A rapid detection method for the bearing capacity of pre-buried steel tube concrete inclined support

Abstract

A method for quickly detecting the bearing capacity of a pre-embedded steel tube concrete inclined support, characterized in that: in advance, a pre-embedded placeholder is prepared, and the specific implementation method includes the following steps: step S5, after the concrete in the steel tube is cured to the design strength, an opening is cut on the inclined support steel tube at the marked position, and the outer tube, foaming material and center column of the pre-embedded placeholder are removed; step S6, a hydraulic jack for bearing capacity detection is placed at the position of the center column of the original pre-embedded placeholder, and the two ends of the hydraulic jack are pressed against the circular steel plates at both ends of the pre-embedded placeholder; step S7, the entire inclined support steel tube is cut in the circumferential direction, and displacement sensors are installed on both sides of the cut inclined support steel tube in line with the axial direction of the inclined support steel tube; step S8, by applying graded pressure and unloading the hydraulic jack and synchronously obtaining the displacement sensor value, the axial bearing capacity value of the steel tube concrete inclined support is obtained by conversion, and it is determined whether the bearing capacity meets the design requirements.

Description

Technical Field

[0001] The present invention relates to the field of foundation pit and slope support engineering, and in particular to a method for quickly detecting the bearing capacity of a pre-buried steel pipe oblique support. The method can quickly detect the result online. Background Art

[0002] In deep foundation pit projects, horizontal supports and inclined supports are two common support methods. Although horizontal supports are widely used, they also have some significant disadvantages: Horizontal supports usually require multiple layers of supports within the foundation pit, which takes up a lot of space, affects the operation of construction machinery and personnel, and reduces construction efficiency; horizontal supports are more suitable for regularly shaped foundation pits, but are more difficult to arrange for irregular or special-shaped foundation pits, and the support effect may not be ideal; when horizontal supports are subjected to uneven force, they are prone to local stress concentration, leading to deformation or even damage of the supporting structure or foundation pit wall; horizontal supports usually require more supporting materials, especially in deep foundation pits, which is costly; the installation and removal process of horizontal supports is complicated, especially when multiple layers of supports are used, which leads to a long construction period; and during the installation and removal process, horizontal supports may disturb the soil around the foundation pit, increasing the risk to adjacent buildings or underground facilities.

[0003] Inclined supports can compensate for these shortcomings: they take up less space, making it easier for construction machinery and personnel to operate within the foundation pit, thereby improving construction efficiency; they can better disperse loads, reduce foundation pit deformation, and improve overall stability, making them particularly suitable for complex geological conditions; they can effectively control the horizontal displacement of the foundation pit wall, reducing deformation risks and improving safety; they are flexible in arrangement and can adapt to irregular or special-shaped foundation pits, providing more uniform support; they are relatively easy to construct and can be installed and removed quickly, which can speed up construction progress and shorten construction periods; they typically use less material, which can reduce project costs; they can effectively control foundation pit deformation and reduce the impact on adjacent buildings and underground facilities; and they have high structural stability, which can reduce the risk of foundation pit collapse and improve construction safety. Therefore, steel tube concrete inclined support technology has been widely used.

[0004] Representative structures and methods of steel tube concrete inclined support technology can be found in the invention patent publication number CN116290003B, which discloses a composite load-bearing inclined support method and system.

[0005] Although steel tube concrete inclined supports have advantages in many aspects, they face some difficulties in bearing capacity testing: the traditional steel tube concrete inclined support bearing capacity testing is to manually chisel out the inclined support in the middle position after all the construction is completed, first cutting off the outer steel pipe, and then chiseling out the concrete inside the steel pipe at the corresponding position; then install the hydraulic jacks and displacement sensors for testing in the corresponding positions in turn, and measure the force and displacement after pressurizing the hydraulic jacks; after the measurement is completed, remove the hydraulic jacks and displacement sensors, re-weld the completely cut steel pipe, and use high-strength concrete to fill the internal cavity of the steel pipe; due to the restrictions on the installation and operation of testing equipment (such as strain gauges, displacement sensors, etc.); the angle of the inclined support may make it difficult to accurately align the installation position and direction of the testing equipment, affecting the accuracy of the test results. Summary of the Invention

[0006] The present invention aims to provide a more convenient and more accurate method for quickly detecting the bearing capacity of a pre-buried steel tube concrete inclined support.

