(1) equipment
The main equipment of pressuremeter test before drilling is pressuremeter. It mainly consists of the following four parts.
1. Side press
It is the most important part of the manometer and consists of a circular metal skeleton and a rubber membrane wrapped around the skeleton. Generally, the pressuremeter has three chambers, with the main chamber (also called test chamber) in the middle and the upper and lower chambers as protection chambers. The main cavity and the protection cavity are not connected with each other, but the protection cavity is connected with the main cavity sandwiched in the middle. During the test, high-pressure water enters the main cavity from the control unit through the intermediate pipeline system, which makes the rubber film expand to the surrounding soil along the radial direction (transverse direction) and oppresses the surrounding soil, thus establishing the relationship between the pressure of the main cavity and the volume deformation increment of the soil. At the same time, water with the same pressure is input into the two protection chambers at the same time, so that the pressure is consistent with that of the main chamber, thus forcing the main chamber to deform synchronously left and right in the horizontal direction. In this way, the soil deformation around the main tunnel can be treated as a plane strain problem.
Fig. 5- 10 Py-2 pipeline (structure) diagram of pressuremeter
There is a water guide pipe in the center of the pressuremeter, which is used to discharge groundwater, so that the pressuremeter can be placed at the test depth smoothly. There are two kinds of lateral pressure: bare pressure and metal armor protective film. For all kinds of clay, you can directly use the bare pressuremeter; If the elastic membrane is damaged by sharp substances such as gravel in the soil layer, a metal armor protective film can be attached to the elastic membrane of the pressuremeter for testing. Its main function is to protect the elastic membrane and make the pressuremeter test run normally.
At present, the outer diameter of PY-2 and PY-3 pressure gauges is 50mm (55mm with metal armored sheath), the length of the test chamber is 250mm, and the volume is 49 1cm3 (594cm3 with metal armored sheath). The total length of pressuremeter is 500mm. The upper cavity and the lower cavity (protection cavity) communicate with each other through a copper conduit, but are isolated from the middle cavity.
2. Pressure and volume control box
Usually, the control unit of the pre-drilling pressuremeter is a box structure set on a tripod. It includes deformation measuring device and voltage stabilizing device. The former mainly includes measuring tubes, auxiliary tubes (only measuring tubes are available in the PY-3 type, with an internal section of 14.32cm2 and a volume of 650cm3), water tanks and various valves. Both the measuring tube and the auxiliary tube are made of plexiglass, the minimum scale is 1 mm, the cross-sectional area of the PY-2 measuring tube is 15.28 cm2, and the PY-3 measuring tube is also equipped with a liquid level indicator, so the resolution can be improved to 0.1mm. The main function of this part is to control the water entering the pressuremeter, and measure the hole wall through the measuring tube or liquid level meter. The pressurizing and stabilizing device comprises a high-pressure nitrogen cylinder or a manual inflator, a gas storage tank, a pressure regulating valve and a corresponding pressure gauge. Both pressurization and stabilization are controlled by pressure regulating valve. The main function of this part of the device is to control the pressure entering the manometer. In a word, the relationship between the pressure acting on the soil and the corresponding volume deformation (realized by measuring the drop of water level in the measuring pipe) is realized through the control box.
3. Pipeline system
The pipeline is a "bridge" connecting the barometer and the control box. Its function is to transport pressure and water from the control box to the pressure gauge. Model PY-2 has two pressure pipes and two water injection pipes, while model PY-3 has two pressure pipes but only one water injection pipe (fig. 5- 1 1). The material of the pipeline is nylon 10 10, which can withstand high pressure, and its length is determined by the maximum test depth, generally more than ten meters long. The pipeline connected to the pressuremeter can be quickly connected to the control box through the quick connector.
Fig. 5-5- 1 1py-3-3 barometer pipeline diagram
4. Hole-forming tools and other accessories
Pre-drilling requires pre-drilling, and its hole-forming tools are mainly spoon drills (Figure 5- 12), with spoon drills, probe rods and earth-lifting drills made of high-strength steel. Suitable for general cohesive soil. For hard soil layer, light drilling rig should be used to make holes.
