A large-scale caisson foundation suspension type in-situ test counterforce system and construction method

Abstract

The present application belongs to the technical field of large bridge sinking well construction, and relates to a large sinking well foundation suspension type in-situ test reaction force system and a construction method. The system comprises a sinking well foundation and a plurality of embedded pipes embedded in the bottom section of the sinking well foundation, wherein a steel rod is arranged in the embedded pipe. The steel rod can extend out of the well wall or the partition beam outside the bottom section of the sinking well foundation and is sleeved with a steel beam. A rigid bearing plate is arranged below the steel beam. A jack is arranged between the rigid bearing plate and the bottom of the steel beam. A plurality of displacement sensors are arranged on the rigid bearing plate. The displacement sensors are connected with a static load tester for real-time recording of in-situ test pressure and sinking amount data. The present application can improve the operation space of the test and detection personnel in the well cabin of the large sinking well foundation, and the test can be carried out at any point position in the well cabin, even close to the well wall. The present application can not only meet the principle of randomly selecting test points, but also meet the requirement of carrying out the test at the most unfavorable position.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of large bridge caisson foundation test detection, and particularly relates to a large caisson foundation suspension type in-situ test reaction force system and a construction method. BACKGROUND

[0002] At present, bridge foundation structures are diversified, and large caisson foundations can adapt to relatively extensive hydrogeological conditions. Large caisson foundations have large burial depth, large stiffness, good overall stability, and can bear large vertical load and horizontal load. Due to the complex geological conditions of the bearing stratum base of the large caisson foundation after sinking into place, especially the complex strata such as soft underlayer and fracture zone in the lower part of the foundation bearing stratum and the uneven distribution of strata in the bearing plane area of the base, it is necessary to perform in-situ test on the large caisson foundation bearing stratum. The purpose is to provide accurate and reliable geotechnical mechanics parameters for large bridge design and optimize bridge design parameters.

[0003] For the narrow space in each well cabin of the large bridge caisson foundation, the reaction force required for in-situ test in the well cabin of the large caisson foundation is large. If the method of stacking weight blocks is used as the reaction force system, a large number of weight blocks are required for stacking, and the stacked weight blocks occupy a large space in the well cabin, so that the test measuring points of the in-situ test cannot be placed as close as possible to the maximum stress support position of the well cabin wall and the partition wall. At the same time, the large number of weight blocks also causes the working space of the test and detection personnel in the well cabin to be narrow, and the safety factor is low. If the anchor pile method is used, it is necessary to perform hole drilling and grouting at the foundation bearing stratum, and the grouting needs to reach the strength of 28d age before it can be used as the reaction force system of the in-situ test. This method is time-consuming, labor-intensive, and has low efficiency, high cost, and increases the detection labor intensity, reduces the detection operation efficiency, and is not environmentally friendly and economical. In summary, the conventional in-situ test reaction force system cannot quickly obtain important geotechnical mechanics parameters in a short construction period. SUMMARY

[0004] The technical problems solved by the present application are: the test and detection operation space in each well cabin of a large bridge caisson foundation is narrow, and the in-situ test point cannot be randomly and uniformly selected, resulting in poor representativeness of the in-situ test point test data; the in-situ test in the well cabin of a large caisson foundation requires a large counterforce, a large number of counterweight blocks, and occupies most of the space in the well cabin, making it difficult to implement in-situ test at the bearing layer of the caisson foundation, and the like technical problems are provided with a suspension type in-situ test counterforce system for a large caisson foundation, which can implement in-situ test at the bearing layer of the foundation at any position in the well cabin or the spacer beam and greatly improve the operation space of the test and detection operation personnel in the well cabin of the large caisson foundation, and the present application can simply, efficiently and quickly build the counterforce required for the in-situ test of the bearing layer of the caisson, greatly simplifying the process and steps of building the counterforce test system, and significantly improving the efficiency and economy of the in-situ test of the large caisson foundation.

