravel layers and boulders.
- the receiver 124 and the transmitter 120 that transmits the elastic wave 102 are arranged at a known position on the ground 104.
- the elastic wave 102 by the PRBS signal is transmitted from the transmitter 120, and the elastic wave 102 propagating through the path 104A in the ground 104 from the transmitter 120 toward the receiver 124 is received by the receiver 124.
- the correlation value between the PRBS signal and the received elastic wave 102 is calculated, and the velocity V and the attenuation rate D of the propagated elastic wave 102 are obtained.
- step S8 From the speed V and the attenuation rate D, the speed Vij and the attenuation rate Dij are obtained for each section Aij by a known tomography method (step S8). Then, a velocity distribution diagram and an attenuation rate distribution diagram are obtained.
- the value of the speed Vij and the value of the attenuation rate Dij are compared with the speed threshold value Vsh and the attenuation rate threshold value Dij, respectively.
- the speed generally has a good correlation with the hardness and porosity of the ground, the speed is high when the ground is sand, the speed is low when the soil is viscous, and bubbles and gas (simply called bubbles) are mixed. On the ground, the speed is reduced.
- the attenuation of the elastic wave is caused by the sum of viscous attenuation, transmission attenuation, scattering attenuation, and the like as described above.
- the viscous damping increases as the particle size increases, that is, the viscous damping increases with sand and decreases with viscous soil.
- Transmission attenuation is attenuation that occurs when passing through objects having different densities. The transmission attenuation increases when passing through a portion having a low density such as bubbles (hereinafter, including gas) in the ground.
- Scattering attenuation is attenuation caused by reflection and scattering when an object larger than 1 ⁇ 4 to 1 ⁇ 2 of the wavelength of the elastic wave 102 such as gravel is present, and becomes large in the ground where there are many gravel layers and boulders.
- the attenuation rate Dij and the speed Vij are combined and classified into cases. That is, an attenuation rate threshold value Dsh and a velocity threshold value Vsh are provided for each of the attenuation rate Dij and the velocity Vij, and a comparison of the attenuation rate Dij and the velocity Vij with respect to the attenuation rate threshold value Dsh and the velocity threshold value Vsh is performed. Determine the state.
- the ground 104 is a sand layer that does not include bubbles and includes gravel. It is determined that it is in the state (sand SA, loose sand LS, gravel (including only gravel) SC CONDITION 1) (step S14).
- the ground 104 does not include bubbles, gas, or gravel. If it is a sand layer and the damping rate Dij is further smaller, it is determined that there is a possibility of hard viscous soil (hard viscous soil TC or tight sand TS state CONDITION 2) (step S16).
- the ground 104 is a viscous soil containing bubbles or gas or It is determined that the state is a viscous soil containing gravel (the state CONDITION 3 of the viscous soil FC containing the bubbles F or the sand FS containing the bubbles F) (step S20).
- the ground 104 is a viscous soil that does not contain bubbles or gas. It is determined that the state is (the state CONDITION 4 of the loose clay soil LC or the clay soil CR) (step S22).
- the speed alone is the gravel SC, the sand SA, and the compacted sand TS in FIG. 6, the loose sand LS, and the hard viscous soil TC, the viscous soil FC including the bubbles F, the sand FS including the bubbles F, And the clay soil CR cannot be distinguished from each other.
- the attenuation rate threshold value Dsh it is possible to distinguish these states by using the attenuation rate threshold value Dsh.
- the analysis apparatus 132 can uniquely determine the state of the ground 104 quickly from the relationship between the speed and the attenuation rate. Note that the state of the ground 104 is not necessarily shown as a cross-sectional image, and it is possible to easily determine the state of the ground 104 and compare each location only by creating FIG.
- the speed threshold value Vsh and the attenuation rate threshold value Dsh are 1.6 km / s and 0.3 dB / kHz / m, respectively.
- the speed and attenuation rate of a general deposited layer are about 1.5 to 1.7 km / s and about 0.1 to 0.3 dB / kHz / m, respectively.
- a speed threshold Vsh and an attenuation rate threshold Dsh may be provided. These threshold values can be corrected by comparing with the boring information.
- the state of the ground 104 is determined from the attenuation rate D based on the attenuation amount AT including the viscous attenuation. For this reason, it is possible to determine the state of the ground 104 more accurately than in the past (a method using only viscous damping or a method not using damping rate).
- the analysis device 132 can also determine the looseness of the ground 104.
- the state of the ground 104 includes sand, loose sand, or gravel, hard viscous soil or compacted sand, viscous soil containing bubbles or sand containing bubbles, loose viscous soil or viscous soil.
