CN108978696B - Open caisson back cover prevention of seepage and displacement monitoring devices - Google Patents

Open caisson back cover prevention of seepage and displacement monitoring devices Download PDF

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CN108978696B
CN108978696B CN201810728518.5A CN201810728518A CN108978696B CN 108978696 B CN108978696 B CN 108978696B CN 201810728518 A CN201810728518 A CN 201810728518A CN 108978696 B CN108978696 B CN 108978696B
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optical fiber
water
pressure sensor
open caisson
distributed optical
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CN108978696A (en
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金炜枫
王鑫
邓陈艳
黄扬飞
其他发明人请求不公开姓名
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Zhejiang Lover Health Science and Technology Development Co Ltd
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    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D23/00—Caissons; Construction or placing of caissons
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
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Abstract

The invention discloses an open caisson bottom sealing seepage prevention and displacement monitoring device, which comprises a water-proof thin plate and a displacement monitoring device, wherein the displacement monitoring device is arranged on the water-proof thin plate; the displacement monitoring device comprises a first rod, a first pressure sensor, distributed optical fibers, a second pressure sensor and a second rod which are connected in sequence, the water-resisting thin plate is horizontally placed, the distributed optical fibers are horizontally placed on the upper surface of the water-resisting thin plate, the first rod and the second rod are vertically placed, and the distributed optical fibers can monitor strain of the upper surface of the water-resisting thin plate. The invention has the advantages of reducing the problem of leakage of the bottom seal of the open caisson caused by the confined water, monitoring whether the bottom seal of the open caisson leaks or not, and monitoring the displacement and the stress of the water-proof thin plate in the bottom seal of the open caisson so as to early warn the overlarge pressure of the confined water below the bottom seal of the open caisson.

Description

Open caisson back cover prevention of seepage and displacement monitoring devices
Technical Field
The invention belongs to the field of geotechnical engineering research, and particularly relates to a device for bottom sealing seepage prevention and displacement monitoring of an open caisson.
Background
The open caisson foundation is a form of underground structure, and is characterized by that firstly, a well-cylindrical open caisson is made on the ground surface, then the soil is continuously dug in the open caisson to make the open caisson gradually sink to a specific elevation under the action of self-weight, then the bottom is sealed. The bottom sealing can prevent groundwater from flowing into the open caisson. When an open caisson foundation is adopted in an area with abundant underground water, in order to balance the influence of underground confined water, the concrete is generally poured by a guide pipe method for bottom sealing, but if the confined water pressure is too high, the bottom sealing is difficult, and the deformation and cracking of the bottom sealing can be caused by the too high confined water pressure.
Disclosure of Invention
The invention provides a device for preventing bottom sealing seepage and monitoring displacement of an open caisson, which aims to solve the problem of leakage and cracking of the bottom sealing of the open caisson caused by confined water and detect displacement and stress of the bottom sealing of the open caisson so as to early warn overlarge pressure of the confined water.
The technical scheme of the invention is as follows: an open caisson back cover seepage prevention and displacement monitoring device comprises a water-proof thin plate and a displacement monitoring device; the displacement monitoring device comprises a data acquisition and analysis system, an optical fiber demodulator, a first rod, a first pressure sensor, a distributed optical fiber, a second pressure sensor and a second rod, wherein the first rod, the first pressure sensor, the distributed optical fiber, the second pressure sensor and the second rod are sequentially connected, the data acquisition and analysis system is sequentially connected with the first pressure sensor and the second pressure sensor, the water-resisting thin plate is horizontally placed, the distributed optical fiber is horizontally placed on the upper surface of the water-resisting thin plate, and the first rod and the second rod are vertically placed. The strain of the upper surface of the water-resisting thin plate can be monitored by the distributed optical fibers, the water-resisting thin plate is circular, the optical fibers pass through the circle center of the water-resisting thin plate, and the center point of the optical fibers is coincided with the circle center of the water-resisting thin plate.
Preferably, the first pressure sensor and the second pressure sensor are both made of piezoelectric ceramics.
