CN102141534B - Seawater invasion monitoring method and distributed conductivity geological disaster monitoring device - Google Patents

Abstract

The invention discloses a seawater intrusion monitoring method, comprising: laying out a host computer and distributed measurement electrodes, the distributed measurement electrodes are arranged in geological disaster seawater intrusion observation wells, and recording the well depth where each electrode is located; selecting the test electrodes, and giving The selected electrode is energized, so that the electrode forms a loop through the well fluid, and the voltage at both ends of the sampling resistor connected in series in the loop is measured; the conductivity value of the well fluid at the electrode is obtained according to the voltage; according to the conductivity value and the location of each electrode The depth of the well is determined as the boundary of fresh water, and the monitoring of seawater intrusion is realized. The invention also discloses a distributed electrical conductivity geological disaster monitoring device. The present invention collects the conductivity values of well fluids at different depths in geological disaster seawater intrusion observation wells, utilizes the linear relationship between the conductivity of water and the salt content, and determines the boundary of fresh water according to the conductivity value and the depth of the well where the electrode is located It is convenient, fast and accurate to complete the monitoring of seawater intrusion.

Description

Seawater intrusion monitoring method and distributed conductivity geological disaster monitoring device

technical field

The invention relates to the technical field of geological disaster monitoring, in particular to a seawater intrusion monitoring method and a distributed electrical conductivity geological disaster monitoring device. the

Background technique

Seawater intrusion is a natural phenomenon in which seawater intrusion infects underground freshwater layers due to the decline of land groundwater levels. That is to say, seawater infiltrates into the terrestrial fresh aquifer with a lower water table through the aquifer (including the aquitard). Under normal circumstances, the water level of fresh land aquifers is higher than that of seawater, but after long-term large-scale pumping of fresh land aquifers, the groundwater level will be lower than that of seawater, causing seawater (salt water) to infiltrate into fresh land aquifers through the permeable layer , thereby destroying groundwater resources. the

According to data, in recent years, seawater intrusion into freshwater aquifers in my country's coastal areas has occurred frequently, involving Liaoning, Hebei, Tianjin, Shandong, Guangxi, Hainan and other provinces from north to south. Among them, the development of seawater intrusion in the Bohai Rim region is particularly rapid. In 2003 alone, the area of seawater intrusion reached 2,457 square kilometers, an increase of 937 square kilometers compared with the end of the 1980s, and an average annual increase of 62 square kilometers (from China Geological Survey bureau). the

The intrusion of seawater into the region will cause groundwater to be formed to varying degrees, which can lead to the deterioration of water quality in coastal areas and the reduction of irrigation water sources; the imbalance of soil ecosystems and the degradation of cultivated land resources; affect industrial and agricultural production; reduce the health of the population and affect social stability; In the end, it will inevitably lead to the deterioration of the natural ecological environment. Great losses have been caused to the property, production and life of the country and the people. the

At present, the domestic response to seawater intrusion is mainly based on monitoring and prevention. The monitoring methods mainly use geophysical prospecting methods, laying seawater intrusion observation holes and isotope index method to monitor seawater intrusion. Seawater intrusion and soil salinization monitoring stations have been established in most areas where transgressions occur in my country, such as Shandong and Hebei provinces, and a certain number of groundwater observation holes have been laid out to monitor seawater intrusion. Quantitative and other methods to monitor seawater intrusion. the

These seawater intrusion monitoring methods mentioned above have a large workload, cumbersome process and poor data processing accuracy. the

Contents of the invention

The problem to be solved by the present invention is to provide a seawater intrusion monitoring method and a distributed conductivity geological disaster monitoring device to overcome the defects of heavy workload, cumbersome process and poor data processing accuracy in the prior art when implementing seawater intrusion monitoring. the

In order to achieve the above object, the technical solution of the present invention provides a kind of seawater intrusion monitoring method, described method comprises the following steps:

