In-situ shear test device and method for new and old concrete junction surface of gravity dam heightening project

Abstract

The invention discloses an in-situ shear test device and method for a new and old concrete junction surface of a gravity dam heightening project. The in-situ shear test device comprises a test platform, a shear loading groove, an L-shaped test block, a flexible shear plate, a shear loading device and a normal loading device, the shear loading groove is formed in the slope surface of the old concrete dam above the test platform; the transverse part of the L-shaped test block is embedded into the shear loading groove, and a flexible shear plate is arranged between the transverse part and the shear loading groove; the vertical part and the slope surface of the old concrete dam form a new and old concrete combination surface; the centroid of the L-shaped test block is positioned on a new and old concrete combination surface; a shear force application axis of the shear loading device is positioned on a new and old concrete junction surface coincidence; and the normal loading device is mounted on the outer side surface of the vertical part of the L-shaped test block and can apply a vertical normal force to the new and old concrete combination surface. The real interface working condition is constructed through the L-shaped test block, the embedded anchoring system and the two-way cooperative loading technology are combined, the problem of construction of the counter force of the inclined dam face is solved, and actually measured data support is provided for anti-sliding stable design of the high-gradient dam body.

Description

Technical Field

[0001] The invention relates to the technical field of in-situ detection of hydraulic structures, in particular to an in-situ shear test device and method for the new-old concrete interface of a gravity dam heightening project. Background Art

[0002] In concrete gravity dam raising projects, the shear strength of the interface between new and old concrete is a key parameter that determines the overall stability and service safety of the dam. Traditional methods for obtaining this parameter rely primarily on indoor direct shear tests with Z-type specimens and on-site in-situ push tests with near-horizontal arrangements. However, these methods are limited to flat-surface testing and are unable to adapt to the strength testing requirements commonly found in actual projects on inclined surfaces (especially high-altitude inclined dam surfaces). In typical dam raising scenarios, the interface between new and old concrete is often located on a steeply inclined surface downstream, with on-site layout angles often exceeding 30°. In this complex environment, traditional testing techniques face multiple and severe challenges, including the following:

[0003] 1. Difficulty in controlling the loading direction: The shear force needs to be applied precisely parallel to the inclined dam surface, rather than in the traditional horizontal direction, which makes it difficult for traditional horizontal loading devices to adapt.

[0004] 2. Difficulty in establishing a reaction force system: Conventional in-situ testing relies on gravity anchoring or a rigid connection to the ground to form a closed force system, balancing shear loads through gravity or ground reaction forces. However, on a dam face with a large inclination (>30°) and at a high altitude (several meters above the dam foot), the direction of gravity is significantly angled with the dam face normal, making it impossible to provide effective normal anchoring. Furthermore, the high altitude prevents the reaction force from being reliably transmitted to the ground. Therefore, it is difficult to construct a self-balancing three-dimensional closed force system within the inclined surface that can simultaneously resist the oblique shear reaction force, the normal reaction force, and their overturning moment.

[0005] 3. Poor reliability of test results: Under non-horizontal arrangement conditions, it is difficult for the induced interface between new and old concrete specimens to fail along the predetermined slip path. Slight deviations in the local structure of the interface may lead to unexpected failure modes, seriously damaging the reliability of the test results.

[0006] 4. Difficulty in equipment deployment: The test equipment is large and heavy, and requires hoisting, positioning, installation, and disassembly on a narrow, inclined, high-altitude work surface. This poses high safety risks, low operating efficiency, and difficulty in ensuring accuracy. Existing equipment lacks modularity and rapid deployment design for this environment.

[0007] 5. Difficulty in repeating tests: During shear tests on test blocks at different heights, the test device must be placed at the correct height to correspond to the joint surface of each test block. The lowest test blocks typically rely on a pre-set concrete test pier as a support platform. However, for test blocks located higher up, the shear loading device is difficult to securely deploy because there is no corresponding solid foundation or platform underneath.

[0008] 6. The height of the dam is very high. After the raising, the dam exceeds 100 meters and the load it bears is huge.

