Instability force monitoring system of top pipe in soft formation and instability force calculation and processing method

Abstract

A system for monitoring the instability of top pipes in soft formations, including multiple pipe sections, with elevation measurement points provided on the inner walls of both sides of the pipe sections, and a level matched with the elevation measurement points provided at one end of the multiple pipe sections; a steel bar strain gauge is welded in the middle of the inner longitudinal main reinforcement on the pipe section near the machine head, and a vibrating string collector for collecting steel bar strain gauge data is installed in the pipe section; four displacement sensors are installed at the pipe section joints at the floating instability location, and the four displacement sensors are used to monitor the changes in the joint spacing; a grouting hole is opened at the bottom of the pipe section at the floating instability location; a tee is installed at the grouting hole on the pipe section at the floating instability location, and the tee is respectively connected to the grouting hole, the grouting pipe and the pressure sensor. The present invention adopts the above structure, which can realize the judgment of whether the pipeline has floating instability, monitor the floating instability location, analyze the development trend and stress state of the pipeline floating instability, and take relevant measures in time to ensure the safety of the pipeline structure.

Description

Technical Field

[0001] The invention relates to the technical field of pipe jacking engineering, and in particular to an instability force monitoring system for a pipe jacking in a soft formation and an instability force calculation and processing method. Background Art

[0002] In long-distance pipe jacking in soft formations, due to the low strength of the soil, when curved jacking is carried out or axis deviation occurs, the pipeline squeezes the surrounding soil, and the soil has poor restraint on the pipeline, so the pipeline deviates from the axis. This spontaneous displacement of the pipeline is called instability on site. In straight pipe jacking, if the pipeline is jacked completely according to the designed axis, the pipeline will not be unstable. However, due to factors such as design errors in the pipeline, uneven compression of the wooden pad, stratum changes, and machine head correction, the deflection of the pipeline cannot be avoided, and there is a risk of instability. At the same time, due to the effect of buoyancy, vertical floating instability usually occurs in straight pipe jacking. After floating instability occurs, the angle of the pipeline connection increases, which is prone to sealing failure and leakage. At the same time, it causes local stress concentration at the pipe end, resulting in cracks or damage to the pipeline, causing the project to fail. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a system for monitoring the instability of a pipe top in a soft formation and a method for calculating and processing the instability, which can determine whether the pipeline has floating instability, monitor the floating instability, analyze the development trend and stress state of the pipeline floating instability, and take relevant measures in time to ensure the safety of the pipeline structure.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a monitoring system for the instability of top pipe in soft formation, comprising a multi-section pipe section, wherein the inner walls on both sides of the pipe section are provided with elevation measurement points, and one end of the multi-section pipe section is provided with a level matched with the elevation measurement point;

[0005] A steel bar strain gauge is welded in the middle of the inner longitudinal main reinforcement on the pipe segment near the machine head, and a vibrating wire collector for collecting steel bar strain gauge data is installed in the pipe segment;

[0006] Four displacement sensors are installed at the pipe joints at the floating instability location, and the four displacement sensors are used to monitor the changes in the joint spacing;

[0007] A slurry discharge hole is provided at the bottom of the pipe section at the floating instability position;

[0008] A tee is installed at the grouting hole on the pipe section at the floating instability position, and the tee is respectively connected to the grouting hole, the grouting pipe and the pressure sensor;

[0009] The data of the displacement sensor and the pressure sensor are collected by a current collector arranged in the pipe segment.

[0010] In a preferred solution, there are four steel bar strain gauges, which are welded on the top, bottom and both sides of the pipe segment respectively.

[0011] In a preferred solution, a slurry discharge pipe with a ball valve is installed at the slurry discharge hole.

[0012] The instability force calculation method based on the above-mentioned soft formation top pipe instability force monitoring system includes the following steps:

[0013] 1) If the pipe segment is completely wrapped by mud, the annular mud density ρ 1 , the net buoyancy per unit length of the pipe section is calculated as follows:

[0014] F 1 =πD 2 ρ 1 g / 4-(D 2 -d 2 )πρ c g / 4

[0015] Where:

[0016] F 1 is the net buoyancy per unit length of the pipe segment, kN / m;

[0017] D is the outer diameter of the pipe segment, m;

[0018] d is the inner diameter of the pipe segment, m;

[0019] g is the acceleration due to gravity, m / s 2 ;

[0020] ρc is the density of concrete, which is 2400kg / m 3 .