A. Arrange the host in a safe place near the geological disaster observation well, arrange the distributed measurement electrodes in the geological disaster body seawater intrusion observation well, and record the well depth of each electrode on the distributed measurement electrodes;

B. Select the test electrode, and energize the selected electrode, so that the electrode forms a loop through the well fluid, and measure the voltage at both ends of the sampling resistor connected in series in the loop;

C. Obtain the conductivity value of the well fluid at the electrode according to the voltage;

D. According to the conductivity value of each electrode on the distributed measuring electrodes and the depth of the well where the electrodes are located, determine the boundary of fresh water, and realize the monitoring of seawater intrusion. the

Wherein, in the step A, the distributed measuring electrodes are distributed along the axial direction perpendicular to the ground in the observation well. the

Wherein, in the step B, the selected electrodes are energized with square wave pulses with a frequency of 1000 Hz, positive and negative pulses with the same amplitude, and a duty cycle of 50%. the

Wherein, in the step C, according to the formula

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ab</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Vm</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}$

Calculate the conductivity value of the well fluid at the electrode; wherein Kx is the conductivity value, Q is the electrode coefficient, V _ab is the voltage value of the square wave pulse, R2 is the resistance value of the sampling resistor, and Vm is the voltage at both ends of the sampling resistor Voltage value, R0 is the resistance value of the cable between the host and the distributed measurement electrodes, and R1 is the resistance value of the voltage dividing resistor.

Wherein, in the step C, the conductivity value of the well fluid at the electrode is calculated according to the formula Kx=10000/(718-290*Vm), wherein the unit of Vm is V, and the unit of Kx is mS/cm. the

The technical solution of the present invention also provides a distributed conductivity geological disaster monitoring device, the device includes a host and distributed measurement electrodes, and the host and distributed measurement electrodes are connected by cables;

The host is arranged in a safe place near the geological disaster body, including:

The electrode selection circuit is used to select the test electrode to be energized;

An electrode power supply circuit for energizing selected electrodes;

The electrode switching circuit is used to switch the selected electrode to the electrode power supply circuit for electrification according to the selection result of the electrode selection circuit;

The signal sampling circuit is used to collect signals from the electrode power supply circuit after power-on and the circuit formed by the well fluid between the electrodes and the electrodes;

The main control unit and data acquisition circuit are used to control and complete electrode selection, electrode switching, data acquisition, processing and storage;

The distributed measuring electrodes are arranged in seawater intrusion observation wells in various locations of the geological disaster body, and are distributed along the axial direction perpendicular to the ground in the observation wells. the

Wherein, the main control unit and the data acquisition circuit include:

The conductivity acquisition unit is used according to the formula

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ab</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Vm</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}$

Calculate the conductivity value of the well fluid at the electrode; where Kx is the conductivity value, Q is the electrode coefficient, V _ab is the voltage value of the square wave pulse, R2 is the resistance value of the sampling resistor, and Vm is the voltage at both ends of the sampling resistor Voltage value, R0 is the resistance value of the cable between the host and the distributed measuring electrodes, and R1 is the resistance value of the voltage dividing resistor;

The boundary determining unit is used to determine the boundary of fresh water according to the conductivity value and the well depth where each electrode on the distributed measuring electrode is located. the

Wherein, the host computer further includes a memory for storing the conductivity value and corresponding electrode state information. the

Wherein, the output of the electrode power supply circuit is a square wave pulse with a frequency of 1000 Hz, positive and negative pulses with the same amplitude, and a duty cycle of 50%. the

Wherein, the number of electrodes on the distributed measuring electrodes is 2 to 30. the

Compared with prior art, technical scheme of the present invention has following advantage:

The present invention collects the electrical conductivity values of the well fluids at different depths in the seawater intrusion observation wells of geological disaster bodies, utilizes the linear relationship between the electrical conductivity of the water and the salt content, and determines the electrical conductivity value and the depth of the well where the electrode is located. It is convenient, fast and accurate to complete the monitoring of seawater intrusion. The test data of the invention has high accuracy and is convenient to be used by the disaster monitoring network. the

