Pile splicing construction method after grouting in silt geology

Abstract

The invention provides a pile splicing construction method for post-pouring piles in sludge geology, and relates to the technical field of post-pouring pile splicing, the construction method comprises the following steps: randomly drawing an engineering pile as a detection pile, sinking a steel casing at the periphery of the engineering pile to be 3 m lower than the top of the pile, and arranging a ladder stand after removing sludge; and the prefabricated steel cage is lowered, detection pile steel bars and steel cage steel bars are bound manually, concrete is poured after a pile cap formwork is arranged on the top, gravel on the outer side of a formwork sleeve is placed, and the detection pile is lengthened to the natural ground. According to the process, through a random pile selection-post extension mode, the representativeness and the standard consistency of a detection sample are ensured; all the engineering piles are in the same batch, the same mixing proportion, the same pouring process and the same age, concrete performance difference, age mismatching, secondary soil disturbance and stiffness mutation caused by traditional preset lengthening are avoided, the static load test result is highly matched with the real stress state of the engineering piles, and the detection precision and the engineering quality are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of post-cast pile connection, and in particular to a construction method for post-cast pile connection in silt geological conditions. Background Art

[0002] The top elevation of the cast pile is much lower than the natural ground elevation. Usually there are the following situations: First, the influence of soft soil layer: When there is a thick soft soil layer on the site, in order to prevent the cast piles from sinking or becoming unstable during construction or use, the cast pile elevation needs to be set lower to increase the embedding depth of the cast piles and improve the stability of the cast piles.

[0003] Second, basement design: If the building has a deep basement, cast piles need to support the basement structure. The cast pile elevation is usually lower than the natural ground to meet the construction and structural requirements of the basement floor.

[0004] In projects with deep silt formations and pile tops far below the natural ground, the current common practice is to designate several cast-in-place piles as static load test piles during the design phase and extend their tops to the ground through a one-time extension. This approach results in significant differences in the process between the test piles (which have been extended and have their tops close to the natural ground) and the conventional engineering piles constructed later (which have not been extended and have their tops far below the natural ground), as shown in the following: First, the difference in concrete pouring technology: the test piles are constructed before the engineering piles, and their parameters such as concrete mix ratio, slump, conduit burial depth control and over-pouring height are often determined according to the on-site conditions at the time; while when the engineering piles are constructed in batches, the raw material batches, mixing time, transportation distance and climatic conditions may change, and the actual pouring parameters are not consistent with those of the test piles.

[0005] Second, differences in age and curing conditions: Test piles must be cast in advance to meet the static load test cycle, and their concrete age is typically 30 to 90 days longer than that of engineering piles. The early concrete strength growth pattern and the aging effects of the pile-soil interface (such as hardening of the mud crust on the pile side and dissipation of pore water pressure) differ from those of engineering piles, directly affecting the performance of lateral friction and end resistance.

[0006] In summary, the above-mentioned process differences make it difficult for the bearing capacity obtained from static load tests to truly reflect the actual load-bearing performance of engineering piles in their final state. The representativeness and reliability of the test conclusions and the deviation from actual engineering practice are generally questioned. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention aims to propose a pile-to-pile construction method after silt geological grouting to solve the problems mentioned in the above background technology section.

[0008] The present invention is achieved through the following technical solutions: A construction method for connecting piles after silt geological grouting, the construction method comprising the following steps: S1. Randomly select all engineering piles that have been constructed and poured, and select a number of engineering piles as test piles; S2. Insert a steel casing around the periphery of the test pile, with the central axis of the steel casing collinear with the central axis of the test pile, and the bottom surface of the steel casing at least 3 meters lower than the top surface of the test pile; S3. Clear the earth and mud between the steel casing and the test pile; S4. Arrange a ladder inside the steel casing; S5. Place the pre-built steel cage into the steel casing. The construction workers enter the steel casing using a ladder and tie the steel bars of the steel cage to the steel bars of the test piles. Then, the construction workers and the ladder move out of the steel casing. S6. Place the template casing in the steel casing, and sleeve the lower end of the template casing on the outer periphery of the top of the test pile; S7. Fill gravel between the steel casing and the formwork sleeve, and place the formwork sleeve above the gravel; S8. Build a pile cap template on top of the gravel, securely connect the pile cap template to the template sleeve, and ensure the height of the pile cap template is close to the natural ground. S9. Fill the space between the pile cap formwork and the formwork sleeve with concrete, and complete the pile-to-pile construction.

[0009] Furthermore, in step S9, the grade of concrete filled in the pile cap formwork and the formwork sleeve is greater than or equal to the grade of concrete used in the test pile.