[0021] 2) Grouting pressure P on the top of the pipe 1 The average value of the grouting pressure measured by the pressure sensor;

[0022] 3) If the steel bar strain gauge is located in the ath pipe section and the steel bar and concrete deform in coordination, the average value of the four steel bar strain gauges ε 1 As the strain of steel and concrete, the jacking force between the machine head and the front a-section pipe section is calculated as follows:

[0023] F a =ε 1 A s E s +ε 1 A c E c

[0024] Where:

[0025] Fa is the jacking force between the machine head and the front a-section pipe joint, kN;

[0026] As and Ac are the cross-sectional areas of steel bars and concrete, respectively. 2 ;

[0027] Es and Ec are the elastic moduli of steel and concrete, respectively, in kPa.

[0028] If the designed elevation and measured elevation of the pipe axis change at the bth and cth pipe sections respectively when the nth pipe section is jacked, and the elevation deviation at the dth pipe section is the largest, that is, the deflection between the pipe sections is the largest;

[0029] At this time, the total jacking force is Fn. If the friction resistance of each pipe section is the same, the vertical component of the jacking force of the dth pipe section is Fn. 2 The approximate calculation is as follows:

[0030] F 2 ={[(F n -f(nb))cosθ 1 -f(bc)]cos(θ 2 -θ 1 )-f(cd)}sin2θ 2

[0031] f=(F n -F a ) / (na)

[0032]

[0033]

[0034] Where:

[0035] f is the friction resistance of a single pipe section, kN;

[0036] h 1 is the elevation deviation of the cth pipe section, m;

[0037] h 2 is the elevation deviation of the dth pipe section, m;

[0038] l is the length of a single tube section, m;

[0039] 4) The soil on the top of the pipe is mainly affected by the grouting pressure, the net buoyancy of the pipeline and the vertical component of the jacking force. If the top of the pipe is in contact with the soil within 180°, the maximum stress on the soil on the top of the pipe is calculated as follows:

[0040]

[0041] Where: η is the ratio of the cover thickness to the outer diameter of the pipe segment.

[0042] 5) Compare the calculated maximum soil stress with the foundation bearing capacity. When the maximum soil stress is greater than the foundation bearing capacity, the soil will be damaged and the floating instability will continue to develop.

[0043] The instability stress processing method based on the above-mentioned soft formation top pipe instability stress monitoring system includes the following steps:

[0044] 1) Reduce the jacking force in the floating instability zone

[0045] The relay room in front of the floating instability zone is used for segmented jacking. The jacking force of the pipe section in front of the instability zone is borne by the relay room in front of the floating instability zone, and the jacking force on the floating instability zone is reduced;

[0046] 2) Pipe joint counterweight

[0047] A guide rail is installed at the bottom of the pipe section in the floating unstable area, and a counterweight vehicle is arranged on the guide rail, and the counterweight block is placed on the counterweight vehicle.

[0048] 3) Pipe top injection of thick mud

[0049] Concentrated mud is obtained by increasing the amount of bentonite on the basis of conventional thixotropic mud, and the concentrated mud is injected into the pipe top in the floating instability zone to fill the void on the pipe top and improve the soil strength.

[0050] In a preferred solution, in the step 1), if the jacking force does not decrease after the front relay room of the floating instability zone is activated, the rear relay room of the floating instability zone is activated.

[0051] In a preferred solution, the relay rooms existing in the floating instability zone are activated synchronously, and additional relay rooms are added in time when they are insufficient.

[0052] In a preferred solution, in step 2), the counterweight block is a concrete block or a steel block, and its mass is determined according to the net buoyancy of the pipe segment and the vertical component of the jacking force.

[0053] In a preferred embodiment, in step 3), the mass ratio of bentonite to water in the concentrated mud is controlled to be above 0.5:1 to reduce the fluidity of the concentrated mud.