[0007] In order to solve the above technical problems, the present invention adopts the following solutions: a method for quickly detecting the bearing capacity of pre-buried steel tube concrete inclined supports;

[0008] In advance, a pre-embedded placeholder is prepared. The shape of the pre-embedded placeholder matches the inner cavity of the oblique support steel pipe, and its length is greater than the minimum length of the hydraulic jack used for load-bearing capacity testing. The specific preparation process of the pre-embedded placeholder is as follows: first, a concentric outer tube of equal length is placed outside a central column; then, circular steel plates are vertically welded to both ends of the central column; and foam material is filled between the outer tube, the central column, and the steel plates at both ends to form the pre-embedded placeholder.

[0009] The specific implementation method includes the following steps:

[0010] Step S1: driving the inclined support steel pipe into the rock and soil by vibration, static pressure, etc.

[0011] Step S2, pouring concrete from the top of the inclined supporting steel pipe downwards;

[0012] Step S3: Place the prepared embedded placeholder into the inclined support steel pipe, tighten and compact it, and mark the embedding position on the outside of the inclined support steel pipe;

[0013] Step S4, pouring the remaining concrete from the top of the inclined supporting steel pipe downward to the steel pipe mouth;

[0014] Step S5: After the concrete in the steel pipe has been cured to the designed strength, an opening is cut on the oblique support steel pipe at the marked location, and the outer pipe, foaming material, and center column of the embedded placeholder are removed;

[0015] Step S6: Place a hydraulic jack for load-bearing capacity testing at the location of the center column of the original embedded placeholder. Press the two ends of the hydraulic jack against the circular steel plates at both ends of the embedded placeholder, with the pressurizing direction consistent with the axial direction of the inclined support steel pipe.

[0016] Step S7: leaving the oblique support steel pipe at the entire cut opening in the circumferential direction, and installing displacement sensors on both sides of the cut oblique support steel pipe in line with the axial direction of the oblique support steel pipe;

[0017] Step S8, by applying pressure to the hydraulic jack in stages and unloading it, and simultaneously obtaining the displacement sensor value, the axial bearing capacity of the steel tube concrete inclined support is obtained by conversion, and it is determined whether the bearing capacity meets the design requirements;

[0018] Step S9, remove the hydraulic jack and displacement sensor; fill the cavity with high-grade concrete; weld the cut oblique support steel pipes and restore them to their original state.

[0019] In the above solution, the specific steps of loading and bearing capacity determination in step 8 are as follows:

[0020] Step 8.1: Use the hydraulic jack to apply pressure in stages to obtain the axial force value Q for each stage. i , i=1~10;

[0021] Step 8.2: Measure the lower displacement sensor measurement value S corresponding to each level of pressure i , i=1~10;

[0022] In step 8.3, the loading process can be terminated if any of the following situations occurs:

[0023] A. Under a certain load level, the deformation of the lower displacement sensor is 5 times the deformation under the previous load level and the total deformation is greater than 60mm;

[0024] B. Under a certain load level, the deformation of the lower displacement sensor is more than twice the deformation of the lower displacement sensor under the previous load level, and has not reached relative stability after 24 hours;

[0025] C. Achieve the maximum load required by the design;

[0026] D. The upper displacement sensor has reached the allowable value;

[0027] F. The curve shows a slow-changing type, and the cumulative measurement value of the lower displacement sensor reaches 60mm;

[0028] Step 8.4: Determine the diagonal bearing capacity N using one of the following six methods: k :

[0029] (1) Determine based on the characteristics of the deformation changing with load: For the steep drop Q-S curve, the load value corresponding to the starting point where the obvious steep drop occurs should be taken;

[0030] (2) Determine based on the characteristics of deformation variation over time: the load value before the tail of the S-lgt curve shows an obvious downward bend should be taken;