[0009] Currently, there is no mature and effective technical solution that can systematically address the above-mentioned key issues, especially in actual dam surface environments with inclination angles greater than 30°. There is no published literature systematically reporting a method and device system for reliably measuring the in-situ shear strength of the interface between new and old concrete under such complex conditions (high altitude, steep slopes, and complex interface structures). Therefore, there is an urgent need to develop a new method and supporting device system for in-situ shear strength testing suitable for dam surfaces with steep slopes, high altitude sites, and complex interfaces (such as keyways under the interface, uneven interface roughness, and widely varying bonding conditions). This method can achieve the goals of a reasonable loading path, a safe device structure, and authentic test data, thus filling a significant gap in current technical means. Summary of the Invention

[0010] The technical problem to be solved by this invention is to address the shortcomings of the above-mentioned existing technologies and provide an in-situ shear test device and method for the interface between new and old concrete in gravity dam raising projects. This method and device, for the first time, presents a complete technical system for in-situ shear strength testing on inclined dam surfaces. By constructing realistic interface conditions with angled L-shaped test blocks and combining a pre-embedded anchoring system with bidirectional collaborative loading technology (shear-normal), the device overcomes the challenge of establishing reaction forces on inclined dam surfaces. The device system features modular hoisting, controllable loading direction, precise structural alignment, and reliable reaction forces. The test directly obtains key shear strength parameters (cohesion c and friction coefficient f), providing measured data support for the anti-sliding stability design of high-slope dam bodies.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is: The invention discloses an in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project, comprising a test platform, a shear loading trough, an L-shaped test block, a flexible shear plate, a shear loading device and a normal loading device.

[0012] The backwater side of the gravity dam has an old concrete dam slope with an inclination angle α.

[0013] The test platform is cast in situ at the foot of the old concrete dam slope and supported on the ground. Its top surface is a test plane perpendicular to the old concrete dam slope.

[0014] There is at least one shear loading groove, which is opened in parallel from top to bottom in the old concrete dam slope above the test plane; wherein the shear loading groove adjacent to the test plane is recorded as the first shear loading groove.

[0015] Each shear loading slot is a rectangular slot, and each shear loading slot has two lateral walls parallel to the test plane, namely the upper lateral wall and the lower lateral wall from top to bottom; among which, the lower lateral wall of the first shear loading slot is coplanar with the test plane to form a shear installation plane.

[0016] The L-shaped test block is a cast-in-place concrete test block, which is L-shaped and includes an integral horizontal part and a vertical part.

[0017] The transverse portion is embedded in the shear loading groove, and the flexible shear plate is arranged between the upper lateral wall of the corresponding shear loading groove. The elastic compression of the flexible shear plate is greater than the in-situ shear displacement of the L-shaped test block.

[0018] The vertical part is connected to the slope of the old concrete dam to form an inclined joint surface between the new and old concrete.

[0019] The bottom surface of the L-shaped specimen is formed as a shear loading plane parallel to the test plane, and the centroid of the L-shaped specimen is located on the interface between the new and old concrete.

[0020] The shear loading device is installed on the shear installation plane, with the top close to the shear loading plane, and the shear force axis is located at the intersection of the new and old concrete interface.

[0021] The normal loading device is installed on the outer side of the vertical part of the L-shaped test block and can apply a vertical normal force to the interface between the new and old concrete.

[0022] A flexible shear plate is also provided between the transverse portion of the L-shaped test block and the bottom surface of the corresponding shear loading slot.

[0023] The flexible shear plate is a polyethylene foam plate.

[0024] The normal loading device comprises a normal loading base plate, a normal reaction frame, a normal jack and a shear displacement limiting component.

[0025] The normal reaction frame includes a normal bottom plate and a normal top plate.

[0026] The normal jack is arranged between the normal bottom plate and the normal top plate.

[0027] The normal top plate is anchored in the old concrete dam slope around the perimeter of the shear loading channel.

[0028] The normal loading base plate is attached to the outer side surface of the vertical portion of the L-shaped test block and can shear and slide synchronously with the L-shaped test block.

[0029] The normal loading base plate is matched with the normal base plate rolling pair.

[0030] The shear displacement limit assembly can limit the maximum shear slip value of the normally loaded base plate.

[0031] The normal top plate is composed of two groups of I-beams arranged in parallel. The middle parts of both sides of each group of I-beams are anchored in the old concrete dam slope around the shear loading groove through anchor rods, sleeves and nuts; among them, the anchor rods and sleeves are clearance-matched.

[0032] The shear displacement limiting assembly is composed of a plurality of limiting rods; each limiting rod connects the normal loading base plate, the normal base plate and the normal top plate, and the limiting rod and the normal base plate are clearance-matched.