[0054] In a preferred solution, a thick mud grouting hole is opened on the pipe top in the floating instability zone, and the stirred thick mud is pumped into the thick mud grouting pipe by a fine stone concrete pump and finally injected into the stratum on the pipe top.

[0055] The present invention provides a system for monitoring the instability stress of a top pipe in a soft formation and a method for calculating and processing the instability stress. By adopting the above structure and method, the present invention has the following beneficial effects:

[0056] (1) It realizes the monitoring of the stress state and displacement changes of the floating instability of the top pipe in soft formations, which is convenient for analyzing the development trend of pipeline instability and judging whether the relevant preventive treatment measures are effective;

[0057] (2) A method for calculating the stress on the soil at the top of the pipe based on the measured data was established. The method can accurately calculate the stress on the soil at the top of the pipe according to the construction parameters and the measured parameters, determine whether instability will occur, and take relevant control measures in a timely manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0059] Figure 1 This is a schematic diagram of pipe jacking elevation monitoring according to the present invention;

[0060] Figure 2 For the present invention Figure 1 Side view of.

[0061] Figure 3 It is a schematic diagram of the machine head jacking force monitoring of the present invention.

[0062] Figure 4 For the present invention Figure 2 Side view of.

[0063] Figure 5 This is a schematic diagram of monitoring the floating instability of the pipe segment of the present invention;

[0064] Figure 6 For the present invention Figure 5 Side view of.

[0065] Figure 7 It is a schematic diagram of calculating the vertical component of the jacking force at the floating instability position of the pipe segment of the present invention;

[0066] Figure 8 It is a schematic diagram of the stratum stress at the floating instability position of the pipe joint of the present invention;

[0067] Fig. 9 A schematic diagram of enabling the relay room of the present invention;

[0068] Fig.10 This is a schematic diagram of the pipe segment counterweight of the present invention;

[0069] Fig.11 It is a schematic diagram of concentrated mud grouting of the present invention.

[0070] In the figure: pipe segment 1, elevation measurement point 2, level 3, machine head 4, inner longitudinal main reinforcement 5, steel bar strain gauge 6, vibrating wire collector 7, grouting hole 8, displacement sensor 9, slurry discharge hole 10, ball valve 11, grouting pipe 12, tee 13, pressure sensor 14, current collector 15, relay room in front of floating instability zone 16, relay room in rear of floating instability zone 17, guide rail 18, counterweight car 19, counterweight block 20, thick mud grouting hole 21, thick mud grouting pipe 22, fine stone concrete pump 23. DETAILED DESCRIPTION

[0071] Embodiment 1:

[0072] like Figure 1-2 As shown, a system for monitoring the instability of a top pipe in a soft formation comprises a multi-section pipe section 1, characterized in that: an elevation measurement point 2 is arranged on the inner wall of both sides of the pipe section 1, and a level 3 cooperating with the elevation measurement point 2 is arranged at one end of the multi-section pipe section 1;

[0073] like Figure 3-4 As shown, a steel bar strain gauge 6 is welded at the middle of the inner longitudinal main reinforcement 5 on the pipe segment 1 near the machine head 4, and a vibrating wire collector 7 for collecting data of the steel bar strain gauge 6 is installed in the pipe segment 1;

[0074] like Figure 5-6 As shown, four displacement sensors 9 are installed at the joints of the pipe section 1 at the floating instability position, and the four displacement sensors 9 are used to monitor the changes in the joint spacing;

[0075] A slurry discharge hole 10 is provided at the bottom of the pipe section 1 at the floating instability position;

[0076] A tee 13 is installed at the grouting hole 8 on the pipe section 1 at the floating instability position, and the tee 13 is respectively connected to the grouting hole 8, the grouting pipe 12 and the pressure sensor 14;

[0077] The data of the displacement sensor 9 and the pressure sensor 14 are collected by a current collector 15 arranged in the pipe segment 1 .

[0078] In a preferred solution, there are four steel bar strain gauges 6 , which are welded on the top, bottom and both sides of the pipe segment 1 respectively.

[0079] In a preferred solution, a slurry discharge pipe with a ball valve 11 is installed at the slurry discharge hole 10. The ball valve 11 is opened to allow the annular slurry to flow out, and its density is tested to calculate the net buoyancy of the pipeline.

