Territory estimation method
The method calculates shear wave velocities at multiple points using depth and frequency formulas, combined with spatial interpolation, to accurately estimate the hard base depth, overcoming inaccuracies in existing methods.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- OHBAYASHI GUMI LTD
- Filing Date
- 2022-06-30
- Publication Date
- 2026-07-29
AI Technical Summary
Existing ground estimation methods struggle to accurately determine the depth of a hard base using microtremor measurements at multiple points.
A method involving the calculation of shear wave velocities at multiple points using formulas based on depth and dominant frequency, combined with spatial interpolation to estimate the depth of the hard base.
Enables accurate estimation of the hard base depth by utilizing ground information from multiple locations, even where continuous microtremor measurements are not possible.
Smart Images
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Abstract
Description
Technical Field
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[0001] The present invention relates to a ground estimation method.
Background Art
[0002] Patent Document 1 discloses a ground estimation method for estimating the depth of a hard base from the measurement results of microtremors constantly measured on the ground.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] By the way, in the ground estimation method described in Patent Document 1, when estimating the depth of the hard base by utilizing ground information such as the measurement results of microtremors constantly measured at multiple points, it has been difficult to estimate accurately.
[0005] An object of the present invention is to accurately estimate the depth of a hard base by utilizing ground information at multiple points.
Means for Solving the Problems
[0006] Some embodiments of the present invention are a ground estimation method for estimating the depth of a hard base below the ground surface, including a first shear wave velocity specifying step of obtaining a first shear wave velocity Vs1 which is the shear wave velocity at a first point, a second shear wave velocity specifying step of obtaining a second shear wave velocity Vs2 which is the shear wave velocity at a second point, and a third shear wave velocity estimating step of estimating a third shear wave velocity Vs3 which is the shear wave velocity at a third point where the depth of the hard base is not investigated, from the first shear wave velocity and the second shear wave velocity. The first shear wave velocity Vs1 is determined based on the depth H1 of the hard bedrock at the first location and the dominant frequency f1, by the formula Vs1 = 4H1 × f1. The second shear wave velocity Vs2 is determined based on the depth H2 of the hard bedrock at the second location and the dominant frequency f2, by the formula Vs2 = 4H2 × f2. The dominant frequency f3 at the third location is determined based on the H / V spectral ratio calculated from the measurement results of ambient tremors at the third location. The ground estimation method is such that the depth H3 of the hard base at the third point is obtained by H3 = Vs3 / (4×f3).
[0007] Other features of the present invention will be revealed in the specification and drawings described below. [Effects of the Invention]
[0008] According to several embodiments of the present invention, the depth of a hard bedrock can be estimated with high accuracy by utilizing ground information from multiple locations. [Brief explanation of the drawing]
[0009] [Figure 1] Figure 1 is an schematic diagram illustrating the ground estimation method of the first embodiment. [Figure 2] Figure 2 is a flowchart showing the procedure for estimating the substrate depth distribution in the first embodiment. [Figure 3] Figure 3 is an explanatory diagram showing how the dominant frequency is determined at the determination points (a to e) in the first embodiment. [Figure 4] Figure 4 is an explanatory diagram showing how the bedrock depth is measured and the shear wave velocity is calculated at the survey site (b,d) in the first embodiment. [Figure 5] Figure 5 is an explanatory diagram showing how the shear wave velocity distribution for the entire site and the bedrock depth distribution are estimated in the first embodiment. [Figure 6] Figure 6 is an explanatory diagram of the inverse distance weighting method, Figure 6A is an explanatory diagram of the target point and surrounding points, and Figure 6B is the calculation formula for the inverse distance weighting method. [Figure 7] Figure 7 shows an example of the actual bedrock depth distribution. [Figure 8] Figure 8 shows an example of the bedrock depth distribution estimated by the ground estimation method of the first embodiment. [Figure 9] Figure 9 shows an example of the bedrock depth distribution estimated using the first modified ground estimation method. [Figure 10] Figure 10 shows an example of the bedrock depth distribution estimated using the second modified ground estimation method. [Figure 11] Figure 11 is a flowchart showing the procedure for estimating the substrate depth distribution in the second embodiment. [Figure 12] FIG. 12 is an explanatory diagram showing a state in which the dominant frequency is determined at the determination points (a, c, e) and the dominant frequency distribution of the entire site is estimated in the second embodiment. [Figure 13] FIG. 13 is an explanatory diagram showing a state in which the base depth is measured at the investigation points (b, d) and the shear wave velocity is calculated in the second embodiment. [Figure 14] FIG. 14 is an explanatory diagram showing a state in which the shear wave velocity distribution of the entire site is estimated and the base depth distribution is estimated in the second embodiment.