- the present invention is not limited to this.
- a plurality of at least one of the speed threshold value Vsh and the attenuation rate threshold value Dsh may be provided to make a more detailed determination.
- the states shown in FIG. 6 can be distinguished.
- the velocity V of the elastic wave 102 (hereinafter, Vij is also expressed as V) between 1.5 km / s and 1.6 km / s, and between 1.6 km / s and 1.7 km / s Are provided with speed thresholds Vsh (two in total).
- the attenuation rate D of the elastic wave 102 (hereinafter, Dij is also expressed as D) is between 0.05 dB / kHz / m and 0.1 dB / kHz / m, 0.1 dB / kHz / m and 0. Between 2 dB / kHz / m, between 0.2 dB / kHz and 0.3 dB / kHz / m, between 0.3 dB / kHz and 0.5 dB / kHz / m, Are respectively provided with attenuation rate threshold values Dsh (four in total).
- the loose viscous soil layer G1 can be discriminated from the velocity of 1.5 km / s, but the boulder S cannot be discriminated.
- the loose sand layer G2 or the tightened viscous soil layer G3 can be discriminated from the speed of 1.6 km / s, one of them cannot be specified.
- the presence of bubbles (ground gas) F in the tightened viscous soil layer G3 cannot be determined.
- the sand layer G4, the gravel layer G5, or the hard-tight clay soil layer G6 is discriminated from the speed of 1.7 km / s, any of them cannot be specified.
- the ground 104 shown in FIG. 7 can be determined with higher accuracy by combining the four attenuation rate threshold values Dsh with the speed threshold value Vsh.
- the damping rate D is 0.05 dB / kHz / m
- the damping rate of the rolling stone S is large (0.2 dB / kHz / m) even at the same speed V.
- the presence of the boulder S can be specified.
- the loose sand layer G2 has a larger damping factor D (0.3 dB / kHz / m versus 0.05 dB / kHz / m). .
- D damping factor
- the viscous soil layer G3 that is tightened with respect to the loose sand layer G2.
- the attenuation rate D of the bubbles F in the tight clay soil layer G3 is much larger (0.5 dB) than that of the loose sand layer G2, the presence of the bubbles F can be specified.
- the decay of the gravel layer G5 is smaller than the damping rate D (0.1 dB) of the sand layer G4.
- the rate D is large (0.5 dB), and the damping rate D of the tight clay soil layer G6 is small (0.05 dB). For this reason, it is possible to easily identify the tightened sand layer G4, the gravel layer G5, and the hard tightened viscous soil layer G6.
- FIG. 8 shows a result of applying the method for determining the state of the ground 104 according to the present embodiment to a velocity distribution map and an attenuation rate distribution map obtained by measuring in an actual landfill along Tokyo Bay.
- the distance between the boring holes 106 is 66 m and 55 m, and the measurement depth is 65 m.
- the diagram shown in FIG. 8A is a velocity distribution diagram
- the diagram shown in FIG. 8B is an attenuation factor distribution diagram.
- the determined state of the ground 104 is indicated by G10 to G19.
- G10 is a loose sand layer (Loose sand)
- G11 is a loose viscous soil layer (Clay; alluvial viscous soil layer)
- G12 is a loose silt layer (Silt: alluvial silt layer) consisting of particles between viscous soil and sand.
- G13 is an alternating layer of sand and silt
- G14 is a tight sand layer (Dense sand)
- G15 is a tight clay layer (Hard Clay)
- G16 is a viscous soil layer It is a bubble (Soil gas; organic gas).
- the wavy arrow mainly represents the difference between sand and clay soil.
- the solid-line arrows mainly represent the difference between saturated and unsaturated formations.
- the area H1 surrounded by the wavy circle is out of line with the solid arrow as compared to the area H2. From this, it is possible to clearly determine the presence of bubbles (organic gas) by providing an appropriate attenuation rate threshold value Dsh between the area H1 and the area H2. That is, the state of the ground 104 is mainly determined by comparing the speed threshold Vsh with the speed threshold Vsh with respect to the particle size of the main component of the ground 104 of sand, silt, or cohesive soil. By comparing mainly with the difference in the saturation state of the ground 104 from the state including bubbles or gravel to the state where the ground 104 is tightened by comparison with the threshold value Dsh, the ground 104 can be more accurately determined.
- the ground 104 includes gravel, sand, or viscous soil, but the present invention is not limited to this.
- it may be an artificial floor such as concrete, a foundation structure, or a bedrock.
- a case where the ground 104 is concrete or rock is described with reference to FIG.
