Cracks and structural joints in the vertical concrete cofferdams of the Three Gorges Project

Chemical grouting for cracks and structural joints in the concrete longitudinal cofferdams of the Three Gorges Project Li Yan\ Li Wei (1. China Gezhouba Group Co., Ltd., Yichang 443002, China; 2. Lengshuijiang Xiangyu Waterproof Co., Ltd., Lengshuijiang 417500, Hunan, China) Vertical, horizontal and horizontal concrete cracks and interlayer seams. The article focuses on cracks, chemical grouting using epoxy screeds in the interstices between seams, caulking and embedding outside the seams, surface spraying, and the use of concrete panels for sealing protection on the surface of the impervious cover sheet. To protect the safety of dams.

1 Overview The longitudinal concrete cofferdam of the Three Gorges Project is distributed on the right side of Zhongbao Island along the direction of the Yangtze River, dividing the vertical section, the dam section and the lower vertical section. The dam section is not only part of the cofferdam but also part of the Three Gorges Dam and is a permanent building of the first grade. The dam section has a total length of 115m and a width of 68m and is divided into right vertical I and right vertical dam sections (the right longitudinal section is divided into the right vertical section by induced joints. According to the project schedule, the third phase of the Three Gorges Project will start an elevation of 160.0m in April 2006. The safety assessment of the following sites started in May in the foundation pit of the upper reaches of the river (RCC cofferdam).Before the safety appraisal and breakwater entry, a crack survey of the dam body was started in January 2006. After inspection, it was found that Longitudinal I dam elevation of 140. 0m or more and right vertical elevation of more than 96.0m above the water surface of the dam have multiple width, length of the vertical, oblique and horizontal cracks and concrete seams, as shown.

In order to ensure the safety of the dam, the design requires that in the low-temperature month (before March 2006), the epoxy resin shall be used to grout the interior of the seam according to the height of the elevation. Grouting, surface spraying, and adhesion of the cover sheet shall be adopted outside the joint. The cover sheet surface is treated with a variety of different forms and methods such as closed protection with concrete panels.

2 Before the cracks are examined, all cracks and interlayer seams in the right longitudinal I and dam section facing the water surface are subject to on-site surveys of relevant contents according to requirements. The census items mainly include: surface seam width, seam depth, seam length, and crack orientation. The location (including elevation), quantity, surface penetration, and presence of dissolved substances. Except for deep seams, the other methods are to use high-pressure water to rinse the concrete surface firstly, then the inspectors shall stand on the hanging baskets and shelves, use the steel tape measure, reading magnifier and naked eye to measure and record from bottom to top and record the results. The ratio of 1:100 is depicted as a map. Check the depth of the seam and select a horizontal concrete seam (height of 180.0m) in the right vertical section I. After the grouting is completed, drill at the crest 185.0m in height, take core and press water (for example). Check both the slurry filling and the seam depth. The right vertical dam section adopts the method of electric drill drilling inclined hole pressure to detect the seam depth for the longer cracks of the seam.

The census result: 25 cracks were found on the right longitudinal I dam surface, among which ~0.23 mm between the seams, and the maximum length of the seams was 16.5 m wide and all were between 0.06 and 0.18 mm, and the maximum length of the seams was 32 m. 3.2m. There are 10 cracks found on the right longitudinal dam surface, and the slit widths are all within 0.1. Table 1 Example of Crack Census Results Table No. Fracture Strike Site No. Elevation Fracture Feature Type of Crack Discovery Date Month-month Slit Wide Slot Deep Slot Vertical Right Vertical I Upstream Dam Surface Vertical Vertical Right I Upstream Dam Surface Vertical Right Vertical I Upstream Dam Surface Transverse Right Vertical Upstream Dam Surface Transverse Right Vertical Upstream Dam Surface Vertical Right Vertical Upstream Dam Surface 155.0m Right Vertical I Dam Section Crack Treatment Diagram (3 Dam joint structure grouting (transverse section between dam sections): In order to prevent seams, and between the first stop of the upper dam surface upstream of the dam body, water-soluble inter-seam grouting is used to grind the slurry into the dam body joints. Interval joints and crack grouting urethane (LW) were grouted, and afterwards, the grouting between the 23rd section of the dam-right I and the right-longitudinal I-right section of the dam was carried out before the interfacial seam and the fracture.

3 Cracks, interlayer seams and structural joints Treatment design 3.1 Right longitudinal I ± Shell 0m or less: Cracks and interlayers are treated with chemical grouting (not mentioned below), because cracks and interlayers The processing method is exactly the same) + chisel embedding fill waterstop material + surface spray cement-based permeability crystalline waterproof material processing.