Fig. 5- 12 pore-forming tool
PY pressuremeter is suitable for testing cohesive soil, silt and sandy soil. If the formation contains angular gravel, etc. A manometer with a metal armored sheath should be used to avoid puncturing the rubber membrane. At present, the test pressure has been increased to 2.5MPa, and the depth can reach 20 m. If materials with higher strength are selected to improve the sealing performance of the valve under high pressure, the test pressure and depth can be improved. Among similar products abroad, the test pressure reaches 12.5MPa (such as Maynard GB pre-drilling pressuremeter) and the test depth can reach 50 m; Some of them reach 70MPa, which can measure hard rocks (for example, Goodman52 10 1 type in America).
(2) Repair and maintenance of pressuremeter
1. Construction and maintenance of main parts of the instrument
(1) diaphragm control valve: Its structure is shown in Figure 5- 13.
Figure 5- 13 Leather Film Control Valve
1- wheel; 2- guide screw; 3— Assembled cover (nut); 4— Valve plug; 5- pressure ring; 6- membrane; 7- Seat
Turn the wheel clockwise, the screw pushes the valve plug to press the film on the hole wall, and the pipeline is disconnected; Turn the wheel counterclockwise, and the rubber film will return to its original position by its own elasticity and internal pressure in the pipeline, and the pipeline will be connected. So as to realize the control function of pipeline opening and closing.
Diaphragm valve has the advantages of good sealing performance and high pressure resistance. Disadvantages: there is no fixed position for opening and closing, and the operation depends on touch. The film is easy to be damaged or cut into the hole, which will block the pipeline and affect the work. When closing the pipeline, the diaphragm valve should not be tightened too tightly. After the work is completed, all valves must be loosened to restore the film to a free state. Once the membrane is damaged, it must be replaced immediately.
The sequence of replacing the rubber film is as follows: unscrew the runner 1, loosen the nut 3, loosen the lead screw 2 and take it off; Use tweezers to take out the pressure ring 5 pressed on the leather membrane, take out the old leather membrane 6 and replace it with a new one. When replacing a new membrane, pay attention to the drum shape of the membrane should be outward. Assembly shall be carried out in the reverse order of disassembly. When assembling lead screw 2, be careful not to screw it too tightly or too loosely. Too tight, the membrane closely fits the orifice, which makes the pipeline not smooth; Too loose, causing water leakage.
(2) Casing joint: Its structure is shown in Figure 5- 14.
Fig. 5- 14 sleeve pipe joint
1- connector; 2- compression nut; 3- sealing ring; 4- Take over
In this joint, the sealing ring 3 is tightly pressed by the pressing nut 2, so that the deformation is closely attached to the connecting pipe and the joint body to form a hard seal. It is not suitable for disassembly after assembly and pressure test. If disassembly and maintenance are needed, the sealing performance will be obviously reduced after assembly. If the working requirements cannot be maintained, the sealing ring must be replaced. The replacement method is as follows: file the sealing ring with a fine tooth file and take it off. Be careful not to file the nozzle and replace it with a new sealing ring. When the damaged sealing ring is removed and the nozzle is found to be deformed, the nozzle must be replaced at the same time to ensure the quality of the joint.
(3) Pressure regulating valve: The structure is shown in Figure 5- 15.
The balance working principle of the pressure regulating valve is as follows: turn the pressure regulating handle 1 clockwise, and the main spring 3 presses the balance diaphragm 4, so that the ejector pin 6 sticks to the overflow port 14, and moves along the axial direction, pushing open the air inlet plug 8, so as to make the working chamber air in. When the air pressure in the working chamber and the pipeline rises to a constant value, the balance diaphragm moves in the opposite direction under the pressure, and the ejector pin is forced by the lower spring 9, and it rises through the lower ejector pin 1 1 and the plug, and the air inlet is closed to stop air intake. When the air pressure in the working chamber and pipeline exceeds the fixed value, the balance diaphragm is affected by the air pressure in the working chamber, which compresses the main spring to move upward, opens the overflow port, releases the residual air, and the air pressure drops to the fixed value. When the air pressure of the working chamber and the pipeline decreases due to the volume change, the balance membrane is influenced by the main spring to close the overflow port, push open the air inlet and increase the air intake. In this way, it circulates continuously to achieve the function of stabilizing voltage.