[0031] (3) When the deformation of the lower displacement sensor under a certain load level is greater than twice the deformation of the lower displacement sensor under the previous load level, and it has not reached relative stability after 24 hours, the previous load value should be used;

[0032] (4) When the Q-S curve shows a slow-changing type, the load value corresponding to a deformation of 60 mm should be taken;

[0033] (5) The upper displacement sensor has reached the allowable value and the maximum load value is taken;

[0034] (6) When the conditions in clauses 1 to 5 of this article are not met, the bearing capacity shall be the maximum load value;

[0035] Step 8.5: Determine whether the diagonal bearing capacity meets the design requirements:

[0036] Step 8.5.1: Calculate the earth pressure of the retaining structure to obtain the reaction force S of the oblique support within the calculation width of the retaining structure. k , when N k / S k When ≥K, the design requirements are met; K is the safety factor;

[0037] Step 8.5.2: Calculate the design value of the axial compressive bearing capacity of the concrete-filled steel tube inclined support N u , when N u ≥ γ 0× γ F ×S k When the design requirements are met; γ 0 is the importance coefficient of the supporting structure, γ F It is the comprehensive partial coefficient of the basic combination of effects.

[0038] In the above solution, when preparing the embedded placeholder, the foam material is flame-retardant foam material, and flame-retardant paint is applied to the outside of the outer tube to avoid the risk of material combustion during subsequent cutting and welding operations, thereby improving safety.

[0039] In the above solution, when preparing the embedded placeholder, the central column is tubular, known as the center tube, and a hole is formed in the center of the circular steel plate, aligned and communicating with the center tube. This hole, which runs vertically through the center of the embedded placeholder, effectively evacuates air from the lower concrete cavity during installation, ensuring a close fit between the circular steel plate at the end and the concrete, ensuring uniform and stable force on both ends of the hydraulic jack during testing.

[0040] Advantages and effects of the present invention:

[0041] 1. By using the method of the present invention, the embedded bearing capacity detection device is prepared in advance, and the detection point layout can be completed during the construction process, avoiding the subsequent manual cutting and chiseling of the steel tube concrete support, simplifying the embedding and construction process, and greatly improving the construction efficiency;

[0042] 2. The method of the present invention has simple structure, reliable quality, quick burial, convenient implementation and wide applicability;

[0043] 3. By pre-setting the central column and the circular steel plate vertically in the method of the present invention, the subsequent hydraulic jack and displacement sensor can achieve effective vertical loading with the end circular steel plate, thereby improving the detection accuracy;

[0044] 4. The embedded placeholders produced by the method of the present invention replace traditional concrete, saving materials, facilitating dismantling, reducing labor and raw material input, and having obvious economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram of the embedded placeholder of the present invention placed in the oblique support steel pipe;

[0046] Figure 2 for Figure 1 Schematic diagram of the cross section of AA in FIG;

[0047] Figure 3 for Figure 1 Schematic cross-section of BB in FIG;

[0048] Figure 4 This is a schematic diagram of the state of the displacement sensor during detection after the embedded placeholder is removed and replaced with a hydraulic jack in the present invention;

[0049] Figure 5 Drawing a Q-S curve diagram for an embodiment of the present invention;

[0050] Figure 6 1 and 2 are S-1gt curves of an embodiment of the present invention.

[0051] In the above figures: 1. Center column; 2. End circular steel plate; 3. Flame-retardant foam material; 4. Outer tube; 5. Flame-retardant coating; 6. Concrete; 7. Diagonal support steel pipe; 8. Hydraulic jack; 9. Upper displacement sensor; 10. Lower displacement sensor; 11. Reference beam. DETAILED DESCRIPTION

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0053] Example: See Figure 1-Figure 4 As shown:

[0054] A method for quickly detecting the bearing capacity of a pre-buried steel tube concrete inclined support, characterized by:

[0055] In advance, a pre-embedded placeholder is prepared. The shape of the pre-embedded placeholder matches the inner cavity of the oblique support steel pipe, and its length is greater than the minimum length of the hydraulic jack used for load-bearing capacity testing. The specific preparation process of the pre-embedded placeholder is as follows: first, a concentric outer tube of equal length is placed outside a central column; then, circular steel plates are vertically welded to both ends of the central column; and foam material is filled between the outer tube, the central column, and the steel plates at both ends to form the pre-embedded placeholder.