MODE FOR CARRYING OUT THE INVENTION
[0010] From the descriptions in the specification and drawings to be described later, at least the following matters will become clear.
[0011] A ground estimation method for estimating the depth of a hard base below the ground surface, comprising: a first shear wave velocity specifying step of obtaining a first shear wave velocity Vs1 which is the shear wave velocity at a first point; a second shear wave velocity specifying step of obtaining a second shear wave velocity Vs2 which is the shear wave velocity at a second point; and a third shear wave velocity estimating step of estimating a third shear wave velocity Vs3 which is the shear wave velocity at a third point where the depth of the hard base is not investigated, from the first shear wave velocity and the second shear wave velocity. When the dominant frequency at the third point is f3, the depth H3 of the hard base at the third point is obtained by H3 = Vs3 / (4 × f3). The ground estimation method becomes clear.
[0012] According to such a ground estimation method, it is possible to accurately estimate the depth of the hard base by utilizing the ground information at a plurality of points. [[ID=2-five]]
[0013] In the ground estimation method, the third shear wave velocity Vs3 is estimated by an interpolation method.
[0014] Thereby, it is possible to accurately estimate the shear wave velocity at a point where the depth of the hard base is not investigated.
[0015] In the ground estimation method, the first shear wave velocity Vs1 is obtained by Vs1 = 4H1 × f1 based on the depth H1 of the hard base and the dominant frequency f1 at the first location, and the second shear wave velocity Vs2 is obtained by Vs2 = 4H2 × f2 based on the depth H2 of the hard base and the dominant frequency f2 at the second location.
[0016] Thereby, when estimating the depth of the hard base, ground information at a plurality of locations can be utilized.
[0017] In the ground estimation method, at least one of the dominant frequency f1 at the first location and the dominant frequency f2 at the second location is estimated by a spatial interpolation method.
[0018] Thereby, even at a location where continuous microtremor measurement cannot be performed, the dominant frequency can be estimated.
[0019] In the ground estimation method, the first shear wave velocity Vs1 and the second shear wave velocity Vs2 are obtained by PS logging respectively.
[0020] Thereby, when estimating the depth of the hard base, ground information at a plurality of locations can be utilized.
[0021] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The same or equivalent components, members, etc. shown in each drawing are denoted by the same reference numerals, and repeated explanations are omitted as appropriate.
[0022] ===First Embodiment=== FIG. 1 is a schematic explanatory diagram of the ground estimation method according to the first embodiment.
[0023] <Definition of directions, etc.> First, directions, etc. will be defined while referring to FIG. 1.
[0024] The direction parallel to the horizontal plane is defined as the "horizontal direction," and the direction perpendicular to the horizontal plane is defined as the "vertical direction." In this embodiment, as will be described later, the ground surface 2 is parallel to the horizontal plane. Therefore, in this embodiment, the "horizontal direction" is also the direction parallel to the ground surface 2, and the "vertical direction" is also the direction perpendicular to the ground surface 2. The vertical direction is sometimes also referred to as the "up and down direction."
[0025] The definitions of directions and other terms described above are also common to other embodiments of this specification unless otherwise specified.
[0026] <Overview of Ground Condition Estimation Method>
[0027] To explain the ground estimation method of this embodiment, the ground 1 that is the subject of ground estimation will be described. As shown in Figure 1, the ground 1 has a ground surface 2, a surface layer 3, and a hard base 4.
[0028] The ground surface 2 is the surface portion of the ground 1. In this embodiment, the ground surface 2 is parallel to the horizontal plane. However, the ground surface 2 does not have to be parallel to the horizontal plane. The surface ground 3 is the ground layer located immediately below (directly beneath) the ground surface 2. The hard basement 4 is the ground layer located below the surface ground 3. The hard basement 4 is the ground layer that is harder than the surface ground 3.
