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New Construction Technique of Highway Bridge
1、Brief introduction and awards of highway bridge construction of No.4 Engineering Company Ltd.
With rapid development of national highway traffic construction, the company successfully forge ahead in the field of broad road bridge construction with strength in technical equipment. Mengwenyan expressway and Guiyang-Weng'an expressway undertaken by the company obtain good reputation in Yunnan and Guizhou, which highlights the company's advantages in road, bridge and tunnel. The company left its footprints in Jiangsu, Shanghai, Zhejiang, Henan, Inner Mongolia, Yunnan, Tianjin, Shandong, Hebei, Liaoning, Guizhou, Guangzhou and other provinces and autonomous regions over the past few decades. The cumulative construction road mileage is 1370km (including the foreign road project of 650km), and the length of the large and medium bridges is 156km. The total amount of the road and bridge project under construction has exceeded 5 billion yuan at present. The company creates repeated miracles in the construction speed in the field of construction. Moreover, the company also continuously sets new records in the aspect of quality management, becoming the flagship in the field of road bridge construction.
Main rewarded projects include：
The eighth contract section project of Zhejiang Nanjing-Hangzhou expressway (Zhejiang Section) Phase II won 2014 national quality project silver award. Quality Control of the Prefabricated Box Girder assumed in the project wins 2005 Tianjin excellent QC achievement award.
Zhejiang Nanjing-Hangzhou expressway (Zhejiang Section) Phase II
Lot XQh of light rail transit from Tianjin downtown to Binhai New Area won 2007 national quality project silver award.
 Light rapid rail transit project from Tianjin downtown to Binhai New Area
The project management achievements of Nanjiang double-line highway bridge project at Tianjin Port won the first prize in 2007 excellent project management achievements of national construction project, and won the golden prize in Tianjin 2007 Haihe River Cup.
Haibin Expressway
Phase II of north section of Haibin Expressway project won the second prize in 2010 Tianjin excellent project management achievements.
 Phase II of north section of Haibin Expressway
Tianjin Highway project won 2012 national quality project silver award, and won 2012 national municipal gold cup demonstration project.
 Tianjin Highway Project
Guiyang-Weng'an expressway project won the second prize in 2015 excellent project management achievements of national construction project
 Guiyang-Weng'an expressway project
2、Scientific and technological achievements of bridge construction of No.4 Engineering Company Ltd.
1）Application of hydraulic climbing formwork of constant-cross-section hollow high pier of highway bridge
The heights of the hollow high piers of Xiaodongshan Bridge of Mengwenyan expressway in Yunnan are respectively: 63.0m, 81.7m, 87.0m and 92.0m. Construction of the high pier is the key to control project construction safety, progress, quality and cost. The traditional climbing formwork and mold rolling process cannot satisfy continuous progress in technical level and people's requirements for concrete appearance quality, durability and construction safety. The hydraulic climbing formwork is adopted for alternative climbing of the template and the mold base guide rail through the hydraulic system. It has the advantages of stable climbing, high safety coefficient, high automation degree, lifting frequency, no template landing, small occupation of construction site, good insulation effects of concrete during winter construction, available template and so on, and is applicable for construction of various high piers.
2）Application of space model analysis stress 3D3S software
Nanjiang double-line highway bridge is mainly located in Haihe River tidal flat and new hydraulic fill sludge area. The thickness of the soft soil layer is 6 to 7m, and it has the features of large span, high load and so on. If the conventional foundation replacement or reinforcement treatment is adopted and then the bracket is erected for construction of the cast-in-place box girder, plenty of construction input and long construction cycle are required, and foundation settlement cannot be controlled. Through comparison and selection, the military girder-scaffold mixed system is adopted. For this reason, we introduce 3D3S spatial steel structure system CAD software for 3D space analysis and checking calculation of design of military girder support system.
64 type military girder solve the difficulties in construction of the large-span cast-in-place bridge support system on the soft soil foundation during construction. 64 type military girder has small settlement and deformation during concrete construction, the bridge concrete structure has no bridge concrete crack caused by settlement, and the bridge floor concrete is smooth. The construction cycle of assembly and installation of the military girder is short, and occupation of the construction site is small.
3）Incremental launching construction technique of 78m steel truss girder of north ring railway overpass bridge of Beijing-Tianjin expressway
The main span of north ring railway overpass bridge project of the fifth contract section at the east section of Beijing-Tianjin expressway is 78m steel truss girder. In order to guarantee normal traffic of railway, the construction technique of incremental launching method is adopted. We control technical preparation for incremental launching construction of steel truss girder, erection of the assembly platform of steel truss girder, construction of the temporary pier, fabrication and installation of the slideway and guide beam, determination of the incremental launching device and position, incremental launching process, so as to guarantee first-time success of incremental launching construction of 78m steel truss girder.
4）Suspended casting and hanging basket construction technique at the special load
In order to satisfy demands for bulk cargo collection and distribution port of Nanjiang double-line highway bridge of Tianjin Port, the design load of the bridge is special load. A 75t three-axle vehicle load with spacing of 10m shall be added based on vehicle exceeding 20 and in combination with actual demands of the port. The bridge reinforcement density is large, 2.8 times of the expressway bridge. The main bridge of the project is (48.6m＋3×64m＋48.6m) variable cross section prestressed concrete continuous box girder, and the suspended casting and hanging basket construction technique is adopted.