[0010] Furthermore, step S4 also includes installing a blower and an air supply pipe; In step S5, the construction personnel continuously ventilate the steel casing through the blower and the air supply pipe before entering the steel casing. After the oxygen content is tested to be qualified, the construction personnel enter the steel casing.

[0011] Furthermore, step S4 also includes installing a water pump in the steel casing, digging a sump on the natural ground, and pumping the silt seepage in the steel casing into the sump by the water pump.

[0012] Furthermore, the diameter of the steel casing is 1 m larger than the diameter of the detection pile.

[0013] Step S7 specifically includes: Fill gravel in layers, add compaction operation between two gravel filling operations, and measure the compaction weight of the gravel after compaction. After the compaction weight of the layered gravel meets the set value, The layered gravel is filled, compacted and measured for compaction weight, and the gravel filling work between the steel casing and the formwork sleeve is completed in this cycle.

[0014] Furthermore, the The compaction density of layered gravel satisfies the following formula:

[0015] In the above formula, Indicates the The required compaction weight of the layered gravel; Indicates the natural weight of the silt; represents the passive earth pressure coefficient of silt; represents the passive earth pressure coefficient of gravel; Indicates the cohesion of silt; Indicates the The depth at the midpoint of a stratified gravel layer.

[0016] The beneficial effects of the present invention are: First, ensure the randomness of testing: there is no need to specify test piles in advance during the design phase. After the foundation pit is formed, any engineering piles can be randomly selected for connection. This fully complies with the specification's requirements for "random and representative" test piles, and avoids the sample bias caused by the traditional "pre-set connection".

[0017] Second, all engineering piles are cast in one go using the same batch of concrete, mix ratio, and conduit pouring process, with identical curing ages. Test piles are randomly selected only after the foundation pit is formed and extended to the ground using the "steel casing-pile connection" process provided in steps S2 to S9 of the present invention. This completely eliminates the systematic differences between engineering and test piles caused by the traditional one-time premature extension process, including differences in concrete properties, age, secondary disturbance of the soil surrounding the piles, and sudden changes in stiffness at the pile-connection interface. This ensures that the static load test results are highly consistent with the actual stress state of the engineering piles. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention provides a flow chart of a pile connection construction method after silt geological grouting.

[0019] Figure 2 This is a schematic diagram of the construction nodes of pile connection after silt geological grouting according to the present invention.

[0020] The above drawings include the following reference numerals: 01. Test pile; 02. Steel casing; 03. Ladder; 04. Steel cage; 05. Gravel; 06. Formwork sleeve; 07. Pile cap formwork; 08. Natural ground; 09. Concrete; 10. Fan; 11. Air duct; 12. Water pump; 13. Sump; 14. Guardrail. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. It should be noted that the description of these embodiments is intended to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0022] Reference Figures 1 to 2 As shown, a construction method for connecting piles after silt geological grouting is provided, and the construction method comprises the following steps: S1. Randomly select all engineering piles that have been constructed and poured, and select a number of engineering piles as test piles 01; S2. Insert a steel casing 02 around the periphery of the test pile 01, with the central axis of the steel casing 02 collinear with the central axis of the test pile 01, and the bottom surface of the steel casing 02 at least 3 meters lower than the top surface of the test pile 01. In this step, use an electric or hydraulic vibratory hammer to clamp the steel casing 02 with a crane or excavator. High-frequency vibration liquefies the sand around the test pile 01, and the steel casing 02 is inserted under the action of gravity. This method is suitable for silty clay, loose formations, and other formations prone to shrinkage or collapse. S3, clear the earth and silt between the steel casing 02 and the detection pile 01; in this step, a rotary excavator is used to remove the earth and silt between the steel casing 02 and the detection pile 01, and a protective railing 14 is set around it to prevent people from falling into the steel casing 02; S4. Ladder 03 is arranged inside the steel casing 02; S5. Place the pre-built steel cage 04 into the steel casing 02. The construction personnel enter the steel casing 02 via the ladder 03 and tie the steel bars of the steel cage 04 to the steel bars of the test pile 01. Then, the construction personnel and the ladder 03 move out of the steel casing 02. S6. Place the template casing in the steel casing 02, and sleeve the lower end of the template casing on the outer periphery of the top of the test pile 01; S7. Fill gravel 05 between the steel casing 02 and the template sleeve 06, and set the template sleeve 06 above the gravel 05; S8. Build a pile cap template 07 on top of the gravel 05. The pile cap template 07 is fixed to the template sleeve 06. The height of the pile cap template 07 is close to the natural ground 08, so that the static load equipment can be directly connected to the pile cap. S9. Fill the space between the pile cap formwork 07 and the formwork sleeve 06 with concrete 09, and complete the post-pile connection construction.

