JP2018017112A - Ground investigation device and ground investigation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground investigation device capable of largely reducing manhours and cost required for a ground investigation, by continuously executing a liquefaction determination and an evaluation of support performance of the ground by a physical exploration.SOLUTION: A ground investigation device 1 investigates an object ground G for executing a liquefaction determination of the ground and an evaluation of support performance, and comprises: a casing 3 penetrated into the object ground; an exciter 4 for imparting vibration to the casing; a plurality of acceleration detectors 5A and 5B arranged at an interval L on the ground surface G1 of the object ground; an arithmetic operation processing part 82 for calculating a propagation average speed based on a detection signal from the acceleration detectors; and a determination-evaluation part 83 for executing the liquefaction determination of the object ground and the evaluation of the support performance. Here, in the determination-evaluation part, the liquefaction determination is executed from a result of imparting vibration of a condition for generating liquefaction by the exciter, and the support performance is evaluated from the propagation average speed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ground investigation device that investigates a target ground in order to perform ground liquefaction determination and evaluation of support performance, and a ground investigation method that uses the ground investigation device.

  The examinations necessary for the safety of the ground basically include whether or not there is a possibility of damage due to liquefaction during an earthquake, and confirmation of support performance to prevent uneven settlement due to long-term load.

  The conventional general liquefaction judgment is based on the ground constant related to the strength of the ground by in-situ tests such as the standard penetration test for medium to large scale buildings and the Swedish sounding (SWS) test for small scale buildings. In conjunction with these tests, the groundwater level is confirmed, the soil sample is collected (sampling) using a sampling device (sampler), and the soil quality is estimated, and the soil sample collected is further detailed if necessary. This is done by analyzing the particle size test.

  As a method for determining liquefaction, Patent Document 1 discloses a converted N value from the ground constant of each soil layer obtained by conducting an SWS test at a construction site, and confirming the groundwater level together with each soil. Disclosed is a technique for estimating the soil quality (whether it is sandy soil) and determining whether it is the ground where liquefaction will occur based on the liquefaction determination chart prepared in advance according to these parameters Has been.

  Further, in Patent Document 2, a casing is inserted into the ground, a ground sample of an arbitrary soil layer is accommodated in a sleeve, and vibration acceleration corresponding to the liquefaction occurrence condition is given to the sample in the casing. A method for directly determining liquefaction is disclosed. According to such a method, it is possible to reduce the man-hours and costs required for liquefaction determination as well as to suppress variations and errors due to investigation.

  On the other hand, the examination of the support performance of the ground for a long-term load is performed based on the ground constant relating to the strength of the ground obtained by the SWS test used in the past liquefaction determination and other standard penetration tests. Here, from the viewpoint of the performance on the structural surface that supports the building, these investigation methods are destructive tests that penetrate the ground statically or dynamically, respectively. Conversion methods have been derived from many experiments and achievements, and are often used in building design.

  For these survey methods, a ground survey method by geophysical exploration that can obtain a ground constant in an elastic region equivalent to the state of actually supporting a building has also been proposed. Non-Patent Document 1 describes “velocity logging” as one of physical exploration. The ground elastic wave velocity logging method shown here uses a borehole drilled during the standard penetration test, and installed the shear wave generated by shaking the ground surface with kayak etc. in the borehole. There are a method for calculating a shear wave velocity by measuring with a geophone, and a method for calculating a shear wave velocity by inserting a device including a vibration generator and a geophone into a hole and performing measurement. These survey methods are also called “PS logging” and have many applications.

  On the other hand, in small-scale buildings, since drilling is rarely performed from the depth of the target ground, site area, or economical viewpoint, Patent Document 3 discloses a simple method of obtaining results equivalent to such velocity logging. The ground survey method by surface wave exploration as disclosed in -5 is being carried out. The investigation methods proposed in these patent documents generate shear waves with an exciter on the ground surface without excavating the ground, and measure with two acceleration detectors installed on the ground surface. The propagation average velocity is calculated from the installation interval and the arrival time difference of the generated shear wave.

  This surface wave exploration method has the advantage of being able to investigate non-destructively and directly know the hardness of the elastic region, but it is difficult to evaluate the soil quality. The problem is that we cannot make detailed examinations about fears. In Patent Document 6, a target layer for determining the necessity of liquefaction determination is specified from the obtained shear wave velocity structure, the phase velocity in the target layer, the corresponding frequency, and the shear wave corresponding to the frequency. Although it is disclosed that the soil properties of the target layer are estimated using the internal attenuation calculated from the vertical amplitude of the soil, and "necessity of liquefaction judgment" is judged, but it is calculated based on many assumptions This is a rough judgment.

  On the other hand, Patent Document 7 discloses a ground survey in which a Swedish sounding test is first performed on the ground to be investigated to determine liquefaction, and when it is determined that the ground is not liquefied, a surface wave exploration test is performed. A method is disclosed.

Japanese Patent No. 4928094 Japanese Patent No. 5526290 Japanese Patent Laid-Open No. 2002-34148 JP 2005-127760 A JP-A-9-178863 JP 2002-55090 A JP-A-2015-196966

Japan Geotechnical Society, “Ground Survey Method and Explanation (Part 1 of 2)”, March 2013, p. 98-107

  However, if the ground survey necessary for each purpose is to be performed individually, the number of man-hours and costs required for the ground survey will be required for each survey.