[0029] In the following description, the rigid foundation 4 may be simply referred to as "foundation 4". In this embodiment, the depth of the rigid foundation 4 relative to the ground surface 2 differs for each region in the horizontal direction. In this embodiment, as shown in Figure 1, the depths of the rigid foundation 4 at points a, b, c, d, and e on the ground surface 2 are Ha, Hb, Hc, Hd, and He, respectively. Note that "Hx" may refer to all depths of the rigid foundation 4 from Ha to He, or to any one of the depths of the rigid foundation 4 from Ha to He.
[0030] Here, "depth of the hard basement 4" refers to the vertical distance from the ground surface 2 to the top surface of the hard basement 4. In other words, the depth of the hard basement 4 is the thickness of the surface ground 3. In the following explanation, "depth of the hard basement 4" may be simply referred to as "basement depth" or "depth." Also, "top surface of the hard basement 4" may be simply referred to as "basement surface."
[0031] Furthermore, the statement that the depth of the hard substrate 4 "differs for each region in the horizontal direction" means that, using the depths Ha to He at points a to e shown in Figure 1, the depths Ha to He are different from each other. However, there may be points among points a to e where the depth of the hard substrate 4 is the same; for example, depth Ha and depth Hc may be equal.
[0032] Furthermore, in this embodiment, as shown in Figure 1, the shear wave velocities in the ground at points a, b, c, d, and e are Vsa, Vsb, Vsc, Vsd, and Vse, respectively. Note that "Vsx" may refer to all of the shear wave velocities Vsa to Vse, or to any one of the shear wave velocities Vsa to Vse.
[0033] Here, "shear wave velocity" refers to the propagation speed of S-waves (also called "transverse waves" or "shear waves") traveling through the ground. Shear wave velocity, along with P-wave velocity (also called "longitudinal waves" or "coarse density waves"), is one of the elastic wave velocities. Elastic wave velocities, including shear wave velocity, are intrinsic propagation velocities in an object (in this case, the ground 1) and are fundamental constants for understanding the dynamic properties of the ground 1 in this embodiment.
[0034] The shear wave velocity Vsx at each of points a to e in ground 1 can be calculated from the depth Hx of the hard bedrock 4 and the dominant frequency fx, which will be described later. Alternatively, the shear wave velocity Vsx can be measured by PS logging using boreholes.
[0035] Furthermore, in this embodiment, as shown in Figure 1, the dominant frequencies at points a, b, c, d, and e are denoted as fa, fb, fc, fd, and fe, respectively. Note that "fx" may refer to all of the dominant frequencies fa to fe, or to any one of the dominant frequencies fa to fe.
[0036] Here, "dominant frequency" refers to the natural frequency of ground 1 and is an indicator of the vibration characteristics of ground 1. Based on the dominant frequency, it is possible to estimate characteristics such as the susceptibility of ground 1 to shaking during an earthquake. The dominant frequency of ground 1 can be determined by measuring the ambient microtremors of ground 1 and analyzing the measurement results of these ambient microtremors.
[0037] More specifically, the dominant frequency can be determined by identifying the frequency at which the H / V spectral ratio (H / V spectrum) calculated from the measurement results of ambient tremors yields the highest value. The upper part of Figure 1 shows the relationship (graph) between the H / V spectral ratio and frequency at each point from point a to point e. As shown in this graph, the frequency at the peak of the H / V spectral ratio can be determined as the dominant frequency. Note that the dominant frequency may also be determined by other methods.
[0038] Here, "continuous tremors" refer to small vibrations that constantly occur in the ground. Generally, among continuous tremors, vibrations with periods shorter than 1 second are thought to be caused by artificial vibration sources resulting from human activity. On the other hand, vibrations with periods longer than 1 second are thought to be caused by natural phenomena such as waves and changes in atmospheric pressure.
[0039] When measuring ambient tremors at points a to e of ground 1, a tremor meter (not shown) is installed on the ground surface 2 at each of points a to e of ground 1. The tremor meter is connected to a computer (not shown) equipped with a memory unit for storing various data and programs, and an arithmetic processing unit for performing various calculations. Processing other than the measurement of ambient tremors is performed by the computer.
