Exploration method for large-depth water-logging goaf of surface iron ore based on transient electromagnetism

Abstract

The invention belongs to the technical field of iron ore open-pit mining, and particularly relates to a transient electromagnetic surface iron ore large-depth ponding goaf exploration method, which comprises the following specific steps: arranging an emission wireframe at the edge of a surface iron ore platform, acquiring an induced voltage signal, and comparing the induced voltage to pre-judge the position of a ponding goaf; adjusting the size of an emission wireframe, laying the emission wireframe in a region suspected to have a water-accumulated goaf below, performing induced voltage signal acquisition, and comparing induced voltage to determine the top position of the water-accumulated goaf; the transmitting wireframe is moved to a first platform below the top of the waterlogged goaf, the signal acquisition probe is moved to the first platform below the platform where the transmitting wireframe is located, the transmitting wireframe and the signal acquisition probe move downwards one by one and perform induced voltage signal acquisition, and induced voltage is compared to determine the bottom position of the waterlogged goaf. According to the method, the range of the waterlogged goaf is judged by comparing the voltage maximum value collected at different platforms with the time corresponding to the voltage maximum value, and potential safety hazards are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of open-pit iron ore mining, and in particular relates to an exploration method for deep waterlogged goafs in open-pit iron ore based on transient electromagnetic technology. Background Art

[0002] With the development of large-scale machinery and equipment, my country has developed numerous large-scale iron mines using open-pit mining. Prior to the adoption of large-scale open-pit mining, due to the lack of large-scale machinery and equipment, many small iron mines employed underground mining, digging from the surface along the ore body deep into the strata. This mining process results in columnar or olive-shaped goafs with large depths and small cross-sections. Due to the depletion of shallow resources or long periods of closure and consolidation, small iron mines often have water accumulation in some goafs. Furthermore, the lack of design and drawings in small mines has resulted in the location of these waterlogged goafs being unknown. These unidentified waterlogged goafs can cause machinery and equipment to fall, or even personnel to fall. Water inrush accidents in goafs can damage equipment within the working face, resulting in economic losses and casualties. To minimize the damage caused by unidentified waterlogged goafs in open-pit iron ore mining, the location of these goafs should be identified before accidents occur, and appropriate preventive measures should be implemented.

[0003] There are many methods for exploring waterlogged goaf. Transient electromagnetic method is widely used for exploring waterlogged goaf due to its advantages such as less influence from terrain and high construction efficiency. However, for the exploration of deep waterlogged goaf in open pit iron mines, transient electromagnetic method has obvious problems. Figure 1 As shown, the transient electromagnetic method stimulates induced eddy currents in the stratum by passing a pulse current into the transmitting wire frame. The induced eddy currents propagate slowly in the water-logged goaf during their propagation into the deep stratum, and the induced eddy currents decay continuously over time, so that the electromagnetic induction signals generated by the induced eddy currents are buried in the electromagnetic noise before they propagate to the deepest part of the water-logged goaf in the open-pit iron mine. It is difficult to collect them through the signal acquisition probe, resulting in the middle and lower parts of the deep water-logged goaf in the open-pit iron mine being difficult to be effectively identified. There are blind spots in the exploration, which can easily lead to accidents and pose a huge safety hazard. Summary of the Invention

[0004] The purpose of the present invention is to provide an exploration method for deep water-logged goafs in open-pit iron mines based on transient electromagnetic technology, so as to solve the problem that traditional exploration methods are difficult to collect data through signal acquisition probes, resulting in the middle and lower parts of deep water-logged goafs in open-pit iron mines being difficult to effectively identify and the existence of blind spots in exploration.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic technology, the specific steps are as follows:

[0007] Step 1: Lay out a transmitting wireframe along the edge of the open-pit iron ore platform and determine the electrical characteristics of the strata based on the stratum distribution shown in existing geological data. Based on the electrical characteristics of the strata, determine the transmission frequency f (in Hz) of the transmitting current in the transmitting wireframe to ensure that the induced voltage signal can reflect the geological information within 100 meters below the platform where the transmitting wireframe is located.

[0008] Step 2: Lay out measurement lines and measurement points on the platform where the transmitting wireframe is located, adjust the transmitting current I in A, and use a signal acquisition probe to collect induced voltage signals at each measurement point. Compare the collected voltages and circle the measurement points with higher induced voltages to predict the presence of water-logged goaf below them.