  Therefore, the present invention provides a ground investigation device capable of significantly reducing the man-hours and costs required for ground investigation by continuously performing liquefaction determination and evaluation of ground support performance by physical exploration, and The purpose is to provide a ground survey method to be used.

In order to achieve the above object, a ground survey device according to the present invention is a ground survey device for surveying a target ground in order to perform liquefaction judgment and evaluation of support performance of the ground, and a casing that penetrates into the target ground. A vibration exciter that vibrates the casing, a plurality of acceleration detectors arranged at intervals on the ground surface of the target ground, and a propagation average velocity based on detection signals from the acceleration detectors An arithmetic processing unit to calculate, and a determination evaluation unit that performs liquefaction determination and support performance evaluation of the target ground, and the determination evaluation unit is provided with vibration under conditions that cause liquefaction by the shaker. The liquefaction determination is performed from the result of the measurement, and the support performance is evaluated from the propagation average speed.
Here, the acceleration detector or the load detector may be arranged on a shaft portion connected to the vibration exciter or the casing.

  Further, the invention of another ground survey device is a ground survey device for surveying a target ground in order to perform ground liquefaction determination and support performance evaluation, and a casing to be penetrated into the target ground, and the casing A vibrator for applying vibration, a vibration frequency measuring unit for measuring the vibration frequency of the vibrator, an arithmetic processing unit for calculating a propagation average speed or ground rigidity from the vibration frequency, liquefaction determination of the target ground, and A determination evaluation unit that evaluates support performance, wherein the determination evaluation unit performs liquefaction determination from a result of applying vibration under conditions that cause liquefaction by the shaker, and the propagation average speed Alternatively, the support performance is evaluated from the ground rigidity.

  Furthermore, a water level sensor is attached to the front end of the casing, and when ground water is detected by the water level sensor, a vibration under a condition that causes liquefaction to be generated by the shaker may be applied. it can.

  Further, a water pressure detector is mounted in the casing, and the pore water pressure is measured by the water pressure detector while vibration is applied by the shaker. It can be set as the structure which determines with liquefaction when the conditions set to (1) are exceeded.

  Further, the determination and evaluation unit may be configured to calculate the allowable bearing force level and the estimated subsidence amount of the ground serving as an evaluation index of the ground support performance from the propagation average speed. Furthermore, the determination / evaluation unit may be configured to calculate a period of the surface layer ground and an amplification factor from the propagation average velocity.

  And the invention of the ground survey method is a ground survey method for surveying the target ground to perform liquefaction judgment and support performance evaluation of the ground using any of the ground survey devices described above, A step of penetrating the casing into the target ground, a step of giving vibration to the casing under conditions that cause liquefaction by the vibrator, and a step of measuring by the acceleration detector, the load detector or the vibration frequency measuring unit And a step of performing liquefaction determination by the determination evaluation unit, and if the result of the liquefaction determination does not determine liquefaction, the arithmetic processing unit calculates the propagation average speed and evaluates support performance. And a process.

  The ground survey device and the ground survey method of the present invention configured as described above include a vibration exciter that vibrates a casing that penetrates the target ground, and an acceleration detector that is disposed on the ground surface. Moreover, in the judgment evaluation part, the liquefaction judgment of a target ground and evaluation of support performance are performed.

  For this reason, it is possible to continuously evaluate the support performance of the ground by liquefaction determination and geophysical exploration, and it is possible to greatly reduce the man-hours and costs required for the ground survey.

  In addition, since the vibration exciter is used for both liquefaction determination and physical exploration, the cost of parts can be reduced and replacement during investigation is unnecessary. Furthermore, since both liquefaction determination and physical exploration are performed, a highly accurate ground survey result can be obtained.

  And if it is an acceleration detector arrange | positioned on the ground surface, since a general purpose accelerometer can be used, it can comprise easily. On the other hand, when the acceleration detector or the load detector is disposed on the shaft portion connected to the shaker or the casing, the ground investigation device can be easily installed and removed.

  In addition, when a vibration frequency measurement unit is provided instead of the acceleration detector, etc., by measuring the vibration frequency of the vibration exciter, the propagation average speed and ground rigidity of the target ground can be determined from the obtained vibration frequency measurement results. Can be sought. For this reason, the evaluation index regarding the support performance of the ground and the ease of shaking of the ground can be calculated from the number of vibrations.

  In addition, if a configuration is provided with a water level sensor, detailed liquefaction determination can be performed only when groundwater is detected, and liquefaction determination is simplified depending on whether or not it is deeper than the groundwater level, and an efficient investigation is performed. Can proceed.

  Furthermore, if the water pressure detector is attached in the casing and the change in excess pore water pressure at the time of applying vibration can be grasped, it is possible to determine with high accuracy whether the ground is liquefied or not. .

  In addition, the determination / evaluation unit can automatically calculate an evaluation index of the support performance of the ground, such as the allowable support strength of the ground and the estimated subsidence amount, from the propagation average speed. Furthermore, it is possible to automatically calculate an evaluation index relating to the ease of shaking of the ground during an earthquake, such as the period of the surface ground and the amplification factor.