[0056] The specific implementation method includes the following steps:

[0057] Step S1: driving the inclined support steel pipe into the rock and soil by vibration, static pressure, etc.

[0058] Step S2, pouring concrete from the top of the inclined supporting steel pipe downwards;

[0059] Step S3: Place the prepared pre-buried placeholder into the inclined support steel pipe 7, tighten and compact it, and mark the buried position on the outside of the inclined support steel pipe, as shown in the following figure: Figure 1 As shown;

[0060] Step S4, pouring the remaining concrete from the top of the inclined supporting steel pipe downward to the steel pipe mouth;

[0061] Step S5: After the concrete in the steel pipe has been cured to the designed strength, an opening is cut on the oblique support steel pipe at the marked position, and the outer tube 4, the foaming material 3 and the central column 1 of the embedded placeholder are removed;

[0062] Step S6: Place the hydraulic jack for load-bearing capacity testing at the location of the center column of the original embedded placeholder. Press the two ends of the hydraulic jack against the circular steel plates 2 at both ends of the embedded placeholder, and keep the pressure direction consistent with the axial direction of the oblique support steel pipe 7.

[0063] Step S7, leaving the oblique support steel pipe at the entire cut opening in the circumferential direction, and installing displacement sensors on both sides of the cut oblique support steel pipe that are consistent with the axial direction of the oblique support steel pipe; Figure 4As shown, the upper displacement sensor 9 and the lower displacement sensor 10 are supported on the reference beam 11 as shown;

[0064] Step S8, by applying pressure to the hydraulic jack in stages and unloading it, and simultaneously obtaining the displacement sensor value, the axial bearing capacity of the steel tube concrete inclined support is obtained by conversion, and it is determined whether the bearing capacity meets the design requirements;

[0065] Step S9, remove the hydraulic jack and displacement sensor; fill the cavity with high-grade concrete; weld the cut oblique support steel pipes and restore them to their original state.

[0066] In step 8, the specific steps of loading and bearing capacity determination are as follows:

[0067] Step 8.1: Use the hydraulic jack to apply pressure in stages to obtain the axial force value Q for each stage. i , i=1~10;

[0068] Step 8.2: Measure the lower displacement sensor measurement value S corresponding to each level of pressure i , i=1~10; draw Q~S curve and S-lgt curve as shown Figure 5 and Figure 6 ;

[0069] In step 8.3, the loading process can be terminated if any of the following situations occurs:

[0070] A. Under a certain load level, the deformation of the lower displacement sensor is 5 times the deformation under the previous load level and the total deformation is greater than 60mm;

[0071] B. Under a certain load level, the deformation of the lower displacement sensor is more than twice the deformation of the lower displacement sensor under the previous load level, and has not reached relative stability after 24 hours;

[0072] C. Achieve the maximum load required by the design;

[0073] D. The upper displacement sensor has reached the allowable value;

[0074] F. The curve shows a slow-changing type, and the cumulative measurement value of the lower displacement sensor reaches 60mm;

[0075] Step 8.4: Determine the diagonal bearing capacity N using one of the following six methods: k :

[0076] (1) Determine based on the characteristics of the deformation changing with load: For the steep drop Q-S curve, the load value corresponding to the starting point where the obvious steep drop occurs should be taken;

[0077] (2) Determine based on the characteristics of deformation variation over time: the load value before the tail of the S-lgt curve shows an obvious downward bend should be taken;

[0078] (3) When the deformation of the lower displacement sensor under a certain load level is greater than twice the deformation of the lower displacement sensor under the previous load level, and it has not reached relative stability after 24 hours, the previous load value should be used;

[0079] (4) When the Q-S curve shows a slow-changing type, the load value corresponding to a deformation of 60 mm should be taken;

