JPH06103247B2 - Soil test equipment - Google Patents

Description

Description: [Industrial application] The present invention relates to a soil test apparatus for inspecting a physical property of a soil sample by applying a load varying in a predetermined cycle to the soil sample.

[Prior Art] In the construction work of buildings and bridges, it is very important to grasp the physical properties of the soil at the construction site in order to secure the strength of the construction. Therefore, conventionally, a soil property inspection, that is, a soil test is performed.

In such a soil test, in addition to the inspection of the particle size and chemical composition of the collected soil sample, the physical properties such as the spring constant are also inspected. This is because, for example, in order to know the strength against shaking of a building, it is necessary to apply a predetermined pressure to the soil sample and to know how much the strain at this time is. Then, in the inspection of such physical properties, a load varying in a predetermined cycle is applied to the soil sample,
There is a liquefaction test that tests when the soil sample liquefies. This liquefaction test is considered to be very important to know the strength of buildings against earthquakes.

And, in applying the load in the conventional soil testing device,
BACKGROUND ART An air actuator is used which has a cylinder and a piston housed in the cylinder, and reciprocates a pistunt by repeatedly introducing and discharging compressed air to and from the cylinder to output a reciprocating force. This is because compressed air can be easily obtained by an air compressor or the like and can be released into the atmosphere when the pressure is released, so that the piping and handling thereof are very simple. A hydraulically driven actuator may be used instead of the air actuator, but in this case, a large pump and a return pipe are required, and there are problems such as liquid leakage.

When performing the liquefaction test, the applied load to the soil sample is detected, and the introduction and discharge of the compressed air to the air actuator of the load application unit are feedback-controlled so that the applied load fluctuates in a predetermined cycle.

[Problems to be Solved by the Invention] However, changes in properties such as liquefaction of soil occur very rapidly, and the spring constant of soil changes greatly here. Therefore,
In normal feedback control, it is not possible to follow the change in stress (applied load) that accompanies a large change in spring constant, and the applied load becomes very small in the vicinity of liquefaction. There was a problem that it could not be done.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a soil test apparatus capable of accurately applying a load in response to a sudden change in load.

[Means for Solving the Problems] In order to achieve the above object, the present invention has a soil sample holding portion for holding a soil sample, a cylinder and a piston housed in the cylinder, and compressed air to the cylinder. The piston is reciprocated by repeating the introduction and discharge of
A load application unit that outputs a reciprocating movement force and applies a load that fluctuates in a predetermined cycle to the soil sample, a load detection unit that detects the load applied to the soil sample, and a soil sample generated by the application of the load. A strain detection unit that detects strain, a spring constant calculation unit that calculates and calculates the spring constant of the soil sample from the relationship between the strain and the load, a target value of the applied load to the soil sample, and the applied load detected by the load detection unit. And the applied load control unit that controls the introduction and discharge of compressed air to and from the load application unit in consideration of the spring constant calculated by the spring constant calculation unit.

[Operation] The soil test apparatus according to the present invention has the configuration as described above, and measures the spring constant and the like while applying a predetermined vibration to the soil sample. In addition, in this measurement, the compressed air is introduced into and discharged from the load applying section in consideration of the spring constant, so that the load on the soil sample can be controlled in response to a sudden change in the property of the soil sample, Various tests can be performed.

[Embodiment] A soil test apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing the overall configuration of the soil test apparatus,
A container 12 that holds a soil sample S that is a subject is held in the casing 10. The container 12 includes a cylindrical portion 12a made of a flexible material such as a rubber film and a bottom portion 12b made of a rigid material. Then, the soil sample S is stored in the container 12 and a soil test is performed.

A pipe 20 is connected to the bottom portion 12b of the container 12, and carbon dioxide gas for deaeration and supply / discharge of pore water level are performed through the pipe 20. In addition, a back pressure system 28 for adjusting the back pressure of the soil sample is provided in the pipe 20 through a valve 22.
Are connected.