It is explanatory drawing which showed the structure of the ground investigation apparatus of this Embodiment. It is a flowchart explaining the ground investigation method of this Embodiment. It is explanatory drawing which showed the structure of the penetration testing machine. It is explanatory drawing which showed the test condition of the upper layer of object ground. It is explanatory drawing which showed the test condition of the intermediate | middle layer of the target ground. It is explanatory drawing which showed the test condition of the lower layer of the target ground. It is a figure explaining the relationship between the period and acceleration of vibration, and seismic intensity. It is the figure which showed an example of the change of excess pore water pressure ratio. It is explanatory drawing which showed the structure of the penetration testing machine of Example 1. FIG. It is explanatory drawing which showed the test condition of the upper layer of object ground. It is explanatory drawing which showed the test condition of the intermediate | middle layer of the target ground. It is explanatory drawing which showed the test condition of the lower layer of the target ground. It is explanatory drawing which showed the structure of the penetration testing machine of Example 2. FIG. It is explanatory drawing which showed the structure of another penetration testing machine of Example 2. FIG. It is a figure explaining the utilization method of the data of the acceleration or load obtained by the ground investigation apparatus of Example 2. FIG. It is a figure explaining the frequency | count of a vibration measured with the ground investigation apparatus of Example 3. FIG. It is explanatory drawing which showed an example of the vibration analysis by a Fourier transform. It is a figure for demonstrating correlation with a frequency and a shear wave velocity (propagation average velocity).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram for explaining the configuration of the ground investigation device 1 of the present embodiment. Moreover, FIG. 2 is a flowchart explaining the process of the ground investigation method of this Embodiment.

  The ground survey device 1 of the present embodiment includes an penetration testing machine 2, acceleration detectors 5A and 5B that measure acceleration generated on the ground surface G1 of the ground G to be surveyed, a penetration testing machine 2 and an acceleration detector 5A, It is mainly configured by a control processing unit 7 of 5B and a PC unit 8 such as a personal computer for storing measurement data and performing various arithmetic processes.

  As shown in FIG. 3, the penetration testing machine 2 is mainly configured by a small excavator 21 serving as a base machine, a casing 3 that penetrates the target ground G, and a vibrator 4 that vibrates the casing 3. .

  The small excavator 21 is a mobile excavator having a simpler configuration than the boring test apparatus, and a crawler type vibro drill excavator or the like can be used. The small excavator 21 has a leader 22 attached to the tip of an arm 23, and can move the slider 24 in the vertical direction along the leader 22 standing in a column shape in the vertical direction.

  The rod 25 that is a shaft portion that can move up and down together with the slider 24 is connected to the casing 3 during the ground survey. The casing 3 is connected to a vibration exciter 4 disposed above, and the vibration of the vertical direction of an arbitrary frequency can be applied to the casing 3 by the vibration exciter 4.

  A water level sensor 61 is attached to the tip of the casing 3. Further, a water pressure detector 62 is attached to the inner space of the casing 3. For this reason, when the tip of the casing 3 enters the formation where the groundwater W exists, the water level sensor 61 detects the casing 3. Further, when ambient water enters the casing 3 and communicates with the groundwater W, the water pressure detector 62 can measure the pore water pressure in the formation.

  As shown in FIG. 1, the acceleration detectors 5A and 5B are installed at an interval L on the ground surface G1 of the target ground G to be investigated. Specifically, two acceleration detectors 5 </ b> A and 5 </ b> B are installed at a position slightly apart from the penetration testing machine 2 and separated by an interval L.

  The control processing unit 7 includes an oscillating unit 71 that controls the vibration of the vibrator 4, a measuring unit 72 that collects data from various sensors and the like, and a signal processing unit that converts the data collected by the measuring unit 72 into a signal. 73 and a communication unit 74 for performing transmission / reception with the PC unit 8.

  The oscillating unit 71 can control the acceleration and period of vibration applied to the vibrator 4. The acceleration and cycle can be arbitrarily set by the PC unit 8. Then, the acceleration and period data of the vibration actually applied by the shaker 4 is collected by the measuring unit 72.

  In the measurement unit 72, detection data of the water level sensor 61 is collected. Further, the data of the water pressure detected by the water pressure detector 62 is also collected by the measuring unit 72.

  The acceleration detectors 5A and 5B are also connected to the measuring unit 72, and the vibration of the casing 3 generated by the vibration exciter 4 propagates through the target ground G and reaches the ground surface G1, whereby the acceleration detector 5A. , 5B.

  The detection signal of the acceleration waveform detected by the acceleration detectors 5A and 5B is subjected to filter processing for noise removal in the signal processing unit 73 and transmitted as measurement data to the PC unit 8 via the communication unit 74. The

  The PC unit 8 includes a data storage unit 81, an arithmetic processing unit 82, a judgment evaluation unit 83, and the like in addition to a general computer configuration such as a communication unit (not shown). In the data storage unit 81, the measurement data collected and transmitted by the measurement unit 72 is accumulated.

  The arithmetic processing unit 82 performs various calculations based on the measurement data stored in the data storage unit 81. Further, the determination evaluation unit 83 performs liquefaction determination of the target ground G and evaluation of support performance based on the measurement data stored in the data storage unit 81 and the value calculated by the calculation processing unit 82.