[0040] At a given location, the depth Hx of an unknown hard bedrock 4 can be estimated from the known shear wave velocity Vsx and the known dominant frequency fx at that location. According to the ground estimation method of this embodiment, as will be described later, when there are multiple locations where the shear wave velocity Vsx and dominant frequency fx are known, the depth of the hard bedrock at a location where the depth is unknown can be accurately estimated by utilizing the ground information (in this case, the shear wave velocity Vsx and dominant frequency fx) at these multiple locations. In other words, the bedrock depth distribution of the entire ground 1 can be accurately estimated by utilizing ground information from multiple locations.
[0041] In Figure 1, points a to e of the ground 1 are aligned in a single direction horizontally. However, in reality, the ground surface 2 of the ground 1 is divided into multiple grid-like sections, and the shear wave velocity Vsx is calculated and the dominant frequency fx is determined for each section. In this embodiment, as an example of these multiple sections, we take up multiple points a to e aligned in a single direction, as shown in Figure 1.
[0042] <Procedure for estimating the distribution of bedrock depth> Figure 2 is a flowchart showing the procedure for estimating the bedrock depth distribution in the first embodiment. Figure 3 is an explanatory diagram showing how the dominant frequency is determined at the determination points (a to e) in the first embodiment. Figure 4 is an explanatory diagram showing how the bedrock depth is measured and the shear wave velocity is calculated at the survey points (b, d) in the first embodiment. Figure 5 is an explanatory diagram showing how the shear wave velocity distribution for the entire site is estimated and the bedrock depth distribution is estimated in the first embodiment.
[0043] Below, as an example of the ground estimation method of this embodiment, the procedure for estimating the bedrock depth distribution of ground 1, including points a to e described above, will be explained. Here, points b and d are considered to be points where the depth of the hard bedrock 4 is known, while points a, c, and e are considered to be points where the depth of the hard bedrock 4 is unknown. That is, as will be described later, the bedrock depth at points b and d will be investigated as bedrock depth investigation points, and the bedrock depth Hb at point b and the bedrock depth Hd at point d will be used as known data. Then, using this known data, the bedrock depths at points a, c, and e, which are points where the bedrock depth has not been investigated, will be estimated. In other words, the bedrock depth distribution of ground 1 will be estimated using known data.
[0044] In the bedrock depth distribution estimation procedure of this embodiment, first, the dominant frequency fx is determined at each of points a to e of the ground 1 (S001). As described above, the dominant frequency at each of points a to e is determined by determining the frequency at which the H / V spectral ratio (H / V spectrum) calculated from the measurement results of ambient tremors takes the highest value. As a result, as shown in Figure 3, the dominant frequencies fa to fe are determined at points a to e.
[0045] Next, at the aforementioned base depth survey locations b and d, the base depth Hb at location b and the base depth Hd at location d are measured (S002). As shown in Figure 4, boreholes are formed down to the actual base surface 5 of the hard base 4, and the base depths Hb and Hd are measured.
[0046] Next, at the aforementioned bedrock depth survey points b and d, the shear wave velocity Vsb at point b and the shear wave velocity Vsd at point d are calculated (S003).
[0047] Here, if we denote the depth of the hard bedrock 4 below the ground surface 2 as H, the shear wave velocity as Vs, and the dominant frequency as f, then the bedrock depth H can be estimated using the dominant frequency f and the shear wave velocity Vs, as shown in the following equation 1.
[0048]
number
[0049] Solving equation 1 for the shear wave velocity Vs, we get the following equation 2.
[0050]
number
[0051] Therefore, using the above-mentioned Equation 2, the shear wave velocity Vsb at point b can be calculated as "4Hb × fb" using the known bedrock depth Hb and the known dominant frequency fb, as shown in Figure 4. Similarly, using the above-mentioned Equation 2, the shear wave velocity Vsd at point d can be calculated as "4Hd × fd" using the known bedrock depth Hd and the known dominant frequency fd, as shown in Figure 4.