[0080] (5) The upper displacement sensor has reached the allowable value and the maximum load value is taken;

[0081] (6) When the conditions in clauses 1 to 5 of this article are not met, the bearing capacity shall be the maximum load value;

[0082] from Figure 5 and Figure 6 It can be seen from the Q~S curve and S-lgt curve that the above conditions 1 to 5 are not met, so the bearing capacity is taken as the maximum load value N k =800kN;

[0083] Step 8.5: Determine whether the diagonal bearing capacity meets the design requirements:

[0084] Step 8.5.1: Calculate the earth pressure of the retaining structure to obtain the reaction force S of the oblique support within the calculation width of the retaining structure. k , when N k / S k When ≥K, the design requirements are met; K is the safety factor; the specific calculation value is: S k =420kN, N k / S k =800 / 420=1.9>K=1.6 (K is the safety factor, take 1.6), so the design requirements are met;

[0085] Step 8.5.2: Calculate the design value of the axial compressive bearing capacity of the concrete-filled steel tube inclined support N u , when N u ≥ γ 0× γ F ×S k When the design requirements are met; γ 0 is the importance coefficient of the supporting structure, γ F It is the comprehensive sub-item coefficient of the basic combination of actions; the specific calculation value is: N u =A× f =142530.92×39.95=5694kN> γ 0× γ F ×S k=1.0×1.25×420=525kN (A is the sum of the area of ​​the steel pipe and the concrete inside the steel pipe, take 142530.92mm 2 ; f The design value of the compressive strength of steel tube concrete is 30.5N / mm 2 ; γ 0 is the importance coefficient of the support structure, which is taken as 1.0; γ F is the comprehensive partial coefficient of the basic combination of actions, taken as 1.25), to meet the design requirements.

[0086] In practice, if the design requirements are not met, the spacing of inclined supports, bearing layer, etc. are adjusted until the design requirements are met.

[0087] When preparing the embedded placeholder, it is preferred to use flame-retardant foam material for the foam material 3 and apply flame-retardant paint on the outside of the outer tube 4 to avoid the risk of material combustion during subsequent cutting and welding operations and improve safety.

[0088] When preparing a pre-embedded placeholder, it's best to use a tubular shape for the center column 1, or the center tube, and define a hole in the center of the circular steel plate 2 that aligns with the center tube. This allows for a vertically penetrating hole in the center of the pre-embedded placeholder, effectively venting air from the concrete below during installation and ensuring a close fit between the circular steel plate and the concrete, ensuring uniform and stable force on both ends of the hydraulic jack during testing.

[0089] In order to facilitate disassembly, the outer tube 4 is preferably a PVC tube.

[0090] This embodiment has the following advantages: By pre-preparing a pre-embedded bearing capacity detection device, the detection points can be positioned and arranged during the construction process, eliminating the need for subsequent manual cutting and chiseling of the steel tube concrete support, simplifying the embedding and construction process and significantly improving construction efficiency. Furthermore, by pre-setting the central column and circular steel plate vertically, the subsequent hydraulic jack and displacement sensor can achieve effective vertical loading relative to the end circular steel plate, improving detection accuracy.