[0023] Through the above design, the beneficial effects of the present invention are: First, ensure the randomness of detection: there is no need to specify the test pile 01 in advance during the design phase. After the foundation pit is formed, any engineering pile can be randomly selected for connection. This fully complies with the specification's requirements for the "randomness and representativeness" of the test pile 01, and avoids the sample bias caused by the traditional "pre-set connection".

[0024] Second, all engineering piles were constructed in a single operation using the same batch of concrete (09), the same mix ratio, and the same conduit pouring process, with identical curing ages. Test piles (01) were randomly selected only after the foundation pit was formed and extended to the surface using the "steel casing (02)-pile connection" process provided in steps S2 through S9 of the present invention. This completely eliminated the systematic differences between engineering piles and test piles (01) caused by the traditional one-time extension process, such as differences in concrete (09) performance, age, secondary disturbance of the soil surrounding the piles, and sudden changes in stiffness at the connection interface. This ensured that the static load test results were highly consistent with the actual stress state of the engineering piles.

[0025] In step S9, the grade of concrete (09) filled within the pile cap formwork (07) and formwork sleeve (06) is greater than or equal to the grade of concrete (09) used in the test pile (01). This ensures that the pile connection and pile cap are stronger than the engineering pile. Furthermore, the steel casing (02) and formwork casing form a circumferential constraint, ensuring that 100% of the test load is transferred to the engineering pile body. The settlement at the top of the test pile (01) represents the actual settlement of the engineering pile, and the test accuracy meets current regulatory requirements.

[0026] Step S4 also includes installing the air blower 10 and the air supply pipe 11; In step S5 , before the construction personnel enter the steel casing 02 , the steel casing 02 is continuously ventilated through the blower 10 and the air supply pipe 11 . After the oxygen content is tested to be qualified, the construction personnel enter the steel casing 02 .

[0027] Step S4 also includes installing a water pump 12 in the steel casing 02, digging a sump 13 on the natural ground 08, and pumping the silt seepage in the steel casing 02 into the sump 13 through the water pump 12 to ensure that there is no water accumulation inside the steel casing 02.

[0028] An independent "dry working well" is formed in the silt layer by a large-diameter steel casing 02, which provides a working space at least 5 meters deep without the need for large-scale slope reduction or additional support. Combined with ventilation and pumping measures, it completely avoids the difficulties in lowering equipment into the pit, slope instability and personnel safety risks caused by traditional "in-pit loading".

[0029] The diameter of the steel casing 02 is 1m larger than the diameter of the detection pile 01, so that the construction workers have sufficient operating space, making it convenient for the construction workers to enter the steel casing 02 through the ladder 03, and then chisel the top of the detection pile 01 to expose the steel bars, and tie the steel bars of the steel cage 04 to the steel bars of the detection pile 01, and then the construction workers and the ladder 03 move out of the steel casing 02.

[0030] Step S7 specifically includes: filling gravel 05 in layers, adding a compaction operation between two operations of filling gravel 05, and measuring the compaction weight of the gravel 05 after compaction. When the compaction weight of the gravel 05 in the first layer meets the set value, the filling operation, compaction operation and compaction weight measurement operation are performed on the layered gravel 05, and the gravel 05 filling work between the steel casing 02 and the template sleeve 06 is completed in this cycle.

[0031] During the filling process of gravel 05, a closed-loop control process of "filling → compaction → compaction weight measurement" for each layer stabilizes the compaction weight of gravel 05 at the designed value, making its lateral stiffness and static earth pressure coefficient equivalent to those of the original silt. The pile connection section is subjected to the same lateral confining pressure as the engineering pile as possible, ensuring that the pile-soil interaction force is not distorted by the pile connection. The ultimate bearing capacity obtained from the static load test is the true value of the engineering pile, thus improving the reliability of the static load test results for test pile 01.

[0032] Furthermore, the The compaction density of layered gravel 05 satisfies the following formula:

[0033] In the above formula, Indicates the The compaction weight that the layered gravel 05 needs to achieve, which reflects the weight index of the gravel 05 after compaction in order to make the gravel 05 layer have the same lateral support force as the original silt layer; Indicates the natural gravity of silt, which is measured by sampling the undisturbed silt soil extracted from the steel casing 02 using test methods (such as the ring knife method, etc.), and represents the weight of the silt per unit volume; represents the passive earth pressure coefficient of silt, which is estimated based on Rankine's earth pressure theory; represents the passive earth pressure coefficient of gravel 05, estimated based on Rankine's earth pressure theory; The cohesion of silt is the cohesive force between silt particles due to physical and chemical reactions. It is measured through geotechnical tests and reflects the ability of silt to resist shear failure. Indicates the The depth at the midpoint of the stratified gravel layer is used to consider the effect of depth on lateral earth pressure. The earth pressure distribution varies at different depths.