Description of drawings

Fig. 1 a is a schematic diagram of seawater intrusion well depth-conductivity variation under the condition that the freshwater water level is lower than the intrusion seawater water level of the present invention;

Figure 1b is a schematic diagram of seawater intrusion well depth-conductivity change under the condition that the freshwater water level is higher than the intruded seawater water level according to the present invention;

Fig. 2 is the system block diagram of a kind of distributed conductivity geological disaster monitoring device of the embodiment of the present invention;

Fig. 3 is the circuit schematic diagram of the host computer of the distributed conductivity geological disaster monitoring device of the embodiment of the present invention;

Fig. 4 is the structural block diagram of the EPC-2901 industrial control panel of the embodiment of the present invention;

Fig. 5 is the A/D input connection schematic diagram of the EPC-2901 industrial control board of the embodiment of the present invention;

Fig. 6 is the 50-pin input and output interface pin Fig. 6 of the MiniISA-8032A of the embodiment of the present invention;

7 is a schematic diagram of the connection of the isolated digital output channel of the MiniISA-8032A of the embodiment of the present invention to drive an external relay;

Fig. 8 is the schematic diagram of the electrode power supply circuit of the embodiment of the present invention;

Fig. 9 is the schematic diagram of the signal sampling circuit of the embodiment of the present invention;

Fig. 10 is the schematic diagram of the electrode switching circuit of the embodiment of the present invention;

Fig. 11 is the flowchart of a kind of seawater intrusion monitoring method of the embodiment of the present invention;

Fig. 12 is the electrical conductivity calculation equivalent circuit diagram of the embodiment of the present invention;

Fig. 13 is the on-site installation schematic diagram of the distributed electrical conductivity geological disaster monitoring device of the embodiment of the present invention;

Figure 14 is the "well depth-conductivity curve" diagram of the H15 observation hole drawn according to the test data table;

Figure 15 is the "well depth-conductivity curve" diagram of the North 20 observation hole drawn according to the test data table;

Figure 16 is the "well depth-conductivity curve" diagram of the observation hole in Nanmeng Village drawn according to the test data table. the

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. the

Since the conductivity of water (formation) is related to its salt content, generally as the salt content increases, the conductivity of water (formation) also increases accordingly. Therefore, the present invention divides the brackish-fresh water level interface by testing the electrical conductivity of the well fluid (formation). Usually the interface between brackish and fresh water levels is a transition zone. Figure 1a and Figure 1b are the schematic diagrams of the seawater intrusion well depth-conductivity variation when the freshwater water level is lower than and higher than the intruded seawater water level, respectively. the

Embodiment one

A system block diagram of a distributed conductivity geological disaster monitoring device according to an embodiment of the present invention is shown in Figure 2, the device includes a host and a plurality of electrodes, and the host is connected to the distributed measuring electrodes by cables;

The circuit schematic diagram of the main engine is shown in Figure 3. The main engine is arranged in a safe place near the geological disaster body, including:

Electrode selection circuit, used to select the test electrode to be energized;

The electrode power supply circuit is used to energize the selected electrodes, and the output of the electrode power supply circuit is a square wave pulse with a frequency of 1000 Hz, positive and negative pulse amplitudes, and a duty cycle of 50%;

The electrode switching circuit is used to switch the selected electrode to the electrode power supply circuit for power supply according to the selection result of the electrode selection circuit;

The signal sampling circuit is used to collect signals from the electrode power supply circuit after power-on and the circuit formed by the well fluid between the electrodes and the electrodes;

The memory is used to store the conductivity value and the state information of the corresponding electrode. the

The main control unit and data acquisition circuit are used to control and complete electrode selection, electrode switching, data acquisition, processing and storage; the main control unit and data acquisition circuit include a conductivity acquisition unit and a boundary determination unit. The conductivity acquisition unit is used according to the formula

