Device and method for regulating temperature to reduce side friction resistance of phc pile

Abstract

The present application discloses a kind of present application relates to pile foundation engineering, soft soil foundation treatment and geotechnical engineering friction reduction control technical field, especially a kind of device and method for regulating temperature and reducing PHC pile side negative frictional resistance.The present application can realize the active reduction of PHC pile side negative frictional resistance.Through setting outside pasting type flexible electric heating cable on the outer surface of PHC pile friction reduction control section, and setting modified asphalt friction reduction layer around the pile, when negative frictional resistance is caused by the settlement of soil body around the pile, modified asphalt friction reduction layer can be heated and softened, the frictional resistance of pile-soil interface is reduced, so as to reduce the downward dragging effect of soil body around the pile on the pile body.The present application can realize the heating of different pile sections.The flexible electric heating cable is divided into several independent heating sections along the length direction of the pile, and each independent heating section is connected to the ground control cabinet through independent power supply line and sectional control switch.The control system only starts the pile section that reaches the control condition, avoids energy waste caused by whole-pile heating, and improves the pertinence of friction reduction control.

Description

Technical Field

[0001] This invention relates to the fields of pile foundation engineering, soft soil foundation treatment and geotechnical engineering friction reduction and control technology, and in particular to a device and method for regulating temperature to reduce the negative skin friction of PHC piles. Background Technology

[0002] In soft soil foundations, fill foundations, and surcharge preloading engineering, PHC pipe piles are widely used in building, bridge, port, and municipal foundation projects due to their advantages such as high bearing capacity, convenient construction, and stable pile quality. When the soil around the pile experiences vertical displacement greater than that of the pile due to factors such as self-weight consolidation, surcharge preloading, changes in groundwater level, or recent fill settlement, the soil will be dragged downwards along the pile, forming negative skin friction on the pile side. Negative skin friction increases the additional axial pressure on the pile, reduces the safety reserve of the pile foundation, and in severe cases, may cause problems such as pile cracking, increased pile top settlement, and uneven foundation settlement. Therefore, reducing the negative skin friction on the side of PHC piles is of great significance for improving the long-term safety of pile foundations in soft soil foundations.

[0003] Existing domestic and international measures for controlling negative skin friction mainly include applying asphalt around the pile, installing plastic sleeves, setting up isolation layers, preloading the foundation, and optimizing pile foundation design. Among these, applying asphalt around the pile can reduce the shear strength of the pile-soil interface by forming a low-friction isolation layer, which is a commonly used method for friction reduction. However, traditional asphalt friction-reducing layers are mostly one-time passive structures, and the material state is basically fixed after construction, making it difficult to adjust according to the settlement of the surrounding soil and changes in negative skin friction. At the same time, the asphalt layer may harden, age, or suffer local damage during long-term service, leading to a decrease in friction-reducing effect.

[0004] Furthermore, existing methods typically lack real-time monitoring of pile stress, relative pile-soil displacement, and asphalt layer condition, making it difficult to promptly determine the location and extent of negative skin friction. When negative skin friction develops concentratedly in localized pile segments, traditional measures struggle to provide segmented control, easily leading to insufficient friction reduction or excessive treatment coverage. For schemes that embed electric heating elements within the concrete protective layer near the outer surface of PHC piles, there are also issues such as complex spiral wiring construction, the potential for extensive trenching or pre-reservation during implementation, and significant impact on the original protective layer and prestressed structure of the pile, hindering project implementation and subsequent maintenance. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the shortcomings of the existing technology by providing a device for reducing negative skin friction on PHC piles by heating the asphalt around the pile with electric heating elements. This device involves setting a modified asphalt friction-reducing layer on the outer surface of the PHC pile. Flexible electric heating cables are arranged along a spiral path on the outer surface of the control pile segments that may generate negative skin friction. These flexible electric heating cables are fixed to the outer surface of the pile by cable fixing clips or arranged in shallow spiral positioning grooves on the outer surface of the pile. The outer surface is sealed with thermally conductive and insulating mortar to form an externally applied heating structure layer. This method combines temperature, strain, and pile-soil relative displacement monitoring devices to determine the development state of negative skin friction. When the corresponding pile segment reaches the control conditions, the electric heating elements are activated to heat the asphalt friction-reducing layer around the pile, softening it and reducing the skin friction at the pile-soil interface, thereby achieving active reduction and segmented control of negative skin friction in the PHC pile.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A device for regulating temperature to reduce the negative skin friction of PHC piles includes a PHC pile, an electric heating mechanism, and a pile perimeter asphalt friction reduction mechanism.

[0008] The PHC piles are installed in soft soil or fill layers;

[0009] The electric heating mechanism is located on the outer periphery of the PHC pile;

[0010] The pile periphery asphalt friction reduction mechanism is located on the outer periphery of the electric heating mechanism;

[0011] The electric heating mechanism heats the pile perimeter asphalt friction-reducing mechanism by electricity, softening it to reduce the negative friction force on the PHC pile.

[0012] Furthermore, the PHC pile is divided into multiple friction reduction control sections along its length; the friction reduction control sections correspond to the soil layer range where the soft soil layer or fill layer has significant settlement in the later stage.

[0013] The electric heating mechanism forms a heating section on each friction-reducing control section of the PHC pile;

[0014] A pile top settlement monitoring meter is installed at the top of the PHC pile to monitor the pile top settlement;

[0015] Layered settlement gauges and layered settlement rings are installed in the soil around the PHC pile to obtain the relative displacement of the pile and soil at various depths.

[0016] A pile axial force sensor is installed at the center of each heating section to obtain the frictional force on the PHC pile in each friction reduction control section;

[0017] When the pile side friction resistance of a certain friction reduction control section of the PHC pile is downward and the relative displacement between the pile and the soil reaches a set threshold, the heating section corresponding to the outer periphery of the friction reduction control section is energized to heat and soften part of the pile periphery asphalt friction reduction mechanism to reduce the negative friction force of the pile periphery soil on the pile body.

