A vibration level real-time evaluation device and method based on microseismic sensor installation

Abstract

The present application relates to the technical field of geotechnical engineering microseismic monitoring, in particular to a vibration level real-time evaluation device and method based on microseismic sensor installation, which comprises a monitoring main mechanism, a real-time evaluation mechanism and a hole collapse prediction mechanism, the hole collapse prediction mechanism comprises a rock debris collection net, a real-time weighing device, a rock debris loading box, a weight display table and a collection net support rod; the rock debris collection net is used to collect the rock debris falling under the influence of vibration, and the rock debris falls in the rock debris loading box through the rock debris falling holes in sequence, and finally falls in the real-time weighing device for weighing, the weight display table displays the weight weighed by the real-time weighing device in real time, and transmits the weight to the monitoring main mechanism for recording and analysis, and the collection net support rod is used to support the rock debris collection net; the device can predict and warn the hole collapse probability, can reduce the monitoring cost, can avoid burying the sensor in the rock mass caused by the hole collapse due to vibration, can ensure that the microseismic monitoring sensor can work continuously, and can improve the microseismic monitoring and early warning quality.

Description

Technical Field

[0001] This invention relates to the field of microseismic monitoring technology in geotechnical engineering, and in particular to a device and method for real-time assessment of vibration levels based on the installation of microseismic sensors. Background Technology

[0002] Against the backdrop of my country's high-quality economic development and the construction of a modern and powerful nation, the surface space occupied by various engineering projects can no longer fully meet the needs of production, daily life, and economic development. Seeking space in deeper underground areas has become a major trend. With the increasing number and depth of underground engineering operations such as tunnels and mining, microseismic activity induced by ground stress is becoming more active, leading to frequent dynamic disasters such as water inrush and rock bursts, posing a huge threat and hidden danger to the safety of workers and the healthy development of the economy.

[0003] Microseismic monitoring technology, based on acoustic emission and seismology, is a novel geophysical exploration technology that monitors and locates the occurrence and development of seismic source activity, analyzes, evaluates, and provides early warning of the dynamic effects on the monitored body. Microseismic monitoring technology features rapid response, high resolution, high sensitivity, long monitoring distance, three-dimensional operation, and real-time monitoring. It is now widely used in deep rock engineering, geotechnical engineering, mining engineering, and water conservancy engineering, and is one of the most effective means of disaster prevention and early warning in underground engineering projects such as tunnels and mining.

[0004] In the process of microseismic monitoring and early warning, the first step is to install sensors. The typical installation steps are as follows: connect the cable between the sensor and the data acquisition system; drill a hole at the sensor's installation location using a pneumatic drill rig; the purpose of installing an accelerometer inside the hole is to reduce the impact of environmental noise on the effective signal during construction; prepare the sensor, quickly insert it into the bottom of the hole using an installation rod, and remove the installation rod after it is firmly bonded to the original rock at the bottom of the hole with quick-setting cement. However, disturbances to the rock mass caused by blasting, rockbursts, and mechanical vibrations often induce the collapse of the sensor installation hole, burying the sensor within the rock mass and making it difficult to retrieve. This increases monitoring costs, interrupts continuous monitoring, and affects disaster monitoring and early warning. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for real-time evaluation of vibration levels based on the installation of microseismic sensors, aiming to solve the problem that existing microseismic monitoring technologies are prone to borehole collapse due to vibration.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a vibration level real-time assessment device based on microseismic sensors, comprising a monitoring main body, a real-time assessment mechanism, and a borehole collapse prediction mechanism. The monitoring main body is connected to the real-time assessment mechanism and the borehole collapse prediction mechanism, respectively. The borehole collapse prediction mechanism includes a rock cuttings collection net, a real-time weighing device, a cuttings box, a weight display table, and a collection net support rod.

[0007] The chip collection box is located at the bottom of the rock chip collection net, the real-time weighing device is located at the bottom of the chip collection box, the weight display is connected to the real-time weighing device, the collection net support rod is located on the side of the rock chip collection net near the real-time weighing device, and the rock chip collection net has rock chip drop holes.

[0008] The number of the real-time weighing device, the chip box, and the weight display table are evenly distributed in three.

