Test device and test method for mechanical properties of internal interface of reinforced cement-soil composite structure

Abstract

The present application relates to a kind of stiff cement-soil composite structure inner interface mechanical property testing device and test method, including the lower pad for placing model pile section, for being contacted with the upper pressing plate of the stiff inner core pile top of model pile section, upper pressing plate is driven lifting by servo test loading system;Lower pad is provided with annular support for being contacted with the bottom of model pile section.The model pile section includes stiff inner core pile, the outer sleeve of the outer side of stiff inner core pile is coaxially arranged, and outer core cement-soil is arranged between the inner wall of outer sleeve and the outer wall of stiff inner core pile.The present application is reasonably designed, and the field production of stiff cement-soil composite pile is changed into indoor test for re-loading test research, and the production step sequence of model pile section is simple, convenient and fast, greatly reduces the manpower, material resources and financial resources required by research, reduces research cost, saves resources, reduces energy consumption, and better reflects the actual situation between stiff cement-soil composite pile and outer core, can obtain the inner interface shear parameter not easy to obtain.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of stiff cement-soil composite structure internal interface mechanical property testing device and test method. BACKGROUND

[0002] Under the construction requirement of resource-conserving and environment-friendly society, low-carbon and sustainable development of engineering field is imperative, and energy-saving and more economical engineering measures and methods are the inevitable choice of development. In the infrastructure of various projects, pile foundation can often provide considerable bearing capacity, but it is accompanied by high cost and large energy and material consumption. In some engineering construction that only requires small bearing capacity, such as the construction of photovoltaic power station on coastal beach, a large amount of resources is wasted to meet the minimum requirement of specification. At this time, if stiff cement-soil composite pile is selected, the cost and energy consumption will be greatly reduced.

[0003] Stiff cement-soil composite pile is a new type of composite pile in which a stiff core pile is vertically implanted into cement-soil mixing pile after the construction of cement-soil mixing pile, and the periphery is wrapped by cement-soil. It has large pile side friction of cement-soil mixing pile and high strength and stiffness of core pile.

[0004] At present, the research method of stiff cement-soil composite pile is mostly field production followed by testing. However, field testing requires a large amount of manpower, material resources and financial resources, and the geological conditions are complex and diverse, which cannot control single variable for parameter analysis, and is not conducive to engineering calculation and numerical simulation analysis. In numerical simulation analysis, the input basic parameters are not accurate enough, and the theoretical numerical simulation model is imperfect, which has a large difference from the real world, and cannot truly reflect the entity situation. Therefore, a stiff cement-soil composite structure internal interface mechanical property testing device and test method are proposed to better reflect the actual situation between the inner and outer cores of stiff cement-soil composite pile, reduce research cost, save resources and reduce energy consumption. SUMMARY

[0005] The present application improves the above-mentioned problems of prior art, i.e. the technical problem to be solved by the present application is to provide a stiff cement-soil composite structure internal interface mechanical property testing device and test method.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: a stiff cement-soil composite structure internal interface mechanical property testing device, comprising a lower pad plate for placing a model pile segment, and an upper pressing plate for contacting the top of the stiff inner core pile of the model pile segment, the upper pressing plate is driven to rise and fall by a servo test loading system; the lower pad plate is provided with an annular support for contacting the bottom of the model pile segment.

[0007] Furthermore, the model pile segment includes a rigid inner core pile, an outer sleeve is coaxially arranged on the outer side of the rigid inner core pile, and an outer core cement soil is arranged between the inner wall of the outer sleeve and the outer wall of the rigid inner core pile.

[0008] Furthermore, the outer sleeve is a plastic tube with a rough inner surface.

[0009] Furthermore, the rigid core pile is a steel pipe.

[0010] Furthermore, the rigid inner core pile is a steel pipe, and the outer surface of the steel pipe is provided with spiral blades extending along the axial direction of the steel pipe, and the spiral blades are located inside the outer core cement soil.

[0011] Furthermore, the outer diameter of the annular support member is the same as the outer diameter of the outer sleeve, and the inner diameter of the annular support member is larger than the outer diameter of the rigid inner core pile.