[0052] Furthermore, the shear wave velocity Vsb at point b and the shear wave velocity Vsd at point d can also be determined by PS logging, rather than using the method described in equation 2 above. PS logging is a geophysical exploration method that uses boreholes to determine the elastic wave velocity, including the shear wave velocity, of the ground 1.
[0053] For PS logging, the down-hole method, in which a vibration source is placed near the ground surface 2 of the ground 1 and a receiver is placed inside the borehole, or the up-hole method, in which a vibration source is placed inside the borehole and a receiver is placed near the ground surface 2 of the ground 1, can be employed. Alternatively, for PS logging, the floating method may be employed, in which a device integrating a vibration source and multiple receivers is placed inside the borehole and measurements are taken continuously while changing the depth of the device without pressing it against the borehole wall.
[0054] Next, at points a, c, and e, where the bedrock depth has not been investigated, the shear wave velocity Vsa at point a, the shear wave velocity Vsc at point c, and the shear wave velocity Vse at point e are estimated (S004). As mentioned above, the bedrock depth has not been investigated at points a, c, and e, so the shear wave velocities Vsa, Vsc, and Vse cannot be determined using equation 2 described above. Therefore, in the bedrock depth distribution estimation procedure of this embodiment, the unknown shear wave velocities Vsa, Vsc, and Vse are estimated by spatial interpolation using the known shear wave velocity Vsb at point b and the known shear wave velocity Vsd at point d, as shown in Figure 5.
[0055] Spatial interpolation is a technique used to estimate unknown data surrounding observed values (in this case, unknown Vsa, Vsc, and Vse) using known data such as observed values (in this case, known Vsb and Vsd). Specifically, in the estimation procedure for the base depth distribution of this embodiment, the unknown Vsa, Vsc, and Vse are estimated using the inverse distance weighting method (IDW), which is a type of spatial interpolation method.
[0056] However, in the procedure for estimating the bedrock depth distribution, spatial interpolation methods other than inverse distance weighting, such as kriging, splines, natural neighbors, and trending, may also be used. Furthermore, in the procedure for estimating the bedrock depth distribution, spatial interpolation methods such as normal distance weighting (NDW), triangulation interpolation (TIN), and irregular triangulation networks may also be used.
[0057] Figure 6 is an explanatory diagram of the inverse distance weighting method, Figure 6A is an explanatory diagram of the target point and surrounding points, and Figure 6B is the calculation formula for the inverse distance weighting method.
[0058] In Figure 6A, points with known data (i.e., peripheral points) are represented by ● (black circles). That is, for peripheral points xi (i=0,1,···N), the value u(xi) at peripheral point xi is considered known data. In this case, the unknown value u(x) of the target point x for which we want to estimate data can be obtained according to the formula shown in Figure 6B. Here, d(x,xi) is the distance between the target point x and the peripheral point xi, and p is the weighting parameter.
[0059] Therefore, the bedrock depth distribution estimation procedure of this embodiment allows for the estimation of shear wave velocities Vsa, Vsc, and Vse at points a, c, and e, where the bedrock depth has not been investigated. In other words, the shear wave velocity distribution for the entire site of ground 1 can be estimated (S004).
[0060] Finally, in the bedrock depth distribution estimation procedure of this embodiment, the bedrock depth distribution of the entire site of ground 1 is estimated (S005). That is, at points a, c, and e, where the bedrock depth is not yet investigated, the bedrock depths Ha, Hc, and He are estimated using the formula 1 described above. Specifically, the bedrock depth Ha at point a can be determined as "Vsa / 4fa" using the estimated shear wave velocity Vsa and the known dominant frequency fb, as shown in Figure 5. Similarly, the bedrock depth Hc at point c can be determined as "Vsc / 4fc" using the estimated shear wave velocity Vsc and the known dominant frequency fc, as shown in Figure 5. Similarly, the bedrock depth He at point e can be determined as "Vse / 4fe" using the estimated shear wave velocity Vse and the known dominant frequency fe, as shown in Figure 5.
[0061] Figure 7 shows an example of the actual bedrock depth distribution. Figure 8 shows an example of the bedrock depth distribution estimated by the ground estimation method of the first embodiment. The "elevation" shown in Figures 7 and 8 corresponds to the bedrock depth.
