JP6034591B2 - Portable cone penetration test method - Google Patents

Description

  The present invention relates to a portable cone penetration test method.

  Conventionally, a portable cone penetration test method is known as an example of a penetration test for measuring ground strength (Non-Patent Document 1). This portable penetration test method is mainly applied to soft ground such as cohesive soil and humus soil, and the operator manually inserts the penetration rod with a cone at the tip of the rod statically. Penetration inside and measure the penetration resistance. The cone is penetrated at a constant speed (10 mm / s), and the value of a load meter attached to the rod is read every time a predetermined depth (100 mm) is reached. Then, the worker evaluates the ground properties based on the depth distribution diagram of the load value D.

Geotechnical Society Standard JGS1431

  However, in the portable cone penetration test method, the friction on the circumferential surface of the rod increases as the measurement depth increases. For this reason, a value higher than the original load value was measured in the deep underground, and an accurate measurement result was not obtained.

  In view of the above-described problems, an object of the present invention is to provide a portable cone penetration test method that takes into consideration the peripheral friction of the rod.

In the portable cone penetration test method, which penetrates the penetration rod with a cone at the tip of the rod into the ground at a constant speed without rotation, and measures the penetration resistance every time the measurement depth is reached,
According to the portable cone penetration test method in which the penetration resistance is measured after the penetration rod is temporarily rotated before reaching the measurement depth so that the peripheral friction of the penetration rod is uniform at all measurement depths .

  The ground property can be determined in a state where the influence of peripheral friction is removed by the portable cone penetration test method. Furthermore, it is preferable to use the Swedish sounding penetration test method in combination and determine the ground properties based on the correlation between the two measured values.

  Moreover, it is preferable that the rotation speed of the penetration rod is set in advance according to the soil quality or the measurement depth.

  Moreover, it is preferable that the rotation speed of the penetrating rod is determined based on fluctuations in rotational load torque.

  According to the portable cone penetration test method of the present invention, the penetration resistance is measured after the penetration rod is rotated before the penetration resistance measurement. In this manner, the penetration resistance of the cone can be detected with high accuracy by removing the earth and sand adhering to the circumferential surface of the rod and removing the circumferential friction.

  In addition, by analyzing the correlation between the measurement value by the portable cone penetration test method and the measurement value by the Swedish sounding penetration test method, it is possible to make a multifaceted and quantitative analysis of the ground properties without depending on the subjectivity and experience of the operator. Evaluation is possible.

  Further, since the rotational speed of the penetrating rod is set in advance according to the soil quality or measurement depth, the inherent peripheral friction is uniformly removed, and the penetration resistance of the cone can be detected.

  Further, since the rotational speed of the penetrating rod is determined based on the fluctuation of the rotational load torque of the penetrating rod, the inherent circumferential friction is more uniformly removed.

It is a perspective view of the automatic penetration testing machine which enforces the penetration testing method concerning the present invention. It is a side view of the automatic penetration testing machine which enforces the penetration testing method concerning the present invention. FIG. 3 is a partially cutaway cross-sectional view taken along line AA in FIG. It is a principal part expanded partial notch sectional view which shows the structure of the chuck | zipper of the automatic penetration test machine which implements the penetration test method which concerns on this invention. It is a figure which shows the structure of the load sensor of the automatic penetration test machine which implements the penetration test method which concerns on this invention. It is a drive system block diagram of each motor by the control unit of the automatic penetration testing machine which implements the penetration testing method concerning the present invention. It is a scatter diagram which plotted the measured value by the portable cone penetration test method and the Swedish sounding penetration test method.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes an automatic penetration testing machine that realizes the portable cone penetration testing method of the present invention. This automatic penetration testing machine 1 has a lifting platform 3 that can be moved up and down along a column 2, and this lifting platform 3 can be rotated by being driven by a weight 3 a having a predetermined weight and a rotation motor 6. A simple chuck 5 and an elevating motor 8 for elevating the elevating platform 3 are loaded. The chuck 5 holds a penetrating rod 4 having a conical cone 4b at the tip of the rod 4a, and penetrates into the ground as the elevator 3 descends.