[0033] Lifting rings are arranged around the top surface of the normal loading base plate, and each lifting ring is connected to the hook of the lifting system through a lifting chain with adjustable length.

[0034] It also includes a tangential sensor, which can monitor the shear slip value of the L-shaped test block in real time.

[0035] The inclination angle α of the slope of old concrete dam can reach 40~50°.

[0036] An in-situ shear test method for the interface between new and old concrete in a gravity dam heightening project comprises the following steps.

[0037] Step 1: excavate rectangular shear loading troughs of different heights on the backwater side of the gravity dam; wherein the upper lateral wall and the lower lateral wall of the shear loading trough are both perpendicular to the slope of the old concrete dam; the lowest shear loading trough is recorded as the first shear loading trough.

[0038] Step 2: A test platform supported on the ground is cast below the shear loading trough, with the top surface of the test platform being coplanar with the lower lateral wall of the first shear loading trough to form a shear installation plane.

[0039] Step 3: Paste a flexible shear plate on the bottom surface of the upper lateral wall of the shear loading slot; wherein the elastic compression of the flexible shear plate pasted on the upper lateral wall is greater than the in-situ shear displacement of the L-shaped test block.

[0040] Step 4, cast-in-place L-shaped test blocks: The vertical portion of the L-shaped test blocks is cast in-place on the old concrete dam slope above the shear loading troughs at different heights to form an inclined interface between the new and old concrete. The horizontal portion of the L-shaped test blocks is cast in-place on the flexible shear plate on the lateral wall of the shear loading trough to form a cast-in-place L-shaped test block. The bottom surface of the L-shaped test block forms a shear loading plane parallel to the test plane, and the centroid of the L-shaped test block is located on the interface between the new and old concrete.

[0041] Step 5: Install the shear loading device on the shear installation plane, with the top close to the shear loading plane, and the shear force axis is located where the new and old concrete interface coincide.

[0042] Step 6: Hoist the normal loading device: The hoisting system hoists the normal loading device to the outside of the vertical part of the L-shaped test block and anchors it in the old concrete dam slope outside the shear loading trough.

[0043] Step 7: Start the normal loading device to apply and maintain the set constant normal stress on the interface between the new and old concrete.

[0044] Step 8: Start the shear loading device and apply shear force to the L-shaped test block along the interface between the new and old concrete until the interface between the new and old concrete is damaged; during this period, the shear displacement and shear force of the L-shaped test block are recorded in real time.

[0045] Step 9: After the test of one test block is completed, the normal and tangential loading devices are hoisted to another test block at the same height for further testing. That is, the test of several test blocks at the same height is carried out horizontally until the test is completed; Step 10: After the test of the test blocks of the same height is completed, another test block of the same height is tested from bottom to top, and so on for the test blocks of different heights.

[0046] In step 6, the hoisting system uses the hoisting chain to hang the four corners of the normal loading base plate of the normal loading device, and adjusts the length of the hoisting chain so that the inclination angle α of the normal loading base plate and the interface between the new and old concrete is the same; after the normal loading device and the old concrete dam slope are anchored, the hoisting system keeps hanging the normal loading base plate, but does not apply any hanging force.

[0047] In step 10, when testing test blocks at different heights, for the second shear loading slot and above, after completing the test at the first shear loading slot, the completed test block is inverted and installed below the second shear loading slot, serving as the reaction force support base for the shear loading device. Precast concrete pads or mountings are inserted into the gap between the inverted test block and the bottom platform to ensure continuity of the overall reaction force system.

[0048] The present invention has the following beneficial effects: In this regard, the core innovation of the device of the present invention is: 1. This invention proposes for the first time an in-situ testing method for the shear strength of the interface between new and old concrete under conditions of a 40° to 50° inclined dam surface, filling the gap that traditional testing methods are unable to carry out loading tests on inclined surfaces.

[0049] 2. This invention directly utilizes the stable dam structure as an anchoring foundation (e.g., anchored to the existing dam body via high-strength anchor rods) and designs a spatial load-bearing frame with adaptive slope angles to establish a highly efficient, rigid, self-balancing closed force system locally on the dam surface. This force system internally balances the applied shear and normal forces and their reactions, effectively resisting multi-dimensional loads and moments, ensuring no slippage, no lift, and no harmful deformation during testing. This reliably establishes stable reaction force support on complex slopes, a problem unattainable with traditional methods. This solves the problem of a non-closed force system when conducting traditional push-shear tests on inclined dam surfaces, enabling smooth shear strength testing on inclined dam surfaces.

