Winter construction technology of Dalian Houyan overpass foundation?

What specifically includes the winter construction technology of Dalian Houyan overpass foundation? The following Zhong Da consults the bidding teacher to answer your questions for your reference.

Shenyang-Dalian expressway 1 Project Overview Houyan Interchange is a transportation hub connecting Shenyang-Dalian expressway, Zhenxing Road of Dalian Development Zone, No.202 National Highway of Heida Line and No.20/KLOC-0 National Highway of Heda Line. It is the only and most perfect land traffic entrance and exit in Dalian. There are 9 bridges in Houyan Interchange, with a total length of 3648-9 meters, and the bridge structures are all prestressed concrete and reinforced concrete continuous beams. 1. 1 Construction conditions The project is located in Dalian, with staggered road networks, convenient transportation and water and electricity, and sufficient road materials. In order to shorten the construction period and improve the economic benefit and investment return of the project, it is imperative to implement the winter sub-project construction of bridge engineering. All the foundation works of this bridge must be completed in winter. 1.2 construction preparation 1-2- 1 Before construction, prepare the raw materials needed for construction, such as cement, sand, stones, templates, etc. according to the engineering quantity. Prepare materials needed for winter construction, such as concrete admixture, thermal insulation material, thermometer, instrument, construction fuel, oil and various mechanical equipment. 1-2-2 determines the winter construction scheme, puts forward the technical measures for the implementation of construction methods, puts forward specific measures to ensure the quality of winter construction projects, and determines the project schedule of winter construction. 1-2-3 Arrange all kinds of professionals (such as temperature measuring personnel, heat preservation personnel and boiler operators) to carry out winter construction, and ask them to be able to foresee and deal with all kinds of professional and technical problems that may occur in the operation, and ask management personnel to be familiar with the winter construction methods of various operations, and put forward predictive opinions on the next stage of construction during the construction. 1.3 construction points Although the bedrock is shallow and the bearing capacity of the basement is good, there are a few caves in some bedrock, so attention should be paid to the influence of caves on the stability of the bridge foundation during construction. The whole process of bridge foundation insulation and cold protection is carried out to ensure the construction quality in winter. 2 Foundation construction According to geological exploration, the bedrock in the bridge area is limestone of Sinian Nanguanling Formation, dolomite of Ganjingzi Formation and sporadic Yanshanian intrusive diabase, and the buried depth of bedrock is greater than 0-3~0-6m. Quaternary strata are artificial deposits, miscellaneous fill and a small amount of alluvial and diluvial silty clay. Because the bedrock is shallow and the bearing capacity of the basement is good, but there are a few caves in some bedrock, attention should be paid to the influence of caves on the stability of bridge foundation during construction. 2. 1 foundation load The bearing capacity of foundation mainly includes the following loads: 2- 1- 1 self-weight of formwork and support. 2- 1-2 box girder reinforced concrete weight. 2- 1-3 Loads of constructors, construction materials and machines during transportation or stacking. 2- 1-4 load generated by vibrating concrete. 2- 1-5 Impact load generated when pouring concrete. 2.2 foundation treatment all the above loads will be transferred to the ground through the support, so the compactness of the foundation will directly affect the overall settlement value. It turns out that the soil on the surface is loam, which is characterized by greatly reduced water intensity. In order to avoid this phenomenon, the foundation must be treated as follows: 2-2- 1 Remove humus soil from the original ground, and compact it before filling. Then layered (each layer is 30cm) filled with permeable materials such as stone slag and concrete slag. The rolling equipment is a C25 or above roller, and the rolling times are controlled by the stone bearing layer, and the vibration rolling is not less than 6~8 times until there is rutting on the surface. The bearing capacity of foundation in soil area is not less than 500KPa by laboratory penetrometer, and the compaction degree by sand filling method should be greater than 95%. The bearing stratum shall be within 70cm below the design elevation of supporting foundation, and the compactness of backfilled weathered rock or mountain skin soil shall be controlled above 95%, and the flatness shall be within 1-5cm. After passing the laboratory test and submitting the test report to the person in charge of the construction site for approval, the next process-sleeper laying under the bowl-type bracket and bracket support can be carried out. 2-2-2 Foundation treatment within the scope of foundation excavation: due to the limitation of the site, large-scale rolling machinery can not be rolled within the scope of foundation excavation, so layered backfill (30cm thick for each layer) or small-scale roller shall be used for rolling, and the density shall be above 9 1%, and large-scale roller shall be used for rolling within 70cm of the bearing layer. The specific standards are the same as above. Set 2-2-3 drainage ditches around the bearing stratum to lead water out of the bearing stratum to prevent rainwater from soaking the supporting foundation. There should be no water around the support to prevent water from soaking the bearing layer and reduce the bearing capacity. 3. Concrete construction 3. 1 Concrete is made of 325 ordinary portland cement with early strength, quick setting and frost resistance. The aggregate is medium coarse sand and 4cm gravel. Aggregate is clean, free of ice, organic matter and other sundries. Cover the two materials for heat preservation in advance, and keep the temperature of aggregate and cement above 0℃. The mixed water is purified water under ice, heated and kept at about 60℃, and additives are added according to the standard. Concrete mix design is the key to concrete quality. See table 1 for the mix proportion of foundation concrete of this project. 3.2 Concrete mixing adopts the method of heating and mixing water to improve the outlet temperature of concrete, and the mixing water temperature should be strictly controlled. For ordinary cement and slag cement with label less than 52-5, the maximum mixing water temperature is 80℃, and for portland cement and ordinary cement with label equal to or greater than 52-5, the maximum mixing water temperature should not exceed 60℃. Ensure that the ex-factory temperature of concrete is not lower than 10℃. 3-2- 1 Heat water in the following ways: ① Heat water with boiler steam. (2) Heat the water with an electric heating rod. (3) Set a water tank and heat it with coal and wood under the water tank. 3-2-2 Concrete mixing time is 50% longer than normal temperature. 3.3 Concrete Transportation 3-3- 1 1t Dump trucks use straw curtains and colored strips to cover concrete, so as to ensure that the concrete pouring temperature is not lower than 5℃. 3-3-2 The concrete mixer should be insulated by heat preservation quilt to ensure that the concrete pouring temperature is not lower than 5℃. 3.4 Concrete pouring 3-4- 1 Concrete pouring shall be arranged as far as possible when the temperature is high during the day. 3-4-2 When pouring concrete on hardened concrete, heating measures should be taken to ensure that the temperature of the joint surface is above 5℃. The following heating measures are adopted: ① steam heating; (2) iodine tungsten lamp irradiation; (3) heating with an electric heating rod. 3.5 concrete curing by heat storage method. For concrete mixed with ordinary cement, its critical frost resistance strength is 40%; The critical frost resistance of concrete mixed with slag cement is 50%. 3-5- 1 After concrete pouring, the top is covered with plastic film and covered with grass curtain, and the outside of the formwork is covered with grass curtain, which is fixed on the formwork with iron wire. 3-5-2 According to the test of curing specimens under the same conditions as the structure, curing can only be stopped when the concrete strength reaches the critical frost resistance strength. Conclusion In the winter construction of bridge foundation, strict foundation treatment and concrete construction quality control are carried out, and the task is completed on time with good quality and quantity, which is well received by the owners and supervisors and saves a lot of money. Through concrete construction control, master the methods of bridge foundation construction and temperature control in winter. Effective measures such as heating water temperature at different temperatures, material insulation and transportation insulation are taken to ensure grouting quality and speed up the project progress. Strive to keep the curing temperature stable and tight, and ensure the concrete strength meets the design requirements.

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