  As shown in FIG. 2, the lifting platform 3 has a sprocket 2b that rotates along a guide chain 2a that is arranged vertically along the column 2, and this sprocket 2b rotates along the guide chain 2a. By doing so, the lifting platform 3 moves up and down. The penetrating rod 4 is loaded with a load of 1 KN by the total weight loaded on the lifting platform 3 and the lifting platform 3.

  As shown in FIG. 3, the sprocket 2 b is connected so as to rotate integrally with the transmission shaft 12 via the planetary gear mechanism 11. On the other hand, a drive gear 13 is attached to the tip of a drive shaft 8a capable of forward and reverse rotation of the elevating motor 8 so as to rotate integrally therewith, and an intermediate gear 14 and a transmission gear 15 mesh with the drive gear 13 in order. ing. Among these, the transmission gear 15 forms a hollow cylinder, and the one-way clutch 16 is press-fitted therein. The outer ring of the one-way clutch 16 rotates integrally with the transmission gear 15, and the inner ring is rotatably supported by the transmission shaft 12. When the elevating motor 8 is driven by the action of the one-way clutch 16 to rotate the sprocket 2b in the direction in which the elevating platform 3 is going to rise (for convenience, this driving is assumed to be normal rotation driving), Drive is transmitted to the transmission shaft 12. For this reason, a load determined by (load 1 KN based on the total weight of the elevator 3) − (ascending force according to the output torque of the elevator motor 8) is applied to the penetrating rod 4. On the other hand, when the elevating motor 8 is driven (for the sake of convenience, this driving is set as reverse driving), the one-way clutch 16 rotates idly. For this reason, it is possible to create a state in which the drive of the lifting motor 8 is not transmitted to the transmission shaft 12, and the penetration rod 4 is loaded with a load of 1 KN based on the total weight of the lifting platform 3.

  A rotary encoder 17 is attached to the transmission shaft 12 and outputs a pulse signal accompanying the rotation of the sprocket 2b. Then, the main control device 80 of the control unit 50, which will be described in detail later, processes the pulse signal and detects the amount of lifting and lowering speed of the lifting platform 3 to calculate the amount of penetration and the penetration speed of the penetration rod 4. .

  The elevating motor 8 is an induction motor, and is driven and controlled by an inverter control device 60 described later in detail. A main driving pulley 18 is attached to the rear end of the drive shaft 8a of the elevating motor 8 so as to be integrally rotatable. A driven pulley 19 is disposed at a position spaced from the main pulley 18 by a predetermined distance, and an endless belt 20 is wound around the pulleys 18 and 19. A rotary encoder 21 is attached to the driven pulley 19 and is configured to detect a pulse signal that accompanies the rotation of the drive shaft 8 a of the elevating motor 8.

  As shown in FIG. 4, the chuck 5 is inserted into a hollow chuck shaft 31 rotatably supported by bearings 45, 46, 47, and 48, and a machine key (not shown) is inserted into the chuck shaft 31. And a flange-type sleeve 32. The sleeve 32 is constantly biased upward by a spring 33 and is configured to be movable while sliding on the outer peripheral surface of the chuck shaft 31. On the other hand, it is configured to rotate integrally with the chuck shaft 31 in the circumferential direction. The chuck shaft 31 is provided with a storage hole that can store the steel ball 34 at a position that divides the outer periphery into three equal parts. The steel ball 34 is fitted into an engaging groove 4 c formed on the outer peripheral surface of the penetrating rod 4 to hold the penetrating rod 4. Further, the inner diameter of the upper portion of the sleeve 32 is formed to be larger than the inner diameter of the chuck shaft 31, and when the sleeve 32 is manually pushed down against the bias of the spring 33, the steel ball 34 is engaged with the penetrating rod 4. Detach from the groove 4c. In this state, when the chuck shaft 31 is rotated together with the sleeve 32 and the steel ball 34 is moved to a position where the engagement groove 4c of the penetration rod 4 is not formed, the penetration rod 4 and the chuck shaft are removed even if the hand is released from the sleeve 32. Since the engagement with 31 is released, the penetrating rod 4 can be removed.