[0018] Furthermore, the PHC pile includes a pile body, the pile body is hollow to form a pile core cavity, and a PHC pile wall is formed on the outer surface of the pile core cavity; a concrete protective layer is provided on the outer periphery of the PHC pile wall; multiple prestressed steel bars are inserted inside the concrete protective layer; and stirrups are wrapped around the outer periphery of the multiple prestressed steel bars.

[0019] The power supply and signal lines are led upward through the core cavity of the pile, and are centrally led and sealed through the pile top lead-in groove, the pile top waterproof cover, and the pile top lead-in sealing joint.

[0020] Furthermore, the electric heating unit includes a flexible electric heating cable arranged in a spiral along the outer surface of the pile body. The flexible electric heating cable is fixed to the outer surface of the PHC pile by a cable fixing buckle. A high-temperature resistant insulation layer and a waterproof protective sleeve are sequentially installed on the outside of the flexible electric heating cable, and the surface is sealed with thermally conductive insulating mortar to form a heating structure layer on the outside of the cable.

[0021] Furthermore, the length of the independent heating section is set according to the length of the friction reduction control section as n turns of the flexible electric heating cable around the pile, where n is a natural number greater than 1;

[0022] The electric heating unit also includes a segmented control switch, a power terminal block, and a grounding wire. The segmented control switch is connected to different independent heating sections to realize individual power on / off control of each independent heating section. The power terminal block is used to unify the wiring of each independent heating section. The grounding wire is connected to the ground to ensure the electrical safety of the entire electric heating unit. All control and wiring components are integrated in the ground control cabinet at the top of the PHC pile.

[0023] Furthermore, the pile perimeter asphalt friction reduction unit includes a base coating, a modified asphalt friction reduction layer, an outer limiting protective layer, a limiting protective layer overlap strip, and a limiting protective layer fixing ring; the base coating is disposed on the outer surface of the thermally conductive and insulating mortar; the modified asphalt friction reduction layer is disposed on the outer surface of the base coating; and the outer limiting protective layer is disposed on the outside of the modified asphalt friction reduction layer and fixed by the limiting protective layer overlap strip and the limiting protective layer fixing ring.

[0024] The outer limiting protective layer is made of a flexible heat-resistant film, which does not affect the fluidity of the modified asphalt friction-reducing layer formed by heating and melting; the limiting protective layer overlap strip and the limiting protective layer fixing ring are set at the pile head and pile tail of the PHC pile on each independent heating section.

[0025] Furthermore, the pile-surrounding soil layered settlement gauge is vertically embedded in the soil around the pile along the outer side of the PHC pile body, and can be anchored to a relatively stable soil layer through its bottom end; when the pile-surrounding soil and soft soil layer or fill layer undergo consolidation settlement or additional settlement, the layered settlement ring moves down synchronously with the soil at the corresponding depth; the pile-surrounding soil layered settlement gauge obtains the settlement amount and settlement development process of the pile-surrounding soil at different depths by sensing, identifying or reading the position changes of each layered settlement ring.

[0026] A method for controlling temperature to reduce negative skin friction of PHC piles includes the following steps:

[0027] Step 1: Based on the engineering survey data, soil compression characteristics, surcharge conditions and negative skin friction calculation results, determine the range of all pile segments with negative skin friction along the depth direction of the PHC pile, and determine them as the skin friction reduction control segments in sequence.

[0028] Within the friction reduction control section, the layout range of the flexible electric heating cable is determined. The flexible electric heating cable is arranged in a spiral shape along the outer surface of the pile body, and a heating section is formed by wrapping around the pile n times outside each friction reduction control section.

[0029] Step 2: A high-temperature resistant insulation layer and a waterproof protective sleeve are sequentially installed on the outside of the flexible electric heating cable, and the surface is sealed with thermally conductive and insulating mortar to form a continuous, smooth heating structure layer on the outside of the cable that has both thermal conductivity and insulation functions.

[0030] After the thermally conductive and insulating mortar reaches its design strength or meets the subsequent construction conditions, a primer layer is evenly applied to its outer surface. After the primer layer reaches a surface dry state, modified asphalt friction-reducing material is continuously applied to form a modified asphalt friction-reducing layer. After the modified asphalt friction-reducing layer is completed, an outer limiting protective layer is set on its outer side. This outer limiting protective layer is made of a flexible heat-resistant film, which will not affect the fluidity of the modified asphalt friction-reducing layer formed by heating and melting. It is fixed by the limiting protective layer overlap strip and the limiting protective layer fixing ring. The limiting protective layer fixing ring is arranged at the pile head and pile tail of each pile section to ensure that the outer limiting protective layer does not loosen significantly during the pile driving process and provides external restraint for the modified asphalt friction-reducing layer during the later heating and softening process.

[0031] Temperature and stress monitoring elements are installed within the friction reduction control section. Platinum resistance temperature sensors are positioned outside the thermally conductive and insulating mortar, close to the modified asphalt friction-reducing layer, to improve the representativeness of temperature monitoring. Axial force gauges for the pile reinforcement are arranged in sections along the corresponding positions of the pile to monitor changes in the axial strain of the PHC pile. A pile top settlement monitoring device and pile top settlement observation markers are installed at the pile top, with the observation markers arranged around the pile top. The pile top settlement monitoring device determines the pile settlement status by receiving the reflected position information from the pile top settlement observation markers. Layered settlement gauges are installed along the PHC... The C-pile is vertically embedded in the soil around the pile on its outer side and can be anchored to a relatively stable soil layer at its bottom end, serving as a relatively fixed benchmark for settlement measurement. When the soil around the pile, soft soil layer, or fill layer undergoes consolidation settlement or additional settlement, the layered settlement rings move down synchronously with the soil at the corresponding depth. The layered settlement gauge senses, identifies, or reads the position changes of each layered settlement ring to obtain the settlement amount and settlement development process of the soil around the pile at different depths, thereby determining the settlement state of the soil around the pile and identifying the relative displacement of the pile and soil and the development state of negative skin friction.