Preferably, the open caisson bottom sealing seepage prevention and displacement monitoring device is provided with a direct current power supply and an ammeter, a positive pole access point and a negative pole access point for measuring resistance are arranged at the edge of the waterproof sheet, the positive pole access point is connected with the positive pole of the direct current power supply, the negative pole of the direct current power supply, the ammeter and the negative pole access point are sequentially connected, the resistance R is calculated through the voltage U of the direct current power supply and the current I measured by the ammeter, and the open caisson bottom seepage prevention and displacement monitoring device comprises a direct current power supply and an ammeter
Figure GDA0002454543180000021
And (4) monitoring the change of the resistance R to judge whether the open caisson bottom sealing has leakage, wherein for example, the sudden reduction of the resistance R indicates that the leakage occurs.
An anti-seepage and displacement monitoring method of an open caisson bottom sealing anti-seepage and displacement monitoring device comprises the following steps:
step 1: the cross section of the open caisson is circular, and the water-resisting thin plate is circular; the lower end of the open caisson is provided with a bottom sealing reinforcing layer, the bottom sealing reinforcing layer can be formed by pouring concrete or mixing cement and soil, the bottom sealing reinforcing layer has the functions of resisting water pressure and preventing seepage at the bottom of the open caisson, a water-proof thin plate is horizontally arranged in the bottom sealing reinforcing layer and can enhance the seepage-preventing capacity of the open caisson bottom sealing, a first pressure sensor and a second pressure sensor are respectively positioned at the upper parts of two ends of a distributed optical fiber, one end of a first rod is connected with the first pressure sensor while the other end is connected with the bottom of the open caisson, one end of a second rod is connected with the second pressure sensor while the other end is connected with the bottom of the open caisson, and the water-proof thin plate can prevent underground confined water from infiltrating along the cracks of the bottom sealing layer;
step 2, displacement monitoring, namely measuring the compression amount of the first rod and the second rod, and setting the length of the first rod to L1Let the second rod length be L2Let the Young's modulus of the first shaft be E1Let the Young's modulus of the second shaft be E2Let the stress measured by the first pressure sensor be σ1Let the stress measured by the second pressure sensor be σ2Let the compression amount of the first rod be Δ s1Let the compression amount of the second rod be Δ s2Then there is a first rod having a compression of
Figure GDA0002454543180000031
The second rod is compressed by
Figure GDA0002454543180000032
Then measuring the relative vertical displacement w of the midpoint of the distributed optical fiber relative to the first pressure sensor1Measuring the relative vertical displacement w of the midpoint of the distributed optical fiber relative to the second pressure sensor2The average relative vertical displacement of the midpoint of the distributed optical fiber relative to the two ends of the distributed optical fiber is wo＝(w1+w2) And/2, finally calculating the absolute vertical displacement of the center of the water-resisting thin plate as w ═ wo+(Δs1+Δs2)/2；
And step 3: checking whether the stress of the water-resisting thin plate exceeds the strength of the water-resisting thin plate: setting the radius of the circular waterproof thin plate as R, the plate thickness of the circular waterproof thin plate as h, the Young modulus of the circular waterproof thin plate as E, the Poisson ratio of the circular waterproof thin plate as v, and taking the displacement at the circle center of the circular waterproof thin plate as the measured average relative displacement w of the midpoint of the distributed optical fiber relative to the two ends of the distributed optical fiberoThen, the maximum stress in the water-barrier sheet is set to σmaxAnd the calculation formula is
Figure GDA0002454543180000033
Let the strength of the water-proof sheet be [ sigma ]]When σ ismax≥[σ]The stress in the water-resisting sheet exceeds the self strength, namely the bottom sealing reinforcing layer and the water-resisting sheet are deformed too much and the deformation is caused by underground confined waterThe water-resisting thin plate is damaged, so that early warning can be provided for overlarge pressure of the confined water on the bottom sealing of the open caisson;
and 4, step 4: and (3) checking whether the bottom sealing of the open caisson has leakage or not: setting a positive electrode access point and a negative electrode access point for resistance measurement at the edge of the waterproof sheet, connecting the positive electrode access point with the positive electrode of a direct current power supply, sequentially connecting the negative electrode of the direct current power supply, an ammeter and the negative electrode access point, calculating a resistance R through the voltage U of the direct current power supply and the current I measured by the ammeter, and adding
Figure GDA0002454543180000034
And (4) monitoring the change of the resistance R to judge whether the open caisson bottom sealing has leakage, wherein for example, the sudden reduction of the resistance R indicates that the leakage occurs.