[0012] Furthermore, the annular support member is a ring-shaped rigid pad.

[0013] Furthermore, the annular support member is a ring-shaped bottom loading stiffness adjustment block, and the bottom loading stiffness adjustment block includes an upper adjustment block and a lower adjustment block that are butted up and down. The stiffness of the upper adjustment block is less than the stiffness of the lower adjustment block, and the butt joint surface between the upper adjustment block and the lower adjustment block is an inclined surface with a higher inner end and a lower outer end.

[0014] Furthermore, it also includes a data acquisition system for collecting test load data and displacement data.

[0015] Another technical solution adopted by the present invention is: a test method for testing the mechanical properties of the interface of a reinforced cement-soil composite structure, comprising the following steps:

[0016] (1) According to the diameter and length of the model pile section required for the test, an outer sleeve with the corresponding inner diameter and length is selected. The length of the model pile section is greater than the length of the outer sleeve. The bottom of the outer sleeve is temporarily sealed with a matching snap-on cap. The space between the snap-on cap and the outer sleeve is waterproofed to facilitate the maintenance of the model pile section in the later stage.

[0017] (2) Pour the cement-soil mixture prepared according to the test requirements into the outer casing in multiple times, and vibrate the pile body after each pouring;

[0018] (3) Lay out the lines and position the pile. Insert the rigid core pile, which is longer than the outer casing, into the center of the outer casing. Vibrate the pile body again so that the cement-soil mixture evenly wraps the rigid core pile. Then smooth the upper surface of the model pile segment.

[0019] (4) After the above steps are completed, pour pure water into the outer casing to maintain the pile segment, and keep the water layer thickness not less than the value required by the specification; or put the entire pile segment into a water tank for maintenance;

[0020] (5) After the specified curing days of the test, the water layer on the surface of the pile section is pumped out, or the pile section is taken out from the water tank, the outer sleeve pipe is removed, and the outer sleeve pipe is not removed from the outer sleeve pipe to simulate the side limit condition of the soil around the pile; the annular support is placed at the center of the lower base plate, the pile section is placed on the annular support, the load is transmitted to the rigid inner core pile through the upper pressing plate, the rigid inner core pile is sheared with the outer core cement soil, and thus the inner interface shear strength of the rigid cement soil composite pile section is obtained; the test load data and displacement data are exported from the data acquisition system, and subsequent analysis is carried out.

[0021] Compared with the prior art, the present application has the following effects: the present application is reasonable in design, and converts the field production and re-loading test research of the rigid cement soil composite pile into indoor test, the production steps of the model pile section are simple, convenient and fast, the manpower, material resources and financial resources required for research are greatly reduced, the research cost is reduced, resources are saved, energy consumption is reduced, and the actual situation between the inner core and the outer core of the rigid cement soil composite pile is better reflected, and the inner interface shear parameter which is not easy to obtain can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a structural schematic diagram of an embodiment of the present application;

[0023] Figure 2 is a structural schematic diagram of a model pile section in an embodiment of the present application;

[0024] Figure 3 is a structural schematic diagram of a bottom loading stiffness adjusting block in an embodiment of the present application.

[0025] In the drawings:

[0026] 1-outer sleeve pipe; 2-outer sleeve pipe cap; 3-outer core cement soil; 4-rigid inner core pile; 5-spiral blade; 6-curing water layer water surface; 7-rigid cushion block; 8-lower base plate; 9-upper pressing plate; 10-lifting rod; 11-cross beam; 12-upper adjusting block; 13-lower adjusting block; 14-model pile section; 15-annular support. DETAILED DESCRIPTION

[0027] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0028] In the description of the present application, it should be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0029] As Figures 1 to 3 shown, the present application is a kind of stiff cement-soil combined structure internal interface mechanical property testing device, for the problems such as high research cost of existing stiff cement-soil combined pile, cannot reflect the actual situation more truly, specific: testing device includes lower pad plate 8 for placing model pile section 14, upper pressing plate 9 for contacting with the top of stiff inner core pile 4 of model pile section 14, the upper pressing plate 9 is driven by servo test loading system to lift;The lower pad plate 8 is provided with annular support 15 for contacting with the bottom of model pile section 14, the inner hole of annular support 15 is conducive to the stiff inner core pile and the outer core cement-soil shear to make room for the stiff inner core pile.