[0005] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0006] A suspension type in-situ test counterforce system for a large caisson foundation, comprising a caisson foundation and a plurality of embedded pipes embedded in the bottom segment of the caisson foundation, the embedded pipes are uniformly and spacedly arranged in the well wall or the spacer beam of the bottom segment of the caisson foundation; a steel bar is arranged in the embedded pipe; one end of the steel bar is installed in the embedded pipe, and the other end can extend out of the well wall or the spacer beam of the bottom segment of the caisson foundation to form a cantilever member, and the extended end of the steel bar can be sleeved with a steel beam; the steel beam can be manually adjusted freely on the steel bar according to the position of the in-situ test point of the foundation bearing layer to form a suspension type counterforce; the in-situ test point is below the steel beam, and a rigid bearing plate is arranged on the in-situ test point; a jack is arranged between the rigid bearing plate and the bottom of the steel beam; when the jack works, the piston at the top of the jack abuts against the steel beam to apply pressure to the rigid bearing plate; a plurality of displacement sensors are arranged on the rigid bearing plate to measure the elongation displacement of the piston of the jack, and then monitor the subsidence amount of the in-situ test point; the displacement sensors are connected with a static load tester to record the data of the in-situ test test pressure and the subsidence amount in real time; the static load tester is used to display the subsidence amount of the displacement sensor and the pressure change amount of the jack in real time.

[0007] As a further improvement of the present application, the embedded pipe is a PVC pipe.

[0008] As a further improvement of the present application, the material of the steel bar is Q235 steel, the diameter of the steel bar is 100-110mm, the length of the steel bar is 1.5m-2.0m, and 2-3 steel bars are arranged, which can pass through the hole reserved in the well wall or the spacer beam.

[0009] As a further improvement of the present application, the bottom segment of the open caisson foundation is C35 anti-seepage cast-in-place concrete, the anti-seepage level is P10 level, the preferred height of the bottom segment of the open caisson foundation is 5.0 m, the length is 25.4 m, and the width is 18.0 m.

[0010] As a further improvement of the present application, the material of the steel beam is Q235 steel, the length of the steel beam is 4.0 m, the beam height of the steel beam is 45 cm, and 2-3 round holes for the steel rod to pass through are formed at the web of the steel beam.

[0011] As a further improvement of the present application, after the steel beam passes through the steel rod, the position can be manually adjusted freely within the remaining length of the steel rod extending out of the well wall or the partition beam, so as to randomly and uniformly select the position of the in-situ test point in the transverse direction.

[0012] The present application also provides a construction method of a reaction force system for in-situ test of a bearing layer of an open caisson foundation, which comprises the following steps:

[0013] Step 1: Pre-burying PVC pipes in the bottom segment of the large open caisson foundation:

[0014] Before binding the steel bars and pouring the concrete in the bottom segment of the open caisson foundation, the PVC pipes are pre-buried in the predetermined positions of the open caisson foundation as reserved holes at a certain interval;

[0015] Step 2: Removing soil and sinking the large open caisson and connecting the next segment of concrete:

[0016] The soil is removed by gradually excavating from the well cabin of the open caisson foundation to the surrounding, the concrete is poured to connect the height at the well wall and the partition beam of the open caisson, and the large open caisson foundation is gradually sunk under the action of the self-weight of the open caisson foundation and the soil removal excavation;

[0017] Step 3: Removing soil and excavating the open caisson foundation to the design bearing layer elevation:

[0018] The open caisson foundation is repeatedly alternated with the soil excavation until the sinking of the open caisson foundation reaches the design bearing layer elevation requirement;

[0019] Step 4: Inserting the steel rod into the reserved PVC pipe and sleeving the steel beam:

[0020] After the open caisson foundation is removed to the design bearing layer elevation position, the steel rod is inserted into the hole of the PVC pipe reserved in the well wall or the partition beam of the bottom segment of the open caisson foundation to form a cantilever member, and temporary fixing measures are taken for the steel rod to avoid horizontal displacement; the steel beam is hoisted into the well cabin of the open caisson by a crane, and the round hole on the steel beam is aligned with one end of the steel rod to sleeve the steel rod, so as to quickly realize the installation of the reaction force system;

[0021] Step 5: Cleaning the in-situ test point and debugging the installation of the jack:

[0022] After the steel beam is sleeved into the steel rod to quickly build the suspension type counterforce, the surface of the bearing layer of the open caisson foundation is cleaned, in order to make the bearing layer of the open caisson foundation bear force more uniformly, a rigid bearing plate is placed on the surface of the soil to be tested in situ, a jack is placed between the rigid bearing plate and the steel beam, and the jack can apply pressure to the rigid bearing plate.