A pipe 20 on the soil sample S side of the valve 22 is connected to a pressure gauge 24 for detecting the pore water pressure during the soil test, and a pipe 20 on the outside of the valve 22 detects back pressure. A pressure gauge 26 for is connected. Therefore, the back pressure of the soil sample S can be adjusted by controlling the back pressure system 28 while monitoring the pressure gauge 26.
Here, the back pressure is adjusted by adjusting the water pressure in the sample by controlling the back pressure of the pressurized water with air after degassing the soil sample S by passing water. This back pressure adjustment is performed in the consolidation step before the rigidity test, and after the compression step, the inside of the sample is sealed with a valve.

In addition, the space around the container 12 and the inside of the casing 10 is
The water holding portion 30 is for applying a binding pressure, and the bottom plate 32 forms a donut-shaped container.

Then, the upper space of this donut-shaped water container is formed airtight, and is connected via a valve 34 to, for example, a restraint pressure system 36 that supplies compressed air so that a predetermined restraint pressure can be applied from the side of the container 12. It has become. Therefore, when performing a soil test, it is possible to apply the same back pressure and confining pressure to the soil sample as at the sampling site of a predetermined depth, and to apply the same triaxial load state as the actual state. Can be simulated and tested.

A pressure gauge 36 for detecting the restraint pressure is connected to the bottom plate 32, and this adjustment can be performed while monitoring the restraint pressure.

At the upper part of the container 12, a piston 40 for applying a predetermined load to the soil sample S is inserted and arranged. The piston 40 is connected to the load applying section 50 by a shaft 42 via a load cell 44 that detects the load. Therefore,
A predetermined load can be applied to the soil sample S while detecting the load output from the load applying unit 50. A displacement detector 46 is connected to the piston 40 so that the position of the piston 40 can be detected.

The load applying section 50 includes a cylinder section 52 formed airtightly, a piston section 54 slidably accommodated in the cylinder section 52, and a servo for switching and introducing compressed air into a space on both sides of the piston section 54 at a predetermined speed. It consists of a valve 56. Then, by the servo valve 56, both side space portions 52a, 52b in the cylinder 52 are formed.
By alternately introducing compressed air to the piston part
The piston 40 is reciprocated through the shaft 42 by reciprocating the shaft 54.

In this example, as the piston portion 54, one having large diameter pistons 54a and 54b and forming a damper chamber 58 between both pistons 54a and 54b is adopted. And the damper room 58
Is divided into two chambers by a partition wall 60 having a small opening and is filled with oil. Therefore, when the piston moves, the oil in the damper chamber 58 moves through the opening, and it is possible to prevent the occurrence of vibration in the piston portion 54 due to the resistance at this time. Also the piston
Belflams 62 for sealing are provided around 54a and 54b to keep the spaces 52a and 52b airtight.

Further, the potentiometer 70 is connected to the piston portion 54 so as to interlock with each other, and the movement distance of the piston 54 is detected by this. It should be noted that the piston 54 and the piston 40 reciprocate in the same manner, but the potentiometer 70 and the displacement detector 42 are attached thereto. This is because the potentiometer 60 detects a large displacement, the displacement detector 42 detects a small displacement, and both are combined to perform a highly accurate measurement.

The operation of the soil test apparatus of this embodiment is controlled by the controller 100. The personal computer 110 sets the operation of the controller 100. Here, the data exchange between the personal computer 110 and the controller 100 is based on the international standard interface GP.
-It is done by IB.

The controller 100 receives the data sent from the personal computer 110 and various sensors, that is, the load cell 44, the potentiometer 70, the displacement sensor 42, and the pressure gauges 26, 36, 34 according to the input of the detection result, and the back pressure system 28, the restraint. Pressure system 3
6. The servo valve 56 is controlled, and the CPU 120 performs a predetermined calculation according to the input data while using the RAM 122.