Specifically: Shanghai Mestre Low-viscosity Epoxy Pulp (LPL) is used as the grouting material. Three days after the grouting is completed, a sink with a width of 8cm and a depth of 5cm is cut along the crack opening, and the vertical crack cutting groove is extended along the two ends of the crack outward by 50cm. The two sides of the sink are staggered with a spacing of 40cm and a spacing of 8cm to create a 520mm anchor. Rib hole, hole depth 30cm. Holes are completed and pressure water is used to wash the holes. After the holes are dried, mark M30 cement mortar into the holes and insert 58mm anchor bars. The total length of the anchor bar is 38cm, the hole is 30cm, and the exposed side is 8cm. The bottom of the slot is 3cm in diameter and the SR-2 plastic waterstop material is used. The outer slot 5cm is filled with 903 mortar, for example.

0m or more: crack treatment using chemical grouting + chisel embedded pre-shrink mortar + surface spray cement-based permeability crystalline waterproof material processing. Specifically: 3 days after chemical grouting is completed (grouting material is the same as above), 5cm deep and 5cm deep along the crack mouth / U "type sink only, vertical cracks gouge lengthening to both ends of the crack 0. 5m. After the completion of the chisel Rinse the tank with pressure water. After the tank is dry, install the pre-shrink mortar in the water tank to fill and compact.

Exposed surface protective measures: All the upstream surface is sprayed with cement-based permeability crystalline waterproof material for protection.

± 0m range: cracks using chemical grouting + chisel embedded fill seal material processing. Specifically: 3 days after the chemical grouting is completed, a sink with a width of 8cm and a depth of 5cm is cut along the crack mouth, and the gouge extends along both ends of the crack outwardly by 0. 5m, and the stop tank is filled with a plastic water stop material SR-2. Filling is completed, and SR anti-seepage cover sheets are attached to the concrete surface for protection. The sides and the top of the SR cover plate are closed by the angle steel of r 305, and the surface of the cover plate is protected by C25F25W10 pumped concrete (slump 16~20cm) pressure wallboard. The board thickness is 25cm, a layer of 51620 steel mesh is arranged in the board, a vertical structure joint is arranged every 6m in the board, and the inlay is filled with a 1cm-thick butcherwood board. The horizontal steel bars in the concrete board are separated by one seam. 30cm long on both sides of the surface of the seam reinforcement brushing Zhejiang green. The dam faces are arranged with 525 anchorages with a spacing of 2mx 2m. The length of the anchor bar is L = 1.5m. The length of the dam surface is 75cm. The surface of the anchor bar, each with a length of 5cm inside and outside the dam surface, must be painted with asphalt (set free section). Such as.

Table 2 Crack treatment Main material Basic performance table Material name Application Performance Performance index 1.LPL epoxy grouting material Grouting Adhesive strength (MPa) 6 Compressive strength (MPa) 50 Elasticity (N/mm2) 21902.SR-2 Plastic Water Sealing Material Filling Groove Adhesion Elongation (25r, Cover Laminate Tear Strength (N) Longitudinal 82-Base Penetration Crystal Waterproof Material Surface Impermeability Compressive Strength (MPa)\18.0 Wet Surface Adhesive Strength (MPa )\1.0 impermeability (MPa)\1.25.903 polymer cement mortar surface impermeability compressive strength (MPa) \ 25.0 tensile strength (MPa) \2. 8 bonding strength (MPa) \2. 0m range: The crack treatment uses a chemical grouting + chisel-filled water-stopping material treatment program, specifically: After the chemical grouting is completed for 3 days, a 8cm-long, 8cm-depth sink is cut along the crack mouth, and the vertical crack chisel is along the two ends of the crack outward. Along the extension 0. 5m, staggered with 40cm hole spacing on both sides of the sink, 8cm row spacing made 520mm anchor holes, hole depth 30cm. Holes completed with pressure water to rinse the hole clean, after the hole is dry, the 58mm anchor bar Into the hole, the total length of the anchor bar is 38cm, the hole is 30cm, and the exposed part is 8cm. After inserting the bar, M30 cement mortar is injected and backfilled. The bottom of the slot is 3cm. SR- 2 plastic sealing material, 5cm outer groove 903 using mortar filling them, to clean the surface of the concrete, cement-based coating permeability crystalline waterproofing materials, see (a) the crack treatment elevation 155.0m FIG.