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ab</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Vm</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="R"\; filenames="DEST\_PATH\_HSB00000477423200021.png,DEST\_PATH\_HSB00000477423200041.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="HSA00000420303700042.png,HSA00000420303700051.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}$

Calculate the conductivity value of the well fluid at the electrode; where Kx is the conductivity value, Q is the electrode coefficient, V _ab is the voltage value of the square wave pulse, R2 is the resistance value of the sampling resistor, and Vm is the voltage at both ends of the sampling resistor Voltage value, R0 is the resistance value of the cable between the host computer and the distributed measuring electrode, R1 is the resistance value of the voltage dividing resistor; the boundary determination unit is used to determine the value of the electrical conductivity according to the conductivity value and the depth of the well where the electrode is located. Freshwater boundaries.

The electrodes are arranged in seawater intrusion observation wells everywhere in the geological disaster body, and are distributed along the axial direction perpendicular to the ground in the observation wells, and the number of electrodes on the distributed measurement electrodes is 2 to 30. the

The device also includes auxiliary equipment (computer, printer, etc.), and a 12V power supply battery. The 12V battery provides power for the system through the power conversion circuit, and the main control circuit controls the whole machine to complete electrode selection, electrode switching, data acquisition, processing and storage. The detection time can be completed through software setting (such as detection several times a day during monitoring). The detected data (conductivity value) is recorded in the memory (card) in chronological order and the electrode serial number, and the conductivity data can be viewed and checked through the computer at any time and drawn by the data processing software of the distributed conductivity geological disaster monitor as "well depth- Conductivity" curve. The well depth-conductivity curve can intuitively reflect the boundary of fresh water. the

Each component of the distributed electrical conductivity geological disaster monitoring device of the present invention will be described in detail below. the

1. Host

(1) Main control unit, data acquisition circuit, and memory: EPC-2901 industrial control board is used, and the purpose of selection is to provide guarantee for further upgrade and development of the system in the future. The structural block diagram of the EPC-2901 industrial control board is shown in Figure 4. EPC-2901 is a scalable embedded industrial control motherboard based on 32-bit ARM7 processor LPC2378, supporting 10/100M Ethernet (industrial level), 1 CAN interface (industrial level), CF card interface, onboard data Flash, A /D conversion, low-power independent RTC and other functions. It can easily realize functions such as CF card and onboard data Flash reading and writing, especially suitable for data recording and communication protocol conversion and other occasions. At the same time, the EPC-2901 industrial control board provides the user with a MiniISA bus interface, through which the MiniISA series intelligent data board can be connected. the

The hardware features are as follows:

Communication: 1-way 10/100M Ethernet; 4-way RS-232C interface (UART1 is Modem port); 1-way CAN interface;

Analog: 4-channel (AIN0～AIN3) analog A/D input, 10-bit resolution, single-channel conversion time as low as 2.44μs, of which AIN3 channel supports 10-bit D/A output;

Digital quantity: 4-way digital buffer input, optional capture input; 4-way digital buffer output, optional PWM output;

External expansion storage: CF card connection; 2MB onboard NOR Flash; 64KB SRAM;

Others: 1 high-speed I ² C bus interface; support MiniISA bus; external hardware watchdog; external RTC clock;

EPC-2901 industrial control motherboard is mainly composed of buffer input/output circuit, serial communication circuit, external storage system, power management and other modules. The system block diagram is shown in Figure 7. the

EPC-2901 industrial control motherboard adopts 5V DC single power supply. The power supply accuracy is required to be within ±5%, and the maximum input current is 2A. It can work stably in a wide temperature range from -40°C to +80°C, meeting various application requirements of industrial-grade products. the

The input and output range of A/D and D/A provided by EPC-2901 is 0~2.5V, so it is necessary to ensure that the signal amplitude input to the A/D input terminal is between 0~2.5V. The schematic diagram of its A/D input connection is shown in Figure 5. the