  A rotating motor 6 is loaded on the elevator 3. The rotation motor 6 is also an induction motor, and is driven and controlled by an inverter control device 70 described later in detail. A main sprocket 36 is attached to the tip of the drive shaft 6 a of the rotation motor 6 via a one-way clutch 35. On the other hand, a driven sprocket 37 is attached to the lower end of the chuck shaft 31, and an endless chain 38 is wound around these sprockets 36, 37 to transmit the rotational drive of the motor 6 for rotation to the chuck shaft 31, thereby 4 rotates. A rotary encoder 7 is attached to the rear end of the drive shaft 6a of the rotation motor 6 and outputs a pulse signal accompanying the rotation of the drive shaft 6a. Then, the main control device 80 of the control unit 50, which will be described in detail later, processes the pulse signal and calculates the rotation speed of the penetrating rod 4.

  As shown in FIG. 5, a washer type load cell 39 is inserted into the chuck shaft 31 as an example of a load sensor. The washer-type load cell 39 includes a pressure receiving portion 41 formed on the lower surface of the sensor body 40 at equal intervals in the circumferential direction, and a support portion formed on the upper surface of the sensor body 40 at equal intervals in the circumferential direction. 42 and a strain gauge 43 attached to the sensor main body 40. With this configuration, the thrust load actually applied to the penetrating rod 4 is transmitted to the pressure receiving portion 41 via the angular ball bearings 45 and 46 and the cylindrical roller bearing 47 that support the chuck shaft 31, and the support portion 42 receives the pressure accordingly. The sensor body 40 becomes distorted with respect to the plate 44 as a fulcrum. When the strain gauge 43 detects this strain, the load applied to the penetrating rod 4 can be detected. The detection value by the washer type load cell 39 is output to the main control device 80 of the control unit 50 described later in detail.

  As shown in FIG. 6, the control unit 50 of the automatic penetration testing machine 1 includes an inverter control device 60 that drives and controls the elevating motor 8, an inverter control device 70 that drives and controls the rotation motor 6, and these inverter control devices. A main control device 80 that issues various drive commands to 60 and 70 and executes calculations based on detection values output from the rotary encoders 7 and 17 and the washer load cell 39, and a storage device in which various drive parameters are stored 90 and an I / 0 interface 100.

  The inverter control device 60 is configured as a drive system that can be used for speed control, torque control, and position control of the lifting motor 8 by a vector control method in which the rotary encoder 21 is combined with the lifting motor 8.

  Therefore, when the portable cone penetration test is performed using the automatic penetration test 1, the inverter control device 60 performs speed control. As the configuration, the converter circuit 61 converts a three-phase AC power source (not shown) to DC, and the inverter circuit 63 converts the DC voltage smoothed by the smoothing capacitor 62 into an AC voltage. The voltage and frequency are given to the lifting motor 8. Then, the arithmetic circuit 65 (MPU) executes feedback control based on the output of the rotary encoder 21, and keeps the rotational speed constant even under the influence of load fluctuations while varying the rotational speed of the elevating motor 8. Thereby, the constant speed penetration of the penetration rod 4 is realizable.

  On the other hand, when the Swedish sounding penetration test is performed using the automatic penetration test 1, the inverter control device 60 executes torque control. As its configuration, the arithmetic circuit 65 (MPU) executes feedback control of the motor current based on the output of the current detector 64 and controls the output torque of the lift motor 8 so that the lift motor 8 corresponds to the test load. The test load determined by (load 1KN based on the total weight of the lifting platform 3) − (lifting force according to the output torque of the lifting motor 8) is applied to the penetrating rod 4. The inverter control device 60 can set a speed limit value and a torque limit value, and executes drive control within a range not exceeding these set values.

  The inverter control device 70 has the same configuration as the inverter control device 60, and includes a converter circuit 71, a smoothing capacitor 72, an inverter circuit 73, a current detector 74, and an arithmetic circuit 75, and the rotary motor 7 is connected to the rotary encoder 7. By using the vector control method in combination, a drive system that can be used for speed control, torque control, and position control of the rotation motor 6 is constructed. With this configuration, the rotational speed, torque, and rotational speed of the penetrating rod 4 are driven and controlled, and the rotational load torque of the penetrating rod 4 is detected based on the load current value of the current detector 74.