[0032] Step 3: After the PHC piles enter the service stage, collect data on pile strain, pile top settlement, pile surrounding soil settlement, and friction-reducing layer temperature at set time intervals; when the foundation is still in the rapid consolidation period, surcharge loading period, or fill growth period, the sampling time interval is selected from 10 min to 2 h; when the foundation enters the later stabilization stage, the sampling time interval is selected from 6 h to 24 h.

[0033] The axial force of the pile at the corresponding depth is calculated based on the strain value collected by the axial force gauge of the pile reinforcement, and the distribution of the pile side friction is calculated back based on the difference in axial force between adjacent monitoring sections. At the same time, the settlement of the soil around the pile in layers is compared with the settlement of the pile to determine the development of the relative displacement between the pile and the soil.

[0034] The PHC pile monitoring sections are divided into normal, warning, and control sections: The normal section is defined as follows: when the relative displacement between the pile and soil is less than 2 mm and the calculated pile side friction does not show a downward effect; the warning section is defined as follows: when the relative displacement between the pile and soil reaches 2–5 mm, or the pile side friction begins to show a downward effect but has not yet reached the control condition; the negative skin friction control section is defined as follows: when the relative displacement between the pile and soil is greater than 5 mm, or the calculated downward pile side friction reaches the set control threshold. These thresholds can be adjusted according to the soil properties, pile diameter, pile length, and allowable additional axial force of different projects.

[0035] Step 4: Once a certain pile segment is identified as a negative skin friction control segment, the corresponding heating segment is activated; after the flexible electric heating cable is energized, heat is generated, and the heat is transferred to the modified asphalt friction-reducing layer through the thermally conductive insulating mortar, causing the modified asphalt friction-reducing layer to gradually change from a relatively hard state to a softened state, thereby reducing the adhesion and skin friction between the pile and the soil interface.

[0036] Furthermore, the control temperature of the modified asphalt friction-reducing layer is selected to be 5-30°C higher than its softening point; during the heating process, the temperature of the friction-reducing layer is fed back in real time by a platinum resistance temperature sensor; when the temperature is lower than the set lower limit, the output power is increased; when the temperature is within the target control range, constant power or pulse-type heat preservation control is maintained; when the temperature exceeds the set upper limit, the power is reduced or heating is paused to prevent excessive flow or local thermal damage to the asphalt layer.

[0037] Furthermore, to avoid excessively long continuous heating times, a heating-heating-pause-retest control method can be adopted; the duration of a single heating session should be controlled between 10 and 60 minutes, and strain and settlement data should be read again after a pause; if the monitoring results show that the negative skin friction of that section has decreased significantly, or the relative displacement increment of the pile and soil has decreased significantly, then the heating of that section should be stopped; if subsequent monitoring results show that the negative skin friction has developed again, then the corresponding heating section should be restarted.

[0038] The present invention has the following beneficial effects:

[0039] (1) The present invention can achieve active reduction of negative skin friction on the side of PHC piles. By setting an external flexible electric heating cable on the outer surface of the PHC pile friction control section and setting a modified asphalt friction reduction layer around the pile, when the settlement of the soil around the pile causes negative skin friction, the modified asphalt friction reduction layer can be heated and softened to reduce the skin friction at the pile-soil interface, thereby reducing the downward drag of the soil around the pile on the pile body.

[0040] (2) This invention enables zoned heating of different pile segments. The flexible electric heating cable is divided into several independent heating segments along the length of the pile, and each independent heating segment is connected to the ground control cabinet through an independent power supply line and a segment control switch. The control system only starts the pile segment that meets the control conditions, avoiding energy waste caused by heating the entire pile and improving the targeting of friction reduction control.

[0041] (3) The present invention can achieve temperature control during the heating process. By setting platinum resistance temperature sensors near the thermally conductive insulating mortar layer and the modified asphalt friction-reducing layer, the temperature of the pile perimeter friction-reducing layer is obtained in real time, and the heating power and heating time are adjusted by the ground control cabinet to keep the modified asphalt friction-reducing layer in a suitable softening state, so as to avoid insufficient temperature affecting the friction-reducing effect or excessive temperature affecting the stability of the structural layer.

[0042] (4) This invention can identify the development state of negative skin friction. By using a pile reinforcement axial force gauge, a pile top settlement monitoring device, and a pile surrounding soil layered settlement gauge, the changes in pile axial force and the relative displacement between the pile and soil are obtained. When the pile side skin friction is downward and the relative displacement between the pile and soil reaches a set threshold, the ground control cabinet starts the corresponding independent heating section for heating.

[0043] (5) The present invention is simpler to construct, making it easier to implement the project and maintain it later. The flexible electric heating cable does not need to be pre-embedded in the concrete protective layer near the outer surface of the PHC pile. Instead, it is directly arranged along the outer surface of the pile after the PHC pile is prefabricated, fixed by cable fixing clips, and then sealed with thermally conductive and insulating mortar. This structure does not require extensive pre-embedding or trenching within the PHC pile protective layer, which reduces the impact on the original protective layer and prestressed structure of the PHC pile, and makes maintenance and replacement more convenient.