[0009] Step 3: Calculate the side length of the small transmitting wireframe using the area of ​​the enclosed area, and place the small transmitting wireframe within the enclosed area. Lay out survey lines and points on the first, second, third, and fourth platforms below the platform where the small transmitting wireframe is located. Use a signal acquisition probe to collect induced voltage signals, and promptly adjust the transmitting current I and transmitting frequency f in the small transmitting wireframe to ensure that the induced voltage signal can reflect the geological information between the platform where the transmitting wireframe is located and the platform where the signal acquisition probe is located.

[0010] Step 4: Compare the acquisition times corresponding to the maximum voltage values ​​collected on the first, second, third, and fourth platforms below the platform where the small transmitting wireframe is located to determine the top position of the water-filled goaf;

[0011] Step 5: Place the small transmitting wire frame on the first platform below the top of the water-logged goaf determined in step 4, and place the small transmitting wire frame in the area where the measuring point where the maximum value of the induced voltage signal is collected is located. Move the signal acquisition probe to the first platform below the platform where the small transmitting wire frame is located, adjust the transmitting current I and the transmitting frequency f, and ensure that the induced voltage signal can reflect the geological information between the platform where the small transmitting wire frame is located and the platform where the signal acquisition probe is located; keep the transmitting current I and the transmitting frequency f unchanged, move the small transmitting wire frame and the signal acquisition probe down platform by platform and collect the induced voltage signal, compare the collected maximum voltage and the collection time corresponding to the maximum value, and determine the bottom position of the water-logged goaf.

[0012] Preferably, in step 1, the conductivity of each rock layer is estimated based on the stratum information reflected by the existing geological data, and the weighted average conductivity E of the stratum within 100m below the platform where the transmitting wireframe is located is calculated according to formula (1): 100 .

[0013] E 100 =ΣD i ·E i / ∑D i (1)

[0014] E in formula (1) i is the conductivity of the i-th layer below the platform where the transmitting wireframe is located, in S / m, D i is the thickness of the i-th layer below the platform where the transmitting wireframe is located, in meters, E 100 The weighted average conductivity of the strata within 100m below the platform where the transmitting wireframe is located, in S / m, ΣD i ≤100m.

[0015] The diffusion speed of the induced eddy current into the deep layer is calculated according to formula (2).

[0016] v=3.18 / (10 -5 ×Et) 1 / 2 (2)

[0017] In formula (2), v represents the velocity of the induced eddy current propagating deep into the formation, in m / s; E is the conductivity of the formation, in S / m; and t is the time, in s.

[0018] Adjust the transmission frequency f according to formulas (3)-(5) to ensure that the induced voltage signal can reflect the geological information within 100m below the platform where the transmitting wireframe is located.

[0019]

[0020] T=(1 / f)>t=t1+t2(5)

[0021] In formulas (3)-(5), t, t1, and t2 are all time units, in seconds, and t0 = 10 -4 s, E in formula (4) w is the conductivity of the water in the goaf, in S / m. In formula (5), T is the acquisition period of the induced voltage signal, in s, and f is the emission frequency of the emission current in the emission frame, in Hz.

[0022] Preferably, in step 2, the emission current I is adjusted to ensure that the induced voltage signal collected when approaching T is five times higher than the power frequency electromagnetic noise, which is usually 5×10 -7 V, that is, the induced voltage signal value collected when the signal acquisition probe approaches time T must be greater than 2.5×10 -6 V.

[0023] Preferably, the side length of the small emission wireframe in step 3 is calculated according to formula (6):

[0024] l=S 1 / 2 (6)

[0025] In formula (6), l is the side length of the small transmitting wire frame, in m, and S is the area of ​​the region with higher induced voltage signal value circled in step 2, in m 2 .

[0026] Preferably, the transmitting current I and the transmitting frequency f in step 3 are adjusted in time according to formulas (7)-(10) to ensure that the induced voltage signal can reflect the geological information between the platform where the small transmitting wire frame is located and the platform where the signal acquisition probe is located, and close to T n The induced voltage signal collected is greater than 2.5×10 -6 V.

[0027] E nH =ΣD i '·E i ' / ΣD i '(7)

[0028]

[0029] T n =(1 / f)>t n =t 1n +t 2n (10)

[0030] In formula (7), E nH is the weighted average conductivity of the stratum between the platform where the small transmitting wireframe is located and the platform where the signal acquisition probe is located in step 3, in S / m, E i ' is the conductivity of the i-th layer below the platform where the transmitting wireframe is located in step 3, in S / m, D i ' is the thickness of the i-th layer below the platform where the launch wireframe is located in step 3, in meters, ΣD i '=nH; In formulas (7)-(9), H is the height of the open pit iron ore step, in m, nH<100m, n means that the signal acquisition probe is located on the nth platform below the platform where the small transmitting wire frame is located in step 3; In formulas (8)-(10), t n , t 1n , t 2n All are time, unit is s.