Here, the outputs from the various sensors are input to the controller 100, but are connected to amplifiers in order to amplify the output signals to a predetermined magnitude. That is, the load cell 44 is the axial load amplifier 132, the potentiometer 60 is the axial displacement (large) amplifier 134, and the displacement detector 42 is the axial displacement (small).
The amplifier 136 and the pressure gauge 26 are connected to a back pressure amplifier 138, the pressure gauge 36 is connected to a restraining pressure amplifier 140, and the pressure gauge 34 is connected to a pore water pressure amplifier 142. Then, the output signal from each sensor is input to the multiplexer 150 via each amplifier and is sequentially input to the A / D converter.
The measurement value of each sensor supplied to 160 and converted into digital data by the A / D converter 152 is supplied to the CPU 120 and the like via the data bus 124. Then, the CPU 120 performs a predetermined calculation according to these input values. Axial load amplifier 13
2. The axial displacement (large) amplifier 134 and the axial displacement (small) amplifier 136 are connected to the CPU 120 via the data bus 124 in order to adjust their zero points (auto zero gain).

On the other hand, the back pressure system 28 and the restraint pressure system 36 are the D / A converter 1
It is connected to the CPU 120 via 60, 162 and the data bus 124, and the calculation result of the CPU 120 is supplied to the back pressure system 28 and the restraint pressure system 36 via the D / A converters 160, 162. Therefore,
The back pressure system 28 and the restraint pressure system 36 can be controlled, and a predetermined back pressure and restraint pressure can be applied to the soil sample S.

The CPU 120 also controls the load applying unit 50. That is, the data from the data bus 124 is converted into analog data via the D / A converter 170, and then, the ladder circuit 172 sets the gain value to a predetermined value, and then the data is supplied to the servo amplifier 174. The output of the servo amplifier 174 is supplied to the servo valve 56, which controls the introduction and discharge of compressed air.

A displacement gauge is attached to the servo valve 56, and the detected value is supplied to the servo amplifier 174 via the displacement detection amplifier 176, thereby performing feedback control of the servo valve 56.

Here, a feature of the present invention is that the servo valve 56 controls the introduction and discharge of compressed air in the cylinder 52 so that the load output from the load cell 44 is always a constant sine wave. Is. This control is CPU1
This is done by the 20. This will be explained next.

When a predetermined load is applied to a general elastic material,
A stress (equal to the magnitude load) proportional to the displacement in the elastic material is generated as in the following equation.

F = -ky where F is stress, k is spring constant, and y is displacement. This is a so-called Hooke's law, and is an expression applied when the displacement y is in the uniaxial direction. Then, the spring constant k of the elastic material is kept constant unless the material is broken. Therefore, if the servo valve 56 is controlled and a predetermined vertical movement is applied to the soil sample S from the load applying section 50,
Displacement y, that is, stress F corresponding to the amount of strain (the same as the applied load because the forces are balanced) is generated, and this is repeated.

However, in the case of the soil sample S, the composition of the soil sample changes according to the application of such a load. In other words, the soil sample S is liquefied in a situation where the particles that have been aggregated are released from the cohesive force between the particles and are separated into individual particles. When such liquefaction occurs,
The stress with respect to the displacement y becomes extremely small. That is, the spring constant k becomes liquefied and decreases particularly rapidly. Therefore,
In such a situation where liquefaction has occurred, the output displacement in the load applying section 50 has to be made suddenly large in order to make the stress a predetermined value. Especially in the soil test where the applied load is applied in a sinusoidal manner,
It is necessary to cope with such a sudden change in output.

Therefore, in the present invention, the control in which the spring constant k of the soil sample S is taken into consideration is adopted for the control of the load applying section 50.

That is, in the CPU 120 of the controller 100, the displacement y is accurately detected from the detection values of the potentiometer 60 and the displacement detector 42, the stress F which is the detection value of the load cell 44 is divided by this displacement amount y, and the spring constant k Are being sought sequentially.