0m range: crack treatment using chemical grouting + chisel embedded pre-shrink mortar material treatment program. After the chemical grouting is completed 3d, a 5cm deep and 5cm deep U/type sink is cut along the fissure, and the vertical crack chisel is extended to both ends of the crack. 0. 5m. After the chisel is completed, flush the tank with pressure water. After the tank is dry, the tank is filled with pre-shrink mortar and back-filled concrete. The cement-based penetrating crystalline waterproof material is applied on the concrete surface for protection. See (b) Crack treatment diagram with an elevation of more than 155.0 m.

4 Basic properties of crack treatment materials The aforementioned dam crack treatment refers to a variety of materials, and the basic properties of the main materials are now listed in Table 2.

5 crack treatment construction 5.1 cracks grouting cracks grouting construction process procedures: crack inspection y surface treatment y mouth y sealing seam y test y crack grouting.

Seam surface treatment: Clean the scum and oil on the concrete surface 10cm wide on both sides of the crack. After grinding, flush the joint surface with high-pressure water to observe the condition of the seam. There is a place where the milk skin seals the seam. The blade picks up the seam and waits until all the seams are open and the concrete surface is air dried before the caulking.

Ribbed mouth: Grout mouth using Shanghai Meister chemical grouting mouth (outside diameter 6mm), with Mestre 1438 epoxy cement as a paste, caulking spacing 20 ~ 30cm mouth, paste the grouting mouth with cotton wire Acetone or toluene scrub. If the seams are not connected, place a mouth at the end of the seam and at the beginning of the next section. As far as possible, place the mouth in a slightly wider and open place. Apply the guide bar and flashlight when attaching the mouth to ensure that the grouting mouth is centered and tightly affixed securely. Number the grouting mouth with paint.

Sealing seam: After the grouting nozzle is affixed for 2~3h and it is firm, use Messite 1438 epoxy mortar to seal seams along the 10cm wide sides of the crack. Sealing thickness 3~5mm (thickness around the bottom of the grout nozzle). During the sealing process, the position of the grouting nozzle is not allowed to move.

Test gas: 24h after the sealing seam test was conducted to check the gas, check the sealing seam seal seam and grouting mouth and seam surface, grouting nozzle and grouting mouth between the smooth, test gas pressure of 0. 2 ~ 0.3MPa. Specifically: the closed condition test gas inspection, blocking the other grouting nozzle except for the inlet grouting nozzle, close the surface of the crack with soapy water full brush, if there is leakage, there will be bubbling phenomenon, the leaked part is re-closed until no longer Outer leakage; inspection of the openness between the grouting nozzles, simultaneous with the inspection of the closing conditions, and inspection from the side to the other side according to the direction of the cracks from bottom to top. The method is to open the grouting nozzles in order and lead the tubes to the transparent water bottle. If there is bubbling, it will be unblocked; if there is no bubbling phenomenon, it will be unclear. The mouth must be cut off and re-attached until smooth.

Grouting pressure: first small and large, requiring slow pulping. The maximum grouting pressure is controlled at an elevation of 150 m or less. 0. The maximum grouting pressure at the upper control is 0.2 MPa. Grouting sequence: Horizontal seams are poured from one end to the other, and vertical seams are poured from bottom to top.

Grouting equipment: Mestre LilyCD15 dual liquid automatic pressure regulation grout pump.

Grouting: Multi-point parallel perfusion, first from No.1, No.3, No.5, No.7 and No.9 nozzles. When the color of slurry to be discharged is normal and the filling time is longer than 30 minutes, and the pressure does not drop, it can be re-irrigated No.2, No.4, No.6, No.8, No.10, No.11, No.13, No.15, No.17, No.19 The mouthpiece, in this way, the perfusion time of each mouth must be greater than 30min. When the open mouth overflows, if the grouting time is less than 30min, the overflow mouth can be temporarily closed until the priming nozzle has a filling time greater than or equal to 30min; When the open nozzle overflows, when the grouting time has reached 30 minutes, the grouting pipe is replaced with overflow nozzle.

When the multi-point parallel infusion is performed, the injection monitor of the injection machine is checked at any time. When it is not possible to determine the amount of pulp coming from a certain nozzle, the valve of other joints is closed, the slurry is taken from the nozzle only, and the monitor of the injection machine is observed, and it can be known. Whether the mouth into the pulp. If a leak is found during the grouting process, priming from the nozzle should be immediately suspended. The surface slurry should be washed with acetone, and then plugged with a plugging agent, followed by grouting from the nozzle.

Ending criteria: When the last five nozzles enter the pulp, the display of the grouting equipment stops feeding and the pressure does not drop. The grouting can be ended after 30 minutes of screen pulping.