Claims

1. A method for quickly detecting the bearing capacity of a pre-buried steel tube concrete inclined support, characterized by: In advance, a pre-embedded placeholder is prepared. The shape of the pre-embedded placeholder matches the inner cavity of the oblique support steel pipe, and its length is greater than the minimum length of the hydraulic jack used for load-bearing capacity testing: the specific preparation process of the pre-embedded placeholder is as follows: first, a concentric outer tube of equal length is placed outside a central column; then, circular steel plates are vertically welded to both ends of the central column; foaming material is filled between the outer tube and the central column and the steel plates at both ends to form the pre-embedded placeholder; the central column is tubular, i.e., the central tube, and a hole is opened in the center of the circular steel plate to align with and communicate with the central tube; The specific implementation method includes the following steps: Step S1: driving the inclined support steel pipe into the rock and soil by vibration, static pressure, etc. Step S2, pouring concrete from the top of the inclined supporting steel pipe downwards; Step S3: Place the prepared embedded placeholder into the inclined support steel pipe, tighten and compact it, and mark the embedding position on the outside of the inclined support steel pipe; Step S4, pouring the remaining concrete from the top of the inclined supporting steel pipe downward to the steel pipe mouth; Step S5: After the concrete in the steel pipe has been cured to the designed strength, an opening is cut on the oblique support steel pipe at the marked location, and the outer pipe, foaming material, and center column of the embedded placeholder are removed; Step S6: Place a hydraulic jack for load-bearing capacity testing at the location of the center column of the original embedded placeholder. Press the two ends of the hydraulic jack against the circular steel plates at both ends of the embedded placeholder, with the pressurizing direction consistent with the axial direction of the inclined support steel pipe. Step S7: leaving the oblique support steel pipe at the entire cut opening in the circumferential direction, and installing displacement sensors on both sides of the cut oblique support steel pipe in line with the axial direction of the oblique support steel pipe; Step S8, by applying pressure to the hydraulic jack in stages and unloading it, and simultaneously obtaining the displacement sensor value, the axial bearing capacity of the steel tube concrete inclined support is obtained by conversion, and it is determined whether the bearing capacity meets the design requirements; Step S9, remove the hydraulic jack and displacement sensor; fill the cavity with high-grade concrete; weld the cut oblique support steel pipes and restore them to their original state.

2. The method for quickly detecting the bearing capacity of a pre-buried concrete-filled steel tube inclined support according to claim 1 is characterized in that: In step 8, the specific steps of loading and bearing capacity determination are as follows: Step 8.1: Use the hydraulic jack to apply pressure in stages to obtain the axial force value Qi for each stage, where i = 1 to 10. Step 8.2, measure the lower displacement sensor measurement value Si corresponding to each graded pressurization, where i = 1 to 10; In step 8.3, the loading process can be terminated if any of the following situations occurs: A. Under a certain load level, the deformation of the lower displacement sensor is 5 times the deformation under the previous load level and the total deformation is greater than 60mm; B. Under a certain load level, the deformation of the lower displacement sensor is more than twice the deformation of the lower displacement sensor under the previous load level, and has not reached relative stability after 24 hours; C. Achieve the maximum load required by design; D. The upper displacement sensor has reached the allowable value; F. The curve shows a slow-changing type, and the cumulative measurement value of the lower displacement sensor reaches 60mm; Step 8.4: Determine the diagonal bearing capacity using one of the following six methods: : (1) Determine based on the characteristics of the deformation changing with load: For the steep drop Q-S curve, the load value corresponding to the starting point where the obvious steep drop occurs should be taken; (2) Determine based on the characteristics of deformation variation over time: the load value before the tail of the S-lgt curve shows an obvious downward bend should be taken; (3) When the deformation of the lower displacement sensor under a certain load level is greater than twice the deformation of the lower displacement sensor under the previous load level, and it has not reached relative stability after 24 hours, the previous load value should be used; (4) When the Q-S curve shows a slow-changing type, the load value corresponding to a deformation of 60 mm should be taken; (5) The upper displacement sensor has reached the allowable value and the maximum load value is taken; (6) When the conditions in clauses 1 to 5 of this article are not met, the bearing capacity shall be the maximum load value; Step 8.5, determine whether the diagonal bearing capacity meets the design requirements: Step 8.5.1, calculate the earth pressure of the retaining structure to obtain the reaction force value of the oblique support within the calculation width of the retaining structure ,when When , the design requirements are met; K is the safety factor; Step 8.5.2, calculate the design value of the axial compressive bearing capacity of the steel tube concrete inclined support ,when When the design requirements are met; is the importance coefficient of the supporting structure, It is the comprehensive partial coefficient of the basic combination of effects.

3. The method for quickly detecting the bearing capacity of a pre-buried concrete-filled steel tube inclined support according to claim 1 is characterized in that: When preparing the embedded placeholder, the foaming material is flame-retardant foaming material, and flame-retardant paint is applied on the outside of the outer tube.

Images