Preferably, the relative vertical displacement w is measured in step 21The method comprises the following steps: firstly, evenly dividing an optical fiber end point from a middle point of a distributed optical fiber to a first pressure sensor into n sections, wherein the length of each section in the distributed optical fiber is delta l, when the radius of a circular waterproof thin plate is R, the delta l is R/n, the optical fiber end point where the first pressure sensor is located is marked as a node 1, a node corresponding to the middle point of the distributed optical fiber is marked as n +1, nodes from the node 1 to the node in the direction of n +1 are marked as 1, 2, 3, …, n, n +1 in sequence, and the strain measured by the ith node of the distributed optical fiber is set asiThe relative vertical displacement w of the midpoint of the distributed optical fiber with respect to the end point of the optical fiber where the first pressure sensor is located1Is calculated by the formula
Figure GDA0002454543180000041
The relative vertical displacement w of the middle point of the distributed optical fiber relative to the end point of the optical fiber where the second pressure sensor is positioned2Is calculated from w1The calculation process is the same.
The invention has the advantages of reducing the problem of leakage of the bottom seal of the open caisson caused by the confined water, monitoring whether the bottom seal of the open caisson leaks or not, and monitoring the displacement and the stress of the water-proof thin plate in the bottom seal of the open caisson so as to early warn that the pressure of the confined water below the bottom seal of the open caisson is overlarge.
Drawings
FIG. 1 is a schematic view of a water-stop sheet, a back-cover reinforcing layer and an open caisson of the present invention;
FIG. 2 is a schematic longitudinal cross-sectional view of a water-resisting sheet according to the present invention;
fig. 3 is a top view of the water-stop sheet according to the present invention.
Fig. 4 is a schematic diagram of the connection between the data acquisition and analysis system and the distributed optical fiber and the pressure sensor according to the present invention.
In the figure, 1, a foundation soil layer, 2, an open caisson, 3, a water-proof thin plate, 4, a bottom sealing reinforcing layer, 5, a distributed optical fiber, 6, a first rod, 7, a second rod, 8, a first pressure sensor, 9, a second pressure sensor, 10, a direct current power supply, 11, a current meter, 12, a positive pole access point, 13, a negative pole access point, 14, an optical fiber demodulator and 15, a data acquisition and analysis system are shown.
Detailed Description
In order to make the technical means, innovative features, objectives and effects of the present invention apparent, the present invention will be further described with reference to the following detailed drawings.
As shown in fig. 1-3, the device for monitoring bottom sealing seepage prevention and displacement of an open caisson comprises a water-proof thin plate 3 and a displacement monitoring device; the displacement monitoring device comprises a data acquisition and analysis system 15, an optical fiber demodulator 14, a first rod 6, a first pressure sensor 8, a distributed optical fiber 5, a second pressure sensor 9 and a second rod 7 which are sequentially connected, wherein the data acquisition and analysis system 15, the optical fiber demodulator 14 and the distributed optical fiber 5 are sequentially connected, the data acquisition and analysis system 15 is respectively connected with the first pressure sensor 8 and the second pressure sensor 9, the waterproof sheet 3 is horizontally arranged, the distributed optical fiber 5 is horizontally arranged on the upper surface of the waterproof sheet 3, and the first rod 6 and the second rod 7 are vertically arranged; the distributed optical fiber 5 can monitor the strain of the upper surface of the water-proof thin plate 3;
the waterproof sheet 3 is circular, the distributed optical fibers 5 pass through the circle center of the waterproof sheet 3, and the center points of the distributed optical fibers 5 are superposed with the circle center of the waterproof sheet 3;
the open caisson bottom sealing seepage prevention and displacement monitoring device is provided with a direct current power supply 10 and an ammeter 11, a positive pole access point 12 and a negative pole access point 13 for measuring resistance, a positive pole access point 12 and a straight pole are arranged at the edge of the waterproof sheet 3The positive pole of the DC power supply 10 is connected, the negative pole of the DC power supply 10, the ammeter 11 and the negative pole access point 13 are connected in sequence, and the resistance R is calculated by the voltage U of the DC power supply 10 and the current I measured by the ammeter, including
Figure GDA0002454543180000051
And (4) monitoring the change of the resistance R to judge whether the open caisson bottom sealing has leakage, wherein for example, the sudden reduction of the resistance R indicates that the leakage occurs.