  Next, a ground survey method using the ground survey device 1 of the present embodiment will be described. FIG. 2 is a flowchart for explaining the survey flow of the ground survey method of the present embodiment.

  First, in step S1, the penetration testing machine 2 is installed on the ground surface G1 of the target ground G, and the acceleration detectors 5A and 5B are installed on the ground surface G1 with an interval L (see FIGS. 1 and 4).

  The casing 3 attached to the penetration testing machine 2 is penetrated stepwise in the vertical direction according to a set measurement unit such as a unit of 25 cm or a unit of 50 cm (step S2).

  Then, when the casing 3 reaches the formation where the liquefaction determination is performed, vibration is applied by the vibration exciter 4. Here, as shown in FIG. 7, there is a certain relationship between the vibration period and the acceleration depending on the magnitude of the seismic intensity.

  For this reason, at the time of excavation for penetrating the casing 3 before the test to a desired depth, a vibration with a high frequency (for example, about 20 Hz to 50 Hz) is applied by the oscillating unit 71 so as not to be a target of earthquake motion. Thus, the casing 3 may be propelled.

  Then, as shown in FIG. 4, the investigation of the upper layer G2 of the target ground G is started. In step S3, vibration is applied to the upper layer G2 based on the magnitude of the earthquake that should be assumed when designing the area where the target ground G is located.

  For example, when building a building with medium seismic intensity of less than 6 seismic intensity as a design target value, as shown in FIG. 7, vibration of 200 gal acceleration is applied to the casing 3 by the vibrator 4 at a cycle of 0.5 sec (2 Hz). Give. The setting of the period and acceleration of the vibration to be applied is performed by the PC unit 8, and the set period and acceleration sine wave vibration is applied from the vibrator 4 to the casing 3 by the control of the oscillation unit 71.

  If the water level sensor 61 attached to the tip of the casing 3 does not detect water in the intrusion process so far, the upper layer G2 can be determined as a formation in which liquefaction below the groundwater W hardly occurs. For example, the determination / evaluation unit 83 can determine “no liquefaction” in a state in which water is not detected by the water level sensor 61 (step S4).

  On the other hand, when the casing 3 vibrates, as schematically shown in FIG. 4, the shear wave P1 propagates through the upper layer G2, and vibrations propagated by the acceleration detectors 5A and 5B installed on the ground surface G1 are detected. (Step S5).

The detection signals detected by the acceleration detectors 5A and 5B are filtered by the signal processing unit 73 and then transmitted to the PC unit 8. In step S <b> 6, the arithmetic processing unit 82 calculates the propagation average velocity V _s .

The propagation average velocity V _s can be calculated from the interval L between the two acceleration detectors 5A and 5B and the arrival time difference of the shear wave P1. And the evaluation index of the support performance of the ground of the upper layer G2 can be calculated from the calculated propagation average velocity V _s (step S7).

Below, the calculation method of the allowable bearing capacity as an evaluation index of the supporting performance of the ground will be described. The calculation formula of the allowable bearing capacity of the ground calculated based on the propagation average velocity V _s differs depending on the soil, such _as the allowable bearing capacity q _{as of} sandy ground and the allowable bearing capacity q _{ac of} the viscous ground. .

<For sandy land>
q _as = ((6.50 × 10 ^-3 ) × 0.954V _s +4.70) × β × B _F × N _γ
<In case of viscous land>
q _ac = 14.63 × 10 ^-4 × α × (0.954V _s ) ^2.2573
Here, α and β are the shape factor of the foundation, _BF is the short side width of the bottom surface of the foundation, and N _γ is the bearing force coefficient. These formulas can be derived, for example, from the bearing capacity formula of Ministry of Land, Infrastructure, Transport and Tourism Notification No. 1113 No. 2 “Method of Determining the Allowable Stress Level of the Ground”.

Furthermore, based on the propagation average velocity V _s , the estimated settlement can be calculated as an evaluation index of the support performance of the ground. Here, the estimated subsidence is an immediate subsidence S _e, there are two types of consolidation settlement amount S _d.

<Immediate settlement amount>
S _e = I _S × (1-ν _s ² ) × (q _s × B) / E '
E '= 0.0019V _s ³ + 1.34V _s ²
Here, I _S is the load level acting on the subsidence coefficient, q _s is basic, B denotes a basic bottom width.

<Consolidation settlement>
S _d = m _v × (σ + Δσ'-P _y ) × h
P _y = 98 × ((0.954V _s ) / 95) ^1.961
Here, m _v is a volume compression coefficient, σ is an effective upper pressure, Δσ ′ is an increased effective underground stress, and h is a layer thickness. These formulas can be derived from the subsidence calculation formula in the “Guidelines for Structural Design of Architectural Buildings (The Architectural Institute of Japan, 2001 edition)”.

Furthermore, it is also possible to estimate the period and the amplification factor of the upper layer G2 as the surface layers from the propagation average velocity V _s. In short, it is possible to grasp the ease of ground shaking during an earthquake.

  The ease of shaking of the ground at the time of the earthquake can be calculated as an evaluation index of the supporting performance of the ground by, for example, a method of calculating the surface layer ground amplification characteristics used in the limit strength calculation. It can also be calculated according to the “2001 calculation example of the limit yield strength calculation method and its explanation (outside the building guidance section of the Housing Bureau, Ministry of Land, Infrastructure, Transport and Tourism)”.