[0050] 3. The present invention constructs an L-shaped new and old concrete interface structure and an integral hoisting loading platform, which solves the engineering problems of high-altitude layout, loading centering and interface slip induction.

[0051] 4. The present invention adopts the inverted reuse of test blocks as the reaction force support method for the upper test, which solves the problem of missing loading platform in high-altitude test, avoids repeated setting up of brackets or additional piers, and ensures the repeated testing of multiple test pieces at different heights.

[0052] 4. The present invention has the characteristics of modular assembly, repeated loading, and strong response data integrity. Nine groups of test verifications have been completed on site in a typical dam heightening project. The loading process is stable and the data reliability is high. It has the prospect of widespread promotion and application in engineering projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The schematic diagram of the structure of the in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project of the present invention is shown.

[0054] Figure 2 A schematic diagram showing the dimensions of the L-shaped test block in the present invention is shown.

[0055] Figure 3 A schematic diagram of the shear force applied by the shear loading device of the present invention is shown.

[0056] Figure 4 Shown is a schematic structural diagram of the tangential loading device of the present invention.

[0057] Figure 5 A three-dimensional line schematic diagram of the normal loading device of the present invention is shown.

[0058] Figure 6 A three-dimensional simulation schematic diagram of the normal loading device in the present invention is shown.

[0059] Figure 7 Shown is a schematic diagram of the installation of the tangential sensor in the present invention.

[0060] Figure 8Shown is a schematic diagram of the installation of the normal sensor in the present invention.

[0061] Figure 9 The schematic diagram shows the structure of multiple groups of shear loading troughs arranged on the backwater side of the gravity dam in the present invention.

[0062] Figure 10 Schematic diagram of the operating sequence of the test method of the present invention; wherein, (a) is a schematic diagram of the L-shaped test block after cast-in-place in steps 1 to 4; (b) is a schematic diagram of the installation of the shear loading device; (c) is a schematic diagram of the normal loading device; (d) is a schematic diagram after connecting to the acquisition system; (e) is the first group of parallel tangential and normal loading tests at the same height; (f) is the second group of parallel tangential and normal loading tests.

[0063] Figure 11 Shows a real-life on-site picture of the normal loading device of the present invention.

[0064] Figure 12 The figure shows a real scene of the on-site installation of the normal loading device of the present invention.

[0065] Among them are: 1. Test platform; 2. L-shaped test block; 201. Vertical portion; 202. Flexible shear plate; 203. Keyway; 3. Shear loading device; 301. Tangential jack; 302. H-shaped loading frame; 303. Rubber gasket; 4. Normal loading device; 401. Normal loading base plate; 402. Roller; 403. Partition plate; 404. Normal base plate; 405. Lifting ring; 406. Stiffening rib plate; 407. Normal jack; 408. I-beam; 409. Sleeve; 410. Limit rod; 411. Anchor rod; 412. Lifting chain; 413. Manual hoist; 414. Nut; 5. Data acquisition system; 501. Tangential sensor; 502. Normal sensor; 6. Hoisting system. DETAILED DESCRIPTION

[0066] The present invention will be further described in detail below with reference to the accompanying drawings and specific preferred embodiments.

[0067] In the description of the present invention, it should be understood that the terms "left side," "right side," "upper," "lower," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Terms such as "first" and "second" do not indicate the importance of components and therefore should not be construed as limitations on the present invention. The specific dimensions used in this embodiment are intended only to illustrate the technical solution and do not limit the scope of protection of the present invention.

[0068] The present invention takes the old dam of Lifan Project as an example. After the dam is raised, it exceeds 100 meters, and the present invention is described in detail.

[0069] like Figure 1 and Figure 2 As shown, an in-situ shear test device for the interface between new and old concrete in a gravity dam raising project includes a test platform 1, a shear loading trough, an L-shaped test block 2, a flexible shear plate 202, a shear loading device 3, a normal loading device 4, a data acquisition system 5 and a hoisting system 6.

[0070] The backwater side of the gravity dam has an old concrete dam slope with an inclination angle of α, where α can be adapted to 40-50°.