[0009] The monitoring main body includes a sensor, quick-acting cement, a signal receiving probe, a hanging nail, a drilling baffle, and a mounting rod. The sensor is connected to the signal receiving probe and the mounting rod respectively. The sensor has a sensor mounting hole. The quick-acting cement is placed inside the sensor mounting hole. The hanging nail is placed on one side of the sensor. The drilling baffle is placed outside the sensor mounting hole.

[0010] The real-time assessment mechanism includes a vibration sensing probe, a vibration measurement unit, an LCD screen, a data transmission line, and a computer. The vibration sensing probe is connected to the sensor and the fast-acting cement. The vibration measurement unit is connected to the sensor and the LCD screen. The data transmission line is connected to the computer, the vibration sensing probe, the vibration measurement unit, the LCD screen, the sensor, and the weight display.

[0011] Secondly, the present invention also provides a method for real-time assessment of vibration levels based on the installation of microseismic sensors, comprising the following steps:

[0012] S1 connects and installs the main monitoring unit, the real-time assessment unit, and the hole collapse prediction unit;

[0013] S2 microseismic signals are collected in real time by the main monitoring agency; the collected information is then transmitted to the real-time assessment agency to observe the spatiotemporal evolution and conduct disaster early warning.

[0014] When high-level vibrations such as blasting, rock bursts, and mechanical vibrations occur, the monitoring main unit collects the vibration level and time, and transmits it to the real-time assessment unit to analyze the spatiotemporal evolution law, the cumulative law of vibration level, and the cumulative change law of rock in the borehole, and predicts the probability of borehole collapse and the probability of disaster.

[0015] This invention discloses a real-time vibration level assessment device based on a microseismic sensor. A rock debris collection net collects rock fragments that fall due to vibration. The rock fragments fall onto the collection net, slide through the rock debris drop holes into a debris collection box, and finally fall into a real-time weighing device below for weighing. A weight display shows the weight measured by the real-time weighing device in real time and transmits it to the monitoring main mechanism for recording and analysis. A collection net support rod supports the rock debris collection net, ensuring it has a certain tilt angle to allow rock debris to slide onto the collection net and into the rock debris drop holes. Through the combined use of the real-time assessment mechanism and the borehole collapse prediction mechanism, this device can predict and warn of borehole collapse probability, reduce monitoring costs, prevent vibration-induced borehole collapse from burying the sensor in the rock mass, ensure continuous operation of the microseismic monitoring sensor, improve the quality of microseismic monitoring and early warning, and solve the problem of existing microseismic monitoring technologies being prone to borehole collapse due to vibration. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a real-time vibration level assessment device based on the installation of microseismic sensors provided by the present invention.

[0018] Figure 2 This is a front view of a vibration level real-time assessment device based on microseismic sensor installation provided by the present invention.

[0019] Figure 3 This is a flowchart of a real-time vibration level assessment method based on the installation of microseismic sensors provided by the present invention.

[0020] In the diagram: 1-Sensor, 2-Sensor mounting hole, 3-Quick-acting cement, 4-Signal receiving probe, 5-Surrounding rock, 6-Hanging nail, 7-Drilling baffle, 8-Mounting rod, 9-Vibration sensing probe, 10-Vibration measurement unit, 11-LCD display screen, 12-Data transmission line, 13-Computer, 14-Cutter cuttings collection net, 15-Cutter cuttings, 16-Real-time weighing device, 17-Cutter cuttings box, 18-Weight display, 19-Cutter cuttings drop hole, 20-Collection net support rod. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] Please see Figures 1 to 2 In a first aspect, the present invention provides a vibration level real-time assessment device based on microseismic sensor installation, including a monitoring main body, a real-time assessment mechanism and a hole collapse prediction mechanism. The monitoring main body is connected to the real-time assessment mechanism and the hole collapse prediction mechanism respectively. The hole collapse prediction mechanism includes a rock cuttings collection net 14, a real-time weighing device 16, a cuttings box 17, a weight display table 18 and a collection net support rod 20.