[0080] Embodiment 2:

[0081] Based on Example 1, the method for calculating the instability force of a top pipe in a soft formation includes the following steps:

[0082] 1) By testing the annular mud density ρ 1 , the net buoyancy per unit length of the pipeline is calculated as follows (assuming that the pipeline is completely wrapped by mud):

[0083] F 1 =πD 2 ρ 1 g / 4-(D 2 -d 2 )πρ c g / 4

[0084] Where:

[0085] F 1 is the net buoyancy per unit length of the pipe segment, kN / m;

[0086] D is the outer diameter of pipe segment 1, m;

[0087] d is the inner diameter of pipe segment 1, m;

[0088] g is the acceleration due to gravity, m / s 2 ;

[0089] ρc is the density of concrete, which is 2400kg / m 3 .

[0090] 2) Grouting pressure P on the top of the pipe 1 The average value of the grouting pressure measured by the pressure sensor 14 is adopted;

[0091] 3) If the steel bar strain gauge 6 is located in the ath pipe section 1, and the steel bar and concrete deform in coordination, then the average value ε of the four steel bar strain gauges 6 is 1 As the strain of steel and concrete, the jacking force between the machine head 4 and the front a-section pipe section 1 is calculated as follows:

[0092] F a =ε 1 A s E s +ε 1 A c E c

[0093] Where:

[0094] Fa is the jacking force between the machine head and the front a-section pipe section 1, kN;

[0095] As and Ac are the cross-sectional areas of steel bars and concrete, respectively. 2 ;

[0096] Es and Ec are the elastic moduli of steel and concrete, respectively, in kPa.

[0097] like Figure 7 As shown in the figure, when the nth pipe segment 1 is jacked, the design elevation and measured elevation of the axis of the pipe segment 1 change at the bth and cth pipe segments 1 respectively, and the elevation deviation at the dth pipe segment 1 is the largest, that is, the deflection between the pipe segments 1 is the largest;

[0098] At this time, the total jacking force is Fn. If the friction resistance of each pipe section 1 is the same, the vertical component of the jacking force of the dth pipe section 1 is Fn. 2 The approximate calculation is as follows:

[0099] F 2 ={[(F n -f(nb))cosθ1 -f(bc)]cos(θ 2 -θ 1 )-f(cd)}sin2θ 2

[0100] f=(F n -F a ) / (na)

[0101]

[0102]

[0103] Where:

[0104] f is the friction resistance of single tube section 1, kN;

[0105] h 1 is the elevation deviation of pipe section 1 of section c, m;

[0106] h 2 is the elevation deviation of the dth pipe section 1, m;

[0107] l is the length of single pipe section 1, m;

[0108] 4) If Figure 8 As shown in the figure, the soil on the top of the pipe is mainly affected by the grouting pressure, the net buoyancy of the pipeline and the vertical component of the jacking force. If the top of the pipe is in contact with the soil within 180°, the maximum stress on the soil on the top of the pipe is calculated as follows:

[0109]

[0110] Where: η is the ratio of the cover thickness to the outer diameter of pipe segment 1.

[0111] 5) Compare the calculated maximum soil stress with the foundation bearing capacity. When the maximum soil stress is greater than the foundation bearing capacity, the soil will be damaged and the floating instability will continue to develop.

[0112] Embodiment 3:

[0113] On the basis of Example 1, the instability stress processing method of the instability stress monitoring system of the top pipe in the soft formation includes the following steps:

[0114] 1) Reduce the jacking force in the floating instability zone

[0115] like Fig. 9 As shown, the relay room 16 in front of the floating instability zone is activated for segmented jacking, and the jacking force of the pipe segment 1 in front of the instability zone is borne by the relay room 16 in front of the floating instability zone, and the jacking force on the floating instability zone is reduced;

[0116] 2) Pipe joint counterweight

[0117] like Fig.10 As shown, a guide rail 18 is installed at the bottom of the pipe segment 1 in the floating instability area, and a counterweight vehicle 19 is arranged on the guide rail 18 , and a counterweight block 20 is placed on the counterweight vehicle 19 .