[0044] (6) The external structural layer of the present invention has good integrity. By enclosing the flexible electric heating cable with thermally conductive insulating mortar, a continuous heating structural layer can be formed, which not only facilitates the outward transfer of heat, but also improves the water resistance, wear resistance and local detachment resistance of the electric heating element; after setting a modified asphalt friction-reducing layer and an outer limiting protection layer on its outer side, the system service stability can be further improved. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the spiral segmented arrangement of the flexible electric heating cable along the outer surface of the PHC pile and the connection of each device in this embodiment.

[0046] Figure 2 This is a partial cross-sectional schematic diagram of the PHC pile perimeter heating element and pile perimeter asphalt friction-reducing layer structure along the pile length direction in this embodiment.

[0047] Figure 3 This is a partial cross-sectional schematic diagram of the PHC pile perimeter heating element and pile perimeter asphalt friction-reducing layer structure along the pile diameter direction in this embodiment.

[0048] Figure 4 This is a schematic diagram of the arrangement of the outer limiting protective layer, lap strip and fixing ring of the asphalt layer of the PHC pile in this embodiment.

[0049] Among them, 1-PHC pile body; 2-pile core cavity; 3-PHC pile wall; 4-concrete protective layer; 5-prestressed steel bar; 6-stirrup; 7-pile end plate; 8-end plate wiring hole; 9-flexible electric heating cable; 10-independent heating section; 11-cable fixing clip; 12-high temperature resistant insulation layer; 13-waterproof protective sleeve; 14-thermally conductive insulating mortar; 15-independent power supply line; 16-pile top lead-in groove; 17-pile top waterproof cover; 18-pile top lead-in sealing joint; 19-segment control switch; 20-power terminal block; 21-bottom anchor; 2 2-Grounding wire; 23-Ground control cabinet; 24-Primer coating; 25-Modified asphalt anti-friction layer; 26-Outer limiting protective layer; 27-Limiting protective layer overlap strip; 28-Limiting protective layer fixing ring; 29-Platinum resistance temperature sensor; 30-Temperature sensor protective sleeve; 31-Pile body reinforcement axial force gauge; 32-Axial force gauge protective sleeve; 33-Pile top settlement monitoring device; 34-Pile top settlement observation mark; 35-Pile perimeter soil layered settlement gauge; 36-Layered settlement ring; 37-Pile perimeter soil; 38-Soft soil layer or fill layer; 39-Data acquisition box; 40-Alarm device. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to the accompanying drawings and specific preferred embodiments.

[0051] In the description of this invention, it should be understood that the terms "left side," "right side," "upper part," "lower part," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. "First," "second," etc., do not indicate the importance of the components, and therefore should not be construed as a limitation of this invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of this invention.

[0052] like Figures 1 to 4 As shown, a device for regulating temperature to reduce the negative skin friction of PHC piles includes a PHC pile body, a pile perimeter asphalt friction reduction unit, an electric heating unit, a monitoring unit, and a control and data processing unit.

[0053] The PHC pile body includes the PHC pile body 1, the pile core cavity 2, the PHC pile wall 3, the concrete protective layer 4, the prestressed steel bars 5, the stirrups 6, and the pile end plate 7. The PHC pile is a centrifugally formed prestressed high-strength concrete pipe pile, and the pile core cavity 2 can serve as the lead-out channel for power supply lines and signal lines. Considering that the PHC pile is a prestressed component, in order to avoid large-scale damage to the concrete protective layer 4 near the outer surface of the pile, the flexible electric heating cable 9 of this invention is not pre-embedded in the concrete protective layer 4, but is arranged on the outer surface of the friction reduction control section of the pile after the PHC pile is prefabricated, and is fixed by the cable fixing buckle 11, or arranged in the shallow spiral positioning groove on the outer surface of the pile, and then sealed with thermally conductive insulating mortar 14 to form a heating structure layer attached to the outer surface of the pile.

[0054] The electric heating unit includes a flexible electric heating cable 9, independent heating sections 10, cable fixing clips 11, a high-temperature resistant insulation layer 12, a waterproof protective sleeve 13, thermally conductive insulating mortar 14, an independent power supply line 15, a pile top lead-in channel 16, a pile top waterproof cover 17, a pile top lead-in sealing joint 18, a segmented control switch 19, a power terminal block 20, a grounding wire 22, and a ground control cabinet 23. The flexible electric heating cable 9 is arranged in a spiral shape along the outer surface of the PHC pile friction reduction control section and is divided into several independent heating sections 10 along the length of the pile. Each independent heating section 10 is connected to the ground control cabinet 23 through an independent power supply line 15, thereby realizing segmented start-up and segmented power adjustment.

[0055] The segmented control switch 19 is connected to different independent heating sections 10 to achieve individual on / off control of each independent heating section 10. This allows for flexible and selective heating of the soil around the pile at specific depths based on the temperature distribution or engineering requirements. The power terminal block 20 is used to centrally manage the power connections of each independent heating section, distributing external power to each heating circuit in an orderly manner to ensure the neatness and safety of the power supply lines. The grounding wire 22, reliably connected to the ground, effectively discharges any leakage current, ensuring the electrical safety of the entire electric heating unit and preventing electric shock accidents. All the above-mentioned control and wiring components, including the segmented control switch 19, the power terminal block 20, and the grounding wire 22, are centrally integrated in the ground control cabinet at the top of the PHC pile. This facilitates centralized monitoring, management, and maintenance by on-site operators and also helps protect electrical components from the influence of the external environment.

[0056] The flexible electric heating cable 9 is fixed to the outer surface of the PHC pile by the cable fixing clip 11 and is covered and sealed by thermally conductive insulating mortar 14. The thermally conductive insulating mortar 14 covers the outside of the flexible electric heating cable 9 to form a continuous protective layer and to transfer heat to the outer modified asphalt friction-reducing layer 25.