[0023] The chip collection box 17 is located at the bottom of the rock chip collection net 14, the real-time weighing device 16 is located at the bottom of the chip collection box 17, the weight display table 18 is connected to the real-time weighing device 16, the collection net support rod 20 is located on the side of the rock chip collection net 14 near the real-time weighing device 16, and the rock chip collection net 14 has rock chip drop holes 19.

[0024] In this embodiment, the number of the real-time weighing device 16, the chip collection box 17, and the weight display table 18 are evenly distributed in threes. The rock chips 15 are mainly rock fragments that fall into the sensor mounting hole 2 due to vibration. Based on the weight change trend of the rock chips 15 and the historical vibration level change process recorded in the sensor mounting hole 2, the collapse of the sensor mounting hole 2 is predicted in real time. The weight change trend of the rock chips 15 refers to the change trend of the three chip collection boxes 17 (G1+G2+G3). The rock chip collection net 14 is used to collect the rock chips that fall due to vibration. The rock chips fall onto the rock chip collection net 14, and after passing through the rock chip drop hole 19, they slide sequentially into the chip collection box 17, and finally fall onto the real-time weighing device below. The weighing device 16 is used to weigh the rock cuttings. The weight display table 18 is used to display the weight weighed by the real-time weighing device 16 in real time and transmit it to the monitoring main body for recording and analysis. The collection net support rod 20 is used to support the rock cuttings collection net 14 and ensure that the rock cuttings collection net 14 has a certain tilt angle so that the rock cuttings 15 can slide off the rock cuttings collection net 14 into the rock cuttings falling hole 19. Through the combined use of the real-time evaluation mechanism and the hole collapse prediction mechanism, this device can predict and warn of the probability of hole collapse, reduce monitoring costs, avoid hole collapse caused by vibration, bury the sensor 1 in the rock body, ensure that the microseismic monitoring sensor can work continuously, improve the quality of microseismic monitoring and early warning, and solve the problem of existing microseismic monitoring technology being prone to hole collapse due to vibration.

[0025] Furthermore, the monitoring main body includes a sensor 1, quick-acting cement 3, a signal receiving probe 4, a hanging nail 6, a drilling baffle 7, and a mounting rod 8. The sensor 1 is connected to the signal receiving probe 4 and the mounting rod 8 respectively. The sensor 1 has a sensor mounting hole 2. The quick-acting cement 3 is disposed in the sensor mounting hole 2. The hanging nail 6 is disposed on one side of the sensor 1. The drilling baffle 7 is disposed on the outside of the sensor mounting hole 2.

[0026] In this embodiment, the sensor 1 is used to collect vibration signals such as micro-vibrations. Excavation disturbs the rock mass, generating micro-fractures accompanied by elastic waves; this signal is also called a micro-vibration signal. The micro-vibration signal is collected by the sensor 1. The upper end of the sensor 1 is connected to the signal receiving probe 4 and the vibration sensing probe 9, the lower end is connected to the mounting rod 8 and the data transmission line 12, and the right side is connected to the vibration measurement unit 10. The sensor mounting hole 2 is drilled at the location where the sensor 1 will be installed using a pneumatic drill, mainly for installing the sensor 1. The sensor mounting hole 2 requires an elevation angle of about 10° to prevent water from entering the bottom of the hole and affecting the operation of the sensor 1, and the length of the drilled hole is not less than 1 meter. The quick-acting cement 3 is mainly used to attach the sensor 1 to the surrounding rock 5 at the bottom of the sensor mounting hole 2. The signal receiving probe 4 is used to receive the micro-vibration signal and transmit the micro-vibration signal to the sensor 1. One end of the signal receiving probe 4 is connected to the... Sensor 1 is connected, with the other end buried in the quick-acting cement 3. The surrounding rock 5 is affected by excavation disturbance, causing localized stress concentration and generating micro-vibration signals. These micro-vibration signals are collected by sensor 1 within the sensor mounting hole 2. The hanging nail 6 is on the surrounding rock 5 outside the sensor mounting hole 2, used to hang the drilling baffle 7. The drilling baffle 7 blocks the sensor mounting hole 2, reducing construction noise interference with sensor 1 and preventing water or rock fragments from the surface of the surrounding rock 5 from entering the sensor mounting hole 2 and interfering with the sensor 1's collection of micro-vibration signals. The mounting rod 8 is used to install and remove sensor 1. During installation, sensor 1 is placed in the corresponding position within the sensor mounting hole 2; during removal, the mounting rod 8 is directly screwed on. One end of the mounting rod 8 is connected to sensor 1, and the other end passes through the drilling baffle 7 outside the sensor mounting hole 2. The mounting rod 8 has extension and retraction functions.