[0118] 3) Pipe top injection of thick mud

[0119] Concentrated mud is obtained by increasing the amount of bentonite on the basis of conventional thixotropic mud, and the concentrated mud is injected into the pipe top in the floating instability zone to fill the void on the pipe top and improve the soil strength.

[0120] In a preferred solution, in the step 1), if the jacking force does not decrease after the front relay room 16 of the floating instability zone is activated, the rear relay room 17 of the floating instability zone is activated.

[0121] In a preferred solution, the relay rooms existing in the floating instability zone are activated synchronously, and additional relay rooms are added in time when they are insufficient.

[0122] In the preferred embodiment, in the step 2), the counterweight block 20 is made of concrete block or steel block, and its mass is determined according to the net buoyancy of the pipe segment 1 and the vertical component of the jacking force. Since the space at the bottom of the pipe increases and is filled with mud when the pipe segment 1 floats up and becomes unstable, a part of the mud at the bottom of the pipe segment should be discharged through the mud discharge hole 10 at the bottom of the pipe when the pipe segment 1 is counterweighted, so that the pipe segment can sink smoothly.

[0123] In the preferred scheme, in the step 3), the mass ratio of bentonite to water in the concentrated mud is controlled at above 0.5:1 to reduce the fluidity of the concentrated mud. When the pipe segment 1 floats and becomes unstable, the soil on the top of the pipe is damaged and the strength is reduced. After the pipe 1 sinks, a large gap will appear on the top of the pipe, which may cause the pipe segment 1 to float again. Therefore, it is necessary to inject concentrated mud into the top of the pipe in the floating and unstable area to fill the gap on the top of the pipe and improve the strength of the soil.

[0124] The preferred solution is Fig.11 In the above-mentioned floating instability zone, a thick mud grouting hole 21 is opened on the pipe top, and the stirred thick mud is pumped into the thick mud grouting pipe 22 by a fine stone concrete pump 23, and finally injected into the stratum on the pipe top.