[0030] In this embodiment, the model pile section 14 includes stiff inner core pile 4, the outer side of the stiff inner core pile 4 is coaxially provided with outer sleeve tube 1, the top and bottom of the outer sleeve tube are open, the inner wall of the outer sleeve tube 1 and the outer wall of the stiff inner core pile 4 are provided with outer core cement-soil 3. It should be noted that during the production of the model pile section, the bottom of the outer sleeve tube is temporarily closed by a matching outer buckle type pipe cap, and the outer buckle type pipe cap and the outer sleeve tube are waterproofed, so as to facilitate the maintenance of the model pile section later. Specifically, a few turns of waterproof adhesive tape are wound between the outer buckle type pipe cap and the outer sleeve tube for waterproofing.

[0031] In this embodiment, the outer sleeve tube 1 is a plastic tube with rough inner surface, so as to better simulate the rough contact surface between the soil around the pile and the outer core.

[0032] In this embodiment, the stiff inner core pile 4 is a steel pipe. In another embodiment, a spiral blade 5 extending along the axis of the steel pipe can also be provided on the outer surface of the steel pipe, and the spiral blade 5 is located inside the outer core cement-soil 3. The stiff inner core pile 4 can also be a plastic tube / rod, a reinforced concrete pile, a wooden stick, bamboo or other different forms and materials to meet the needs of different research topics, and the outer core cement-soil material can also be replaced by concrete or other materials. When studying the effect of the steel pipe with spiral blade on the improvement of the internal interface shear strength of the cement-soil combined pile without spiral blade or other stiff core pile materials, the following formula can be used to solve and calculate the internal interface parameter λ based on the test result data to study the degree of improvement of the shear strength:

[0033] In the formula: S — vertical compressive bearing capacity test value (N) of the test pile section; u — the circumference of the inner core pile of the test pile section (m); λ — the shear strength coefficient of the inner interface corresponding to f cu the inner interface; f cu — the unconfined compressive strength (Pa) of the same ratio of cement soil test block under standard conditions with a side length of 70.7 mm; l — the vertical length (m) of the contact surface between the inner core pile and the outer core cement soil pile of the test pile section.

[0034] In this embodiment, the outer diameter of the annular support 15 is the same as the outer diameter of the outer sleeve 1, and the inner diameter of the annular support 15 is greater than the outer diameter of the stiff inner core pile 4.

[0035] In this embodiment, the annular support 15 is a rigid pad 7 in the shape of a ring. The rigid pad in the shape of a ring can also be replaced by a bottom loading stiffness adjustment block in the shape of a ring, which includes an upper adjustment block 12 and a lower adjustment block 13 that are vertically connected, the stiffness of the upper adjustment block 12 is less than that of the lower adjustment block 13, and the connecting surface of the upper adjustment block 12 and the lower adjustment block 13 is a slope with the inner end high and the outer end low, that is, it has a certain slope rate. When the bottom loading stiffness adjustment block is used for support, with the loading, the bottom loading stiffness adjustment block gradually presents different compression deformations from the center to the outside, so as to simulate the condition that when the inner interface of the actual pile body is damaged, the stiffness of the soil within a certain range of the stiff inner core pile end decreases with the increase of the distance from the inner core pile due to compaction. Preferably, the rigid pad and the bottom loading stiffness adjustment block are the same in shape and size.

[0036] In this embodiment, a data acquisition system for acquiring test load data and displacement data is also included, and after the test is completed, the test load data and displacement data are exported from the data acquisition system for subsequent analysis.

[0037] In this embodiment, the testing device further includes a pair of upper and lower beams 11 that are distributed and supported, the lower pad plate 8 is arranged on the lower beam 11 at the lower end, and the pair of beams 11 has a pair of left and right lifting rods 10.