[0031] Preferably, the specific content of determining the top position of the water-filled goaf in step 4 is as follows: compare the voltages collected from the first platform, the second platform, the third platform, and the fourth platform below the platform where the small transmitting wire frame is located, and compare the maximum voltage V collected from each platform. nm The corresponding acquisition time t nm , V nm Indicates the maximum value of the induced voltage signal collected by the nth platform below the platform where the small transmitting wire frame is located, in V. nm Vnm The corresponding acquisition time is in seconds. When n < N, formula (11) is satisfied, and when n ≥ N, formula (12) is satisfied. It is assumed that the top of the water-filled goaf is located below the horizontal plane of the Nth platform below the platform where the launch frame is located, and above the horizontal plane of the N+1th platform below the platform where the launch frame is located.

[0032] t 1(n+1) -t 1n =t (n+1)m -t nm (11)

[0033] t 1(n+1) -t 1n <t (n+1)m -t nm (12)

[0034] where t 1n The time required to satisfy formula (8), in seconds.

[0035] If the top position of the water-filled goaf is still not found on the first platform, second platform, third platform, and fourth platform below the small emission wireframe, move the emission wireframe in step one to the first platform below the platform, and repeat steps one, two, three, and four in sequence until the top position of the water-filled goaf is determined.

[0036] Preferably, the transmitting current I and the transmitting frequency f in step 5 are adjusted in time according to formulas (13)-(16) to ensure that the induced voltage signal can reflect the geological information between the platform where the small transmitting wire frame is located and the platform where the signal acquisition probe is located, and the induced voltage signal collected when approaching T' is greater than 2.5×10 -6 V.

[0037] E 3H2 =∑D i ”·E i ” / ∑D i ”(13)

[0038]

[0039] T'=(1 / f)>t'=t1'+t'2 (16)

[0040] E in formula (13)-(16) 3H / 2 The weighted average conductivity of the stratum between the platform where the small transmitting wireframe is located and the platform where the signal acquisition probe is located, as well as the stratum within H / 2 below the platform where the signal acquisition probe is located, in S / m, E i " is the conductivity of the i-th layer of the ground below the platform where the small emission wireframe is located in step 5, in S / m, D i" is the thickness of the i-th layer of the ground below the platform where the small emission wireframe is located in step 5, in m, ∑D i ”=3H / 2.

[0041] The transmitting frequency f is continuously adjusted during the process of moving the small transmitting wire frame and the signal acquisition probe downward step by step, so that formulas (13)-(16) are valid; and the transmitting current I is adjusted to ensure that the induced voltage signal collected near T' is greater than 2.5×10 -6 V.

[0042] Comparing the voltages collected on each platform in step 5, the bottom position of the water-logged goaf can be determined if the collected voltages have the following characteristics: The maximum voltage collected on the qth platform below the circled range of the small emission wire frame in step 3 is V′ qm , unit is V, maximum voltage V' qm The corresponding time is t' nm , the unit is s; when q<Q, all V′ qm Equal, all t′ qm The same is true; when q=Q, V′ Qm >V′ q ' m , and t' Qm <t' qm It is believed that the bottom of the water-filled goaf is located above the Qth platform horizontal plane below the circled range of the small emission wire frame in step three, and below the Q-1th platform horizontal plane below the circled range of the small emission wire frame in step three.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) By deploying transmitting wireframes and signal acquisition probes on different platforms in an open-pit iron mine, segmented exploration can be conducted in deep water-logged goaf areas. The closer the transmitting wireframes and signal acquisition probes are to the water-logged goaf areas, the higher the quality of the exploration signals and the more refined the exploration.