- the ground 104 will be determined as the rock mass R2 without a crack (CONDITION2). If the speed V obtained is smaller than the speed threshold Vsh, it is found that the ground 104 has a crack. At this time, if the obtained attenuation rate D is larger than the attenuation rate threshold value Dsh (for example, 0.3 dB / kHz / m), it can be determined that bubbles (including gas) exist between the cracks CR1 ( CONDITION3).
- the obtained attenuation rate D is smaller than the attenuation rate threshold value Dsh, it can be determined that water or other substance exists between the cracks CR2 (CONDITION 4).
- the PRBS signal which is a pseudo-random signal
- the PRBS signal is correlated with the received elastic wave 102, so that the ground 104 has a high S / N ratio.
- Analysis can be performed.
- the path 104A is between the transmitter 120 and the receiver 124, and in determining the state of the ground 104, basically a transmitted wave is used, so that a higher S / N ratio can be ensured. .
- the ground 104 With a measurement resolution more than several tens of times the conventional one. For example, if the velocity of the elastic wave 102 in the ground 104 is 2 km / s, the resolution is about 5 m in the prior art, but in the above embodiment, the resolution is about 0.2 m. Since the frequency band of background noise (such as traffic noise on the ground 104 and construction noise) is low, it can be made less susceptible to background noise.
- background noise such as traffic noise on the ground 104 and construction noise
- the elastic wave 102 tends to attenuate exponentially as the frequency increases, and it is difficult to propagate the high-frequency elastic wave 102 over a long distance.
- the energy of the elastic wave 102 can be dispersed on the time axis by using the PRBS signal, the elastic wave 102 having a higher frequency than the conventional one (about several meters) can be propagated for several hundred meters. In the above embodiment, it is confirmed that 400 m or more is propagated at 1 kHz, and 20 m or more is propagated even at 30 kHz.
- the elastic wave 102 can be propagated over a long distance using a high frequency, and it is highly affected by noise (including vibration) on the ground 104 with high accuracy. Measurement can be performed to determine the state of the ground 104.
- the structure of the ground 104, local looseness, cavities, existence of gravel, etc. can be visualized over a wide range at once, and the state of the ground 104 can be determined with high accuracy. It is possible to avoid misinterpretation. Specifically, the following is possible.
- the attenuation of the elastic wave 102 in the actual ground 104 is obtained and used to determine the state of the ground 104. For this reason, the velocity V of the elastic wave 102 in the ground 104 and the attenuation rate D can be combined, and the state of the ground 104 can be accurately determined.
- the elastic wave 102 can be propagated over a long distance even when a high carrier frequency is used. As a result, highly accurate measurement and measurement that is not affected by background noise (traffic noise, construction noise, etc. on the ground 104) are possible.
- a method using electromagnetic waves instead of the elastic waves 102 is also conceivable.
- electromagnetic waves are easily absorbed in the presence of water and are vulnerable to electrical noise.
- it is difficult to apply the method using electromagnetic waves to places where there are steel towers, urban areas, and below the surface of groundwater or seawater for this reason, in tomography using electromagnetic waves, Applications tend to be limited to use above groundwater levels).
- the elastic wave 102 is used in the above-described embodiment, the above-described restriction is not imposed, and the present invention can be widely applied as compared with the case where an electromagnetic wave is used.
- the above-described embodiment can be investigated without limiting the place such as the place where oil or natural gas is buried or the place of odorous gas (organic gas) such as methane gas.
- the above embodiment is an effective technique for preventing disasters such as odorous gas ejection when striking for construction of a structure in a bay (Tokyo Bay, Osaka Bay, etc.).
- the piezoelectric ceramic or the magnetostrictive material is used for the transmitter 120.
- the present invention is not limited to this, and another one may be used.
- the elastic wave 102 is based on a single carrier frequency modulated with a pseudo-random signal.
- the pseudo-random wave does not necessarily have to be used.
- the pseudo-random signal is a PRBS signal using an M sequence, the present invention is not limited to this, and the pseudo-random signal may be a Gold sequence, a Barker sequence, or the like.
- the correlation calculation between the pseudo-random signal and the received elastic wave 102 is performed, but the present invention is not necessarily limited to this.
- the transmitter 120 and the receiver 124 are arranged in the borehole 106, the ground information on the pole surface of the ground 104 and the noise transmitted from the surface are minimized, and the accuracy is high.
- the state of the ground 104 can be grasped. That is, in the above-described embodiment, the receiver 124 that has been conventionally disposed on the surface of the ground 104 in order to prevent a decrease in the wave line density can be omitted, but the present invention is not necessarily limited to this.