[0062] Comparing Figures 7 and 8, it can be seen that there is no significant difference between the actual bedrock depth distribution and the estimated bedrock depth distribution, indicating that the depth of the hard bedrock can be estimated with good accuracy. In other words, the ground estimation method of this embodiment can accurately estimate the depth of the hard bedrock by utilizing ground information from multiple locations.
[0063] <Variation> Figure 9 shows an example of the bedrock depth distribution estimated using the first modified ground estimation method.
[0064] In the foundation depth distribution estimation procedure of this embodiment described above, unknown shear wave velocities Vsa, Vsc, and Vse were estimated by spatial interpolation using the known shear wave velocity Vsb at point b and the known shear wave velocity Vsd at point d (S004 in Figure 2). However, it is also possible to obtain the average shear wave velocity Vave from the known shear wave velocity Vsb and the known shear wave velocity Vsd, and use the average shear wave velocity Vsave as an estimated value of the shear wave velocity for the entire site. In other words, in the foundation depth distribution estimation procedure of the first modified example, a uniform average shear wave velocity Vsave is used as the shear wave velocity for the entire site to estimate the foundation depth Hx.
[0065] However, the average shear wave velocity Vsave may differ from the shear wave velocity Vsd at point b and the shear wave velocity Vsd at point d. Therefore, the bedrock depth H is estimated using an average shear wave velocity Vsave that differs from the actual value in Equation 1 above. Consequently, the estimated bedrock depth distribution for the entire site of ground 1 may also differ from the actual bedrock depth distribution for the entire site of ground 1.
[0066] Comparing Figures 7 and 9, there is no significant difference between the actual bedrock depth distribution and the estimated bedrock depth distribution. However, the difference is larger compared to the case using the spatial interpolation method shown in Figure 8, resulting in an unnatural distribution for large sites. Therefore, in cases where a certain degree of unnatural distribution is acceptable, or for small sites, the bedrock depth estimation procedure of the first modified example can be used to accurately estimate the depth of the hard bedrock by utilizing ground information from multiple locations.
[0067] Figure 10 shows an example of the bedrock depth distribution estimated using the second modified ground estimation method.
[0068] In the second modified example's procedure for estimating the bedrock depth distribution, the known shear wave velocity Vsb at point b and the known shear wave velocity Vsd at point d are used, while the shear wave velocity for the entire site excluding points b and d can also be taken as the average shear wave velocity Vave. In other words, in the second modified example's procedure for estimating the bedrock depth distribution, the aforementioned uniform average shear wave velocity Vsave is used as the shear wave velocity for the entire site, while the known shear wave velocities Vsb and Vsd are used to estimate the bedrock depth Hx for points b and d.
[0069] In the estimation procedure for the bedrock depth distribution of the second modified example, compared to the estimation procedure for the bedrock depth distribution of the first modified example, even if the average shear wave velocity Vsave differs from the shear wave velocity Vsd at point b and the shear wave velocity Vsd at point d, the values at points b and d can be interpolated using known shear wave velocities Vsb and Vsd.
[0070] Comparing Figures 7 and 10, there is no significant difference between the actual bedrock depth distribution and the estimated bedrock depth distribution. However, the difference is still large compared to the case using the spatial interpolation method shown in Figure 8, and in the case of large sites, the distribution becomes unnatural. Therefore, in cases where a certain degree of unnatural distribution is acceptable, or in the case of small sites, even in the second modified example, the depth of the hard bedrock can be estimated accurately by utilizing ground information from multiple locations.
[0071] ===Second Embodiment=== Figure 11 is a flowchart showing the procedure for estimating the bedrock depth distribution in the second embodiment. Figure 12 is an explanatory diagram showing how the dominant frequency is determined at the determination points (a, c, e) and the dominant frequency distribution for the entire site is estimated in the second embodiment. Figure 13 is an explanatory diagram showing how the bedrock depth is measured at the survey points (b, d) and the shear wave velocity is calculated in the second embodiment. Figure 14 is an explanatory diagram showing how the shear wave velocity distribution for the entire site is estimated and the bedrock depth distribution is estimated in the second embodiment.