[0045] (2) With the change of the transmitting wireframe and the position of the signal acquisition probe, combined with the timely adjustment of the transmitting current and transmitting frequency, more exploration data is obtained while improving the data quality; and the high-quality exploration data controls the influence of other variables other than geological information on the exploration data to the greatest extent, so that the exploration data can fully reflect the changes in geological information;

[0046] (3) Based on a large amount of high-quality exploration data, by comparing the maximum voltage values ​​and the time corresponding to the maximum values ​​collected on different platforms, the scope of the water-logged goaf in the open-pit iron mine is jointly determined. This increases the basis for determining the water-logged goaf in addition to the induced voltage signal itself, greatly improving the exploration accuracy of the water-logged goaf in the open-pit iron mine, achieving effective identification of different platforms, eliminating blind spots in exploration, and avoiding safety hazards. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic diagram of the transient electromagnetic method principle and induced eddy current propagation in the background technology of the present invention;

[0048] Figure 2 Schematic diagram of open-pit iron ore mining form and waterlogged goaf in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of laying out a launch wireframe on platform 1 to conduct a trial exploration of a goaf area in an embodiment of the present invention;

[0050] Figure 4 Schematic diagram of stratum distribution within 100 meters below platform 1 in an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of a suspected goaf area discovered after exploration on Platform 1 in an embodiment of the present invention;

[0052] Figure 6 This is a schematic diagram of arranging a small transmitting wire frame on platform 1 and measuring points on platform 2 to collect induced voltage signals in an embodiment of the present invention;

[0053] Figure 7 This is a schematic diagram of arranging a small transmitting wire frame on platform one and measuring points on platform three to collect induced voltage signals in an embodiment of the present invention;

[0054] Figure 8 This is a schematic diagram of arranging a small transmitting wire frame on platform one and measuring points on platform four to collect induced voltage signals in an embodiment of the present invention;

[0055] Figure 9 This is a schematic diagram of arranging a small transmitting wire frame on platform one and measuring points on platform five to collect induced voltage signals in an embodiment of the present invention;

[0056] Figure 10 This is a schematic diagram of arranging a small transmitting wire frame on platform 4 and measuring points on platform 5 to collect induced voltage signals in an embodiment of the present invention;

[0057] Figure 11 This is a schematic diagram of arranging a small transmitting wire frame on platform five and measuring points on platform six to collect induced voltage signals in an embodiment of the present invention;

[0058] Figure 12 This is a schematic diagram of collecting induced voltage signals by laying out a small transmitting wire frame on platform six and measuring points on platform seven in an embodiment of the present invention.

[0059] Explanation of the accompanying reference numerals: 1. Transmitter wire frame; 2. Induced eddy current; 3. Water-logged goaf; 4. Platform one; 5. First connecting line; 6. Generator; 7. Second connecting line; 8. Transmitter controller; 9. Signal acquisition probe; 10. Arranged measuring points; 11. Iron-bearing quartzite; 12. Conglomerate iron ore; 13. Quartzite; 14. Area where measuring points with higher induced voltage values ​​are located; 15. Small transmitting wire frame; 16. Platform two; 17. Platform three; 18. Platform four; 19. Platform five; 20. Platform six; 21. Platform seven. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0061] A method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic technology, the specific steps are as follows:

[0062] Step 1: If Figure 2-3 As shown, the open pit iron ore mining step height H = 15m, the transmission wire frame 1 is arranged along the edge of the platform 4, the transmission wire frame 1 and the generator 6 are connected by a first connecting line 5, and the generator 6 and the transmission controller 8 are connected by a second connecting line 7, as shown in FIG. Figure 4 As shown in Figure 1, according to existing geological data, the strata within 100 m below platform 4 are distributed as follows: 0 m-42 m is iron-bearing quartzite 11, with a thickness of D1 = 42 m; 42 m-75 m is conglomerate iron ore 12, with a thickness of D2 = 33 m; 75 m-100 m is quartzite 13, with a thickness of D3 = 25 m. The conductivity of the rock samples of each stratum measured by the conductivity meter is: E1 = 2 × 10 - 3 S / m; E2 of conglomerate iron ore 12 = 4×10 -3 S / m; E3 of quartzite 13 = 10 -3 S / m; Calculate the weighted average conductivity E of the stratum within 100m below the platform where the transmitting wireframe 1 is located according to formula (1) 100 .

[0063] E 100 =ΣD i ·E i / ∑D i (1)

[0064] E in formula (1) i is the conductivity of the i-th layer below the platform where the transmitting wireframe is located, in S / m, D iis the thickness of the i-th layer below the platform where the transmitting wireframe is located, in meters, E 100 is the weighted average conductivity of the stratum within 100m below the platform where the transmitting wireframe is located, in S / m, ∑D i ≤100m, E is calculated according to formula (1) 100 =2.41×10 -3 S / m.

