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Anchoring Construction Technologies of Rubber Dam Bag

1.Introduction

The rubber is a kind of burgeoning hydraulic structures taken high strength fiber synthetic materials as framework. Water resisting layer of rubber dam is consists of synthetic rubber with low-weight characteristic. Usually, through anchoring synthetic rubber on the riverbed concrete floor to form a closed space structure, furthermore, the enclosed space structure is filled with water or inflated to come into being a dam body. Its span can be adjustable and its height is flexible. Seepage flow is low when blocking water and resistance is low during water release. These characteristics can’t be found in traditional dams. This paper takes anchorage problem in Pingxiang Jiangxi province rubber dam as an example, exploring the anchorage design of rubber dam bag, waterproof and leak proof ,etc, for improving construction quality of designed rubber dam and expanding the application fields of rubber dam.

2.Anchoring mode of rubber dam bag

Anchoring of rubber dam bag is key factor in constructing rubber dam. Anchoring position of dam bag bears the pull force from rubber dam along with side tension of rubber dam after water retaining. Currently, the anchoring method of rubber dam bag mainly has three kinds: concrete wedge anchor, bolt anchoring, capsule filled water to anchor.
2.1.Concrete wedge anchor
The concrete wedge anchor working by utilizing concrete to create a wedge with certain weight and it is fixed in the anchor groove, thus, the rubber dam bag can be fixed under each other squeezing effect of concrete wedge. In addition, the anchor groove need to be designed into trapezoidal or boot shape, but the requirement of material is changed in different different periods: for the anchor groove with boot  shape, the concrete wedge has to be used in the front wedge and the later wedge; with the regard to the trapezoid anchor groove, the front wedge is obliged to take concrete wedge, the later wedge can be a concrete wedge or a wooden wedge.
2.2.Bolt anchoring
It can take two ways non-perforating bolt or perforate bolt to anchor while the bolt is used for anchoring treatment. It is worth mentioning that the latter method has a wide range of application, the bolts are made of stainless steel or carbon steel and 20# channel steel is the main platen material. When manufacturing the press plate, the plate shall be adopt common materials, like concrete, cast iron, etc. For bolt anchoring method, if using the general bolt, prone to occur leakage and other issues, nevertheless The use of stainless steel bolts with higher cost which is out of line with low cost merit of rubber dam.
2.3.Capsule filled water to anchor.
Capsule filled water to anchor is new-style anchoring method and has the advantage of construction convenient, inexpensive and so on. Through the water filling capsules, the use of pressure to rubber dam and rubber dam bottom gasket pressed into the anchoring slot, in consequence of the huge water pressure, the rubber dam bag and anchorage slot wall has great friction to offset the dam bag tension, played a role in fixing the rubber dam bag. This way is simpler in whole construction and cheaper to disassemble. But in order to ensure the pressure inside the capsule is sufficient, need real-time pressure detection of a capsule, if it is found that the pressure is insufficient, must be promptly filled with water, which resulted in the increase of management cost.