Monitoring in the grouting process: When the horizontal interlayer seam grouting is more than 150.0m in elevation, arrange a dial gauge every 10m around horizontal seams to control the increase of cracks to no more than 100Lm. 5.2 Chisel Grooving After the material chemical grouting is completed 3 days, the chiseler cuts the groove along the joint using a cutting machine first, and then uses a steel drill to cut the “U”-shaped sink in accordance with the above-mentioned technical requirements along the crack, and then fills the water stop material.

SR-2 plastic water-stopping material: first flush the tank with pressured water, and then dry it in the tank. In the "U*-type tank, evenly coat the first plastic water stop material primer, and dry naturally at room temperature for 1 hour. Brush the second primer, dry it at room temperature for 0.5h or bake with the lamp until the surface is dry, touch the hand and touch it without touching the hand to fill it in. When the filling is completed, press the SR-2 into thin strips. The principle of 'first in and then out' followed by layering along the trough, and finally hammered with a wooden hammer to be dense, the surface flush with the top of the *U* type trough.

Pre-shrink mortar backfill: Pre-shrink mortar is mixed by artificial ingredients and mortar mixer. Before backfilling, apply a thick cement slurry with a water to cement ratio of 0.5:1. When backfilling, tamper with wooden rakes until a small amount of slurry appears on the surface and close with a flat surface with a trowel. After the pre-shrinking mortar was backfilled, it was timely sprinkled and maintained in a moist state for 7 days.

903 Mortar backfilling: Mix 903 polymer cement mortar waterproof cement with cement and sand according to the proportion. Apply a 903 waterproof plastic puree in the tank before backfilling. Then backfill according to the pre-shrinking mortar backfill method.

5.3 Construction of Anchor Bars The hole of 20 anchor bars shall be drilled with a hand drill, with a hole depth of 30 cm, staggered on both sides, and the hole shall be flushed with pressure water after the final hole. After drying, water shall be injected into the M30 cement mortar, and then the anchor The ribs are inserted into the holes.

5.4 affixed SR cover sheet First clean the concrete surface. After the concrete surface is dry, drill the expansion bolt holes at the two ends of the SR cover piece to install the expansion bolts, neoprene strips and r30 angle steel. The bolt hole spacing is 100 cm and the hole diameter is 10 mm. • Apply the first plastic water stop material primer evenly on the SR cover sheet adhesive part, and let it dry naturally for 1 hour at room temperature. Then apply the second end primer glue, dry naturally at room temperature for 0.5 hours or bake it to a dry surface. You can touch the hand and touch it without touching the cover.

When the paste is applied, tear off the inner film of the cover sheet, and then grasp the upper end of the cover sheet to flatten the cover sheet and stick it on the wall. While using the round stick, stick the SR cover sheet against the concrete surface with a round stick, and then use the r30. Angle steel, neoprene strips will be crushed at both ends of the SR cover plate, tighten the 510mm expansion bolts to securely fasten. The SR-2 plastic material is used for butting between each cover sheet to fill the gap between the cover sheets and flatten it with a round stick. The covering cover must not be less than 20cm thick, and the exposed part should be covered with transparent tape. It must not contaminate the cover sheet. When slipping the concrete, the slide should be covered with planks to cover the cover sheet at the material feed point to prevent damage. The topmost SR cover sheet is fixed at the top with r30 angle bar besides the two ends. The stencil strips were sealed with SR-2 plastic waterstops through the cover sheets.

5.5 concrete pressure wall plate right vertical wall concrete mixer truck transported from the mixing floor to the scene, through the pump pipe to the fracture after the delivery of the warehouse. And from left to right on both sides of the partition board uniform material, vibrating concrete vibrated using a long hose vibrator vibrator, the thickness of each blank layer 40cm, concrete pouring speed control is not greater than 0.8m / h. 5.6 cement base Permeable Crystalline Waterproof Material Coated Cementitious Permeable Crystalline Waterproof Material adopts KT-1. It removes the floating ash and oil stain on the concrete surface before painting, and cleans and wets the dam surface. Use clean water and KT- according to the required ratio. 1 mix, use a special brush brush, regular spray water conservation.

6 Grouting method of dam structural joints Grouting of dam structural joints is to discharge the left vertical section I of the dam section I, and the right longitudinal section I to the right section of the vertical dam section, perfuse the LW slurry, and the surface treatment, joints, and seals of the joints Sewing, gas testing, grouting methods, grouting equipment, etc. are all equivalent to vertical cracks.

7 Crack grouting effect inspection 7.1 Drilling After core and water pressure 0m concrete horizontal interlayer seam grouting is completed 7 days later, the core is drilled for core inspection. From the coring situation, the seams were well cemented and no seam surface slurry was filled, indicating that the seam depth was less than 50cm. The pressure water used 0. 2MPa pressure, the leakage rate was 0, and the inter-layer seams (wall surfaces) were not leaky.