[0023] Step 6, in-situ test such as deformation modulus and foundation bearing capacity is carried out:

[0024] A displacement sensor is arranged on the rigid bearing plate, the displacement sensor is connected to a static load tester, the jack abuts against the steel beam upward, under the action of the counterforce of the steel beam, the rigid bearing plate can be applied with downward pressure and the soil can be caused to generate a subsidence amount, and the static load tester is used to record the change amount of the subsidence amount and the pressure in real time to obtain test data of the in-situ test.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] Compared with the conventional counterforce system such as the pile-up method and the anchor pile method, the suspension type in-situ test counterforce system for the large open caisson foundation is beneficial to improve the operation space of the test and detection personnel in the well cabin of the large open caisson foundation and can randomly and uniformly select in-situ test points at any position in the well cabin, and the counterforce required for the in-situ test of the bearing layer of the open caisson foundation can be simply, efficiently and quickly built, so that the process and steps of building the counterforce system are greatly simplified, and the detection and operation efficiency of the in-situ test of the large open caisson foundation is significantly improved.

[0027] On the basis of obtaining the geotechnical mechanics parameter results of the in-situ test of the large open caisson foundation, the design parameters of the large bridge can be optimized, the construction efficiency is improved, the construction period is compressed, and the engineering cost can be saved to a certain extent.

[0028] The in-situ test of the bearing layer of the open caisson foundation under multiple working conditions such as natural working condition and saturated working condition can be carried out in the well cabin of the open caisson, and multiple in-situ test points can be simultaneously tested in multiple well cabins, so that the in-situ test results are enriched and the detection and operation efficiency of the in-situ test is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a PVC pipe hole position diagram of a bottom segment of an open caisson foundation reserved by the embodiment of the present application;

[0030] Figure 2 is an installation position diagram of an open caisson foundation, a steel rod and a steel beam in the process of building the suspension type in-situ test counterforce system for the large open caisson foundation of the embodiment of the present application;

[0031] Figure 3is a schematic diagram of a steel rod of an embodiment of the present application;

[0032] Figure 4 is a schematic diagram of the linkage working of a steel beam, a rigid bearing plate, a jack and a displacement sensor of an embodiment of the present application;

[0033] Figure 5 is a construction flow chart of a construction method of a large-scale caisson foundation suspension type in-situ test counterforce system of the present application;

[0034] In the drawings, the following are marked: 1, caisson foundation bottom section; 2, well cabin; 3, partition beam; 4, steel rod; 5, steel beam; 6, pre-buried pipe; 7, jack; 8, rigid bearing plate; 9, displacement sensor; 10, static load tester; DETAILED DESCRIPTION

[0035] The present application will be further described below in conjunction with the drawings and embodiments. It should be noted that the specific embodiments of the present application are only for the purpose of more clearly describing the technical solutions, and cannot be regarded as a limitation on the protection scope of the present application.

[0036] Please refer to Figures 1-5 A large-scale caisson foundation suspension type in-situ test counterforce system, comprising a caisson foundation and a plurality of pre-buried pipes 6 pre-buried in the caisson foundation bottom section 1, the pre-buried pipes 6 are uniformly and spacedly arranged in the well wall or partition beam 3 of the caisson foundation bottom section 1; the pre-buried pipes 6 are provided with steel rods 4; one end of the steel rod 4 is installed in the pre-buried pipe 6, and the other end can extend out of the well wall or partition beam 3 of the caisson foundation bottom section 1 to form a cantilever member, and the extended end of the steel rod can be sleeved with a steel beam 5; the steel beam 5 can be manually freely adjusted on the steel rod 4 according to the position of the in-situ test point of the foundation bearing layer to form a suspension type counterforce; the in-situ test point is below the steel beam 5, and a rigid bearing plate 8 is arranged on the in-situ test point; a jack 7 is arranged between the rigid bearing plate 8 and the bottom of the steel beam 5, and the piston at the top of the jack 7 abuts against the steel beam 5 when the jack 7 is working, for applying pressure to the rigid bearing plate 8; a plurality of displacement sensors 9 are arranged on the rigid bearing plate 8 for measuring the elongation displacement of the piston of the jack 7 and monitoring the subsidence amount of the in-situ test point; the displacement sensors 9 are connected with a static load tester 10 for real-time recording of the data of the in-situ test test pressure and subsidence amount; the static load tester 10 is used for real-time display of the subsidence amount of the displacement sensor and the pressure change amount of the jack.