An anti-seepage and displacement monitoring method of an open caisson bottom sealing anti-seepage and displacement monitoring device comprises the following steps:
step 1: an open caisson 2 is arranged in the foundation soil layer 1, the cross section of the open caisson 2 is circular, and the waterproof sheet 3 is circular; the lower end of the open caisson 2 is provided with a bottom sealing reinforcing layer 4, bottom sealing reinforcement is performed, the bottom sealing reinforcing layer 4 can be formed by pouring concrete or mixing cement and soil, the bottom sealing reinforcing layer 4 has the functions of resisting water pressure and preventing seepage at the bottom of the open caisson 2, a water-proof thin plate 3 is horizontally arranged in the bottom sealing reinforcing layer 4, the water-proof thin plate 3 enhances the anti-seepage capability of the bottom sealing of the open caisson 2, a first pressure sensor 8 and a second pressure sensor 9 are respectively positioned at the upper parts of two ends of a distributed optical fiber 5, one end of a first rod 6 is connected with the first pressure sensor 8, the other end of the first rod is connected with the bottom of the open caisson 2, one end of a second rod 6 is connected with the second pressure sensor 9, the other end of the second rod is connected with the bottom of the open caisson 2, and the water-proof thin plate 3 can;
step 2, displacement monitoring, namely, firstly measuring the compression amount of the first rod 6 and the second rod 7, and setting the length of the first rod 6 to L1Let the second lever 7 be L in length2The Young's modulus of the first shaft 6 is set to E1The Young's modulus of the second shaft 7 is set to E2Let us say that the stress measured by the first pressure sensor 8 is σ1Let us say that the stress measured by the second pressure sensor 9 is σ2Let the compression amount of the first rod 6 be Δ s1Let the compression amount of the second rod 7 be Δ s2Then there is a compression of the first rod 6 of
Figure GDA0002454543180000061
The second rod 7 is compressed by an amount of
Figure GDA0002454543180000062
The relative vertical displacement w of the midpoint of the distributed optical fiber 5 with respect to the first pressure sensor 8 is then measured1Measuring the relative vertical displacement w of the midpoint of the distributed optical fiber 5 relative to the second pressure sensor 92The average relative vertical displacement of the middle point of the distributed optical fiber 5 relative to the two ends of the distributed optical fiber is wo＝(w1+w2) And/2, finally calculating the absolute vertical displacement of the center of the water-resisting thin plate 3 as w ═ wo+(Δs1+Δs2)/2；
And step 3: checking whether the stress of the water-resisting thin plate 3 exceeds the strength of the water-resisting thin plate 3: setting the radius of the circular waterproof thin plate 3 as R, the plate thickness of the circular waterproof thin plate 3 as h, the Young modulus of the circular waterproof thin plate 3 as E, the Poisson ratio of the circular waterproof thin plate 3 as v, and taking the displacement at the circle center of the circular waterproof thin plate 3 as the measured average relative vertical displacement w of the middle point of the distributed optical fiber 5 relative to the two ends of the distributed optical fiber 5oThen, the maximum stress in the water-stop sheet 3 is set to σmaxAnd the calculation formula is
Figure GDA0002454543180000071
Let the strength of the water-proof sheet 3 be [ sigma ]]When σ ismax≥[σ]The stress in the water-resisting sheet 3 exceeds the strength of the water-resisting sheet, namely the bottom sealing reinforcing layer 4 and the water-resisting sheet 3 are deformed too much and the water-resisting sheet 3 is damaged due to underground pressure-bearing water, so that early warning can be provided for the excessive pressure of the pressure-bearing water on the bottom sealing of the open caisson 2;
and 4, step 4: and (3) checking whether the bottom sealing of the open caisson 2 leaks: setting a positive pole access point 12 and a negative pole access point 13 for resistance measurement at the edge of the waterproof sheet 3, connecting the positive pole access point 12 with the positive pole of the direct current power supply 10, sequentially connecting the negative pole of the direct current power supply 10, the ammeter 11 and the negative pole access point 13, calculating the resistance R through the voltage U of the direct current power supply 10 and the current I measured by the ammeter 11, and calculating the resistance R through the voltage U of the direct current power supply 10 and the current I measured by the ammeter 11
Figure GDA0002454543180000072
The open caisson 2 is judged whether to leak or not by monitoring the change of the resistance R, for example, the sudden reduction of the resistance R indicates that the leakage occurs.