[0038] In this embodiment, the test method for the mechanical properties of the inner interface of the stiff cement-soil composite structure includes the following steps:

[0039] (1) according to the required test to make model pile section diameter and length selection corresponding inner diameter size, length of the sleeve tube, the length of the model pile section is greater than the length of the sleeve tube, the bottom of the sleeve tube is temporarily closed with the matched outer buckle type pipe cap, the outer buckle type pipe cap and the sleeve tube are wrapped with several layers of waterproof tape for waterproof treatment, so as to facilitate the maintenance of the model pile section in the later period;

[0040] (2) the cement soil mixture prepared according to the test requirements is poured into the sleeve tube in several times, and the pile body is vibrated after each pouring;

[0041] (3) positioning by laying out the line, the rigid inner core pile with a length greater than the sleeve tube is implanted in the center of the sleeve tube, and the pile body is vibrated again, so that the cement soil mixture uniformly wraps the rigid inner core pile; then an oil brush with a wide blade is used to rotate and smooth the upper surface of the model pile section;

[0042] (4) after the above steps are completed, pure water is poured into the sleeve tube to maintain the pile section, and the water layer thickness is not less than the specified value; or the pile section is put into a water tank for maintenance;

[0043] (5) after the specified maintenance days of the test, the surface water layer of the pile section is drained, or taken out from the water tank, the outer buckle type pipe cap at the lower end of the sleeve tube is removed, the pile section is not taken out from the sleeve tube to simulate the side limit condition of the soil around the pile; the annular support is placed at the center of the bottom plate, the pile section is placed on the annular support, the load is transmitted to the rigid inner core pile through the upper pressing plate, the rigid inner core pile is cut off from the outer core cement soil, and the inner interface shear strength of the rigid cement soil composite pile section is obtained; the test load data and displacement data are exported from the data acquisition system, and then subsequent analysis is carried out.

[0044] The advantages of the present application are:

[0045] (1) the field production of the rigid cement soil composite pile is converted into indoor test, the production steps of the model pile section are simple, convenient and fast, which greatly reduces the manpower, material resources and financial resources required for research, reduces the research cost, saves resources and reduces energy consumption;

[0046] (2) through the flexible combination and disassembly of the sleeve tube and the pipe cap, the model pile section used for mechanical test can be conveniently made, the annular rigid pad block with a slightly larger inner diameter than the outer diameter of the rigid cement soil composite pile core is placed in the test device, the upper pressing plate is loaded, the model pile section is not taken out from the sleeve tube to simulate the side limit condition of the soil around the pile, the shear strength of the inner and outer core contact interface which is not easy to obtain in engineering is obtained, which is convenient for formula calculation, parameterization research and provides accurate parameters for engineering calculation and numerical simulation analysis;

[0047] (3) By replacing the annular rigid thick pad with a bottom-loaded stiffness adjustment block, the stiffness of the soil within a certain range of the inner core pile end decreases with the increase of the distance from the inner core pile due to compaction, better simulating the actual conditions and obtaining more accurate inner and outer core contact interface shear strength and parameters;

[0048] (4) Avoid the problem of large differences between the input parameters, the theoretical model is not perfect, and the real world in the numerical simulation analysis, truly reflect the relationship between the physical world in the inner and outer core of the pile.

[0049] If the present application discloses or involves mutually fixed connecting parts or structural parts, unless otherwise stated, the fixed connection can be understood as: detachable fixed connection (such as bolt or screw connection), and can also be understood as: non-detachable fixed connection (such as riveting, welding), of course, the mutually fixed connection can also be replaced by an integral structure (such as using casting process to make an integral shape) (except for obvious cases that cannot use integral forming process).

[0050] In addition, the terms used to represent the position relationship or shape in any of the technical solutions disclosed above include the approximate, similar or close state or shape unless otherwise stated.

[0051] Any component provided by the present application can be assembled from multiple individual components, or can be a single component manufactured by integral forming process.

[0052] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application and not to limit it; although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: the specific embodiments of the present application can be modified or some technical features can be replaced by equivalent; without departing from the spirit of the technical scheme of the present application, it should be covered in the technical scheme range of the present application claimed by the present application.