[0071] The test platform 1 is stabilized at the dam foot of the old concrete dam slope by cast-in-place and drilled reinforcement, and supported on the ground. Its top surface is a test plane perpendicular to the old concrete dam slope.

[0072] In order to test the shear strength of the joint surface of test blocks at different heights, shear loading troughs need to be set up under the test blocks of the test group at different heights. The shear loading troughs are opened in parallel from top to bottom in the old concrete dam slope above the test plane; among them, the shear loading trough close to the test plane is recorded as the first shear loading trough.

[0073] In this embodiment, there are three groups of test blocks of different heights, and three groups of shear loading slots of different heights are set to facilitate the repetition of subsequent tests. Figure 9 As shown, each group of test blocks is equipped with three parallel test platforms, and three shear loading slots are arranged in parallel from top to bottom on the top of each test platform.

[0074] Each shear loading slot is a rectangular slot, and each shear loading slot has two lateral walls parallel to the test plane, namely the upper lateral wall and the lower lateral wall from top to bottom; among which, the lower lateral wall of the first shear loading slot is coplanar with the test plane to form a shear installation plane.

[0075] The L-shaped test block is a cast-in-place concrete test block, which is L-shaped and includes an integral horizontal part and a vertical part.

[0076] The transverse portion is embedded in the shear loading groove, and the flexible shear plate is arranged between the upper lateral wall of the corresponding shear loading groove. The elastic compression of the flexible shear plate is greater than the in-situ shear displacement of the L-shaped test block.

[0077] The vertical portion is connected to the old concrete dam slope to form an inclined new and old concrete interface. Further, the new and old concrete interface can be provided with keyways 203 of different shapes and sizes according to actual conditions.

[0078] The bottom surface of the L-shaped test block is formed into a shear loading plane parallel to the test plane, and the centroid of the L-shaped test block is located on the interface between the new and old concrete, so that the centroid of the L-shaped test block is aligned with the axis of subsequent shear force application, as shown in the following figure. Figure 3 As shown, the torque effect is reduced, the shear force is ensured to be transmitted in the same direction as the interface axis, and the eccentric effect and torsional damage during the loading process are avoided, thereby improving the pure shear characteristics of the test loading and the data reliability.

[0079] The centroid of the L-shaped test block is mainly obtained by effectively controlling the size ratio of the vertical and horizontal parts of the L-shaped test block. As shown in the figure, the lengths of AB, BC, CD, DE, and EG are T, M, H, S, and N respectively; when the centroid of the L-shaped test block is located on the interface between the new and old concrete, the following constraints must be met: M 2 T=S 2 (T+H) In the embodiment, several groups of value intervals are given for reference. H can be in the range of 0.9-1.15m, S is 0.15-0.25m, T is 0.3-0.45m, M is in the range of 0.2-0.40m, and N does not affect the centroid control and can be set according to actual needs.

[0080] A flexible shear plate 202 is also provided between the transverse portion of the L-shaped test block and the bottom surface of the corresponding shear loading groove. It is preferably a polyethylene foam plate with a thickness of 2 cm and is used to induce a shear failure path. In the present invention, by locally weakening the interface bonding strength and forming a stress release zone, there is only one new-old bonding surface during the test process, and the induced shear failure develops stably along the new-old concrete bonding surface to avoid deviation of the failure surface. The deadweight of the upper part of the corner generates a certain shear component under the condition of slope layout, forming additional shear stress on the interface. When the data is subsequently processed and the shear force actually acting on the bonding surface is calculated according to the formula, corrections are made without affecting the comparative analysis between groups.

[0081] The shear loading device is installed on the shear installation plane, with the top close to the shear loading plane, and the shear force axis is located at the intersection of the new and old concrete interface.

[0082] The normal loading device is installed on the outer side of the vertical part of the L-shaped test block, which can apply a vertical normal force to the interface between the new and old concrete. The structure of the normal loading device is preferably as follows: Figure 4 As shown, it includes a tangential jack 301 , an H-shaped loading frame 302 and a rubber gasket 303 .

[0083] The above-mentioned rubber gasket is arranged on the top of the H-shaped loading frame and fits the shear loading plane, which can provide a buffer and convert the load applied by the tangential jack into a surface force as much as possible.

[0084] The H-shaped loading frame is a rigid structure that can provide stable reaction force support and ensure the loading direction.