Measuring the relative vertical displacement w in the step 21The method comprises the following steps: firstly, evenly dividing an endpoint of an optical fiber 5 from a midpoint of the distributed optical fiber 5 to a first pressure sensor 8 into n segments, wherein the length of each segment in the distributed optical fiber 5 is delta l, when the radius of the circular waterproof sheet 3 is R, the delta l is R/n, the endpoint of the optical fiber 5 where the first pressure sensor 8 is located is recorded as a node 1, a node corresponding to the midpoint of the distributed optical fiber 5 is recorded as n +1, nodes from the node 1 to the node in the direction of n +1 are recorded as 1, 2, 3, …, n, n +1 in sequence, and strain measured by the ith node of the distributed optical fiber 5 is set asiThe relative vertical displacement w of the midpoint of the distributed optical fiber 5 with respect to the end point of the optical fiber 5 where the first pressure sensor 8 is located1Is calculated by the formula
Figure GDA0002454543180000081
The relative vertical displacement w of the middle point of the distributed optical fiber 5 relative to the end point of the optical fiber 5 where the second pressure sensor 9 is located2Is calculated from w1The calculation process is the same.

Claims (5)

1. The utility model provides an open caisson back cover prevention of seepage and displacement monitoring devices which characterized in that: the device comprises a waterproof sheet and a displacement monitoring device; displacement monitoring devices contains data acquisition analytic system, optic fibre demodulation appearance and the first pole, first pressure sensor, distributed optical fiber, second pressure sensor and the second pole that connect gradually, data acquisition analytic system, optic fibre demodulation appearance and distributed optical fiber connect gradually, data acquisition analytic system is connected with first pressure sensor and second pressure sensor respectively, water proof sheet metal level is placed, distributed optical fiber horizontal placement is at water proof sheet metal upper surface, first pole and the vertical placing of second pole, the water proof sheet metal is circular, distributed optical fiber passes through the centre of a circle of water proof sheet metal, and the coincidence of optic fibre mid point and water proof sheet metal centre of a circle.
2. The open caisson bottom sealing seepage prevention and displacement monitoring device of claim 1, wherein: the first pressure sensor and the second pressure sensor are both made of piezoelectric ceramics.
3. The open caisson bottom sealing seepage prevention and displacement monitoring device of claim 1, wherein: the open caisson bottom sealing seepage prevention and displacement monitoring device is provided with a direct current power supply and an ammeter, a positive pole access point and a negative pole access point for measuring resistance are arranged on the edge of the waterproof thin plate, the positive pole access point is connected with the positive pole of the direct current power supply, and the negative pole of the direct current power supply, the ammeter and the negative pole access point are sequentially connected.