(2) Electrode selection circuit: use MiniISA-8032A MiniISA bus digital input/output card. The bus provides 16 isolated digital input channels and 16 isolated digital output channels, using two MiniISA-8032A to complete the selection of 30 conductivity electrodes by driving the relay. MiniISA-8032A completes electrical connection with EPC-2901 industrial control motherboard through MiniISA bus. The 50-pin input and output interface pins of MiniISA-8032A are shown in Figure 6, and Figure 7 is a schematic diagram of the connection of an isolated digital output channel to drive an external relay. the

The functions of MiniISA-8032A 50-pin input and output interface pins are shown in Table 1:

Table 1

Pin Function IDIn(n＝0～15) Isolated digital input IDOn(n＝0～15) Isolated digital output EXCOM Isolated digital input ground EGND Isolated digital output ground PCOM Digital output protection diode

(3) Electrode power supply circuit: The conductivity of the liquid is measured by inserting a measuring electrode with an alternating electric field into the solution to be measured, so as to reduce the polarization. Through experiments, choosing 1000Hz can achieve better precision. At the same time, the symmetry of the pulse signal generated by the AC signal source has a great influence on the measurement accuracy. Generally, the amplitude of the positive and negative pulses should be the same, and the duty cycle is 50%. Only in this way can the equivalent current flowing through the solution be 0, and the properties of the solution will not be changed and ionization will be reduced during the measurement process. the

The electrode power supply circuit uses an integrated circuit CD4046, which is mainly composed of a phase comparator (PC) and a voltage-controlled oscillator (VCO). Using its excellent VCO circuit, an oscillator with high stability and 50% duty cycle is built, and a 1000Hz control signal is output to the CD4053 control terminal. Use CD4053 to realize the time-sharing gate voltage, and output a square wave pulse with a duty cycle of 50% at the output of CD4053 to supply electrodes. The schematic diagram of the electrode power supply circuit is shown in Figure 8. the

Referring to Figure 8, the ±8V power supply is provided by the integrated voltage regulator IC7808 and 7908, which has a strong load capacity. When the external load resistance is not very small (≥5Ω), the voltage is constant at ±8V with little fluctuation. The follow-up circuit is composed of a pair of diodes (conducting voltage drop is 0.7V) and a pair of voltage regulator tubes (Vz=5V). When the output of CD4053 is a high-level pulse, the right channel in the above figure is turned on and the left channel is cut off. When the output of CD4053 is a low-level pulse, the left channel is turned on and the right channel is cut off. No matter which way is turned on, the junction voltage drop of the diode and the voltage regulation of the Zener tube can guarantee a constant voltage of 0.7V+5V=5.7V. In this way, an alternating 5.7V square wave voltage will appear on the conductivity cell. Experiments show that the symmetry is very good. the

(4) Signal sampling circuit: The signal sampling circuit is composed of a sampling resistor circuit, a phase sensitive detection circuit, and a noise reduction filter circuit. The circuit schematic diagram of the signal sampling circuit is shown in Fig. 9 . the

Since the divided voltage signal obtained from the sampling resistor is a bipolar pulse signal, and the A/D input signal range provided by EPC-2901 is 0-2.5V unipolar, it is necessary to convert the AC signal into a DC signal. Due to the existence of the diode junction voltage drop (0.7V), the ordinary phase-sensitive detection circuit composed of rectifier diodes cannot pass a small voltage division signal, which affects the measurement accuracy and dynamic range. In order to improve these performances, an integrated computing A phase-sensitive detection circuit composed of an amplifier and a switch circuit. the