[0065] The diffusion speed of the induced eddy current 2 into the deep layer is calculated according to formula (2).

[0066] v=3.18 / (10 -5 ×Et) 1 / 2 (2)

[0067] In formula (2), v represents the velocity of the induced eddy current 2 propagating deep into the formation, in m / s; E is the conductivity of the formation, in S / m; and t is the time, in s.

[0068] Adjust the transmission frequency f in Hz according to formulas (3)-(5) to ensure that the induced voltage signal can reflect the geological information within 100 m below the platform where the transmitting wireframe is located.

[0069]

[0070] T=(1 / f)>t=t1+t2(5)

[0071] In formulas (3)-(4), t, t1, and t2 are time units in seconds, and t0 = 10 -4 s, E in formula (4) w The conductivity of the water in the goaf is S / m. After measurement, E w =39S / m, T is the induced voltage signal acquisition period, unit is s, f is the emission frequency of the emission current in the emission wire frame, unit is Hz. Calculation results: t1 = 1.55×10 -4 s, t2=1.03×10 -1 s, set the transmission frequency f to 8 Hz, T = 1.25 × 10 -1 S.

[0072] Step 2: If Figure 3 As shown in the figure, the open-pit iron ore platform 1 is 1800m long and 35m wide. A 10m×10m measuring point 10 network is arranged on the platform 14. The transmission frequency f=8Hz. The signal acquisition probe 9 is used for trial signal acquisition. When the transmission current I=12A, when the signal acquisition time is 1.25×10 -1 s, the induced voltage signal is 5×10 -6V, which is greater than five times the power frequency electromagnetic noise, sets the emission current I to 12A, collects the induced voltage signal at each measuring point, and circles the area 14 where the measuring point with the higher induced voltage value is located.

[0073] Step 3: If Figure 5-6 As shown in the figure, the area 14 where the induced voltage value is higher is 405m 2 According to formula (6), the side length of the small transmitting wire frame 15 is calculated to be l = 20m.

[0074] l=S 1 / 2 (6)

[0075] In formula (6), l is the side length of the small transmitting wire frame 15, in m, and S is the area of ​​the area where the induced voltage signal value is higher, which is circled in step 2, in m. 2 .

[0076] like Figure 6-Figure 9 As shown, the small transmitting wire frame 15 is arranged within the range of platform 1 4, and a 10m×10m measuring point network is arranged on platform 2 16, platform 3 17, platform 4 18, and platform 5 19, and the signal acquisition probe 9 is used to collect the induced voltage signal; according to formulas (7)-(10), the transmitting frequency f is adjusted in time to ensure that the induced voltage signal can reflect the geological information between the platform where the transmitting wire frame is located and the platform where the signal acquisition probe is located, and the transmitting current I is adjusted to ensure that the transmitting current I is close to T n The induced voltage signal collected is greater than 2.5×10 -6 V.

[0077] E nH =∑D i '·E i ' / ∑D i ' (7)

[0078]

[0079] T n =(1 / f)>t n =t 1n +t 2n (10)

[0080] In formula (7), E nH is the weighted average conductivity of the stratum between the platform where the small transmitting wireframe is located and the platform where the signal acquisition probe is located, in S / m, E i ' is the conductivity of the i-th layer below the platform where the small transmitting wireframe is located, in S / m, D i ' is the thickness of the i-th layer below the platform where the small transmitting wireframe is located, in m, ∑D i'=nH; In formulas (7)-(9), H is the height of the open-pit iron ore step, H=15m, nH<100m, n represents the signal acquisition probe located on the nth platform below the platform where the small transmitting wire frame is located; In formulas (8)-(10), t n , t 1n , t 2n All are time, unit is s.

[0081] According to the existing geological data, we can calculate: 11 =1.1×10 -4 s, t 21 =6.38×10 -3 s;t 12 =1.17×10 -4 s, t 22 =1.6×10 -2 s;t 13 =1.26×10 -4 s, t 23 =2.99×10 -2 s;t 14 =1.37×10 -4 s, t 24 =4.82×10 -2 s, when the signal acquisition probe 9 is collecting signals on the platform 2 16, the transmission frequency f is set to 128 Hz, T = 7.81 × 10 -3 s; When the signal acquisition probe 9 is performing signal acquisition on platform three 17, the transmission frequency f is set to 55Hz, T = 1.82×10 -2 When the signal acquisition probe 9 is performing signal acquisition on the platform 18, the transmission frequency f is set to 30Hz, T = 3.33 × 10 -2 s; When the signal acquisition probe 9 is performing signal acquisition on platform V 19, the transmission frequency f is set to 20 Hz, T = 5.0 × 10 -2 After trial signal acquisition, when the emission current I = 10A, the induced voltage signals collected on platform 216, platform 317, platform 418, and platform 519 are all greater than 2.5×10 -6 V, so the emission current I is set to 10A.