4. The seepage-proofing and displacement-monitoring method of the open caisson closing seepage-proofing and displacement-monitoring device according to any one of claims 1 to 3, wherein the seepage-proofing and displacement-monitoring method comprises the following steps: which comprises the following steps:
step 1: the cross section of the open caisson is circular, and the water-resisting thin plate is circular; a bottom sealing reinforcing layer is arranged at the lower end of the open caisson, the bottom sealing reinforcing layer can be formed by pouring concrete or mixing cement and soil, a waterproof sheet is horizontally arranged in the bottom sealing reinforcing layer, a first pressure sensor and a second pressure sensor are respectively positioned at the upper parts of two ends of the distributed optical fiber, one end of a first rod is connected with the first pressure sensor, the other end of the first rod is connected with the bottom of the open caisson, one end of a second rod is connected with the second pressure sensor, and the other end of the second rod is connected with the bottom of the open caisson;
step 2, displacement monitoring, namely measuring the compression amount of the first rod and the second rod, and setting the length of the first rod to L1Let the second rod length be L2Let the Young's modulus of the first shaft be E1Let the Young's modulus of the second shaft be E2Let the stress measured by the first pressure sensor be σ1Let the stress measured by the second pressure sensor be σ2Let the compression amount of the first rod be Δ s1Let the compression amount of the second rod be Δ s2Then there is a first rod having a compression of
Figure FDA0002483514900000021
The second rod is compressed by
Figure FDA0002483514900000022
Then theMeasuring the relative vertical displacement w of the midpoint of the distributed optical fiber relative to the first pressure sensor1Measuring the relative vertical displacement w of the midpoint of the distributed optical fiber relative to the second pressure sensor2The average relative vertical displacement of the midpoint of the distributed optical fiber relative to the two ends of the distributed optical fiber is wo＝(w1+w2) And/2, finally calculating the absolute vertical displacement of the center of the water-resisting thin plate as w ═ wo+(Δs1+Δs2)/2；
And step 3: checking whether the stress of the water-resisting thin plate exceeds the strength of the water-resisting thin plate: setting the radius of the circular waterproof thin plate as R, the plate thickness of the circular waterproof thin plate as h, the Young modulus of the circular waterproof thin plate as E, the Poisson ratio of the circular waterproof thin plate as v, and taking the displacement at the circle center of the circular waterproof thin plate as the measured average relative displacement w of the midpoint of the distributed optical fiber relative to the two ends of the distributed optical fiberoThen, the maximum stress in the water-barrier sheet is set to σmaxAnd the calculation formula is
Figure FDA0002483514900000023
Let the strength of the water-proof sheet be [ sigma ]]When σ ismax≥[σ]The stress in the water-resisting sheet exceeds the strength of the water-resisting sheet, namely the bottom sealing reinforcing layer and the water-resisting sheet are deformed too much and the water-resisting sheet is damaged due to underground pressure-bearing water, so that early warning can be provided for the overlarge pressure of the pressure-bearing water on the bottom sealing of the open caisson;
and 4, step 4: and (3) checking whether the bottom sealing of the open caisson has leakage or not: setting a positive electrode access point and a negative electrode access point for resistance measurement at the edge of the waterproof sheet, connecting the positive electrode access point with the positive electrode of a direct current power supply, sequentially connecting the negative electrode of the direct current power supply, an ammeter and the negative electrode access point, calculating a resistance R through the voltage U of the direct current power supply and the current I measured by the ammeter, and adding
Figure FDA0002483514900000031
And (4) monitoring the change of the resistance R to judge whether the open caisson bottom sealing has leakage, wherein for example, the sudden reduction of the resistance R indicates that the leakage occurs.
5. An open caisson according to claim 4The seepage-proofing and displacement monitoring method of the bottom sealing seepage-proofing and displacement monitoring device is characterized in that: measuring the relative vertical displacement w in the step 21The method comprises the following steps: firstly, evenly dividing an optical fiber end point from a middle point of a distributed optical fiber to a first pressure sensor into n sections, wherein the length of each section in the distributed optical fiber is delta l, when the radius of a circular waterproof thin plate is R, the delta l is R/n, the optical fiber end point where the first pressure sensor is located is marked as a node 1, a node corresponding to the middle point of the distributed optical fiber is marked as n +1, nodes from the node 1 to the node in the direction of n +1 are marked as 1, 2, 3, …, n, n +1 in sequence, and the strain measured by the ith node of the distributed optical fiber is set asiThe relative vertical displacement w of the midpoint of the distributed optical fiber with respect to the end point of the optical fiber where the first pressure sensor is located1Is calculated by the formula
Figure FDA0002483514900000032
The relative vertical displacement w of the middle point of the distributed optical fiber relative to the end point of the optical fiber where the second pressure sensor is positioned2Is calculated from w1The calculation process is the same.
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