[0057] The pile perimeter asphalt friction reduction unit includes a base coating layer 24, a modified asphalt friction reduction layer 25, an outer limiting protective layer 26, a limiting protective layer overlap strip 27, and a limiting protective layer fixing ring 28. The base coating layer 24 is applied to the outer surface of the thermally conductive and insulating mortar 14 or the corresponding structural layer on the outer surface of the PHC pile, and is used to improve the bonding stability between the modified asphalt friction reduction layer 25 and the underlying layer. The modified asphalt friction reduction layer 25 is continuously wrapped around the outer surface of the externally applied heating structural layer. The outer limiting protective layer 26 is applied to the outer side of the modified asphalt friction reduction layer 25, and is used to reduce the damage to the friction reduction layer caused by external friction, collision, and disturbance of the surrounding soil during pile driving. At the same time, it plays a limiting role in the asphalt material during the heating and softening process, preventing local loss, accumulation, or uneven thickness of the asphalt layer.

[0058] The monitoring unit includes a platinum resistance temperature sensor 29, a temperature sensor protective sleeve 30, a pile reinforcement axial force gauge 31, an axial force gauge protective sleeve 32, a pile top settlement monitoring device 33, a pile top settlement observation marker 34, a pile perimeter soil layered settlement gauge 35, and a layered settlement ring 36. The platinum resistance temperature sensor 29 is arranged near the modified asphalt friction-reducing layer 25 to monitor the temperature of the friction-reducing layer; the pile reinforcement axial force gauge 31 is segmented and arranged in the center of each independent heating section 10 to monitor the axial strain changes at different depths of the PHC pile; the pile top settlement monitoring device 33 is used to monitor pile top settlement; and the pile perimeter soil layered settlement gauge 35 is used to monitor the settlement of the pile perimeter soil 37 at different depths.

[0059] Each independent heating section 10 is equipped with one platinum resistance temperature sensor 29 and one set of pile steel reinforcement axial force gauges 31. Four measuring points can be arranged along the circumference of the monitoring section, with each measuring point located at the midpoint of the axial force monitoring section. By comparing the settlement data of the pile top with the settlement data of the layered soil around the pile, the downward displacement trend of the soil relative to the pile body can be identified; by the strain difference and axial force difference between adjacent monitoring sections, the change of pile side friction along the depth direction can be calculated.

[0060] The control and data processing unit includes a ground control cabinet 23, a data acquisition box 39, a data transmission cable, and an alarm 40. The data acquisition box 39 is used to collect strain, temperature, and settlement data. The ground control cabinet 23 is used to determine the development status of negative friction resistance based on the monitoring results and to control the start / stop, heating power, and heating time of each independent heating section 10. The alarm 40 is used to issue alarm signals when temperature exceeds limits, strain is abnormal, current is abnormal, leakage occurs, short circuit occurs, or sensor malfunctions.

[0061] The specific usage process of the device for regulating temperature to reduce the negative skin friction of PHC piles in this implementation is as follows:

[0062] Step 1: PHC pile preparation and electrothermal unit arrangement, details are as follows:

[0063] Based on engineering survey data, soil compression characteristics, surcharge conditions, and negative skin friction calculation results, the range of pile segments where negative skin friction may occur along the depth direction of PHC piles is determined, and this range is designated as the friction reduction control section. The friction reduction control section typically corresponds to a soft soil layer, fill layer 38, or a soil layer with significant subsequent settlement.

[0064] After the PHC piles are prefabricated, the outer surface of the friction reduction control section is treated with a base layer to remove laitance, dust, oil, and loose particles, ensuring the pile surface is clean, dry, and flat. The layout range of the flexible electric heating cable 9 is determined within the friction reduction control section. The flexible electric heating cable 9 is arranged spirally along the outer surface of the pile and divided into several independent heating sections 10 along the pile length. Each independent heating section 10 is approximately three turns around the pile. A non-heating interval is reserved between adjacent independent heating sections 10 to reduce heat interference between adjacent pile sections. Each independent heating section 10 is connected to the ground control cabinet 23 via an independent power supply line 15. The power supply and signal lines are led upwards through the pile core cavity 2 and centrally routed and sealed via the pile top lead-in groove 16, the pile top waterproof cover 17, and the pile top lead-in sealing joint 18.

[0065] Step 2: Construction of the heating structural layer sealing and friction-reducing layer, details of which are as follows:

[0066] After the cable is fixed, a high-temperature resistant insulation layer 12 and a waterproof protective sleeve 13 are sequentially installed on the outside of the flexible electric heating cable 9, and the surface is sealed with thermally conductive insulating mortar 14, so that a continuous, smooth heating structure layer with thermal conductivity and insulation is formed on the outside of the cable.

[0067] Temperature and stress monitoring elements are installed within the friction reduction control section. A platinum resistance temperature sensor 29 is positioned outside the thermally conductive and insulating mortar 14, close to the modified asphalt friction-reducing layer 25, to improve the representativeness of temperature monitoring. Axial force gauges 31 for the pile reinforcement are arranged in sections along the corresponding positions of the pile body to monitor changes in the axial strain of the PHC pile. A pile top settlement monitoring device 33 and pile top settlement observation markers 34 are installed at the pile top. Eight pile top settlement observation markers 34 are arranged around the pile top. The pile top settlement monitoring device 33 determines the pile foundation settlement status by receiving the reflected position information from the pile top settlement observation markers 34. The layered settlement gauge 35 is vertically embedded in the soil 37 around the pile along the outside of the PHC pile body 1, and can be fixed to a relatively stable soil layer through its bottom anchor 21, so as to serve as a relatively fixed settlement measurement benchmark. When the soil 37 around the pile and the soft soil layer or fill layer 38 undergo consolidation settlement or additional settlement, the layered settlement ring 36 moves down synchronously with the soil at the corresponding depth. The layered settlement gauge 35 obtains the settlement amount and settlement development process of the soil 37 around the pile at different depths by sensing, identifying or reading the position changes of each layered settlement ring 36, thereby judging the settlement state of the soil 37 around the pile and identifying the relative displacement of the pile and soil and the development state of negative skin friction.