[0037] The caisson foundation bottom section 1 is C35 anti-seepage cast-in-place concrete, the anti-seepage grade is P10 grade, and the height of the caisson foundation bottom section 1 is preferably 5.0 m, the length is 25.4 m, and the width is 18.0 m. In particular, during the construction of binding steel bars, the pre-buried pipes 6 are pre-buried at the caisson foundation bottom section 1 as reserved holes.

[0038] The embedded pipe 6 is a PVC pipe, preferably a pipe with a diameter of 120 mm, and the length of the embedded pipe 6 is set according to the designed thickness of the shaft wall or the cross beam 3, and the embedded pipe 6 is arranged with 4-6 embedded pipes in the longitudinal and transverse directions of the shaft wall or the cross beam 3 of the caisson foundation bottom section 1, so as to randomly and uniformly select the position of the in-situ test point in the longitudinal and transverse directions when the caisson foundation bottom section 1 is inserted into the steel bar 4.

[0039] The steel bar 4 is made of Q235 steel, preferably has a diameter of 100-110 mm, and preferably has a length of 1.5-2.0 m, and the steel bar 4 is arranged with three steel bars in the shaft wall or the cross beam 3 of the caisson foundation bottom section 1. According to the modeling theoretical calculation, the single steel bar 4 can bear a shear force of 98 kN. Further, the steel bar 4 serves as a fulcrum of the in-situ test reaction force system inserted in the large caisson shaft wall or the cross beam 3, and mainly serves as a support for the steel beam 5 and a reverse shear.

[0040] The steel beam 5 is preferably made of Q235 steel, has a length of 4.0 m, and has a beam height of 45 cm, and 2-3 circular holes are arranged at the web of the steel beam 5 for the steel bar 4 to pass through, so as to facilitate the steel beam 5 to be sleeved into the steel bar 4. The single steel beam 5 can bear a force of 700 kN, and the four steel beams 5 can simultaneously bear a force of 5600 kN, which can fully meet the in-situ test of the deformation modulus of the bearing stratum of the large caisson foundation and the bearing capacity of the foundation.

[0041] As a further improvement of the present application, after the steel beam 5 passes through the steel bar 4, the position of the steel beam 5 can be manually adjusted in the remaining length of the steel bar 4 extending out of the shaft wall or the cross beam 3, so as to randomly and uniformly select the position of the in-situ test point in the transverse direction.

[0042] The present application also provides a construction method of the reaction force system of the in-situ test of the bearing stratum of the caisson foundation, which comprises the following steps:

[0043] Step 1, embedding PVC pipe in large caisson foundation bottom section:

[0044] When the steel bars are bound in the bottom section of the caisson foundation, the PVC pipe is embedded in the predetermined position of the caisson foundation as a reserved hole before pouring the concrete, and in the embodiment, the embedded pipe 6 is a PVC pipe, and the diameter of the PVC pipe is preferably 120 mm, and the PVC pipe is embedded at a distance of at least 0.2 m from the bottom surface of the caisson foundation bottom section 1.