3.Design of concrete wedge anchoring

Based on the consideration of management cost and safety, the concrete wedge anchor method is adopted in Pingxiang rubber dam in Jiangxi province.
The common anchor line layout of concrete wedge anchorage is single line anchorage layout and double line anchorage layout. The rubber dam in Jiangxi Pingxiang adopts double line anchorage layout.
3.1.Design of anchorage slot for rubber dam
The trapezoid and boots are the two forms of anchorage slots. If the shape of anchorage slots is trapezoid, the notch section is relatively narrow, deep groove cross-section is relatively wide, inner part of the body is straight, no extreme projections, fixing the rubber dam bag mainly relies on the friction of wedge wall and groove body parts; for the boots form, the latter wedge of boots shape anchorage groove does not directly contact with the rubber dam bag, The rubber dam bag in boot shaped anchor slot just by the pressure, and not rely on friction force to fix the rubber dam bag, which makes the corresponding extension of life of rubber dam bag. Therefore, Pingxiang rubber dam adopted the shape of boots anchor groove way, the rubber dam bag like pillow, rubber dam height 2. 4m, groove depth 0. 22m, groove width is 1m, the specific shape see below.
The boots shape anchorage slot picture of Pingxiang rubber dam
3.2.Wedge cross section design of rubber dam
Wedge of rubber dam play a role in fixing rubber dam bag and required with certain gravity. In addition, Rubber dam wedge material also needs to have a certain degree of durability, to ensure that the rubber dam wedge in the entire rubber dam operation without significant hidden danger. In terms of force, both the front wedge and the latter wedge are only bear the positive pressure acting on the wedge surface of the rubber dam. However, due to the complex working conditions, the wedge has to be subjected to hammering at the later stage and it’s need to install steel bar to improve the overall strength of latter wedge.

4.Construction of rubber dam anchoring

The quality of anchorage directly affects the safety of rubber dam. For the rubber dam which is constructed with concrete wedge anchorage like Pingxiang rubber dam in Jiangxi, the anchorage slot shall be installed on the floor. Moreover, the notch line and the bottom line of the anchor groove on the floor should be straight, and the whole groove surface is not allowed to appear convex phenomenon.
4.1.Anchorage groove forming
Anchorage groove forming construction has the two construction methods of one-time forming and obligate two times molding. The one-time forming requires that the anchor slot template be suspended in the design position first, and then the concrete pouring construction is carried out to ensure the one-time molding; the obligate two times molding need to be separated out of the anchoring slot size through the template, and then pour the concrete, remove the template and clean the anchor slot thoroughly after the concrete strength meets the requirements, support the new template, and finally complete the operation of the two stage concrete pouring.
Pingxiang rubber dam is one-time forming of concrete construction method, mainly in order to save time, shorten the construction period, reduce the process and labor input. Although steel products are used more in the layout of the formwork, but the integrity of the concrete is better, and in general, it is still a good economic construction method. Before constructing, installing a row angle iron on both  sides of formwork of anchor groove in advance, then being process in welding operation on the angle iron to insure the steel bar bracket firmly fixed on the angle iron, finally, fastening the anchor groove template that causes anchorage slot templates and accessories are systematic and one-time forming while concrete pouring. Moreover, it’s significant to pay attention to the symmetry of the angle in the process of concrete pouring, in order to prevent the exposed angle iron corroding. Meanwhile, it’s necessary to select connect method about the supporting framework and bottom template, to avoid burr exposure occurs when removal of the template.
4.2.Prefabricating anchoring wedge
In order to ensure the anti impact ability of the anchor wedge, the better integrity set-shaped steel formwork is adopted in the template manufacture. Prior to the use of shaped steel templates, careful correction is required to ensure dimensional accuracy. In the construction process, the control line is arranged around the anchor slot ahead of time, and the control point is arranged at the important node position. It is necessary to use high-precision theodolite to observe at any time during the manufacture, so as to ensure that the anchor groove does not have displacement in the left and right direction. If the displacement occurs, the concrete must be corrected before it is solidified. At the same time, it is necessary to set up the elevation points at the top of the anchor groove template, and control the elevation of the anchor base-plate trough the elevation of the anchor slot roof. In this case, the level is used for real-time observation, and if the displacement occurs, the concrete needs to be corrected before the concrete is solidified.
In the process of mixing concrete, it is necessary to do a good job of pouring material proportioning, to ensure the full mixing of steel fiber, to avoid problems such as group, knot and so on. After the completion of the above construction operation, also need to do the maintenance of concrete operation, making the concrete in a humid state. In addition, it is necessary to ensure the synchronism of the vibration operation of both sides of the concrete, so as to prevent the uneven force of the two sides of the anchor groove.
4.3.The dam bag anchorage fixing
Before the installation of rubber dam bag body, need to carefully check whether the anchorage slot is smooth, whether steel is exposed, whether there are prominent edges. Polishing the part where doesn’t reach the requirement, about the sharp edges and burrs, they shall be corrected so that the whole slot body with better integrity and smoothness. In dismantling the template, the parts should be carefully checked to ensure that the template is removed without leaving any sharp slag. 
After careful inspection, making the rubber dam bag corresponding to the preset control point and control line, the rubber dam bag with the edge of the rope tight, artificial fixed at a predetermined position, and from the center to the left and right sides started anchoring, it is absolutely impossible to segment the anchor. When anchoring, the rubber dam bag tape leveling aligned predetermined anchor position, putting into laminated wood, then folding up bottom pad and the front wedge is put into the slot immediately, finally, adding the latter wedge and compacted with the hammer so that the wedge is tight.
4.4.Water filling test of dam bag
All kind of debris on the floor shall be clean up after installation of rubber dam bag, then carrying out the water filling test. Water filling test of Pingxiang rubber dam bag is divided into three stages: the first stage is filled with water to the height of the dam in half, and then stop 2h, in the meantime, carefully check whether the dam bag is flat, discounts and other undesirable phenomena, starting the second phase after checking correctly; the second stage of water filling to the dam height of 80%, and then stop 5h, during this period, carefully check whether the dam bag is flat, whether there is water leakage and other adverse phenomena, after checking, entered the third stage; the third stage water filling to the design dam height, and then stop 8h, during this period, carefully check whether the dam bag is flat, whether there is leakage and other undesirable phenomena, if there is no adverse phenomenon, the water filling test is finished and begin encapsulation of anchorage slot.