[0068] After the thermally conductive and insulating mortar 14 reaches its design strength or meets the subsequent construction conditions, a primer layer 24 is evenly applied to its outer surface. After the primer layer 24 reaches a surface dry state, a modified asphalt friction-reducing material is continuously applied to form a modified asphalt friction-reducing layer 25. After the modified asphalt friction-reducing layer 25 is constructed, an outer limiting protective layer 26 is installed on its outer side. This outer limiting protective layer 26 is composed of a flexible heat-resistant film, which will not affect the fluidity of the modified asphalt friction-reducing layer 25 formed by heating and melting. It is fixed by the limiting protective layer overlap strip 27 and the limiting protective layer fixing ring 28. The limiting protective layer fixing ring 28 is arranged at the pile head and pile tail of each pile segment to ensure that the outer limiting protective layer 26 does not loosen significantly during the pile driving process, and provides external restraint for the modified asphalt friction-reducing layer 25 during the subsequent heating and softening process.

[0069] After the PHC pile is driven to the design elevation, the platinum resistance temperature sensor 29, the pile reinforcement axial force gauge 31, the pile top settlement monitoring device 33, and the pile surrounding soil layered settlement gauge 35 are initially calibrated. The initial temperature, initial strain, initial settlement at the pile top, and initial settlement data of the pile surrounding soil layered settlement are recorded as the reference values ​​for subsequent negative skin friction identification and heating control.

[0070] Step 3: Service monitoring and negative friction resistance identification, details of which are as follows:

[0071] After the PHC piles enter the service stage, the data acquisition box 39 collects data on pile strain, pile top settlement, pile surrounding soil settlement, and anti-friction layer temperature at set time intervals. When the foundation is still in the rapid consolidation period, surcharge loading period, or fill growth period, the sampling time interval is selected from 10 min to 2 h; when the foundation enters the later stabilization stage, the sampling time interval is selected from 6 h to 24 h.

[0072] The ground control cabinet 23 calculates the axial force of the pile at the corresponding depth based on the strain value collected by the pile reinforcement axial force gauge 31, and calculates the distribution of pile side friction resistance based on the difference in axial force between adjacent monitoring sections; at the same time, it compares the settlement of the soil around the pile with the settlement of the pile to determine the development of the relative displacement between the pile and the soil.

[0073] The PHC pile monitoring sections are divided into normal, warning, and control sections: The normal section is defined as follows: when the relative displacement between the pile and soil is less than 2 mm and the calculated pile side friction does not show a downward effect; the warning section is defined as follows: when the relative displacement between the pile and soil reaches 2–5 mm, or the pile side friction begins to show a downward effect but has not yet reached the control condition; the negative skin friction control section is defined as follows: when the relative displacement between the pile and soil is greater than 5 mm, or the calculated downward pile side friction reaches the set control threshold. These thresholds can be adjusted according to the soil properties, pile diameter, pile length, and allowable additional axial force of different projects.

[0074] Step 4: Heating, softening, and friction reduction control

[0075] Once a pile segment is identified as a negative skin friction control segment, the ground control cabinet 23 activates the corresponding independent heating segment 10. The flexible electric heating cable 9 generates heat upon energization, which is then transferred via the thermally conductive insulating mortar 14 to the modified asphalt friction-reducing layer 25. This causes the modified asphalt friction-reducing layer 25 to gradually soften from a relatively hard state, thereby reducing the adhesion and skin friction between the pile and the soil interface.

[0076] The controlled temperature of the modified asphalt friction-reducing layer 25 is selected to be 5–30°C higher than its softening point. For example, when the softening point of the modified asphalt material used is 60°C, its target working temperature can be set to 65–90°C. During the heating process, the platinum resistance temperature sensor 29 provides real-time feedback on the friction-reducing layer temperature. When the temperature is below the set lower limit of 65°C, the ground control cabinet 23 increases the output power; when the temperature is within the target control range of 65–90°C, it maintains constant power or pulse-type heat preservation control; when the temperature exceeds the set upper limit of 90°C, it reduces the power or suspends heating to prevent excessive flow or localized thermal damage to the asphalt layer.

[0077] To avoid excessively long continuous heating times, a heating-holding-pause-retest control method can be adopted. The duration of a single heating cycle should be controlled between 10 and 60 minutes, and strain and settlement data should be read again after a pause. If the monitoring results show a significant decrease in negative skin friction or a significant decrease in the relative displacement increment between the pile and soil, heating of that section should be stopped; if subsequent monitoring results show that negative skin friction develops again, the corresponding independent heating section 10 should be restarted.

[0078] Step 5: Segmented Control and Safety Protection

[0079] Ground control cabinet 23 controls the corresponding independent heating section 10 according to the monitoring results of each pile segment, heating only the pile segment that meets the control conditions, rather than heating the entire PHC pile as a whole, so as to improve the targeting of control and reduce energy consumption. For soft soil foundation projects with long-term consolidation settlement, a periodic inspection combined with trigger-type heating can be used; for surcharge construction or backfill loading stage, an instantaneous trigger-type heating method under high-frequency monitoring can be used.

[0080] To ensure safe operation of the unit, the ground control cabinet 23 is equipped with temperature upper limit protection, current abnormality protection, leakage protection, and sensor fault alarm functions. When any of the following situations occur in any pile segment, the unit immediately cuts off the power supply to the corresponding independent heating section 10, and the alarm 40 issues an alarm signal: (i) the temperature of the anti-friction layer exceeds the set safety upper limit; (ii) the pile strain increases abnormally in a short period of time; (iii) leakage, short circuit, or current abnormality occurs in the power supply line; (iv) the temperature sensor, strain gauge, or settlement monitoring device experiences signal interruption. The data acquisition box 39 synchronously records the time of abnormality, the abnormal pile segment number, and the corresponding monitoring data for subsequent analysis and maintenance.