The main controller 80 is configured to perform the following operations when performing a portable cone penetration test. First, a descending speed command (10 mm / s according to the Geotechnical Society standard) is issued to the inverter control device 60. Then, while monitoring the penetration depth of the penetration rod 4 with the rotary encoder 17, the detection value Qc (unit: kN) of the washer-type load cell 39 is read at every measurement depth (according to the Board Engineering Society standard). However, before the measurement depth is reached (for example, 2 mm before the measurement depth is reached), the main control device 80 issues a descent stop command to the inverter control device 60 and also removes the circumferential friction of the rod 4a. A rotation command is issued to the inverter device 70. About the rotation speed of the penetration rod 4 at this time, the optimal value obtained as a result of repeating a field test according to soil quality or measurement depth is preset. After the end of the rotation, a lowering speed command is issued again to the inverter control device 60, and the detection value Qc (unit: kN) of the washer type load cell 39 when the measurement depth is reached is read. By dividing this detected value Qc by the bottom area (unit: m ² ) of the cone 4b, the cone penetration resistance qc (unit: kN / m ² ) is calculated. When the measurement is completed to a predetermined depth, the cone penetration resistance qc for each measurement depth is displayed on a monitor or printed out.

  The rotation speed of the penetrating rod 4 at the time of the rotation command may be determined based on fluctuations in the rotational load torque of the penetrating rod 4. In this method, when it is settled at a predetermined rotational load torque or when the fluctuation of the rotational load torque becomes small, it can be estimated that the peripheral friction has been removed, and accordingly, a rotation stop command is issued. Thus, by confirming the removal of the peripheral friction, the cone penetration resistance qc can be detected more uniformly and with high accuracy.

  On the other hand, when the Swedish sounding penetration test is performed using the automatic penetration test 1, the cone 4b is replaced with a screw point (not shown). Swedish sounding penetration tests include a self-sinking penetration test and a rotary penetration test. In the self-sinking penetration test, the penetration amount of the penetration rod is measured by applying stepwise test loads of 50N, 150N, 250N, 500N, 750N, and 1KN without rotating the penetration rod 4. The main control device 80 is configured to execute the following operation when performing the self-sinking penetration test of the Swedish sounding penetration test. First, a torque command corresponding to a target test load is issued to the inverter control device 60, and feedback control based on a detection signal of the washer load cell 39 is executed. In this feedback control, a deviation between a target test load and a load actually applied to the penetrating rod is calculated, and a correction torque command value is issued to the main controller 80 based on this deviation. Thus, the main controller 80 is configured to calculate the penetration amount based on the pulse signal output from the rotary encoder 17 in a state where a target test load is applied.

  Subsequently, the rotational penetration test of the Swedish sounding penetration test measured the number of revolutions of the penetration rod required to penetrate the penetration rod at a predetermined depth (25 cm) with the maximum load (1 KN) applied to the penetration rod 4. To do. The main control device 80 is configured to execute the following operation when performing the rotation penetration test. First, a reverse drive command is issued to the inverter control device 60, and a load of 1 KN based on the total weight of the lifting platform 3 is applied to the penetrating rod 4 by idling of the one-way clutch 16. Then, a rotation command is issued to the inverter control device 70, and the rotational speed of the penetration rod 4 required to penetrate a predetermined depth (25 cm) while monitoring the penetration depth by the rotary encoder 17 is output from the rotary encoder 7. Calculate based on the signal.