  After the survey of the upper layer G2 is completed, the casing 3 is inserted again, and the survey of the intermediate layer G3 of the target ground G is started as shown in FIG. Since the intermediate layer G3 is a formation deeper than the groundwater W, the water level sensor 61 attached to the tip of the casing 3 detects water during penetration, and the detection data is transmitted to the PC unit 8.

  For this reason, in the intermediate layer G3, first, liquefaction is determined (step S4). When determining liquefaction, as described in step S3, vibration is applied to the intermediate layer G3 based on an earthquake that should be assumed at the time of design.

  When vibration is applied to the intermediate layer G3 by the casing 3, in the formation where liquefaction may occur, the pore water pressure increases as shown in FIG. Since the water pressure detector 62 is attached inside the casing 3, it is possible to capture the change in the pore water pressure of the intermediate layer G3 when the vibration is applied.

  Underground stress is usually applied to the stratum, and the difference between underground stress due to overload and pore water pressure in each layer is the effective stress in the ground, but the pore water pressure is excessive. As it increases, the effective stress becomes almost zero and liquefaction occurs.

  FIG. 8 shows an example of the change in the excess pore water pressure ratio. The stage where the excess pore water pressure ratio is close to 1.0 is a state in which the effective stress has almost disappeared. That is, it is determined that the layer is a layer in which crystallization occurs.

  Accordingly, when the excess pore water pressure ratio calculated by the calculation processing unit 82 from the pore water pressure measurement data detected by the water pressure detector 62 exceeds a predetermined threshold, liquefaction occurs in step S4. It is determined that When the intermediate layer G3 having the liquefaction occurrence location GW is determined to be a liquefied layer, it is determined that effective ground reinforcement needs to be performed.

  For this reason, it is not necessary to calculate the evaluation index of the subsequent support performance of the ground for the intermediate layer G3. That is, since the support performance of the intermediate layer G3 is improved by the ground reinforcement, the calculation at this time becomes unnecessary.

  After the survey of the intermediate layer G3 is completed, the casing 3 is inserted again, and the survey of the lower layer G4 of the target ground G is started as shown in FIG. Since the lower layer G4 is also a formation deeper than the groundwater W, the determination evaluation unit 83 performs liquefaction determination.

If it is determined that liquefaction has not occurred (step S4) by performing excitation (step S3) based on the assumed earthquake condition, the acceleration detector 5A for the ground surface G1 that detects the shear wave P2 propagated through the lower layer G4. , 5B, the propagation average velocity V _s is calculated (step S6). Then, in step S7, the evaluation index of the supporting performance of the ground of the lower layer G4 is calculated from the calculated propagation average speed V _s.

  Next, the operation of the ground survey device 1 of the present embodiment and the ground survey method using the same will be described.

  The ground survey device 1 of the present embodiment configured as described above includes a vibration exciter 4 that vibrates the casing 3 that penetrates the target ground G, and acceleration detectors 5A and 5B that are disposed on the ground surface G1. It has. Moreover, in the determination evaluation part 83, liquefaction determination of the target ground G and evaluation of support performance are performed.

  For this reason, it is possible to continuously evaluate the support performance of the ground by liquefaction determination and geophysical exploration, and it is possible to greatly reduce the man-hours and costs required for the ground survey.

First, since the vibration exciter 4 is used for both liquefaction determination and physical exploration, the parts cost of the penetration tester 2 can be reduced. Furthermore, in order to perform both liquefaction determination and physical exploration during the survey, the penetration test machine 2 does not require replacement, so the number of man-hours and costs are reduced compared with the case where the survey is performed with a separate device. be able to.
Moreover, since the general-purpose accelerometer can be used if it is the acceleration detectors 5A and 5B arranged on the ground surface G1, it can be configured easily.

  And if it is the ground investigation apparatus 1 of this Embodiment, since both liquefaction determination and physical exploration are performed, multi-faceted judgment will be possible and a highly accurate ground investigation result can be obtained.

  Further, if the water level sensor 61 is attached to the tip of the casing 3, a detailed liquefaction determination based on the excess pore water pressure ratio or the like can be performed only when the groundwater W is detected. In other words, by simplifying the determination of liquefaction depending on whether it is deeper than the groundwater level, it becomes possible to investigate the formation without fear of liquefaction in a short time, and the investigation can be carried out efficiently.

  Furthermore, the water pressure detector 62 is attached in the casing 3 so that the change in the excess pore water pressure at the time of applying the vibration can be grasped, so that it is determined with high accuracy whether the ground is liquefied or not. Will be able to.

In addition, the judgment and evaluation unit 83 can automatically calculate an evaluation index of the ground support performance such as the allowable ground support strength and the estimated subsidence amount from the propagation average velocity V _s . Furthermore, the evaluation index regarding the ease of shaking of the ground at the time of the earthquake, such as the period of the surface ground and the amplification factor, can be automatically calculated by the judgment evaluation unit 83.

  Hereinafter, Example 1 of a form different from the above-described embodiment will be described with reference to FIGS. The description of the same or equivalent parts as the contents described in the above embodiment will be described with the same terms or the same reference numerals.