[0081] The aforementioned PHC pile model, independent heating section length, flexible electric heating cable arrangement, modified asphalt friction-reducing layer thickness, temperature control threshold, number of monitoring points, and arrangement method are all preferred embodiments and are not intended to limit the present invention. Adjustments can be made according to actual conditions based on different engineering geological conditions, pile diameter, pile length, soft soil layer thickness, and negative skin friction control requirements.

[0082] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A device for regulating temperature to reduce negative skin friction of PHC piles, characterized in that: This includes PHC piles, an electric heating mechanism, and a pile perimeter asphalt friction reduction mechanism; The PHC piles are installed in soft soil or fill layers; The electric heating mechanism is located on the outer periphery of the PHC pile; The pile periphery asphalt friction reduction mechanism is located on the outer periphery of the electric heating mechanism; The electric heating mechanism heats the pile perimeter asphalt friction-reducing mechanism by electricity, softening it to reduce the negative friction force on the PHC pile.

2. The device for reducing the negative skin friction of PHC piles by regulating temperature according to claim 1, characterized in that: The PHC pile is divided into multiple friction reduction control sections along its length; the friction reduction control sections correspond to the soil layer range where the soft soil layer or fill layer has significant settlement in the later stage. The electric heating mechanism has a heating section on each friction-reducing control section of the PHC pile; A pile top settlement monitoring meter is installed at the top of the PHC pile to monitor the pile top settlement; Layered settlement gauges and layered settlement rings are installed in the soil around the PHC pile to obtain the relative displacement of the pile and soil at various depths. A pile axial force sensor is installed at the center of each heating section to obtain the frictional force on the PHC pile in each friction reduction control section; When the pile side friction resistance of a certain friction reduction control section of the PHC pile is downward and the relative displacement between the pile and the soil reaches a set threshold, the heating section corresponding to the outer periphery of the friction reduction control section is energized to heat and soften part of the pile periphery asphalt friction reduction mechanism to reduce the negative friction force of the pile periphery soil on the pile body.

3. The device for reducing the negative skin friction of PHC piles by regulating temperature according to claim 2, characterized in that: The PHC pile includes a pile body, the pile body is hollow to form a pile core cavity, and a PHC pile wall is formed on the outer surface of the pile core cavity; a concrete protective layer is provided on the outer periphery of the PHC pile wall; multiple prestressed steel bars are inserted inside the concrete protective layer; and stirrups are wrapped around the outer periphery of the multiple prestressed steel bars. The power supply and signal lines are led upward through the core cavity of the pile, and are centrally led and sealed through the pile top lead-in groove, the pile top waterproof cover, and the pile top lead-in sealing joint.

4. The device for reducing the negative skin friction of PHC piles by regulating temperature according to claim 3, characterized in that: The electric heating unit includes a flexible electric heating cable arranged in a spiral along the outer surface of the pile. The flexible electric heating cable is fixed to the outer surface of the PHC pile by cable fixing clips. A high-temperature resistant insulation layer and a waterproof protective sleeve are sequentially installed on the outside of the flexible electric heating cable, and the surface is sealed with thermally conductive insulating mortar to form a heating structure layer on the outside of the cable.

5. The device for regulating temperature to reduce negative skin friction of PHC piles according to claim 4, characterized in that: The length of the independent heating section is set according to the length of the friction reduction control section, which is the number of times the flexible electric heating cable is wound around the pile, where n is a natural number greater than 1; The electric heating unit also includes a segmented control switch, a power terminal block, and a grounding wire. The segmented control switch is connected to different independent heating sections to realize individual power on / off control of each independent heating section. The power terminal block is used to unify the wiring of each independent heating section. The grounding wire is connected to the ground to ensure the electrical safety of the entire electric heating unit. All control and wiring components are integrated in the ground control cabinet at the top of the PHC pile.

6. The device for reducing the negative skin friction of PHC piles by regulating temperature according to claim 4, characterized in that: The pile perimeter asphalt friction reduction unit includes a base coating, a modified asphalt friction reduction layer, an outer limiting protective layer, a limiting protective layer overlap strip, and a limiting protective layer fixing ring; the base coating is disposed on the outer surface of the thermally conductive and insulating mortar; the modified asphalt friction reduction layer is disposed on the outer surface of the base coating; and the outer limiting protective layer is disposed on the outside of the modified asphalt friction reduction layer and fixed by the limiting protective layer overlap strip and the limiting protective layer fixing ring. The outer limiting protective layer is a flexible heat-resistant film that does not affect the fluidity of the modified asphalt friction-reducing layer formed by heating and melting; the limiting protective layer overlap strip and the limiting protective layer fixing ring are set at the pile head and pile tail of the PHC pile on each independent heating section.

7. The device for regulating temperature to reduce negative skin friction of PHC piles according to claim 4, characterized in that: The pile-perimeter soil layered settlement gauge is vertically embedded in the soil around the pile along the outer side of the PHC pile body and can be anchored to a relatively stable soil layer through its bottom end. When the soil around the pile and the soft soil layer or fill layer undergo consolidation settlement or additional settlement, the layered settlement ring moves down synchronously with the soil at the corresponding depth. The pile-perimeter soil layered settlement gauge obtains the settlement amount and settlement development process of the soil around the pile at different depths by sensing, identifying or reading the position changes of each layered settlement ring.