[0027] Furthermore, the real-time evaluation mechanism includes a vibration sensing probe 9, a vibration measurement unit 10, an LCD screen 11, a data transmission line 12, and a computer 13. The vibration sensing probe 9 is connected to the sensor 1 and the fast-acting cement 3. The vibration measurement unit 10 is connected to the sensor 1 and the LCD screen 11. The data transmission line 12 is connected to the computer 13, the vibration sensing probe 9, the vibration measurement unit 10, the LCD screen 11, the sensor 1, and the weight display table 18.

[0028] In this embodiment, the vibration sensing probe 9 is used to sense vibration and transmit the vibration signal to the vibration measurement unit 10 through the data transmission line 12. One end of the vibration sensing probe 9 is connected to the sensor 1, and the other end is buried in the quick-acting cement 3. The right side is connected to the data transmission line 12. The vibration measurement unit 10 is used to measure the vibration level. One end is connected to the vibration sensing probe 9 through the data transmission line 12, and the other end is connected to the LCD screen 11 through the data transmission line 12. The left side of the vibration measurement unit 10 is attached to the sensor 1. The LCD screen 11 displays the vibration level measured by the vibration measurement unit 10 in real time. The LCD screen 11 is attached to the borehole baffle 7. The data transmission line 12 is used to transmit signals. The computer 13 is used to record and analyze data in real time, such as recording and analyzing the mass of rock cuttings 15, recording and analyzing micro-vibration signals, recording and analyzing vibration levels, etc. The computer 13 is connected to the weight display 18, the sensor 1, and the LCD screen 11 through the data transmission line 12, and the computer 13 is placed in a safe location tens or hundreds of meters away from the construction site, unaffected by construction.

[0029] Please see Figure 3 Secondly, the present invention also provides a method for real-time assessment of vibration levels based on the installation of microseismic sensors, comprising the following steps:

[0030] S1 connects and installs the main monitoring unit, the real-time assessment unit, and the hole collapse prediction unit;

[0031] Specifically, a drilling rig is used to drill the sensor mounting hole 2 at the location where the sensor 1 is to be installed. The sensor mounting hole 2 is at least 1 meter deep and has a certain tilt angle to prevent water from accumulating at the bottom of the sensor mounting hole 2, which would affect the acoustic emission signal monitoring.

[0032] Three real-time weighing devices 16 and chip collection boxes 17 are connected to each other and placed at the bottom of the sensor mounting hole 2. The three chip collection boxes 17 are in contact with each other to prevent rock chips 15 from falling and thus preventing weighing. Rock chip falling holes 19 are reserved at corresponding positions on the rock chip collection net 14, and the collection net support rod 20 is connected to the bottom of the rock chip collection net 14. The rock chip collection net 14 and the collection net support rod 20 are placed into the sensor mounting hole 2. The rock chip collection net 14 forms a triangle in the sensor mounting hole 2, and the top is connected to the top of the sensor mounting hole 2. The lower part is connected to the bottom sides of the sensor mounting hole 2 by the collection net support rod 20; rock cuttings 15 can slide from top to bottom through the rock cuttings collection net 14 and fall into the cuttings box 17 through the rock cuttings drop hole 19, and then enter the real-time weighing device 16 for weighing. The weighing result is transmitted to the weight display table 18 through the data transmission line 12 to display the weight in real time, and further transmitted to the computer 13 through the data transmission line 12 for data recording and analysis. If the weight G1+G2+G3 of the rock cuttings 15 suddenly increases in a short period of time, the probability of hole collapse increases.