Then, as shown in FIG. 3, control is performed according to the spring constant k.

In the figure, the command value CS for the applied load is the subtractor 200
Is supplied to. The load FB detected by the load cell 44 is supplied to the subtractor 200, and the difference between the command value CS and the actually applied load FB is obtained by subtracting FB from CS.

Then, in the normal case, the control data of the servo valve 56 is only changed so as to eliminate this deviation.
In the control according to the present invention, the gain coefficient K corresponding to the spring constant k at that time is calculated, and the gain valve K is used to change the control value for the servo valve 56.

Here, this spring constant k is the change in applied load (f1-f0)
Is an absolute value k = | f1−f0 | / | y1−y0 | divided by the change in displacement (y1−y0). From this spring constant k, the gain coefficient K is the characteristic of the servo valve 56, which is the controlled device. The result obtained in consideration of is calculated from a table stored in advance. The multiplier 202 multiplies (CS-FB), which is the output value of the subtractor 200, by the gain coefficient K.

In this way, proportional control according to the difference between the control value CS and the actual applied load FB can be performed, but in this example, the control accuracy is improved, the offset is reduced, and it is stabilized. A multiplier 204 is provided to add control and perform so-called PI control. Then, the result obtained at each control time obtained in the multiplier 204 is added to the adder 206.
And the control value u for the servo valve 56 is obtained.

That is, in the adder 204, the calculation of Δu = Δu + (ΔT / TS) · (CS-FB) is performed, and the value of the deviation for each control time ΔT is added to the entire Δu to calculate a new Δu. ing.

The output value u output from the adder 206 is u = K (CS-FB) + Δu.

Therefore, in this embodiment, the servo valve 56 can be controlled by using the gain coefficient K corresponding to the spring constant k of the soil sample S, and the sudden change of the spring constant k of the soil sample S can be dealt with. It is possible to apply a desired load.

Here, in the control considering the above-mentioned spring constant k,
Change in applied load f (stress) (f1-f0) and displacement y
When the change in (distortion amount) (y1-y0) is very small,
The true spring constant k cannot be obtained due to noise inevitably generated in the detector. For this reason, if the spring constant k that deviates from the true spring constant k is used for control, the applied load is rather controlled and the deviation with respect to the command signal CS becomes large. Therefore, it is better to set a desired limit for the control considering the spring constant k.

That is, when the noise amount Δf for the applied load and the noise amount Δy for the displacement are set, deviations (f1−f0), (y1) are set in order to prevent the calculated spring constant from being greatly deviated from the actual spring constant. If -y0) does not exceed a certain value, control by spring constant calculation is not performed. That is, α and β are defined separately, and control is not performed when the following deviation is small.

f1−f0 <αΔf y1−y0 <βΔy When the displacement y is very small, it often occurs especially at the beginning of the test.

Further, in order to reduce the influence of noise in the detector, in the range where the response of the control system described above is not significantly affected,
A moving average filter may be applied to the output value of the detector to smooth the output value of the detector to some extent.

As described above, according to the apparatus of this embodiment, since the control is performed in consideration of the spring constant as described above, even when the spring constant k of the soil sample S is greatly changed, the command value for the applied load is set. It is possible to apply a load to the soil sample S according to CS.

Further, in the case of control in such a test in which the soil sample S has a large change, there are cases where sufficient control cannot be performed only by control in which the spring constant k is considered. Therefore, if observer control is performed, this can be further improved.

That is, since the change in the state of the soil sample S can be predicted to some extent, a model corresponding to this is made,
Here, the simulation is always performed in consideration of the change of the spring constant k. Then, if the gain or the like in the control system is changed according to the result obtained by this simulation, it becomes possible to follow even a very large change.

Next, an example procedure of an actual soil test will be described based on FIG.