[0045] Step 2, removing soil and sinking the large caisson and connecting the next section of concrete:

[0046] The soil is removed from the caisson foundation well cabin 2, the steel bars are bound and the concrete is poured at the caisson wall and caisson beam 3 to connect the height, and the caisson foundation is sunk under the weight of the soil removal excavation and the concrete of the caisson foundation itself;

[0047] Step 3, the soil removal excavation of the caisson foundation reaches the design bearing layer elevation:

[0048] The concrete of the caisson foundation and the soil excavation are repeatedly alternated until the sinking depth of the caisson foundation reaches the design bearing layer elevation requirement;

[0049] Step 4, the steel bar 4 is inserted into the reserved PVC pipe and the steel beam 5 is sleeved:

[0050] After the caisson foundation is removed to the design bearing layer elevation position, the steel bar 4 is inserted into the reserved PVC pipe hole of the caisson foundation bottom segment 1 wall or beam 3 to form a cantilever member, and temporary fixing measures are taken for the steel bar 4 to avoid horizontal displacement of the steel bar 4; the steel beam 5 is hoisted into the caisson well cabin 2, and the round hole on the steel beam 5 is aligned with one end of the steel bar 4 to be sleeved into the steel bar 4, and the suspended counterforce system is quickly built;

[0051] Step 5, clean the in-situ test point and debug the installation of the jack 7:

[0052] After the suspended counterforce system is quickly built by sleeving the steel beam 5 into the steel bar 4, the surface of the caisson foundation bearing layer soil is cleaned, and the rigid bearing plate 8 is placed on the soil surface, and the jack 7 is placed between the rigid bearing plate 8 and the steel beam 5, so that the caisson foundation bearing layer soil is stressed more uniformly when the jack 7 applies pressure to the rigid bearing plate 8;

[0053] Step 6, in-situ test of deformation modulus and foundation bearing capacity:

[0054] The displacement sensor 9 is arranged on the rigid bearing plate 8, the displacement sensor 9 is connected to the static load tester 10, the jack 7 is upwardly abutted against the steel beam 5, under the action of the counterforce of the steel beam 5, the downward pressure can be applied to the rigid bearing plate 8 and the soil settlement can be generated, and the test data such as the settlement and the pressure change are recorded in real time by the displacement sensor 9 and the static load tester 10.

[0055] The in-situ test includes deformation modulus test and foundation bearing capacity test. The deformation modulus test is carried out in the rock-soil body such as gravel soil, sand, silt and silty clay by using a 0.25㎡ bearing plate to carry out hierarchical cyclic loading and unloading according to the design bearing capacity characteristic value and other related parameters, according to the shape coefficient I0 of the rigid bearing plate 8, the Poisson's ratio μ of the soil, the diameter or side length d of the bearing plate, the pressure of the linear section of the P-S curve and the settlement corresponding to the pressure P and other parameters, the deformation model of the corresponding load test is obtained by calculation according to the formula .

[0056] The foundation bearing capacity test is a kind of plate load test (PLT), which is an in-situ test method for applying load to the foundation soil step by step on a rigid bearing plate 8 of a certain area, and measuring the pressure and deformation characteristics of the foundation soil, which reflects the comprehensive properties of the strength and deformation of the foundation soil within 1.5-2.0 times the diameter or width of the bearing plate under the bearing plate.

[0057] The application can quickly build the counterforce system required by the caisson bearing stratum foundation in-situ test, and randomly and uniformly select the in-situ test points at any position in the well cabin. It not only meets the principle of random and uniform extraction of in-situ test points, but also greatly simplifies the process and steps of building the counterforce system of the in-situ test, improves the operation space of the test and detection in the well cabin, significantly improves the efficiency of the in-situ test of the large-scale caisson foundation, and the suspension type in-situ test counterforce system can be used to carry out the in-situ test of the caisson bearing stratum foundation under natural and saturated working conditions at the same time, and in multiple caisson cabins 2 at the same time, which greatly improves the test efficiency.

[0058] The above description is a detailed description of the preferred embodiment of the application, but the embodiment is not used to limit the scope of the patent application of the application, and any equivalent changes or modifications made under the technical spirit of the application should belong to the patent scope covered by the application.