[0085] The top center point of the above-mentioned tangential jack is aligned with the interface between the new and old concrete to ensure that the shear stress is evenly transmitted along the slip path, avoiding interface flipping, local opening or damage path deviation caused by eccentric loading.

[0086] like Figure 5 、 Figure 6 and Figure 11 As shown, the normal loading device includes a normal loading base plate 401, a normal reaction frame, a normal jack 407 and a shear displacement limiting assembly.

[0087] The normal reaction frame includes a normal bottom plate 404 and a normal top plate.

[0088] The normal top plate is anchored in the existing concrete dam slope outside the shear loading trough. In this embodiment, the normal top plate is preferably composed of two sets of parallel I-beams 408. The middle portions of both sides of each set of I-beams are anchored in the existing concrete dam slope outside the shear loading trough via anchor rods 411, sleeves 409, and nuts 414. The anchor rods are pre-buried in the existing concrete dam slope outside the shear loading trough. The anchor rods and sleeves have a clearance fit (preferably greater than the maximum shear slip value of the L-shaped test block). The anchor rods extend from the top of the sleeves and are anchored via nuts.

[0089] The normal jack is arranged between the normal bottom plate and the normal top plate. In this embodiment, there are preferably four normal jacks, and two normal jacks are arranged between each group of I-beams and the normal bottom plate. The connection between the loading end of the normal jack and the normal bottom plate is preferably provided with several stiffening ribs 406 along the circumferential direction.

[0090] The normal loading base plate is attached to the outer side surface of the vertical portion of the L-shaped test block and can shear and slide synchronously with the L-shaped test block.

[0091] The normal loading base plate cooperates with the normal base plate rolling pair. The preferred setting is that the normal loading base plate and the normal base plate are preferably arranged with several rollers 402 in parallel, and a partition 403 is arranged between adjacent rollers. The top of the partition is preferably welded to the bottom of the normal base plate, and the height is less than the roller diameter.

[0092] Furthermore, the top surface of the normal loading base plate is provided with lifting rings 405 on all sides, and each lifting ring is connected to the hook of the lifting system via a length-adjustable lifting chain 412. The length of the lifting chain is preferably adjusted by a manual hoist 413.

[0093] The shear displacement limit assembly can limit the maximum shear slip value of the normally loaded base plate.

[0094] The shear displacement limit assembly is a plurality of limit rods 410; each limit rod connects the normal loading base plate, the normal base plate and the normal top plate, and the limit rod and the normal base plate are clearance matched, and the clearance value is preferably greater than the maximum shear slip value of the L-shaped test block.

[0095] like Figure 7 and Figure 8 As shown, the data acquisition system further includes a tangential sensor 501 and a normal sensor 502; wherein, the tangential sensor can monitor the shear slip value of the L-shaped test block in real time; and the normal displacement sensor can monitor the normal displacement value of the L-shaped test block.

[0096] An in-situ shear test method for the interface between new and old concrete in a gravity dam heightening project comprises the following steps.

[0097] Step 1: excavate a rectangular shear loading trough on the backwater side of the gravity dam; wherein the upper lateral wall and the lower lateral wall of the shear loading trough are both perpendicular to the slope of the old concrete dam.

[0098] In this embodiment, three groups of shear loading grooves are preferably excavated in parallel from bottom to top, namely the first shear loading groove, the second shear loading groove and the third shear loading groove. The key grooves in the three groups of shear loading grooves can be the same or different.

[0099] Step 2: Cast a test platform supported on the ground below the shear loading trough, with the top surface of the test platform coplanar with the lower lateral wall of the first shear loading trough to form a shear mounting surface. In this embodiment, the test block strength grade is C25, and the curing period is at least 14 days.

[0100] Step 3: Paste a flexible shear plate on the bottom surface of the upper lateral wall of the shear loading slot; wherein the elastic compression of the flexible shear plate pasted on the upper lateral wall is greater than the in-situ shear displacement of the L-shaped test block.

[0101] Step 4, cast-in-place L-shaped test block: cast the vertical portion of the L-shaped test block on the old concrete dam slope above the shear loading trough to form an inclined interface between the new and old concrete; cast the horizontal portion of the L-shaped test block on the flexible shear plate on the lateral wall of the shear loading trough to form a cast-in-place L-shaped test block; the bottom surface of the L-shaped test block forms a shear loading plane parallel to the test plane, and the centroid of the L-shaped test block is located on the interface between the new and old concrete.