In order to improve the precision of the phase-sensitive detection circuit, reduce the temperature drift, and improve the linearity and symmetry of the circuit, the circuit components are carefully selected. The operational amplifiers F1 and F2 used in the phase-sensitive detection circuit use AD620, a high-precision, low-power consumption, low-drift, wide-voltage, and low-cost instrumentation amplifier. AD620 has a low input voltage noise of 9nV/√Hz at 1kHz. F1 forms a non-inverting amplifier, and F2 forms an inverting amplifier. The two amplifiers amplify the input signal in the same and anti-phase units respectively, and two voltage signals with the same amplitude and frequency and a phase difference of 180° are obtained at the output end. Under the control of the synchronous signal (1000Hz), the analog electronic switch 4053 at the back gates two signals with phase difference in time division. When the synchronization signal is i1, half period (high level), 4053 outputs the first half period (high level) of the in-phase signal, and when the synchronization signal is negative half period (low level), 4053 outputs the second half of the in-phase signal period (high level). In this way, the detected DC signal is obtained at the output terminal of 4053. the

Because the DC signal output by 4053 is mixed with power supply noise and circuit interference, a noise reduction filter circuit is added to the output of 4053, and the high-precision, low-power, and low-cost TL062 general-purpose operational amplifier is used to meet the measurement requirements. Accuracy requirements. the

(5) Electrode switching circuit: The schematic diagram of the electrode switching circuit is shown in Figure 10. The circuit is mainly composed of 30 double-open and double-close relays. The 30 relays are controlled by MiniISA-8032A to switch on and off 30 conductance electrodes in sequence. The relay uses a small solid-state relay AGN200A4H with stable and reliable performance, which has small size, light weight (0.7G ultra-lightweight type), low power consumption (<100mw), high sensitivity, and the coil contacts can withstand high voltage AC1,500V and withstand shock voltage 1.5KV. the

2. Cables and electrodes

The cable uses a 68-core shielded signal cable. The electrode uses an industrial online two-electrode platinum electrode, which consists of 30 conductivity electrodes. The waterproof sealing of the 30 conductivity electrodes and the connecting cables is very important. Considering the underwater pressure, corrosion and other reasons, a lot of experiments have been done on the joints by dipping insulating paint, filling silica gel, high-voltage tape and insulating tape winding, in order to meet the waterproof and anti-corrosion requirements. . Finally, the electrodes are sequentially connected with multi-core cables to form distributed measurement electrodes. The electrode spacing is one meter (the number of electrodes used and the electrode spacing can be determined according to the actual situation of the monitoring well), the serial numbers from top to bottom are 1 to 30, and the maximum measurement control range is 29 meters. the

Example two

A flow chart of a seawater intrusion monitoring method according to an embodiment of the present invention is shown in Figure 11, comprising the following steps:

Step s1, deploying the host computer and distributed measurement electrodes. Arrange the host in a safe place near the geological disaster body, arrange the distributed measurement electrodes in the seawater intrusion observation well of the geological disaster body, and record the well depth where each electrode is located; the distributed measurement electrodes are perpendicular to the ground in the observation well Distributed along the axial direction. the

Step s2, select the test electrode, and energize the selected electrode, so that the electrode forms a loop through the well fluid, and measure the voltage across the sampling resistor connected in series in the loop. In this embodiment, a square wave pulse with a frequency of 1000 Hz, positive and negative pulses with the same amplitude, and a duty ratio of 50% is used to energize the selected electrodes. the

Step s3, obtaining the conductivity value of the well fluid at the electrode according to the voltage. In this example, according to the formula

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ab</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Vm</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="R"\; filenames="DEST\_PATH\_HSB00000477423200021.png,DEST\_PATH\_HSB00000477423200041.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="HSA00000420303700042.png,HSA00000420303700051.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}$

Calculate the conductivity value of the well fluid at the electrode; where Kx is the conductivity value, Q is the electrode coefficient, V _ab is the voltage value of the square wave pulse, R2 is the resistance value of the sampling resistor, and Vm is the voltage at both ends of the sampling resistor Voltage value, R0 is the resistance value of the cable between the host and the distributed measurement electrodes, and R1 is the resistance value of the voltage dividing resistor.