7.2 Analysis of grouting results The cracks in the upstream section of the right dam were started from March 12, 2006 and completed on March 24, with a total slurry volume of 28,207 ml. Crack grouting was 429. 2 linear meters and the average unit weight was 65.72 ml/. m. Grouting Results Random Sampling As shown in Table 3. Table 3. Example of crack grouting results Table No. Fractures Basic Condition Crack Grouting Construction Type Length Maximum Width Seam Deep Seam Joints Irrigation Time (March 2006) Irrigation Time (2006) March) Filling Duration H Pure Immersion Volume Sulfur Demand Description Vertical Slot Right Vertical I Vertical Slot Right Vertical I Vertical Slot Right Vertical I Horizontal Right Right and Horizontal Right Right and Vertical Right Vertical Crack Width Maximum and Minimum Or equal to 0.1mm and greater than or equal to 0. 2mm cracks pure infusion statistics analysis. A total of 139.5m cracks less than or equal to 0.1mm, 0~50cm depth calculation, the area is 0~69.75m2, the theoretical volume of 6975ml, according to statistics of grouting results, actually poured into the pulp material 7230ml, slightly larger than the theoretical volume, from the grouting According to records, a small number of orifices have a large grouting phenomenon, indicating that there are local defects in concrete and are filled. Greater than or equal to 0. 2mm crack total 47. Slot depth is calculated by 0~50cm, then the area is 0~23.55m2, the theoretical volume is 4710ml. According to statistics of grouting results, 3 ml of slurry material is actually poured, which is slightly equal to the theoretical volume. Grouting effect is obvious.

Impregnability (unit consumption) analysis. Crack consumption less than or equal to 0.1mm 52. 5ml / m, greater than or equal to 0. 2mm crack consumption 75.2ml / m. Large crack width is large, but conversely, a small crack width is smaller unit consumption. In accordance with the rule of grouting and irrigation of cracks.

Slurry analysis. In the process of grouting, there is a string of pulp, indicating that the seam surface is better connected and the spacing of the grouting nozzle is reasonable.

7.3 Appearance inspection When the grouting is finished, the seam is observed at the end of grouting for 3 days. Generally, a wide area of ​​the seam is observed. The consolidation body of the LPL slurry is seen, and there is no solid body in the narrow seam, indicating that the width of the seam is related to the injection effect.

8 Conclusion This article only from the construction point of view, the introduction of cracks, interlaminar joints design and treatment methods, construction and inspection results, a simple introduction of the dam structure joints grouting method, for the causes and qualitative cracks, etc., have not been analyzed.

Three Gorges Project concrete longitudinal cofferdam body facing surface concrete cracks and interlayer seams, structural joints adopted grouting, chisel embedding, surface spraying, adhesive cover slip cover and concrete closed plate protection in the form of treatment, inspection and base The test of water in the pit has no abnormal phenomena, which proves that the treatment plan is reasonable and the construction quality meets the design requirements.

The concrete grouting method is the same for concrete cracks, interlayer seams and structural joints, and for the preparation of chemical grouting construction specifications for concrete cracks (China Gezhouba Group is currently compiling the power industry standard “Code for Chemical Grouting Construction of Hydraulic Structures”). To the effect.

According to the design requirements, in order to understand the effects of crack treatment, a long seam surface was selected within the elevation range of 70.49+263.5m in the right vertical dam section, and the monitoring of buried cracks with large gaps was currently under observation. This achievement needs to be obtained subsequently.

(Continued from page 121) Table 3 Temperature stress of concrete surface during cold wave strikes MPa Cooling amplitude Temperature stress Concrete age 7d Concrete age 28d Unprotected 0. Thick foam plastic board 0.02m thick foam plastic board Unprotected 0. Thick foam plastic Board 0.02m thick bubble 4 Conclusion The sudden drop in temperature during the cold wave has an important influence on the temperature and temperature stress of the concrete, which is related to the development of concrete surface cracks.

The principle of superposition is an effective method to analyze the temperature and temperature stress of massive concrete under the action of cold wave, and has good accuracy and convergence.

During the sudden drop in temperature, the surface of the concrete dam has a large tensile stress, which is the main cause of surface cracks. After the insulation measures are taken on the surface of the concrete dam, the surface temperature stress can be effectively reduced. Therefore, in order to prevent cracks, during the cold wave should pay great attention to the concrete surface insulation measures. Moreover, before the onset of the cold wave, suitable materials should be selected for surface protection according to the type of cold wave and the extent of temperature drop, and its surface tension.