8. A method for reducing the negative skin friction of PHC piles by regulating the temperature using the device described in any one of claims 4 to 7, characterized in that: Includes the following steps: Step 1: Based on the engineering survey data, soil compression characteristics, surcharge conditions and negative skin friction calculation results, determine the range of all pile segments with negative skin friction along the depth direction of the PHC pile, and determine them as the skin friction reduction control segments in sequence. Within the friction reduction control section, the layout range of the flexible electric heating cable is determined. The flexible electric heating cable is arranged in a spiral shape along the outer surface of the pile body, and a heating section is formed by wrapping around the pile n times outside each friction reduction control section. Step 2: A high-temperature resistant insulation layer and a waterproof protective sleeve are sequentially installed on the outside of the flexible electric heating cable, and the surface is sealed with thermally conductive and insulating mortar to form a continuous, smooth heating structure layer on the outside of the cable that has both thermal conductivity and insulation functions. After the thermally conductive and insulating mortar reaches its design strength or meets the subsequent construction conditions, a primer layer is evenly applied to its outer surface. After the primer layer reaches a surface dry state, modified asphalt friction-reducing material is continuously applied to form a modified asphalt friction-reducing layer. After the modified asphalt friction-reducing layer is completed, an outer limiting protective layer is set on its outer side. This outer limiting protective layer is made of a flexible heat-resistant film, which will not affect the fluidity of the modified asphalt friction-reducing layer formed by heating and melting. It is fixed by the limiting protective layer overlap strip and the limiting protective layer fixing ring. The limiting protective layer fixing ring is arranged at the pile head and pile tail of each pile section to ensure that the outer limiting protective layer does not loosen significantly during the pile driving process and provides external restraint for the modified asphalt friction-reducing layer during the later heating and softening process. Temperature and stress monitoring elements are installed within the friction reduction control section. Platinum resistance temperature sensors are positioned outside the thermally conductive and insulating mortar, close to the modified asphalt friction-reducing layer, to improve the representativeness of temperature monitoring. Axial force gauges for the pile reinforcement are arranged in sections along the corresponding positions of the pile to monitor changes in the axial strain of the PHC pile. A pile top settlement monitoring device and pile top settlement observation markers are installed at the pile top, with the observation markers arranged around the pile top. The pile top settlement monitoring device determines the pile settlement status by receiving the reflected position information from the pile top settlement observation markers. Layered settlement gauges are installed along the PHC... The C-pile is vertically embedded in the soil around the pile on its outer side and can be anchored to a relatively stable soil layer at its bottom end, serving as a relatively fixed benchmark for settlement measurement. When the soil around the pile, soft soil layer, or fill layer undergoes consolidation settlement or additional settlement, the layered settlement rings move down synchronously with the soil at the corresponding depth. The layered settlement gauge senses, identifies, or reads the position changes of each layered settlement ring to obtain the settlement amount and settlement development process of the soil around the pile at different depths, thereby determining the settlement state of the soil around the pile and identifying the relative displacement of the pile and soil and the development state of negative skin friction. Step 3: After the PHC piles enter the service stage, collect data on pile strain, pile top settlement, pile surrounding soil settlement, and friction-reducing layer temperature at set time intervals; when the foundation is still in the rapid consolidation period, surcharge loading period, or fill growth period, the sampling time interval is selected from 10 min to 2 h; when the foundation enters the later stabilization stage, the sampling time interval is selected from 6 h to 24 h. The axial force of the pile at the corresponding depth is calculated based on the strain value collected by the axial force gauge of the pile reinforcement, and the distribution of the pile side friction is calculated back based on the difference in axial force between adjacent monitoring sections. At the same time, the settlement of the soil around the pile in layers is compared with the settlement of the pile to determine the development of the relative displacement between the pile and the soil. The PHC pile monitoring sections are divided into normal, warning, and control sections: The normal section is defined as follows: when the relative displacement between the pile and soil is less than 2 mm and the calculated pile side friction does not show a downward effect; the warning section is defined as follows: when the relative displacement between the pile and soil reaches 2–5 mm, or the pile side friction begins to show a downward effect but has not yet reached the control condition; the negative skin friction control section is defined as follows: when the relative displacement between the pile and soil is greater than 5 mm, or the calculated downward pile side friction reaches the set control threshold. These thresholds can be adjusted according to the soil properties, pile diameter, pile length, and allowable additional axial force of different projects. Step 4: Once a certain pile segment is identified as a negative skin friction control segment, the corresponding heating segment is activated; after the flexible electric heating cable is energized, heat is generated, and the heat is transferred to the modified asphalt friction-reducing layer through the thermally conductive insulating mortar, causing the modified asphalt friction-reducing layer to gradually change from a relatively hard state to a softened state, thereby reducing the adhesion and skin friction between the pile and the soil interface.

9. The method for reducing the negative skin friction of PHC piles by regulating temperature according to claim 8, characterized in that: The controlled temperature of the modified asphalt friction-reducing layer is selected to be 5-30℃ higher than its softening point; during the heating process, the temperature of the friction-reducing layer is fed back in real time by a platinum resistance temperature sensor; when the temperature is lower than the set lower limit, the output power is increased; when the temperature is within the target control range, constant power or pulse-type heat preservation control is maintained; when the temperature exceeds the set upper limit, the power is reduced or heating is paused to prevent excessive flow or local thermal damage to the asphalt layer.

10. The method for reducing the negative skin friction of PHC piles by regulating temperature according to claim 8, characterized in that: By adopting a heating-insulation-pause-retest control method, the duration of a single heating cycle is controlled within 10 to 60 minutes. After a pause, strain and settlement data are read again. If the monitoring results show that the negative skin friction of the section has decreased significantly, or the relative displacement increment of the pile and soil has decreased significantly, the heating of that section is stopped. If subsequent monitoring results show that the negative skin friction has developed again, the corresponding heating section is restarted.

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