Among them, when the conductivity is measured, a low pulse voltage is used for power supply, and the influence of the distributed capacitance of the electrodes (conductivity cell) can be ignored. The equivalent circuit diagram for conductivity calculation is shown in Figure 12. Among them, Rx is the resistance of the measured liquid, which is obtained by Ohm's law

V _ab =(Vm/R2)*(Rx+R0+R1+R2),

That is, Rx=(Vab*R2)/Vm-(R0+R1+R2). the

Since the conductivity of the measured liquid is Kx=Q/Rx, it can be concluded that

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ab</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; Vm</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="R"\; filenames="DEST\_PATH\_HSB00000477423200021.png,DEST\_PATH\_HSB00000477423200041.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="HSA00000420303700042.png,HSA00000420303700051.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}$

In this embodiment, electrode coefficient Q=10 (cm ⁻¹ ), V _ab =5.7V, R0 measured with a multimeter is 64Ω, R1=100Ω, R2=126Ω.

Therefore, the formula for calculating conductivity is:

Kx＝10/(718-290*Vm)------unit: S/cm (Vm unit is volt);

Because of the conductivity measurement range of the distributed conductivity geological disaster monitoring device design of the present invention is 0.5-60 (mS/cm), the final conductivity calculation formula is:

Kx＝10000/(718-290*Vm)

Wherein, the unit of Vm is V, and the unit of Kx is mS/cm. the

In step s4, according to the conductivity value and the depth of the well where the electrode is located, the boundary of salty and fresh water is determined, so as to monitor the intrusion of seawater. the

Embodiment three

The on-site installation schematic diagram of the distributed electrical conductivity geological disaster monitoring device of the present invention is shown in Figure 13, put main frame, storage battery, cable in the cabinet next to the observation hole, and distributed measuring electrode is put in suitable position below the water level (for convenience It is advisable to observe the change of conductivity). the

The distributed electrical conductivity geological disaster monitoring device of the present invention has been installed and used in some areas of Beidaihe and Nandaihe, and has achieved good results. The actual measurement results in this area will be described below. the

1. Table 2 shows the test data of the H15 observation hole in the Beidaihe seaside shrimp pond. The depth of the well is 20 meters, the water level is 0 meters, and the measured depth is 19 meters. Figure 14 is the "well depth-conductivity curve" diagram of the H15 observation hole drawn according to the test data table. the

Table 2

2. Table 3 shows the test data of Beidaihe Jinhaiwan Resort North 20 observation hole. The depth of the hole is 23 meters, the water level is 3 meters, and the measured depth is 3-22 meters. Fig. 15 is the "well depth-conductivity curve" diagram of the Bei 20 observation hole drawn according to the test data table. the

table 3

3. Table 4 shows the test data of the observation hole of the motor-driven well house in Nanmeng Village, Nandai. The depth of the well is 80 meters, the water level is 5 meters, and the measured depth is 6-75 meters. Figure 16 is the observation hole of Nanmeng Village drawn according to the test data table "Well Depth-Conductivity Curve" graph. the

Table 4

The present invention collects the electrical conductivity values of the well fluids at different depths in the seawater intrusion observation wells of geological disaster bodies, utilizes the linear relationship between the electrical conductivity of the water and the salt content, and determines the electrical conductivity value and the depth of the well where the electrode is located. It is convenient, fast and accurate to complete the monitoring of seawater intrusion. The test data of the present invention has high accuracy and is convenient to be used by the disaster monitoring network. The present invention mainly has the following characteristics:

1. Reliable system operation: The electronic components of the distributed conductivity geological disaster monitor are selected according to industrial standards, and the circuit board is designed according to the principle of electromagnetic compatibility, which can ensure the normal operation and reliability of the system. the

2. Wide range of application: the distributed conductivity geological disaster monitor can measure the conductivity of other occasions that meet the requirements. the

3. Many monitoring electrodes: The distributed measuring electrodes of the distributed conductivity geological hazard monitor can be configured with up to 30 electrodes according to customer needs. the

4. Large monitoring range: the maximum distance between distributed measuring electrodes is 1 meter, and the change of conductivity can be monitored within a range of 29 meters. the