  In Example 1, a penetration tester 9 having a configuration different from that of the above embodiment will be described. As shown in FIG. 9, the penetration tester 9 of the first embodiment is mainly composed of an SWS tester 91 serving as a base machine, a casing 3A that penetrates the target ground G, and a vibration exciter 4A that applies vibration to the casing 3A. Configured.

  The SWS testing machine 91 is a Swedish sounding testing machine with a track record in ground surveys of small buildings. The SWS testing machine 91 includes a weight portion 92 for loading a load stepwise on a screw point used in a Swedish sounding (SWS) test.

  The casing 3 </ b> A is connected to a rod 93 that is a shaft portion of the SWS testing machine 91. Moreover, the casing 3A is connected to a vibration exciter 4A disposed above, and the vibration of the arbitrary frequency can be applied to the casing 3A by the vibration exciter 4A.

  Further, a water level sensor 61 is attached to the tip of the casing 3A. A water pressure detector 62 is attached to the inner space of the casing 3A. Note that the configurations of the acceleration detectors 5A and 5B, the control processing unit 7, and the PC unit 8 are the same as those of the penetration testing machine 2 described in the above embodiment, and thus detailed description thereof is omitted.

  Next, the ground investigation method using the ground investigation apparatus provided with the penetration testing machine 9 of the first embodiment will be described. First, in step S1, the penetration tester 9 is installed on the ground surface G1 of the target ground G, and the acceleration detectors 5A and 5B are installed on the ground surface G1 with an interval L (see FIG. 10).

  The casing 3A attached to the penetration testing machine 9 is penetrated stepwise in the vertical direction according to the measurement unit, and when the casing 3A reaches the formation where the liquefaction determination is performed, vibration is applied by the vibrator 4A. Will be.

  Here, when the SWS test is performed on the target ground G before the ground investigation by the penetration testing machine 9, the test hole can be used. At that time, a casing 3A having a diameter slightly larger than the test hole is inserted into the test hole.

  Then, as shown in FIG. 10, the investigation of the upper layer G2 of the target ground G is started. In the penetration process so far, if the water level sensor 61 attached to the tip of the casing 3A does not detect water, the determination evaluation unit 83 performs a simplified determination of “no liquefaction”.

  Subsequently, a sinusoidal vibration having a period and acceleration set by the PC unit 8 based on the magnitude of an earthquake to be assumed when designing an area with the target ground G is applied to the casing 3A by the vibration exciter 4A.

When the casing 3A vibrates, the shear wave P1 propagated through the upper layer G2 is detected by the acceleration detectors 5A and 5B and transmitted to the PC unit 8 via the control processing unit 7. Based on this measurement data, the arithmetic processing unit 82 calculates the propagation average velocity V _s .

Furthermore, from the calculated propagation average velocity V _s , an allowable bearing force level and an estimated settlement amount are calculated as an evaluation index of the supporting performance of the ground of the upper layer G2. After the investigation of the upper layer G2 is completed in this way, the casing 3A is inserted again, and the investigation of the intermediate layer G3 of the target ground G is started as shown in FIG.

  Since the intermediate layer G3 is a formation deeper than the groundwater W, the water level sensor 61 attached to the tip of the casing 3A detects water during penetration, and the detection data is transmitted to the PC unit 8.

  In the intermediate layer G3, first, the determination evaluation unit 83 determines liquefaction. If it is determined that the layer is a layer in which liquefaction occurs, the investigation of the intermediate layer G3 is finished, and the casing 3A is again penetrated toward the lower layer G4.

Subsequently, as shown in FIG. 12, the investigation of the lower layer G4 of the target ground G is started. Since this lower layer G4 is also a formation deeper than the groundwater W, the determination evaluation unit 83 performs liquefaction determination, and when it is determined that liquefaction has not occurred, the propagation average velocity V _s is calculated. Based on this, an evaluation index of the support performance of the lower layer G4 is calculated.

  Since the ground investigation device of Example 1 configured in this way constitutes the penetration tester 9 based on the SWS tester 91, it is easy to add a ground investigation on the extension line after the SWS test is performed. Can be.

In this case, since the same test hole as the SWS test can be used, penetration of the casing 3A becomes easy. Furthermore, the soil properties can be comprehensively determined together with the ground constant, which is the test result of the SWS test.
Other configurations and functions and effects are substantially the same as those of the above-described embodiment or other examples, and thus description thereof is omitted.

  Hereinafter, Example 2 of a form different from the above-described embodiment and Example 1 will be described with reference to FIGS. In addition, about the description of the part same or equivalent to the content demonstrated in the said embodiment or Example 1, it attaches | subjects and demonstrates the same term or the same code | symbol.

  In the second embodiment, the acceleration detectors 5A and 5B are not installed on the ground surface G1 as in the ground survey device 1 described in the embodiment and the first embodiment, but an acceleration detector or a load detector is used. A ground investigation device constituted by the penetration testing machines 2A and 9A provided will be described.

  First, the penetration testing machine 2A will be described with reference to FIG. The penetration testing machine 2A has the same configuration as the penetration testing machine 2 described in the above embodiment. The difference is that an acceleration detector 26 is attached to a rod 25 that is a shaft portion that connects the vibration exciter 4 or the vibration exciter 4 and the casing 3 of the penetration testing machine 2A.