[0082] Step 4: Compare the voltages collected on platform 2 16, platform 3 17, platform 4 18, and platform 5 19, and compare the maximum voltage V nm The corresponding acquisition time t nm Determine the top position of the water-filled goaf 3; V nm It represents the maximum value of the induced voltage signal collected by the nth platform below the platform 4 where the small transmitting wire frame is located, in V, t nm Vnm The corresponding acquisition time, in seconds, is the maximum voltage value and the acquisition time data corresponding to the maximum voltage value collected at platform 2 16, platform 3 17, platform 4 18, and platform 5 19: t 1m =1.08×10 -4 s, t 2m =1.15×10 -4 s, t 3m =2.36×10 -3 s, t 4m =1.19×10 - 2 s; V 1m =1.47×10 -2 V, V 2m =1.39×10 -2 V, V 3m =1.27×10 -2 V, V 4m =1.09×10 -2 V, when n < 2, it satisfies formula (11), and when n ≥ 2, it satisfies formula (12). It is considered that the top of the water-filled goaf 3 is located below the horizontal plane 17 of platform three and above the horizontal plane 18 of platform four.

[0083] t 1(n+1) -t 1n =t (n+1)m -t nm (11)

[0084] t 1(n+1) -t 1n <t (n+1)m -t nm (12)

[0085] where t 1n The time required to satisfy formula (8), in seconds.

[0086] Step 5: If Figure 10 As shown, the small transmitting wire frame 15 is arranged on the platform 4 18, and the small transmitting wire frame 15 is arranged on the platform 4 18. 3m At the measuring point, the signal acquisition probe 9 moves to the platform 5 19, and the emission frequency f of the emission current in the small emission wire frame 15 is adjusted in time according to formulas (13)-(16), and the emission frequency is set to 128Hz, T'=7.81×10 -3 s, when the emission current is I = 10A, the induced voltage signals collected on each platform are close to 7.81×10 -3 s, the induced voltage signals are all greater than 2.5×10 - 6 V, so the emission current I is set to 10A.

[0087] E 3H2 =ΣD i ”·E i ” / ΣD i ”(13)

[0088]

[0089] T'=(1 / f)>t'=t1'+t'2 (16)

[0090] E in formula (13)-(15) 3H / 2 The weighted average conductivity of the strata between platform 4 18 and platform 5 19, and the strata within H / 2 below platform 5 19, in S / m, E i " is the conductivity of the i-th layer below platform 4 18, in S / m, D i ” is the thickness of the i-th layer below platform 4 18, in meters, ∑D i ”=3H / 2.

[0091] like Figure 11-12 As shown, the small transmitting wire frame 15 and the signal acquisition probe 9 are moved down platform by platform to platform seven 21. During the implementation process, the change in the conductivity of the stratum between two adjacent platforms has little effect on the transmitting frequency. During the downward movement, the transmitting frequency f = 128 Hz is kept unchanged, and the transmitting current I = 10 A is kept unchanged.

[0092] Comparing the maximum voltage and the time corresponding to the maximum value collected at platform 5 19, platform 6 20 and platform 7 21, V4' m =0.92×10 -2 V, V5' m =0.92×10 -2 V, V6' m =1.24×10 -2 V;t' 4m =4.05×10 -3 s, t' 5m =4.05×10 -3 s, t' 6m =1.94×10 -3 s, V′ qm The maximum value of the induced voltage signal collected on the qth platform below the platform 14 is t', which is obtained by placing the small transmitting wire frame 15 on the platform 4 18, moving the signal acquisition probe 9 to the platform 5 19, and moving the small transmitting wire frame 15 and the signal acquisition probe 9 downwards one platform at a time. qm V′ qmThe induced voltage signals collected on each platform have the following characteristics, which can be used to determine the bottom position of the water-filled goaf 3: V′ 4m =V′ 5m <V′ 6m , and t′ 4m =t′ 5m >t′ 6m , it is believed that the bottom of the water-logged goaf 3 is located above the horizontal plane 21 of platform seven and below the horizontal plane 20 of platform six.