[0102] Step 5: Install the shear loading device on the shear installation plane, with the top close to the shear loading plane, and the shear force axis is located where the new and old concrete interface coincide.

[0103] Step 6: Hoisting the normal loading device: The hoisting system hoists the normal loading device to the outside of the vertical part of the L-shaped test block and anchors it in the old concrete dam slope outside the shear loading groove. Figure 12 As shown in the figure, the hoisting system uses hoisting chains to hang the four corners of the normal loading base plate of the normal loading device, and adjusts the length of the hoisting chain to make the inclination angle α of the normal loading base plate and the interface between the new and old concrete the same; after the normal loading device is anchored to the old concrete dam slope, the hoisting system keeps hanging the normal loading base plate, but does not apply any hanging force.

[0104] Step 7: Start the normal loading device to apply and maintain the set constant normal stress on the interface between the new and old concrete.

[0105] Step 8: Start the shear loading device and apply shear force to the L-shaped test block along the interface between the new and old concrete until the interface between the new and old concrete is damaged; during this period, the shear displacement and shear force of the L-shaped test block are recorded in real time.

[0106] Step 9: After the test of one test block is completed, the normal and tangential loading devices are hoisted to another test block at the same height for further testing. That is, several test blocks at the same height are tested horizontally until completion.

[0107] Step 10: When there are multiple groups of shear loading slots and the first group of tests is completed, the normal loading device is depressurized and transferred to the second shear loading slot above. At this time, the test blocks that have completed the test on the first shear loading slot are rotated up and down and installed on the lower bottom surface of the second shear loading slot. The test blocks of the first group are used as the reaction support piers for placing the shear loading device for the second group of tests. The gap between the rotated first group of test blocks and the lowest test platform is filled with pre-cast concrete test blocks to maintain the stability of the reaction piers. Repeat steps 6 to 8 to complete multiple groups of in-situ shear tests at different heights.

[0108] After the test of the test blocks of the same height is completed, another group of test blocks of the same height is tested from bottom to top, and so on for the test groups of different heights.

[0109] When testing test blocks at different heights, for the second shear loading slot and above, after completing the test at the first shear loading slot, the completed test block is inverted and installed below the second shear loading slot to serve as the reaction force support base of the shear loading device. Pre-cast concrete pads or embedded components are inserted into the gap between the inverted L-shaped test block and the bottom platform to ensure continuity of the overall reaction force system.

[0110] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the scope of protection of the present invention.

Claims

1. An in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project, characterized by: It includes a test platform, a shear loading trough, an L-shaped test block, a flexible shear plate, a shear loading device and a normal loading device; The backwater side of the gravity dam has an old concrete dam slope with an inclination angle α; The test platform is cast in situ at the foot of the old concrete dam slope and supported on the ground. Its top surface is the test plane perpendicular to the old concrete dam slope. There is at least one shear loading slot, which is arranged in parallel from top to bottom in the old concrete dam slope above the test plane; wherein the shear loading slot adjacent to the test plane is recorded as the first shear loading slot; Each shear loading slot is a rectangular slot, and each shear loading slot has two lateral walls parallel to the test plane, namely, an upper lateral wall and a lower lateral wall from top to bottom; wherein the lower lateral wall of the first shear loading slot is coplanar with the test plane, forming a shear installation plane; The L-shaped test block is a cast-in-place concrete test block, which is L-shaped and includes an integrally arranged horizontal part and vertical part; The transverse portion is embedded in the shear loading groove, and the flexible shear plate is arranged between the transverse portion and the upper lateral wall of the corresponding shear loading groove, and the elastic compression of the flexible shear plate is greater than the in-situ shear displacement of the L-shaped test block; The vertical part is connected with the slope of the old concrete dam to form an inclined interface between the new and old concrete; The bottom surface of the L-shaped specimen is formed as a shear loading plane parallel to the test plane, and the centroid of the L-shaped specimen is located at the interface between the new and old concrete; The shear loading device is installed on the shear installation plane, with the top close to the shear loading plane, and the shear force axis is located at the intersection of the new and old concrete interface; The normal loading device is installed on the outer side of the vertical part of the L-shaped test block and can apply a vertical normal force to the interface between the new and old concrete.