[0033] After preparing the sensor mounting hole 2 and the hole collapse prediction module, begin preparing the sensor 1. Install the signal receiving probe 4 and the vibration sensing probe 9 on the top of the sensor 1. Connect the mounting rod 8 to the bottom of the sensor 1. Attach the vibration measurement unit 10 to the right side of the sensor 1. Use the data transmission cable 12 to connect the vibration sensing probe 9, the vibration measurement unit 10, the LCD screen 11, and the computer 13 in sequence, and connect the sensor 1 and the computer 13 using the data transmission cable 12. At this point, the sensor 1 is ready. Attach the quick-acting cement 3 to the top of the sensor 1, and wrap it around the signal receiving probe 4 and the vibration sensing probe 9. Use the mounting rod 8 to insert the sensor 1, the signal receiving probe 4, the vibration sensing probe 9, the vibration measurement unit 10, and the data transmission cable 12 together into the sensor mounting hole 2, and bring the quick-acting cement 3 to the bottom of the sensor mounting hole 2 until the quick-acting cement 3 solidifies. After the quick-acting cement 3 solidifies, the sensor 1 is installed. The hanging nail 6 is fixed on the surrounding rock 5 above the outside of the sensor mounting hole 2, and the drilling baffle 7 is used to block the sensor mounting hole 2. On the one hand, it can reduce the interference of construction noise on the sensor 1, and on the other hand, it can prevent water or rock fragments generated during construction from entering the sensor mounting hole 2 and interfering with the sensor 1 in collecting micro-vibration signals.

[0034] S2 microseismic signals are collected in real time by the main monitoring agency; the collected information is then transmitted to the real-time assessment agency to observe the spatiotemporal evolution and conduct disaster early warning.

[0035] Specifically, when the surrounding rock 5 is disturbed by construction, microseismic signals are generated inside, and these signals propagate to the surrounding area. When the signals reach the vicinity of the signal receiving probe 4, they are collected by the probe and transmitted to the sensor 1. The sensor 1 then transmits the microseismic signals to the computer 13 via the data transmission line 12, analyzes the spatiotemporal evolution of the microseismic signals, and provides early warning of potential disasters.

[0036] When high-level vibrations such as blasting, rock bursts, and mechanical vibrations occur, the monitoring main unit collects the vibration level and time, and transmits it to the real-time assessment unit to analyze the spatiotemporal evolution law, the cumulative law of vibration level, and the cumulative change law of rock in the borehole, and predicts the probability of borehole collapse and the probability of disaster.

[0037] Specifically, when high-level vibrations such as blasting, rock bursts, or mechanical vibrations occur, the vibration sensing probe 9 embedded in the quick-acting cement 3 collects vibration signals and transmits them to the vibration measurement unit 10 via the data transmission line 12. The vibration measurement unit 10 analyzes the vibration level and then transmits it to the LCD screen 11 via the data transmission line 12 for real-time display of the vibration level. The vibration level and occurrence time are also transmitted to the computer 13 via the data transmission line 12 for analysis. The probability of borehole collapse is predicted by comprehensively analyzing the cumulative change law of vibration level and the cumulative change law of rock cuttings 15 in the borehole. The probability of disaster occurrence is predicted by comprehensively analyzing the spatiotemporal evolution law of microseismic signals and the cumulative change law of vibration level.