Pressure regulating valve is the key component of the instrument. The accuracy of pressure regulating valve directly affects the accuracy of test results; When in use, it is not allowed to turn the pressure regulating handle for invalid pressure regulation without connecting the air source or air pressure. After the work, the handle should be released immediately to restore the main spring to normal state, so as to prolong its working life and maintain considerable accuracy.
Common faults of pressure regulating valve and their solutions;
① After pressure adjustment, the pressure pointer "creeps": the creepage is mainly caused by the dust accumulated on the surface of the blockage in the airflow medium, so that the air inlet and the blockage cannot be closed; Secondly, due to long-term use, the surface of the plug has obvious dents, resulting in uneven surface, which can not be sealed with the air inlet. Disassembly method: unscrew the lower air chamber 12, take out the plug from the guide sleeve 13, and clean the surface of the plug with alcohol under a magnifying glass to make it free of dust. At the same time, scrub the end face of the air inlet with tweezers and alcohol cotton wool; When cleaning, pay attention to prevent surface bumps and scratches. If you look at the existing scratches and protrusions under the magnifying glass, you must replace the plug or air inlet.
Figure 5- Structure Diagram of Pressure Regulating Valve 15
1- handle; 2— Upper cylinder; 3- main spring; 4- Balance diaphragm; 5— Valve body; 6- ejector pin; 7— Air inlet; 8- plug; 9— Lower spring; 10- adjusting screw; 11-lower the ejector pin; 12-lower air chamber; 13- guide sleeve; 14-overflow port
② Air consumption of overflow port: that is, the overflow port automatically exhausts when it does not exceed the rated working pressure. The elimination method is to increase the contact pressure between the ejector pin and the overflow port. Tighten the adjusting screw 10 clockwise until there is no gas consumption (considering the sensitivity of the pressure regulating valve, it is not advisable to tighten it too tightly). If gas is still consumed, the overflow port must be removed, and its contact surface must be ground to make it contact with the spherical surface of the ejector pin evenly.
③ Air leakage in the lower air chamber: generally, it is caused by the aging of the sealing sleeve of the lower ejector pin, and the sealing sleeve needs to be replaced at this time.
(4) Quick connector: Its composition structure is shown in Figure 5- 16. Due to frequent use, the sealing ring 2 is worn and the sealing performance is affected, so it must be replaced immediately. After the test is completed, remove the quick connector sleeve 3 and put on the sheath to prevent sediment from entering the catheter from the sleeve opening and damaging the instrument.
Figure 5- 16 quick connector
1- socket; 2- sealing ring; 3- intubation
(5) Sidepressor: Sidepressor is a probe for detection. Its structure is shown in Figure 5- 17.
Figure 5- 17 Structure Diagram of Side Press
1- pressure guide and water guide pipe; 2- elastic membrane; 3-casing leakage; 4- central catheter; 5- copper connector; 6— Internal clamping ring; 7— Protective cover for pipeline assembly; 8- spelling a hat; 9— External clamping ring
When the elastic membrane of the pressure gauge is damaged and needs to be replaced, the replacement sequence is as follows:
(1) Cut the old film with a knife, remove the pipe splicing boots 7, loosen the splicing caps 8 of each copper joint, remove the old film, and simultaneously remove the inner and outer pressure rings 6, 9 and splicing caps on the copper joints at both ends;
(2) Remove the leakage sleeves of the upper and lower auxiliary cavities and clean up the impurities;
(3) coating soap liquid on the inner wall of the new film, inserting it from one side pressing end, passing through the outer pressing ring of the middle copper joint from the end, leaking the bushing from the middle cavity, making the position of the new film exactly the same as that of the side pressing frame, and inserting it into the two outer pressing rings of the middle copper joint;
(4) Turn over one end of the new film (when turning over, pay attention to coating soap solution between the films to make it smooth) until the position of the pressure ring in the copper joint is exposed;
⑤ Install the inner compression ring and tighten the split cap with a hook wrench;
⑥ Install the leaky pipe tile at the upper end (pay attention to the inspection number), and turn the upside-down end film back;
⑦ Put on an outer pressure ring, an inner pressure ring and a splicing cap in turn;
8 The other end is also operated in the order of ④-⑦.
Note: After assembly, each part of the membrane must be closely attached to the frame of the side press to prevent looseness.
2. Assembly and use of instruments
(1) Instrument assembly: supported by tripod and connected with M20 knurled copper nut.