2. The in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project according to claim 1, characterized in that: A flexible shear plate is also provided between the transverse portion of the L-shaped test block and the bottom surface of the corresponding shear loading slot.

3. The in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project according to claim 1 or 2, characterized in that: The flexible shear plate is a polyethylene foam plate.

4. The in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project according to claim 1, characterized in that: The normal loading device includes a normal loading base plate, a normal reaction frame, a normal jack and a shear displacement limit assembly; The normal reaction frame includes a normal bottom plate and a normal top plate; The normal jack is arranged between the normal bottom plate and the normal top plate; The normal top plate is anchored in the old concrete dam slope at the periphery of the shear loading channel; The normal loading base plate is attached to the outer side of the vertical part of the L-shaped test block and can shear and slide synchronously with the L-shaped test block; The normal loading base plate and the normal base plate rolling pair cooperate; The shear displacement limit assembly can limit the maximum shear slip value of the normally loaded base plate.

5. The in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project according to claim 4, characterized in that: The normal top plate consists of two sets of I-beams arranged in parallel. The middle part of each set of I-beams is anchored in the old concrete dam slope outside the shear loading groove through anchor rods, sleeves and nuts. The anchor rods and sleeves are in clearance fit. The shear displacement limiting assembly is composed of a plurality of limiting rods; each limiting rod connects the normal loading base plate, the normal base plate and the normal top plate, and the limiting rod and the normal base plate are clearance-matched.

6. The in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project according to claim 4, characterized in that: Lifting rings are arranged around the top surface of the normal loading base plate, and each lifting ring is connected to the hook of the lifting system through a lifting chain with adjustable length.

7. The in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project according to claim 1, characterized in that: It also includes a tangential sensor, which can monitor the shear slip value of the L-shaped test block in real time.

8. The in-situ shear test device for the interface between new and old concrete in a gravity dam heightening project according to claim 1, characterized in that: The inclination angle α of the slope of old concrete dam can reach 40~50°.

9. An in-situ shear test method for the interface between new and old concrete in a gravity dam heightening project, characterized by: The steps include: Step 1: excavate a rectangular shear loading trough on the backwater side of the gravity dam; wherein the upper and lower lateral walls of the shear loading trough are perpendicular to the slope of the old concrete dam; the lowermost shear loading trough is recorded as the first shear loading trough; Step 2: Cast a test platform supported on the ground below the shear loading trough, with the top surface of the test platform coplanar with the lower lateral wall of the first shear loading trough to form a shear installation plane; Step 3: affixing a flexible shear plate to the bottom surface of the upper lateral wall of the shear loading tank; wherein the elastic compression of the flexible shear plate affixed to the upper lateral wall is greater than the in-situ shear displacement of the L-shaped test block; Step 4, cast-in-place L-shaped test block: The vertical portion of the L-shaped test block is cast in-place on the old concrete dam slope above the shear loading trough, forming an inclined interface between the new and old concrete. The horizontal portion of the L-shaped test block is cast in-place on the flexible shear plate on the lateral wall of the shear loading trough, thereby forming an in-place L-shaped test block. The bottom surface of the L-shaped test block forms a shear loading plane parallel to the test plane, and the centroid of the L-shaped test block is located at the interface between the new and old concrete. Step 5: Install the shear loading device on the shear installation plane, with the top close to the shear loading plane and the shear force axis located where the new and old concrete interface coincides. Step 6: Hoisting the normal loading device: The hoisting system hoists the normal loading device to the outside of the vertical part of the L-shaped test block and anchors it in the old concrete dam slope outside the shear loading trough; Step 7: Start the normal loading device to apply and maintain the set constant normal stress on the interface between the new and old concrete; Step 8: Start the shear loading device and apply shear force to the L-shaped test block along the interface between the new and old concrete until the interface between the new and old concrete is damaged; during this period, the shear displacement and shear force of the L-shaped test block are recorded in real time.

10. The in-situ shear test method for the interface between new and old concrete in a gravity dam heightening project according to claim 9, characterized in that: In step 6, the hoisting system uses the hoisting chain to hang the four corners of the normal loading base plate of the normal loading device, and adjusts the length of the hoisting chain so that the inclination angle α of the normal loading base plate and the interface between the new and old concrete is the same; after the normal loading device and the old concrete dam slope are anchored, the hoisting system keeps hanging the normal loading base plate, but does not apply any hanging force.

Images