[0038] The above-disclosed embodiments are merely preferred embodiments of the vibration level real-time assessment device and method based on the installation of micro-vibration sensors of the present invention. Of course, they should not be construed as limiting the scope of the present invention. Those skilled in the art can understand that implementing all or part of the above embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for real-time vibration level assessment based on the installation of microseismic sensors, comprising a real-time vibration level assessment device, characterized in that, The vibration level real-time assessment device includes a monitoring main body, a real-time assessment mechanism, and a borehole collapse prediction mechanism. The monitoring main body is connected to both the real-time assessment mechanism and the borehole collapse prediction mechanism. The borehole collapse prediction mechanism includes a rock cuttings collection net, a real-time weighing device, a cuttings loading box, a weight display, and a collection net support rod. The cuttings loading box is located at the bottom of the rock cuttings collection net, the real-time weighing device is located at the bottom of the loading box, the weight display is connected to the real-time weighing device, and the collection net support rod is located on the side of the rock cuttings collection net near the real-time weighing device. The rock cuttings collection net has rock cuttings drop holes. The monitoring main body includes a sensor, quick-acting cement, a signal receiving probe, a hanging nail, a drilling baffle, and a mounting rod. The sensor is connected to the signal receiving probe and the mounting rod respectively. The sensor has a sensor mounting hole. The quick-acting cement is placed inside the sensor mounting hole. The hanging nail is placed on one side of the sensor. The drilling baffle is placed outside the sensor mounting hole. The real-time assessment device includes a vibration sensing probe, a vibration measurement unit, an LCD screen, a data transmission line, and a computer. The vibration sensing probe is connected to the sensor and the fast-acting cement. The vibration measurement unit is connected to the sensor and the LCD screen. The data transmission line is connected to the computer, the vibration sensing probe, the vibration measurement unit, the LCD screen, the sensor, and the weight display. The real-time vibration level assessment method includes the following steps: Step 1: Connect and install the main monitoring unit, the real-time assessment unit, and the borehole collapse prediction unit; The specific steps are as follows: Drill a sensor mounting hole at the location where the sensor is to be installed. The sensor mounting hole should be at least 1 meter deep and have a certain tilt angle to prevent water from accumulating at the bottom of the sensor mounting hole and affecting the acoustic emission signal monitoring. Three real-time weighing devices and the chip collection box are connected to each other and placed at the bottom of the sensor mounting hole. The three chip collection boxes are in contact with each other to prevent rock chips from falling and thus preventing weighing. Rock chip drop holes are reserved at corresponding positions on the rock chip collection net, and a collection net support rod is connected to the bottom of the rock chip collection net. The rock chip collection net and the collection net support rod are placed into the sensor mounting hole. The rock chip collection net forms a triangle in the sensor mounting hole, with the top connected to the top of the sensor mounting hole and the bottom of the sensor mounting hole connected to both sides by the collection net support rod. Rock chips slide from top to bottom on the rock chip collection net and fall into the chip collection box through the rock chip drop holes. Then, they enter the real-time weighing device for weighing. The weighing result is transmitted to the weight display table in real time via the data transmission line and further transmitted to the computer via the data transmission line for data recording and analysis. If the weight of rock chips G1+G2+G3 suddenly increases in a short period of time, the probability of hole collapse increases. Step 2: Microseismic signals are collected in real time by the monitoring main unit; and the collected information is transmitted to the real-time assessment unit to observe the spatiotemporal evolution and conduct disaster early warning. The specific steps are as follows: When the surrounding rock is disturbed by construction, micro-seismic signals are generated inside. The micro-seismic signals propagate to the surrounding area. When they reach the vicinity of the signal receiving probe, they are collected by the signal receiving probe and transmitted to the sensor. The sensor transmits the micro-seismic signals to the computer through the data transmission line, analyzes the spatiotemporal evolution of the micro-seismic signals, and then provides early warning of disasters. Step 3: When high-level vibrations such as blasting, rock bursts, or mechanical vibrations occur, the main monitoring mechanism collects the vibration level and time, and transmits it to the real-time assessment mechanism to analyze the spatiotemporal evolution, cumulative vibration level, and cumulative change of rock in the borehole, and predict the probability of borehole collapse and the probability of disaster. The specific steps are as follows: When a high-level vibration such as blasting, rockburst, or mechanical vibration occurs, the vibration sensing probe embedded in the quick-acting cement collects the vibration signal and transmits it to the vibration measurement unit via the data transmission line. The vibration measurement unit analyzes the vibration level and then transmits it to the LCD screen via the data transmission line for real-time display of the vibration level. The vibration level and occurrence time are also transmitted to the computer via the data transmission line for analysis. The probability of borehole collapse is predicted by comprehensively analyzing the cumulative change law of vibration level and the cumulative change law of rock cuttings in the borehole. The probability of disaster occurrence is predicted by comprehensively analyzing the spatiotemporal evolution law of microseismic signals and the cumulative change law of vibration level.

2. The method for real-time assessment of vibration level based on the installation of microseismic sensors as described in claim 1, characterized in that, The number of weight display tables is 3.

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