Claims

1. A method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic technology, characterized in that: The specific steps are as follows: Step 1: Lay out a transmitting wireframe along the edge of the open-pit iron ore platform and determine the electrical characteristics of the strata based on the stratum distribution shown in existing geological data. Based on the electrical characteristics of the strata, determine the transmission frequency f (in Hz) of the transmitting current in the transmitting wireframe to ensure that the induced voltage signal can reflect the geological information within 100 meters below the platform where the transmitting wireframe is located. Step 2: Lay out measurement lines and measurement points on the platform where the transmitting wireframe is located, adjust the transmitting current I in A, and use a signal acquisition probe to collect induced voltage signals at each measurement point. Compare the collected voltages and circle the areas where the induced voltage signals are higher, predicting the presence of water-logged goaf below them. Step 3: Calculate the side length of the small transmitting wireframe using the area of ​​the enclosed area, and place the small transmitting wireframe within the enclosed area. Lay out survey lines and points on the first, second, third, and fourth platforms below the platform where the small transmitting wireframe is located. Use a signal acquisition probe to collect induced voltage signals, and promptly adjust the transmitting current I and transmitting frequency f in the small transmitting wireframe to ensure that the induced voltage signal can reflect the geological information between the platform where the transmitting wireframe is located and the platform where the signal acquisition probe is located. Step 4: Compare the acquisition times corresponding to the maximum voltage values ​​collected on the first, second, third, and fourth platforms below the platform where the small transmitting wireframe is located to determine the top position of the water-filled goaf; Step 5: Place the small transmitting wire frame on the first platform below the top of the water-logged goaf determined in step 4, and place the small transmitting wire frame in the area where the measuring point where the maximum value of the induced voltage signal is collected is located. Move the signal acquisition probe to the first platform below the platform where the small transmitting wire frame is located, adjust the transmitting current I and the transmitting frequency f, and ensure that the induced voltage signal can reflect the geological information between the platform where the small transmitting wire frame is located and the platform where the signal acquisition probe is located; keep the transmitting current I and the transmitting frequency f unchanged, move the small transmitting wire frame and the signal acquisition probe down platform by platform and collect the induced voltage signal, compare the collected maximum voltage and the collection time corresponding to the maximum value, and determine the bottom position of the water-logged goaf.

2. The method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic detection according to claim 1, characterized in that: In step 1, the conductivity of each rock layer is estimated based on the stratum information reflected by the existing geological data, and the weighted average conductivity E of the stratum within 100m below the platform where the transmitting wireframe is located is calculated according to formula (1): 100 . AND 100 =∑D i ·AND i / ∑D i (1) E in formula (1) i is the conductivity of the i-th layer below the platform where the transmitting wireframe is located, in S / m, D i is the thickness of the i-th layer below the platform where the transmitting wireframe is located, in meters, E 100 The weighted average conductivity of the stratum within 100m below the platform where the transmitting wireframe is located, in S / m, ∑D i ≤100m. The diffusion speed of the induced eddy current into the deep layer is calculated according to formula (2). v=3.18 / (10 -5 ×Et) 1 / 2 (2) In formula (2), v represents the velocity of the induced eddy current propagating deep into the formation, in m / s; E is the conductivity of the formation, in S / m; and t is the time, in s. Adjust the transmission frequency f according to formulas (3)-(5) to ensure that the induced voltage signal can reflect the geological information within 100m below the platform where the transmitting wireframe is located. T=(1 / f)>t=t1+t2(5) In formulas (3)-(5), t, t1, and t2 are all time units, in seconds, and t0 = 10 -4 s, E in formula (4) w is the conductivity of the water in the goaf, in S / m. In formula (5), T is the acquisition period of the induced voltage signal, in s, and f is the emission frequency of the emission current in the emission frame, in Hz.

3. The method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic detection according to claim 1, characterized in that: In step 2, the emission current I is adjusted to ensure that the induced voltage signal collected when it is close to T is five times higher than the power frequency electromagnetic noise. Usually, the power frequency electromagnetic noise is 5×10 -7 V, that is, the induced voltage signal value collected when the signal acquisition probe approaches time T must be greater than 2.5×10 -6 V. Preferably, the side length of the small emission wireframe in step 3 is calculated according to formula (6): l＝S 1 / 2 (6) In formula (6), l is the side length of the small transmitting wire frame, in m, and S is the area of ​​the region with higher induced voltage signal value circled in step 2, in m 2 .