[0072] In the estimation procedure for the bedrock depth distribution of the first embodiment described above, the dominant vibration frequency fx was determined at each of points a to e of the ground 1 (S001 in Figure 2). However, there are cases where ambient vibration measurements cannot be performed at points a to e of the ground 1. As in this embodiment, there are cases where, for example, a building exists at points b and d of the ground 1, making it impossible to measure ambient vibrations. For this reason, it is not possible to determine the dominant vibration frequency fx by measuring ambient vibrations at points b and d of the ground 1.
[0073] Therefore, in the substrate depth distribution estimation procedure of this embodiment, the dominant frequency fb at point b and the dominant frequency fd at point d are estimated using spatial interpolation.
[0074] In the bedrock depth distribution estimation procedure of this embodiment, first, the dominant frequency fx is determined at each of points a, c, and e of the ground 1 (S101). The dominant frequencies fa, fc, and fe at each of points a, c, and e are determined by determining the frequency at which the H / V spectral ratio (H / V spectrum) calculated from the measurement results of ambient tremors takes the highest value, as described above. As a result, the dominant frequencies fa, fc, and fe are determined at points a, c, and e, as shown in Figure 12.
[0075] Next, the dominant frequency fb at point b and the dominant frequency fd at point d are estimated using spatial interpolation (S102). Alternatively, the dominant frequency fb at point b and the dominant frequency fd at point d may be obtained by averaging the dominant frequencies fa, fc, and fe.
[0076] Next, at the aforementioned base depth survey points b and d, the base depth Hb at point b and the base depth Hd at point d are measured (S102). As shown in Figure 13, boreholes are formed up to the actual base surface 5 of the hard base 4, and the base depths Hb and Hd are measured.
[0077] Next, at the aforementioned bedrock depth survey points b and d, the shear wave velocity Vsb at point b and the shear wave velocity Vsd at point d are calculated (S103).
[0078] Therefore, using the above-mentioned Equation 2, the shear wave velocity Vsb at point b can be calculated as "4Hb × fb" using the known bedrock depth Hb and the estimated dominant frequency fb, as shown in Figure 13. Similarly, using the above-mentioned Equation 2, the shear wave velocity Vsd at point d can be calculated as "4Hd × fd" using the known bedrock depth Hd and the estimated dominant frequency fd, as shown in Figure 13.
[0079] Furthermore, the shear wave velocity Vsb at point b and the shear wave velocity Vsd at point d can also be determined by PS logging, rather than using the method described in equation 2 above.
[0080] Next, at points a, c, and e, where the bedrock depth has not yet been investigated, the shear wave velocity Vsa at point a, the shear wave velocity Vsc at point c, and the shear wave velocity Vse at point e are estimated (S104). In this embodiment, the bedrock depth distribution estimation procedure also uses the known shear wave velocity Vsb at point b and the known shear wave velocity Vsd at point d to estimate the unknown shear wave velocities Vsa, Vsc, and Vse using spatial interpolation, as shown in Figure 14.
[0081] Therefore, even with the bedrock depth distribution estimation procedure of this embodiment, the shear wave velocities Vsa, Vsc, and Vse can be estimated at points a, c, and e, where the bedrock depth has not been investigated. In other words, the shear wave velocity distribution for the entire site of ground 1 can be estimated (S104).
[0082] Finally, in the bedrock depth distribution estimation procedure of this embodiment, the bedrock depth distribution of the entire site of ground 1 is estimated (S105). That is, at points a, c, and e, where the bedrock depth is not yet investigated, the bedrock depths Ha, Hc, and He are estimated using the formula 1 described above. Specifically, the bedrock depth Ha at point a can be determined as "Vsa / 4fa" using the estimated shear wave velocity Vsa and the known dominant frequency fb, as shown in Figure 14. Similarly, the bedrock depth Hc at point c can be determined as "Vsc / 4fc" using the estimated shear wave velocity Vsc and the known dominant frequency fc, as shown in Figure 14. Similarly, the bedrock depth He at point e can be determined as "Vse / 4fe" using the estimated shear wave velocity Vse and the known dominant frequency fe, as shown in Figure 14.