  Excavation while applying vibration by the small excavator 21 means that the load test is dynamically performed on the ground, so that the same result as the test for obtaining the shear rigidity can be obtained. Therefore, by attaching an acceleration detector 26 (or load detector) to the vibration exciter 4 or the rod 25, the penetration testing machine 2A itself can measure acceleration and the like.

  When the casing 3 of the penetration testing machine 2A is dug into the target ground G while being vibrated by the vibrator 4, as shown at the left end of FIG. The intrusion will be repeated. Within the same formation, even if there is some variation, almost the same acceleration (or load) will be measured, and if the boundary is exceeded, the acceleration (or load) will also change.

  On the other hand, a state where the measured value of acceleration (or load) is close to 0 is considered to be a state where liquefaction has occurred. Therefore, when the value detected by the acceleration detector 26 is smaller than the threshold value, the determination / evaluation unit 83 can determine that the layer is a layer in which liquefaction occurs.

  Then, when the acceleration measurement data is weighted and averaged at a certain depth (for example, in units of 1 cm), as shown in the center of FIG. 15, the ground stiffness for each section (for each stratum) is calculated. It can be used as an evaluation index of support performance.

  Furthermore, since the calculated ground rigidity approximates the shear wave velocity (propagation average velocity) as shown in the right end of FIG. 15, the ground support such as the allowable bearing force and the estimated subsidence amount as described in the above embodiment is used. An evaluation index of support performance can also be calculated.

  On the other hand, the penetration tester 9A shown in FIG. 14 has the same configuration as the penetration tester 9 described in the first embodiment. The difference is that an acceleration detector 94 is attached to a rod 93 which is a shaft portion for connecting the vibrator 4A of the penetration tester 9A or the vibrator 4A and the casing 3A.

In the ground investigation device provided with the penetration testing machines 2A and 9A of Example 2 configured as described above, the acceleration detectors 26 and 94 (or load detectors) are arranged on the vibrators 4 and 4A or the rods 25 and 93, respectively. Therefore, it is not necessary to separately install the acceleration detectors 5A and 5B, and the ground survey device can be easily installed and removed.
Other configurations and functions and effects are substantially the same as those of the above-described embodiment or other examples, and thus description thereof is omitted.

  Hereinafter, Example 3 of a form different from the above-described embodiment and Examples 1 and 2 will be described with reference to FIGS. In addition, about the description of the part same or equivalent to the content demonstrated in the said embodiment or Example 1, 2, it attaches | subjects and demonstrates the same term or the same code | symbol.

  In the third embodiment, the acceleration detectors 5A and 5B are installed on the ground surface G1 as in the ground survey device 1 described in the embodiment and the first embodiment, or the acceleration detection is performed as described in the second embodiment. Rather than using a ground surveying device composed of penetration testers 2A and 9A equipped with a vibration detector or a load detector, a ground surveying device configured to measure the number of vibrations of the vibrators 4 and 4A is used. .

  In the ground investigation device, as described in the above embodiment and Examples 1 and 2, the target ground G is vibrated by the vibrators 4 and 4A. Therefore, in the third embodiment, the number of vibrations of the vibrators 4 and 4A is measured by the vibration number measuring unit.

  As the vibration frequency measurement unit for measuring the vibration frequency, for example, a device that measures vibration from signals output from the vibrators 4 and 4A can be used. In order to obtain the number of vibrations, the vibration generated per unit time can be simply read. In addition, when excavating at a constant speed, the vibration generated per unit depth can be used as the number of vibrations.

  FIG. 16 exemplifies the relationship between the load and the depth when oscillating 5 times to make a 1 cm excavation. Since the number of vibrations is a value correlated with the frequency, vibration analysis by Fourier transform can be performed as shown in FIG. Here, FA in FIG. 17 indicates a peak corresponding to the number of vibrations generated by the ground investigation device, and FB indicates the dominant frequency of the target ground G.

Here, the dominant frequency FB of the target ground G is considered to be due to the soil ground stiffness k in the affected range of the vibration and the soil weight m in the affected range. The influence range and weight of the vibration will differ depending on the soil type. In other words, it can be said that it can be determined to some extent for each soil type. That is, the ground stiffness k of the target ground G is obtained by multiplying the frequency f by the coefficient (m) for each soil.
f = (k / m) ^0.5 / 2π (1)

Further, the shear wave velocity V (propagation average velocity) obtained by the ground survey method by surface wave exploration is also a numerical value correlated with the ground stiffness k. For this reason, as shown in FIG. 18, from the correlation between the dominant frequency FB and the shear wave velocity V for each soil, the following equation replaced with the frequency f is obtained.
V = β _S · f (2)
Here, the coefficient β _S is a coefficient specified for each soil type. When the coefficient β _S of a certain soil quality was obtained based on the actually measured value, a value of β _S = 1.2 was obtained. Thus, by calculating the coefficient β _S for each soil, the propagation average velocity (V) can be directly calculated from the frequency f.

Furthermore, when the above formulas (1) and (2) are arranged, they are expressed by the following formula (3).
k = α _S · f ² (3)
Here, the coefficient α _S is a coefficient defined by the vibration influence range and the soil weight m in the influence range. In short, by setting α _S for each soil, it is possible to obtain the ground stiffness k directly from the frequency f (Hz) by the equation (3).