[0034] Through the combined effect of the above parameters, a correlation is established between the compaction weight of gravel 05 and the mechanical properties of the original silt after the silt is replaced with gravel 05, so as to ensure the consistency of the lateral support effect on the test pile 01 after the replacement.

[0035] If the extracted undisturbed silt is simply reinjected between the steel casing 02 and the test pile 01, the silt will be disturbed again, completely destroying its structure, increasing its porosity and causing a sharp drop in strength. Furthermore, the water content cannot be restored to its original state, reducing the lateral effective stress. The narrow annular space between the steel casing 02 and the pile shaft is difficult to compact in layers, which can easily lead to the formation of weak interlayers or localized voids. For these reasons, the lateral support force will be significantly lower than that of the undisturbed silt, making it impossible to guarantee equivalent stress to the engineering pile. Therefore, replacing the gravel 05 with the sand and gravel and controlling the compaction weight in a closed loop can improve the reliability of the subsequent static load test results.

[0036] The invention provides a method for connecting piles after silt geological grouting, which provides a feasible method for post-inspection of engineering piles, ensures construction safety, meets static load detection requirements, is beneficial to the overall quality control of engineering piles, has little impact on construction progress, and saves costs.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0038] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0039] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for connecting piles after grouting in silt geology, characterized by: The construction method comprises the following steps: S1. Randomly select all engineering piles that have been constructed and poured, and select a number of engineering piles as test piles; S2. Insert a steel casing around the periphery of the test pile, with the central axis of the steel casing collinear with the central axis of the test pile, and the bottom surface of the steel casing at least 3 meters lower than the top surface of the test pile; S3. Clear the earth and mud between the steel casing and the test pile; S4. Arrange a ladder inside the steel casing; S5. Place the pre-built steel cage into the steel casing. The construction workers enter the steel casing using a ladder and tie the steel bars of the steel cage to the steel bars of the test piles. Then, the construction workers and the ladder move out of the steel casing. S6. Place the template casing in the steel casing, and sleeve the lower end of the template casing on the outer periphery of the top of the test pile; S7. Fill gravel between the steel casing and the formwork sleeve, and place the formwork sleeve above the gravel; S8. Build a pile cap template on top of the gravel, securely connect the pile cap template to the template sleeve, and ensure the height of the pile cap template is close to the natural ground. S9. Fill the space between the pile cap formwork and the formwork sleeve with concrete, and complete the pile-to-pile construction.

2. The method for connecting piles after grouting in silt geology according to claim 1, characterized in that: In step S9, the grade of concrete filled in the pile cap formwork and the formwork sleeve is greater than or equal to the grade of concrete used in the test pile.

3. The method for connecting piles after grouting in silt geology according to claim 1, characterized in that: Step S4 also includes installing a blower and an air supply pipe; In step S5, the construction personnel continuously ventilate the steel casing through the blower and the air supply pipe before entering the steel casing. After the oxygen content is tested to be qualified, the construction personnel enter the steel casing.

4. The method for connecting piles after grouting in silt geology according to claim 1, characterized in that: Step S4 also includes installing a water pump in the steel casing, digging a sump on the natural ground, and pumping the silt seepage in the steel casing into the sump by the water pump.

5. The method for connecting piles after grouting in silt geology according to claim 1, characterized in that: The diameter of the steel casing is 1 meter larger than the diameter of the detection pile.

6. The method for connecting piles after grouting in mud geology according to claim 1, characterized in that: Step S7 specifically includes: Fill gravel in layers, add compaction operation between two gravel filling operations, and measure the compaction weight of the gravel after compaction. After the compaction weight of the layered gravel meets the set value, The layered gravel is filled, compacted and measured for compaction weight, and the gravel filling work between the steel casing and the formwork sleeve is completed in this cycle.

7. The method for connecting piles after grouting in silt geology according to claim 6, characterized in that: The said The compaction density of layered gravel satisfies the following formula: In the above formula, Indicates the The required compaction weight of the layered gravel; Indicates the natural weight of the silt; represents the passive earth pressure coefficient of silt; represents the passive earth pressure coefficient of gravel; Indicates the cohesion of silt; Indicates the The depth at the midpoint of a stratified gravel layer.

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