[0083] ===Summary=== This is a ground estimation method for estimating the depth of the hard bedrock 4 below the ground surface 2. The ground estimation method includes a first shear wave velocity identification step to determine the first shear wave velocity Vs1 (Vsb), which is the shear wave velocity at a first point (e.g., point b). The ground estimation method also includes a second shear wave velocity identification step to determine the second shear wave velocity Vs2 (Vsd), which is the shear wave velocity at a second point (e.g., point d). The ground estimation method also includes a third shear wave velocity estimation step to estimate the third shear wave velocity Vs3 (Vsc), which is the shear wave velocity at a third point (e.g., point c), where the depth of the hard bedrock 4 is not yet investigated, from the first and second shear wave velocities. When the dominant frequency at the third point is f3 (fc), the depth H3 (Hc) of the hard bedrock 4 at the third point is determined by H3 = Vs3 / (4 × f3).
[0084] This ground estimation method allows for accurate estimation of the depth of the hard bedrock 4 by utilizing ground information from multiple locations.
[0085] In the ground estimation method, the third shear wave velocity Vs3 is estimated using spatial interpolation. This allows for accurate estimation of the shear wave velocity at locations where the depth of the hard bedrock 4 has not been investigated.
[0086] In the ground estimation method, the first shear wave velocity Vs1 is calculated based on the depth H1(Hb) and dominant frequency f1(fb) of the hard bedrock 4 at the first location using the formula Vs1 = 4H1 × f1, and the second shear wave velocity Vs2 is calculated based on the depth H2(Hd) and dominant frequency f2(fd) of the hard bedrock 4 at the second location using the formula Vs2 = 4H2 × f2. This allows for the use of ground information from multiple locations when estimating the depth of the hard bedrock 4.
[0087] In the ground condition estimation method, at least one of the dominant vibration frequency f1 at the first location and the dominant vibration frequency f2 at the second location is estimated using spatial interpolation. This makes it possible to estimate the dominant vibration frequency even at locations where ambient vibration measurements cannot be performed.
[0088] In the ground estimation method, the first shear wave velocity Vs1 and the second shear wave velocity Vs2 are determined by PS logging. This allows for the use of ground information from multiple locations when estimating the depth of the hard bedrock.
[0089] ===Other=== The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved without departing from its spirit, and it goes without saying that the present invention includes equivalents thereof. [Explanation of Symbols]
[0090] 1 ground 2 Ground surface 3 Surface ground 4. Rigid substrate (substrate) 5. Actual surface of the base 6. Estimated base surface
Claims
1. A ground estimation method for estimating the depth of the hard bedrock below the ground surface, A first shear wave velocity determination step to determine the first shear wave velocity Vs1, which is the shear wave velocity at the first point, The second shear wave velocity determination step involves determining the second shear wave velocity Vs2, which is the shear wave velocity at the second location, and A third shear wave velocity estimation step in which a third shear wave velocity Vs3, which is the shear wave velocity at a third location where the depth of the hard bedrock is not yet investigated, is estimated from the first shear wave velocity and the second shear wave velocity, It has, The first shear wave velocity Vs1 is determined based on the depth H1 of the hard bedrock at the first location and the dominant frequency f1, using the formula Vs1 = 4H1 × f1. The second shear wave velocity Vs2 is determined based on the depth H2 of the hard bedrock at the second location and the dominant frequency f2, using the formula Vs2 = 4H2 × f2. The dominant frequency f3 at the third location is determined based on the H / V spectral ratio calculated from the measurement results of ambient tremors at the said third location. The depth H3 of the hard substrate at the third location is calculated using the formula H3 = Vs3 / (4 × f3). Ground estimation method.
2. The dominant frequency f3 of the third location is determined as the frequency that takes the highest value based on the H / V spectral ratio calculated from the measurement results of ambient tremors at the third location. The ground condition estimation method according to claim 1.
3. The third shear wave velocity Vs3 is estimated using spatial interpolation. The ground condition estimation method according to claim 1.
4. At least one of the dominant frequency f1 at the first location and the dominant frequency f2 at the second location is estimated by spatial interpolation. The ground condition estimation method according to claim 1.
5. The first shear wave velocity Vs1 and the second shear wave velocity Vs2 are determined by PS logging, respectively. The ground condition estimation method according to claim 1.