Then, by adjusting the coefficient α _S , the frequency f (Hz) can be simply replaced with the number of vibrations per unit time. In addition, when excavating at a constant speed, the coefficient α _S can be adjusted so that the number of vibrations per unit depth can be replaced with the frequency f.

In addition, when relative changes in ground hardness are compared in the depth direction, the coefficient α _S may be adjusted on the assumption that the load value P is multiplied in order to weight the vibration load value P. it can.

Since the ground investigation device according to the third embodiment configured as described above includes the vibration frequency measurement unit, the vibration frequency of the vibrators 4 and 4A can be measured. Then, by obtaining the propagation average speed and the ground rigidity k of the target ground G from the obtained measurement results of the number of vibrations, it is possible to calculate an evaluation index regarding the support performance of the ground and the ease of shaking of the ground.
Other configurations and functions and effects are substantially the same as those of the above-described embodiment or other examples, and thus description thereof is omitted.

  The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to this embodiment or example, and the design changes are within the scope of the present invention. Are included in the present invention.

  For example, in the above-described embodiments and examples, the configuration including the water level sensor 61 and the water pressure detector 62 has been described, but the configuration is not limited thereto. For example, when liquefaction determination is performed regardless of the presence or absence of groundwater, the water level sensor 61 can be omitted. Even if the water pressure detector 62 is omitted, it is possible to determine whether or not liquefaction has occurred from the detection results of the acceleration detectors 5A, 5B, 26, and 94.

1 Ground survey device 2 Penetration testing machine 25 Rod (shaft)
3 Casing 4 Exciters 5A, 5B Acceleration detector 61 Water level sensor 62 Water pressure detector 82 Arithmetic processing unit 83 Judgment evaluation unit 9 Penetration tester 93 Rod (shaft)
3A Casing 4A Exciter 2A, 9A Penetration testing machine 26, 94 Acceleration detector G Target ground G1 Ground surface W Groundwater L Interval
V _s propagation average speed

Claims (8)

A ground surveying device that surveys the target ground in order to perform ground liquefaction judgment and support performance evaluation,
A casing that penetrates into the target ground;
A vibrator for applying vibration to the casing;
A plurality of acceleration detectors arranged at intervals on the ground surface of the target ground;
An arithmetic processing unit that calculates a propagation average velocity based on a detection signal from the acceleration detector;
A determination evaluation unit that performs liquefaction determination and support performance evaluation of the target ground,
The determination and evaluation unit performs liquefaction determination based on a result of applying vibration under conditions that cause liquefaction by the shaker, and supports performance from the propagation average speed. Survey equipment. A ground surveying device that surveys the target ground in order to perform ground liquefaction judgment and support performance evaluation,
A casing that penetrates into the target ground;
A vibrator for applying vibration to the casing;
An acceleration detector or a load detector disposed on a shaft connected to the shaker or casing;
An arithmetic processing unit that calculates a propagation average velocity based on a detection signal from the acceleration detector or the load detector;
A determination evaluation unit that performs liquefaction determination and support performance evaluation of the target ground,
The determination and evaluation unit performs liquefaction determination based on a result of applying vibration under conditions that cause liquefaction by the shaker, and supports performance from the propagation average speed. Survey equipment. A ground surveying device that surveys the target ground in order to perform ground liquefaction judgment and support performance evaluation,
A casing that penetrates into the target ground;
A vibrator for applying vibration to the casing;
A vibration frequency measuring unit for measuring the vibration frequency of the shaker;
An arithmetic processing unit that calculates a propagation average speed or ground rigidity from the number of vibrations,
A determination evaluation unit that performs liquefaction determination and support performance evaluation of the target ground,
In the determination evaluation unit, liquefaction determination is performed from a result of applying vibration under conditions that cause liquefaction by the shaker, and support performance is evaluated from the propagation average speed or ground rigidity. Ground investigation device.   A water level sensor is attached to a tip of the casing, and when ground water is detected by the water level sensor, vibration of a condition that causes liquefaction is applied by the shaker. The ground investigation device according to any one of 1 to 3.   A water pressure detector is mounted in the casing, and the pore water pressure is measured by the water pressure detector while vibration is applied by the shaker, and the pore water pressure is arbitrarily set in the judgment and evaluation unit. The ground investigation device according to any one of claims 1 to 4, wherein the ground investigation device is determined to be liquefied when the measured condition is exceeded.   6. The determination evaluation unit calculates an allowable bearing force level and an estimated subsidence amount of the ground serving as an evaluation index of the supporting performance of the ground from the propagation average speed. 6. Ground survey equipment.   The ground evaluation device according to any one of claims 1 to 6, wherein the determination evaluation unit calculates a period and an amplification factor of the surface layer ground from the propagation average velocity. A ground survey method for surveying a target ground using the ground survey device according to any one of claims 1 to 6, in order to perform ground liquefaction determination and support performance evaluation,
Penetrating the casing into the target ground;
Providing the casing with vibrations under conditions that cause liquefaction by the vibrator;
A step of performing measurement by the acceleration detector, load detector or vibration frequency measurement unit;
Performing the liquefaction determination by the determination evaluation unit;
A ground investigation method comprising: a step of calculating the propagation average speed by the arithmetic processing unit and evaluating the support performance when the liquefaction determination does not determine liquefaction.