First, the soil sample S is set in the container 12 (S1). Then, the soil sample S is subjected to preliminary consolidation (S2). If necessary, the soil sample S is melted (S3). This is because the ordinary soil sample S is preserved while being frozen and retaining its physical properties.

Next, through a pipe 20, carbon dioxide (CO ₂ ) was added to the soil sample S.
To remove air such as oxygen and nitrogen in the soil sample (S4). When such deaeration is finished, deaerated water is supplied to the soil sample S through the pipe 20 to remove the soil sample S.
After washing with water, the pores in the soil sample are filled with water (S5).

Then, the back pressure from the back pressure system 28 is applied (S6), and it is confirmed whether the B value (B value is the amount of change in pore water pressure divided by the amount of change in restraint pressure) at this time is more than a predetermined value. Yes (S7, S
8). In this example, it is confirmed that the B value is 0.95 or more.

Next, a constraint pressure is applied to the soil sample S from the constraint pressure application system 36 (S9). Then, after the soil sample S is subjected to a predetermined compaction (S10, S11), it is confirmed whether the B value at that time is equal to or more than a predetermined value, and the test proceeds (S12, S13).

In this way, when the soil sample S is ready, a rigidity test is conducted, which controls the strain (displacement) y and the stress (load) f (S21, S22) while maintaining a predetermined load f.
Is applied to the soil sample S (S23). Then, the spring constant k can be obtained from the relationship between the load f and the strain y at this time, and the rigidity test is achieved. If necessary, the conditions are changed and the rigidity test is further conducted (S24).

When the rigidity test is completed, the next test is performed.

When the rigidity test is completed, a liquefaction test is subsequently performed. In this case, while applying a predetermined sine curve load (S31), it is detected how many times the load has been applied before liquefaction. Whether or not the liquid has liquefied is determined by the stress strain y becoming sufficiently large (S3
1). For example, liquefaction is judged when the stress strain reaches 1%, 5%, 10%, etc. This value depends on the test conditions and is 12% MAX. When the time of liquefaction is measured in this way, the liquefaction test is completed (S3
3). Further, when the load application reaches 1000 times, it is determined that the liquid is not liquefied and the process is forcibly ended (S34).

In this way, a soil test can be performed.

[Effects of the Invention] As described above, according to the soil test apparatus of the present invention, the introduction and discharge of the compressed air to the load application unit is changed and controlled according to the spring constant of the soil sample. Even when the physical properties of the soil change suddenly, the control corresponding to this can be performed and an accurate soil test can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of a soil test apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a controller 100 for controlling the load application unit 50 in the same embodiment, FIG. 3 is a block diagram for explaining the function of the controller 100 in the same embodiment, and FIG. 4 is a flow chart diagram for explaining the test procedure in the same embodiment. 12 ... Container (soil sample holding part) 42 ... Displacement sensor (displacement detecting part) 50 ... Load applying part 52 ... Cylinder 54 ... Piston 56 ... Servo valve 44 ... Load cell (load detecting part) 100 ... Controller S ... Sat sample

Claims (1)

[Claims] 1. In a soil test apparatus for inspecting the physical properties of a soil sample by applying a load that fluctuates in a predetermined cycle to the soil sample, a soil sample holding section for holding the soil sample, and a cylinder and a cylinder are housed in the cylinder. And a load applying section that reciprocates the piston by repeating the introduction and discharge of compressed air to and from the cylinder to output a reciprocating movement force and apply a load that fluctuates in a predetermined cycle to the soil sample. , Load detection unit that detects the load applied to the soil sample, strain detection unit that detects the strain of the soil sample caused by the load application, and calculate the spring constant of the soil sample from the relationship between strain and load The spring constant calculation unit compares the target value of the applied load on the soil sample with the applied load detected by the load detection unit, and the calculated value is calculated by the spring constant calculation unit. Soil test apparatus characterized by having a applied load controller for controlling the introduction discharge of compressed air to the load application part in consideration of the spring constant was.