With the above method, in the Swedish sounding penetration test, the number of half revolutions (Nsw) per 1 m of penetration amount at the test load (Wsw) is measured. Based on the Wsw and Nsw, the uniaxial compressive strength qu (unit: kN / m ² ) by the Swedish sounding penetration test is obtained by the following conversion formula.
qu = 45Wsw + 0.75Nsw (conversion formula)

  FIG. 7 shows the uniaxial compressive strength qu according to the Swedish sounding penetration test at the site A, the portable cone penetration test of the present invention (hereinafter sometimes referred to as rotary type) with the rotation of the rod 4a, and the rotation of the rod. The relationship with the cone penetration resistance qc by the conventional portable cone penetration test (henceforth a non-rotating type) which is not accompanied is shown by the scatter diagram. As a result of obtaining these correlations, the rotational correlation coefficient R1 was 0.680, and the non-rotational correlation coefficient R2 was 0.446. Further, when the sample correlation coefficient r1 of 18 samples by the rotary method was read from the test table (not shown), the rotary correlation coefficient R1 was larger than the significance level of 0.01%. (R1> r1). On the other hand, when the sample correlation coefficient r2 of 14 samples by the non-rotation type was read from the test table, the non-rotation type correlation coefficient R2 was smaller than the significance level of 0.01% (R2 < r2).

  From the above results, it can be seen that there is a highly significant correlation between the rotary cone penetration resistance pc and the uniaxial compressive strength qu from the Swedish sounding penetration test. On the other hand, it can be seen that there is no correlation in the non-rotating type. Therefore, the rotational type has a smaller variation in detection values than the non-rotational type, and the penetration resistance can be detected with high accuracy. However, at the other site B, there was a ground where it could be judged that “there is no correlation between the rotary cone penetration resistance pc and the uniaxial compressive strength qu by the Swedish sounding penetration test”. From this result, it can be inferred that the B site is not the ground to be inspected in the Swedish sounding penetration test and the portable cone penetration test, but other special soils. Conventionally, the determination of ground properties is a method of reading a distribution map in which measured values are recorded, and what has been left to the operator's experience is to analyze the correlation of measured values of each test as in the present invention. It becomes possible to determine the ground properties in a multifaceted and quantitative manner.

DESCRIPTION OF SYMBOLS 1 Automatic penetration test machine 2 Support | pillar 2a Guide chain 2b Sprocket 3 Elevating stand 3a Weight 4 Penetration rod 4a Rod 4b Cone 4c Engaging groove 5 Chuck 6 Motor for rotation 7 Rotary encoder 6a Drive shaft 8 Lifting motor 8a Drive shaft 11 Planetary gear Mechanism 12 Transmission shaft 13 Drive gear 14 Intermediate gear 15 Transmission gear 16 One-way clutch 17 Rotary encoder 18 Drive pulley 19 Drive pulley 20 Endless belt 21 Rotary encoder 31 Chuck shaft 32 Sleeve 33 Spring 34 Steel ball 35 One-way clutch 36 Drive sprocket 37 Drive sprocket 38 Endless chain 39 Washer type load cell 40 Load cell main body 41 Pressure receiving part 42 Supporting part 43 Strain gauge 44 Pressure receiving plate 45, 46 Angular ball bearings 47, 48 Cylindrical roller bearing 50 Control unit 60, 70 Invar Motor controller 61 or 71 converter circuits 62 and 72 smoothing capacitor 63 and 73 an inverter circuit 64, 74 a current detector 65, 75 arithmetic circuits (MPU)
80 Main controller 90 Storage device 100 I / 0 interface

Claims (4)

In the portable cone penetration test method, which penetrates the penetration rod with a cone at the tip of the rod into the ground at a constant speed without rotation, and measures the penetration resistance every time the measurement depth is reached,
A portable cone penetration test method, wherein the penetration resistance is measured after the penetration rod is temporarily rotated before reaching the measurement depth so that the circumferential friction of the penetration rod becomes uniform at all measurement depths .   2. The portable cone penetration test method according to claim 1, wherein ground properties are determined based on a correlation between a measurement value obtained by the portable cone penetration test method and a measurement value obtained by a Swedish sounding penetration test method.   3. The portable cone penetration test method according to claim 1, wherein the number of revolutions of the penetration rod is preset according to soil quality or measurement depth.   4. The portable cone penetration test method according to claim 1, wherein the number of revolutions of the penetrating rod is determined based on fluctuations in rotational load torque.

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