Claims

1. A device for testing the mechanical properties of the interface of a reinforced cement-soil composite structure, characterized by: It includes a lower pad for placing the model pile segment and an upper pressure plate for contacting the top of the rigid inner core pile of the model pile segment. The upper pressure plate is driven to rise and fall by the servo test loading system. The lower pad is provided with an annular support member for contacting the bottom of the model pile segment. The model pile segment comprises a rigid inner core pile, an outer sleeve is coaxially arranged on the outer side of the rigid inner core pile, and an outer core cement soil is arranged between the inner wall of the outer sleeve and the outer wall of the rigid inner core pile; The annular support member is a ring-shaped bottom loading stiffness adjustment block, which includes an upper adjustment block and a lower adjustment block that are butted up and down. The stiffness of the upper adjustment block is smaller than that of the lower adjustment block, and the butt joint surface between the upper adjustment block and the lower adjustment block is an inclined surface with a higher inner end and a lower outer end. The bottom of the outer sleeve is temporarily sealed with a matching snap-on cap, and waterproofing is performed between the snap-on cap and the outer sleeve.

2. The device for testing the mechanical properties of the internal interface of a reinforced cement-soil composite structure according to claim 1, characterized in that: The outer sleeve is a plastic tube with a rough inner surface.

3. The device for testing the mechanical properties of the internal interface of a reinforced cement-soil composite structure according to claim 1, characterized in that: The rigid inner core pile is a steel pipe.

4. The device for testing the mechanical properties of the internal interface of a reinforced cement-soil composite structure according to claim 1, characterized in that: The rigid inner core pile is a steel pipe, and the outer surface of the steel pipe is provided with spiral blades extending along the axial direction of the steel pipe, and the spiral blades are located inside the outer core cement soil.

5. The device for testing the mechanical properties of the inner interface of a reinforced cement-soil composite structure according to claim 1, characterized in that: The outer diameter of the annular support member is the same as the outer diameter of the outer sleeve, and the inner diameter of the annular support member is larger than the outer diameter of the rigid inner core pile.

6. The device for testing the mechanical properties of the internal interface of a reinforced cement-soil composite structure according to claim 5, characterized in that: The annular support member is a ring-shaped rigid spacer.

7. The device for testing the mechanical properties of the inner interface of a reinforced cement-soil composite structure according to claim 1, characterized in that: It also includes a data acquisition system for collecting test load data and displacement data.

8. A test method for testing the mechanical properties of the interface within a reinforced cement-soil composite structure, characterized by: The method comprises adopting the device for testing the mechanical properties of the inner interface of a reinforced cement-soil composite structure as claimed in any one of claims 1 to 7, and comprising the following steps: (1) According to the diameter and length of the model pile section required for the test, an outer sleeve with the corresponding inner diameter and length is selected. The length of the model pile section is greater than the length of the outer sleeve. The bottom of the outer sleeve is temporarily sealed with a matching snap-on cap. The space between the snap-on cap and the outer sleeve is waterproofed to facilitate the maintenance of the model pile section in the later stage. (2) Pour the cement-soil mixture prepared according to the test requirements into the outer casing in multiple times, and vibrate the pile body after each pouring; (3) Lay out the lines and position the pile. Insert the rigid core pile, which is longer than the outer casing, into the center of the outer casing. Vibrate the pile body again so that the cement-soil mixture evenly wraps the rigid core pile. Then smooth the upper surface of the model pile segment. (4) After the above steps are completed, pour pure water into the outer casing to maintain the pile segment, and keep the water layer thickness not less than the value required by the specification; or put the entire pile segment into a water tank for maintenance; (5) After the specified curing days, the surface water layer of the pile segment is completely drained, or the pile segment is removed from the water tank, and the outer cap at the lower end of the outer casing is removed. The pile segment does not escape from the outer casing to approximately simulate the lateral limit conditions of the soil around the pile. An annular support is placed at the center of the lower pad, and the pile segment is placed on it. The load is transferred to the rigid core pile through the upper pressure plate, so that the rigid core pile and the outer core cement soil are sheared apart, thereby obtaining the shear strength of the interface between the rigid cement soil composite pile segment. The test load data and displacement data are exported from the data acquisition system for subsequent analysis.

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