Claims

1. A system for monitoring the instability of a top pipe in a soft formation, comprising a plurality of pipe sections (1), characterized in that: The inner walls of both sides of the pipe section (1) are provided with elevation measurement points (2), and one end of the multi-section pipe section (1) is provided with a level (3) that matches the elevation measurement points (2); A steel bar strain gauge (6) is welded to the middle of the inner longitudinal main reinforcement (5) on the pipe segment (1) adjacent to the machine head (4), and a vibrating wire collector (7) for collecting data of the steel bar strain gauge (6) is installed in the pipe segment (1); Four displacement sensors (9) are installed at the joints of the pipe section (1) at the floating instability location, and the four displacement sensors (9) are used to monitor changes in the joint spacing; A slurry discharge hole (10) is provided at the bottom of the pipe section (1) at the floating instability position; A tee (13) is installed at the grouting hole (8) on the pipe section (1) at the floating instability position, and the tee (13) is respectively connected to the grouting hole (8), the grouting pipe (12) and the pressure sensor (14); The data of the displacement sensor (9) and the pressure sensor (14) are collected by a current collector (15) arranged in the pipe section (1); The above-mentioned method for calculating the instability force of the top pipe instability force monitoring system in soft formations comprises the following steps: 1) If the pipe segment (1) is completely wrapped by mud, by testing the annular mud density ρ1, the net buoyancy per unit length of the pipe segment (1) is calculated as follows: ； Where: F1 is the net buoyancy per unit length of the pipe segment (1), kN / m; D is the outer diameter of the pipe segment (1), m; d is the inner diameter of the pipe segment (1), m; g is the acceleration due to gravity, m / s 2 ; ρc is the density of concrete, which is 2400kg / m 3 ; 2) The grouting pressure P1 of the stratum on the pipe top is the average value of the grouting pressure measured by the pressure sensor (14); 3) If the steel bar strain gauge (6) is located at the ath pipe section (1), and the steel bar and concrete deform in coordination, the average value ε1 of the four steel bar strain gauges (6) is taken as the strain of the steel bar and concrete, and the jacking force between the machine head (4) and the ath pipe section (1) is calculated as follows: ； Where: Fa is the thrust force between the machine head and the front a-section pipe section (1), kN; As and Ac are the cross-sectional areas of steel bars and concrete, respectively. 2 ; Es and Ec are the elastic moduli of steel and concrete, respectively, kPa; When the nth pipe segment (1) is jacked, the designed elevation and the measured elevation of the axis of the pipe segment (1) change in angle at the bth and cth pipe segments (1), respectively, and the elevation deviation at the dth pipe segment (1) is the largest, that is, the deflection between the pipe segments (1) is the largest; At this time, the total jacking force is Fn. If the friction resistance of each pipe section (1) is the same, the vertical component F2 of the jacking force of the dth pipe section (1) can be approximately calculated as follows: ； ； ； ； Where: f is the frictional resistance of a single pipe section (1), kN; h1 is the elevation deviation of the cth pipe section (1), m; h2 is the elevation deviation of the dth pipe section (1), m; l is the length of a single pipe section (1), m; 4) The soil on the top of the pipe is mainly affected by the grouting pressure, the net buoyancy of the pipe and the vertical component of the jacking force. If the top of the pipe is in contact with the soil within 180°, the maximum stress on the soil on the top of the pipe is calculated as follows: ； Where: η is the ratio of the cover thickness to the outer diameter of the pipe segment (1); 5) Compare the calculated maximum soil stress with the foundation bearing capacity. When the maximum soil stress is greater than the foundation bearing capacity, the soil will be destroyed and the floating instability will continue to develop; The above-mentioned instability stress processing method of the instability stress monitoring system of the top pipe in soft formation comprises the following steps: 1) Reduce the jacking force in the floating instability zone; The relay room (16) in front of the floating instability zone is activated to carry out segmented jacking, and the jacking force of the pipe section (1) in front of the instability zone is borne by the relay room (16) in front of the floating instability zone, and the jacking force on the floating instability zone is reduced; 2) Pipe joint counterweight; A guide rail (18) is installed at the bottom of the pipe section (1) in the floating unstable area, and a counterweight vehicle (19) is arranged on the guide rail (18), and a counterweight block (20) is placed on the counterweight vehicle (19); 3) Inject thick mud into the pipe top; Concentrated mud is obtained by increasing the amount of bentonite on the basis of conventional thixotropic mud, and the concentrated mud is injected into the pipe top in the floating instability zone to fill the void on the pipe top and improve the soil strength.

2. A system for monitoring the instability of top pipe in soft formations according to claim 1, characterized in that: There are four steel bar strain gauges (6), which are respectively welded on the top, bottom and both sides of the pipe section (1).

3. The instability force monitoring system for top pipe in soft formation according to claim 1 is characterized by: A slurry discharge pipe with a ball valve (11) is installed at the slurry discharge hole (10).

4. The instability stress processing method of the instability stress monitoring system of the top pipe in soft formation according to claim 1 is characterized by: In the above step 1), if the jacking force does not decrease after the front relay room (16) of the floating instability zone is activated, the rear relay room (17) of the floating instability zone is activated.

5. The instability stress processing method of the instability stress monitoring system of the top pipe in soft formation according to claim 4 is characterized by: The relay rooms existing in the floating instability zone are activated synchronously, and additional relay rooms are added in time when they are insufficient.

6. The instability stress processing method of the instability stress monitoring system of the top pipe in soft formation according to claim 1 is characterized by: In the step 2), the counterweight block (20) is a concrete block or a steel block, and its mass is determined according to the net buoyancy of the pipe segment (1) and the vertical component of the jacking force.

7. The instability stress processing method of the instability stress monitoring system of the top pipe in soft formation according to claim 1 is characterized by: In the step 3), the mass ratio of bentonite to water in the concentrated mud is controlled to be above 0.5:1 to reduce the fluidity of the concentrated mud.

8. The instability stress processing method of the instability stress monitoring system of the top pipe in soft formation according to claim 7 is characterized by: A thick mud grouting hole (21) is opened on the pipe top of the floating instability zone, and the stirred thick mud is pumped into the thick mud grouting pipe (22) by a fine stone concrete pump (23) and finally injected into the stratum on the pipe top.

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