4. The method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic detection according to claim 1, characterized in that: In step 3, the transmitting current I and the transmitting frequency f are adjusted in time according to formulas (7)-(10) to ensure that the induced voltage signal can reflect the geological information between the platform where the small transmitting wire frame is located and the platform where the signal acquisition probe is located, and close to T n The induced voltage signal collected is greater than 2.5×10 -6 V. AND nH =∑D i '·AND i ' / ∑D i '(7) T n =(1 / f)>t n =t 1n +t 2n (10) In formula (7), E nH is the weighted average conductivity of the stratum between the platform where the small transmitting wireframe is located and the platform where the signal acquisition probe is located in step 3, in S / m, E i ' is the conductivity of the i-th layer below the platform where the transmitting wireframe is located in step 3, in S / m, D i ' is the thickness of the i-th layer below the platform where the launch wireframe is located in step 3, in meters, ΣD i '=nH; In formulas (7)-(9), H is the height of the open pit iron ore step, in m, nH<100m, n means that the signal acquisition probe is located on the nth platform below the platform where the small transmitting wire frame is located in step 3; In formulas (8)-(10), t n , t 1n , t 2n All are time, unit is s.

5. The method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic detection according to claim 1, characterized in that: The specific content of determining the top position of the water-filled goaf in step 4 is as follows: compare the voltages collected on the first, second, third, and fourth platforms below the platform where the small transmitting wire frame is located, and compare the maximum voltage V collected on each platform. nm The corresponding acquisition time t nm , V nm Indicates the maximum value of the induced voltage signal collected by the nth platform below the platform where the small transmitting wire frame is located, in V. nm V nm The corresponding acquisition time is in seconds. When n < N, formula (11) is satisfied, and when n ≥ N, formula (12) is satisfied. It is assumed that the top of the water-filled goaf is located below the horizontal plane of the Nth platform below the platform where the launch frame is located, and above the horizontal plane of the N+1th platform below the platform where the launch frame is located. t 1(n+1) -t 1n =t (n+1)m -t nm (11) t 1(n+1) -t 1n <t (n+1)m -t nm (12) where t 1n The time required to satisfy formula (8), in seconds. If the top position of the water-filled goaf is still not found on the first platform, second platform, third platform, and fourth platform below the small emission wireframe, move the emission wireframe in step one to the first platform below the platform, and repeat steps one, two, three, and four in sequence until the top position of the water-filled goaf is determined.

6. The method for exploring deep waterlogged goaf in open-pit iron mines based on transient electromagnetic detection according to claim 1, characterized in that: In step 5, the transmitting current I and the transmitting frequency f are adjusted in time according to formulas (13)-(16) to ensure that the induced voltage signal can reflect the geological information between the platform where the small transmitting wire frame is located and the platform where the signal acquisition probe is located, and the induced voltage signal collected when approaching T' is greater than 2.5×10 -6 V. E 3H / 2 =ΣD” i ·E” i / S.D. i (13) T'=(1 / f)>t'=t1'+t'2 (16) E in formula (13)-(16) 3H / 2 The weighted average conductivity of the stratum between the platform where the small transmitting wireframe is located and the platform where the signal acquisition probe is located, as well as the stratum within H / 2 below the platform where the signal acquisition probe is located, in S / m, E” i The conductivity of the i-th layer of the ground below the platform where the small emission wireframe is located in step 5, in S / m, D” i is the thickness of the i-th layer of the ground below the platform where the small emission wireframe is located in step 5, in meters, ∑D” i =3H / 2. The transmitting frequency f is continuously adjusted during the process of moving the small transmitting wire frame and the signal acquisition probe downward step by step, so that formulas (13)-(16) are valid; and the transmitting current I is adjusted to ensure that the induced voltage signal collected near T' is greater than 2.5×10 -6 V. Comparing the voltages collected on each platform in step five, the bottom position of the water-logged goaf can be determined if the collected voltages have the following characteristics: The maximum value of the induced voltage signal collected on the qth platform below the circled range of the small transmitting wire frame in step three is V' qm , unit is V, maximum value of induced voltage signal V' qm The corresponding time is t' qm , unit is s; When q<Q, all V' qm Equal, all t' qm Also equal; when q=Q, V' Qm >V' q ' m , and t' Qm <t' qm It is believed that the bottom of the water-filled goaf is located above the Qth platform horizontal plane below the circled range of the small emission wire frame in step three, and below the Q-1th platform horizontal plane below the circled range of the small emission wire frame in step three.

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