(2) Connection between high-pressure nitrogen bottle and instrument: If a high-pressure nitrogen source is used, connect the air inlet end of the instrument accessory pressure gauge with the nitrogen bottle, connect the air outlet with a φ6× 1 nylon tube, and connect the other end with the connector marked "nitrogen source" on the instrument.
3. Debugging of pressure gauge
Before work, the instrument should be debugged to check whether it is normal; If there is any abnormality, it must be handled and eliminated to avoid work interruption.
(1) Water injection standard inspection before work: water injection shall be carried out according to the operation sequence. If it is found that the water injection is slow or not, it means that the water injection system has been blocked or blocked. The common fault is the water injection valve, which is usually caused by the valve membrane sticking to the orifice. At this time, it is not necessary to disassemble the valve, and the fault can be eliminated by "recoil method". The elimination method is: pressurize the gas storage tank to above 0.5MPa, close the drain valve and zero adjustment valve, open other valves, and slowly pressurize the pipeline (put the lateral pressure device into the calibration cylinder before pressurization, and open the water filling cover of the water tank). When you hear the sound of water in the water tank, it means that the pipeline is unobstructed. When the pressure is above 0.5MPa, if there is still no noise in the water tank, the pipeline is seriously blocked. At this point, the pipeline must be removed for inspection. Generally, the blocked parts are the water injection valve and the pipeline from the water injection valve to the water tank, and other parts should not be easily removed.
(2) Water seepage inspection of elastic membrane: after the instrument is filled with water, under the condition of no external force constraint, stand the lateral pressure device beside the instrument and slowly pressurize the lateral pressure device to 0.05MPa；; When the elastic membrane expands, check whether there is leakage on the membrane. If there is leakage, replace the elastic membrane immediately.
(3) Instructions for use of inner sleeve:
Fig. 5- 18 3-hole catheter (the number in the figure is the hole number)
This kind of inner casing is special for No.3 hole. When doing the calibration test of elastic membrane binding force, the pipe should be pulled out from the No.3 hole; After the test, reinsert it for other tests.
This inner sleeve can be used in 1 2 and nitrogen source.
4. Adjustment and instruction of display instrument
(1) Connect the instrument to the power supply and connect the output plug of the electric measuring tube; Preheating for half an hour before testing and calibration.
(2) When calibrating, you need to pull out the No quick plug. 1 and No.2 holes, and replace them with plug connecting pipes dedicated for this instrument, so that they can not communicate with No.2 holes.
(3) Calibration process:
Fig. 5- 19 1.2 and special casing for nitrogen source hole
(1) Water injection According to the operation sequence, fill the water level of the measuring pipe to the zero scale line, and then adjust the zero adjustment knob until the output of the display instrument is 400mV；;
(2) Open the water injection valve, slightly pressurize it (the pressure should be less than 0.05MPa, and return the water to the water tank) to gradually reduce the water level of the measuring tube to 400mm, and adjust the zero adjustment knob until the instrument output is zero;
(3) Repeatedly adjust several times according to the above method, and the display instrument can record on the spot;
④ Never adjust the zeroing lock nut. Zero adjustment has been debugged before the instrument leaves the factory, and will be adjusted when cleaning the instrument and measuring tube.
(III) Ex-factory inspection standards for instruments
The main inspection items of PY piezometer before leaving the factory are:
(1) stability: the allowable fluctuation value within the initial adjustment range of 1min should be less than or equal to 0.0025MPa under various working pressures.
(2) Sealing: Under the rated working pressure, cut off the gas source for 4 hours, and the instrument pressure drop shall be less than or equal to 0.1MPa;
(3) voltage regulation value: the maximum voltage regulation value should not be lower than 2.5MPa.
(4) Water injection: When the water injection pressure is less than 0.05MPa, the working cavity and circuit should be filled within 5 minutes;
(5) Cleanliness of the water tank: There should be no sundries in the water tank that cause pipeline blockage and affect the transparency of the measuring tube;
(6) Pressure resistance of quick connector and instrument pipeline: not less than 2.5MPa.
(7) Absolute error of the liquid level indicator: When the whole stroke is 400 mm, the absolute value of the maximum error between the displayed number and the marked number of the liquid level indicator should not exceed 4 mm. ..