Claims

1. A counterforce system for a large caisson foundation suspended in-situ test, characterized in that: The system includes a caisson foundation and several pre-embedded pipes embedded in the bottom segment of the caisson foundation. These pre-embedded pipes are evenly spaced within the well wall or partition beams of the bottom segment of the caisson foundation. Each pre-embedded pipe contains a steel rod. One end of each steel rod is installed inside the pre-embedded pipe, and the other end extends beyond the well wall or partition beam of the bottom segment of the caisson foundation to form a cantilever component. A steel beam is fitted onto the extended end of the steel rod. The steel beam is manually and freely adjusted on the steel rod according to the location of the in-situ test point of the foundation bearing layer, forming a suspended reaction force. The in-situ test point is located below the steel beam, and a rigid bearing is provided at the in-situ test point. A rigid bearing plate is used; a jack is installed between the rigid bearing plate and the bottom of the steel beam; when the jack is working, its piston at the top abuts against the steel beam to apply pressure to the rigid bearing plate; several displacement sensors are arranged on the rigid bearing plate to measure the extension displacement of the jack piston, thereby monitoring the settlement at the in-situ test point; the displacement sensors are connected to a static load tester to record the data of the in-situ test pressure and settlement in real time; the static load tester is used to display the settlement of the displacement sensors and the change in jack pressure in real time. The steel bar is made of Q235 steel, with a diameter of 100-110mm and a length of 1.5m to 2.0m.

2. The reaction system for in-situ test of large caisson foundation according to claim 1, wherein: The embedded pipe is a PVC pipe.

3. The reaction system for in-situ test of large caisson foundation according to claim 1, wherein: The bottom segment of the caisson foundation is made of C35 anti-seepage cast-in-place concrete with an anti-seepage grade of P10. The bottom segment of the caisson foundation is 5.0m high, 25.4m long, and 18.0m wide.

4. The reaction system for in-situ test of large caisson foundation according to claim 1, wherein: The steel beam is made of Q235 steel, with a length of 4.0m and a beam height of 45cm. The web of the steel beam has 2 to 3 round holes for steel bars to pass through.

5. A construction method of the reaction force system for the caisson foundation bearing stratum in-situ test according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Pre-embed PVC pipes in the bottom segments of the large caisson foundation: Before binding the reinforcing bars and pouring the concrete at the bottom section of the caisson foundation, PVC pipes are pre-embedded at predetermined positions at certain intervals as reserved holes. Step 2: The large caisson is sunk and the next section of concrete is added: The soil is gradually removed from the caisson foundation chamber and excavated outwards. Concrete is poured into the caisson walls and caisson partition beams to add height. Under the weight of the caisson foundation and the effect of soil removal and excavation, the large caisson foundation gradually sinks. Step 3, excavation of the caisson foundation to the designed bearing layer elevation: the construction of the caisson foundation and the earthwork excavation are carried out alternately until the caisson foundation sinks to the designed bearing layer elevation. Step 4: Insert steel bars into the pre-reserved PVC pipes and install steel beams: After the caisson foundation is lowered to the designed bearing layer elevation, steel bars are inserted through the holes in the pre-reserved PVC pipes in the bottom section of the caisson foundation wall or partition beam to form cantilever components. Temporary fixation measures are taken for the steel bars to prevent horizontal displacement. The steel beams are then hoisted into the caisson chamber using a crane, and the round holes on the steel beams are aligned with one end of the steel bars to insert them into the steel bars, quickly realizing the installation of the reaction system. Step 5, clean up the in-situ test point and debug the installed jack: after the steel beam is quickly built into the steel rod to build the suspended counterforce, the surface of the soil body of the caisson foundation bearing layer is cleaned up, in order to make the soil body of the caisson foundation bearing layer be stressed more uniformly, a rigid bearing plate is placed on the surface of the soil body to be tested, and a jack is placed between the rigid bearing plate and the steel beam, the jack can apply pressure to the rigid bearing plate; Step 6, perform in-situ tests such as deformation modulus and foundation bearing capacity: a displacement sensor is arranged on the rigid bearing plate, the displacement sensor is connected to a static load tester, the jack is upwardly abutted against the steel beam, under the action of the counterforce of the steel beam, the rigid bearing plate is applied with downward pressure and the soil body is caused to have a subsidence amount, and through the displacement sensor and the static load tester, the change amount of the subsidence amount and the pressure is recorded in real time to obtain the test data of the in-situ test.

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