- either or both of the transmitter 120 and the receiver 124 may be disposed on the surface of the ground 104. At that time, the transmitter 120 and the receiver 124 can be easily arranged.
- the velocity V and the damping rate D of the elastic wave 102 are obtained by correlating the pseudo-random signal and the elastic wave 102.
- the means for obtaining the attenuation rate D is not limited.
- the velocity Vij and the attenuation rate Dij for each section Aij are further obtained from the velocity V and the attenuation rate D of the elastic wave 102 by the tomography method, and the state of the ground 104 for each section Aij is determined therefrom.
- the present invention is not limited to this.
- the state of the ground 104 may be roughly determined from the velocity V and the attenuation rate D of the elastic wave 102 in the previous stage of the tomography method.
- the present invention uses elastic waves (including acoustic waves) to visualize the structure of the ground, including concrete structures and rocks, and the presence of local loosening, cavities, gravel, etc., in a wide range, non-destructively. It can be applied to the research method.
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Abstract
Description
AT(dB) =AWi(dB)―AWo(dB) (1)
D(dB/m)=AT(dB)/f(kHz)/L(m) (2)
減衰量=距離減衰+粘性減衰+透過減衰+散乱減衰 (3)
102…弾性波
104…地盤
104A…経路
106…ボーリング孔
112…周波数発生器
114…位相変換器
116…DA変換器
118…発信増幅器
120…発信機
124…受信機
126…受信フィルタ
128…AD変換器
130…データ記録器
132…解析装置
Claims (7)
- 弾性波を用いて地盤を非破壊で可視化して調査する地盤調査方法において、
前記地盤の既知の位置に受信機と前記弾性波を発信する発信機とを配置し、
該発信機から前記弾性波を発信させ、
該発信機から前記受信機に向かう前記地盤中の経路を伝播してきた前記弾性波を該受信機で受信し、
該伝播してきた該弾性波の減衰率と速度とを求めて、
該減衰率と速度のそれぞれに対して1つ以上の減衰率閾値と速度閾値とを設け、該減衰率閾値と速度閾値に対する該減衰率及び速度の比較により前記地盤の状態を判定することを特徴とする地盤調査方法。 - 前記地盤の状態を、前記速度に対する前記速度閾値との比較により、砂、シルト、若しくは粘性土の前記地盤の主成分の粒度の違いについて主に判定し、
更に、前記減衰率に対する前記減衰率閾値との比較により、気泡若しくは礫を含む状態から前記地盤の締まった状態までの前記地盤の飽和状態の違いについて主に判定することを特徴とする請求項1に記載の地盤調査方法。 - 前記地盤の状態を、砂、ゆるい砂、若しくは砂礫の状態と、硬い粘性土若しくは締まった砂の状態と、気泡を含む粘性土若しくは気泡を含む砂の状態と、ゆるい粘性土若しくは粘性土の状態と、に判定することを特徴とする請求項2に記載の地盤調査方法。
- 前記地盤がコンクリート又は岩盤であり、前記速度閾値により該地盤の亀裂の有無を判定し、前記減衰率閾値により該亀裂の間に存在する地盤構成媒体を判定することを特徴とする請求項1に記載の地盤調査方法。
- 前記弾性波は擬似ランダム信号で変調された単一のキャリア周波数に基づくことを特徴とする請求項1乃至4のいずれかに記載の地盤調査方法。
- 前記擬似ランダム信号と前記受信された弾性波との相関演算を行うことで、前記減衰率と速度とを求めることを特徴とする請求項1乃至5のいずれかに記載の地盤調査方法。
- 前記発信機と受信機がすべて前記地盤の内部に配置されることを特徴とする請求項1乃至6のいずれかに記載の地盤調査方法。
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JP2012252007A (ja) * | 2011-06-02 | 2012-12-20 | Schlumberger Holdings Ltd | 無効負荷を駆動するシステム、方法及び装置 |
JP2015229822A (ja) * | 2014-06-03 | 2015-12-21 | 大成建設株式会社 | 土留め構造および土留め構造の構築方法 |
JP2018194472A (ja) * | 2017-05-18 | 2018-12-06 | Jfeシビル株式会社 | 孔内プローブ並びに、これを用いた地盤の孔内検層装置及び方法 |
JP2019167726A (ja) * | 2018-03-23 | 2019-10-03 | 五洋建設株式会社 | 地盤構造推定方法 |
JP2020008368A (ja) * | 2018-07-05 | 2020-01-16 | 株式会社安藤・間 | 地山弾性波測定方法 |
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