5.Analysis and Countermeasures of Common Water Leakage

The leakage of rubber dam is mainly caused by improper construction. According to the construction experience of rubber dam in Pingxiang rubber dam, the reasons for leakage of rubber dam are summarized as follows;
  • Anchor groove concrete surface is not flat. If the concrete vertical construction of the anchoring slot unreasonable or uneven plane, it will affect the quality of anchorage operation and cause water leakage problem. In order to prevent this phenomenon, in the construction, it’s need to carefully check the anchorage concrete rubber dam surface and timely treatment uneven place.
  • Water leakage at lap joint of dam. The water leakage at the dam lap joint is mainly caused by the serious gap between the tape joint of water stop and the size of the cushion. In order to prevent this phenomenon, it is necessary to ensure the accuracy of water stop strip cutting before construction, and avoid the situation of inaccurate docking. Shall be combined with the specific width of cushion to determine the dam size, to ensure consistent with the standard size and the tightness of anchorage, eliminate the water leakage problem fundamentally.
  • The bottom pad is scratched in the transportation, construction. The bottom pad in the transportation, construction will emerge scratches that leads rubber dam bag appears tiny holes which will cause water leakage of concrete dam. For preventing this phenomenon, it is necessary to clean the construction equipment on site and eliminate the construction sundries as much as possible while constructing. If there is a hole in the rubber dam bag, need to use tape repair.
  • The thick of laminated wood is excessively. The bottom laminated wood is too thick will lead to deformation of the rubber dam bag, and leakage caused by improper connection with the bottom plate, it’s difficult to deal with such problems in general, we can only give priority to prevention. Construction must strictly comply with the process, can not be arbitrarily changed.

6.Conclusion

This paper takes the rubber dam construction in Pingxiang as an example,  Systematically introduces all kinds of details need to pay attention to the rubber dam construction, for the main technical aspects, such as rubber dam anchorage, anchorage installation problems in detail. In addition, the various problems in the construction process of rubber dam are analyzed in detail, and the corresponding countermeasures are put forward according to the specific problems.
Three years after the completion of the rubber dam in Pingxiang, there is no serious water leakage, the overall work is normal, indicating that the construction method is appropriate, other similar projects can draw lessons from this.

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