5. Flexible data collection time setting: Distributed conductivity geological disaster monitor, data collection time can be set freely from 5 minutes to 24 hours. the

6. High accuracy of measurement data: Because the conductivity measurement is carried out in a static state for a long time, it avoids the measurement data error caused by artificial on-site measurement due to artificial disturbance of the water body. the

7. The curve display is intuitive: the data processing software of the distributed conductivity geological disaster monitor can arrange the "well depth-conductivity" curves of several days, weeks, months or one year in sequence, and the change of conductivity with time is clear at a glance . the

8. Small power consumption: the power supply is turned on and off at regular intervals to reduce power consumption, so that the instrument can work for a longer period of time without supervision. the

9. Diversified power supply: The distributed conductivity geological disaster monitor is powered by 12V power supply, which can be powered by solar panels or 220V AC to 12V DC. the

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. These improvements and modifications It should also be regarded as the protection scope of the present invention. the

Claims (4)

1. a distributed conductivity geologic hazard monitoring device is characterized in that described device comprises main frame and a plurality of electrode, is connected by cable between described main frame and the electrode;

Described main frame is laid near the safe part of geologic hazard body, comprising:

Electrode is selected circuit, is used for selecting test electrode to be switched on;

The electrode power supply circuit is used for giving the electrifying electrodes of selecting; It is 50% square-wave pulse that described electrode power supply circuit is output as amplitude unanimity, dutycycle that frequency is 1000Hz, positive negative pulse stuffing;

The electrode commutation circuit is used for the selection result according to described electrode selection circuit, the electrode of selecting is switched to the electrode power supply circuit switch on;

Signal sample circuit is used for signals collecting is carried out in the loop that well liquid between electrode power supply circuit, electrode and electrode after the energising forms;

Main control unit and data acquisition circuit are used for control and finish electrode selection, electrode switching, data acquisition process and storage;

Described electrode is laid in the geologic hazard body seawater intrusion inspection well everywhere, in axial direction distributes perpendicular to ground in described inspection well;

Described signal sample circuit is made up of sampling resistor loop, phase-sensitive detection circuit, noise reduction filtering circuit, forms phase-sensitive detection circuit by integrated operational amplifier and on-off circuit; In the phase-sensitive detection circuit, first operational amplifier (F1) is formed in-phase amplifier, second operational amplifier (F2) is formed inverting amplifier, two amplifiers carry out same, anti-phase unit to input signal respectively and amplify, obtaining at output terminal is that two amplitudes, frequency are identical, the voltage signal that the phase phasic difference is 180 °, wherein said input signal are the magnitude of voltage at the sampling resistor two ends in the sampling resistor loop; Simulant electronic switch is under synchronizing signal control, and described two the dephased signals of timesharing gating obtain the direct current signal that detection goes out at the output terminal of simulant electronic switch.

2. distributed conductivity geologic hazard monitoring device as claimed in claim 1 is characterized in that described main control unit and data acquisition circuit comprise:

The conductivity acquiring unit is used for according to formula

$\mathrm{Kx}=\frac{Q}{(V_{\mathrm{ab}}*R2)/\mathrm{Vm}-(R0+R1+R2)}$

Calculate the conductivity values of described electrode place well liquid; Wherein Kx is conductivity values, and Q is the electrode coefficient, V _AbBe the magnitude of voltage of described square-wave pulse, R2 is the resistance value of sampling resistor, and Vm is the magnitude of voltage at sampling resistor two ends, and R0 is the resistance value of the cable between described main frame and the electrode, and R1 is the resistance value of divider resistance;

The boundary determining unit is used for the well depth according to described conductivity values and described electrode place, is specified to the boundary situation of fresh water.

3. distributed conductivity geologic hazard monitoring device as claimed in claim 2 is characterized in that described main frame also comprises storer, is used for the status information of the electrode of the described conductivity values of storage and correspondence.

4. as each described distributed conductivity geologic hazard monitoring device of claim 1 to 3, it is characterized in that described electrode is 2 to 30.

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