One of the most important tasks of large-span multi-span continuous beam bridge cantilever construction is deflection control. We timely adjust various construction parameters through strict monitoring during construction, so as to finally guarantee average height difference of 8mm and maximum height difference of 1.8mm at joint section, which satisfies requirements for standard 3cm.
4）Stayed-cable bridge without backstays
The separating interchange project at tourist road of TC-8 contract section of Tangcao Expressway undertaken by the company is a harp-shaped cable-stayed bridge without backstays. The single-tower double-cable plane prestressed concrete stayed-cable bridge is adopted at the upper part, the span length combination of the main bridge is (43+73)m, the group pile composite foundation is adopted for the main tower, and the ribbed abutment and bored pile foundation are adopted for the abutment.
Many new processes and new methods are adopted in the stayed-cable bridge during construction, such as 80m deep pile foundation construction. 2 drilling machines of the rotary drilling rig and spin drilling rig are adopted for alternative pore forming process. The concrete mix ratio with high performance and low hydration heat is selected during construction of 2500m3 massive concrete bearing platform. Multi-layer water-cooling cycle radiating pipes are arranged, and success is obtained in pouring temperature control and no crack on the surface; All-round scaffold and mold rolling concrete pouring process outside the leaning tower; stiff skeleton method construction process in the leaning tower; stress control and adjustment process of the stayed cable. These construction methods and processes have certain significance in future construction of the stayed-cable bridge.
5）Application of steel plate pile envelope structure of deep foundation pit of soft ground in the tide level change area
12＃ pier platform and 13＃ pier platform of main bridge of Nanjiang double-line highway bridge are located in the main watercourse of Haihe River. The water level difference between the highest and the lowest is about 3.50m, and the deepest elevation of the riverbed is about -3.10m. The tidal current is the irregular semidiurnal tidal current, and changes in the tidal current are great, generally between 3m and 4m. We adopt the steel plate pile envelope structure of deep foundation pit of soft ground in the tide level change area for the first time.
Larsen IV steel sheet pile is adopted for the foundation pit support (Q345). After the envelope system is formed, the key is guarantee no much seepage in the foundation pit. The water stop effects of Larsen IV steel sheet pile are relatively ideal. There will be no much water inflow generally as long as the steel sheet pile is straight and engaged closely. In addition, a layer of 8m wide geotextile is wrapped outside the steel cofferdam after cofferdam closure, and a layer of 12m wide waterproof cloth is wrapped on the geotextile for water resistance. The roll edge is adopted at the vertical outsourcing for compaction. The upper end of the geotextile and the waterproof cloth shall be bound with the roof of the steel sheet pile through the lead wire, and the lower end shall be sunk into the sludge with the binding reinforcement. Meanwhile, the surroundings can be compacted with the sand bag to reach relatively ideal water stop effects.
The stress and strain monitoring equipment are installed on the steel sheet pile and the support system respectively during construction, which are mainly responsible for monitoring flexural deformation of the steel sheet pile, stress strain of the support, stability in the soil surrounding the foundation pit, adjacent building and overall stability of the foundation pit. The measured deformation data is controlled within the range allowed in the design.
3、Scientific and technological achievements of road construction of No.4 Engineering Company Ltd.
1）Research on slope stability and protection technique of high fill subgrade of expressway in karst mountain area
Slope stability and protection technique of the high fill subgrade in the karst mountain area are subject to detailed research and analysis, which summarizes features of key technologies in high fill subgrade filling, deformation monitoring and side slope protection, analysis and calculation of high side slope protection in the karst mountain area, as well as environmental during protection. According to the local filler conditions, analyze and summarize situation of the filling test section, select the reasonable subgrade filling method, formulate the strict high fill subgrade deformation monitoring scheme, and arrange the drainage facilities to guarantee subgrade slope stability. It solves the technical problems possible encountered during high fill subgrade filling process in a certain degree and guarantee slope stability, and provides technical preparation for similar high fill subgrade filling and side slope protection or construction in the related fields.
2）Mechanical brushing process of concrete pavement
The concrete surface layer shall be subject to brushing treatment before paving of asphalt concrete surface layer on the concrete pavement or deck. For the traditional manual brushing process, the worker labor intensity is high, and it is very difficult to ensure brushing quality. With increasing promotion of paving construction of concrete pavement slip form, the traditional pavement brushing technique cannot satisfy requirements for project progress and project quality. In such situation, we cooperate with Gaoyuan Company to develop the mechanical brushing machine for concrete pavement. It is successfully applied on Zhangjiakou-Shijiazhuang expressway, and satisfactory effects are obtained.
3）Slip form paving construction of continuously reinforced concrete pavement
The slip form construction technique of the cement concrete pavement has the features of rapid construction speed, high efficiency, pavement intensity, flatness, good durability and so on. Technique of slip form paver is started late in China, and the slip form construction technique is applied and promoted in recent years. The slip form paving construction technique of continuously reinforced concrete pavement is firstly adopted in the pavement work of Zhangjiakou-Shijiazhuang expressway, and good effects are received. It has the following features:
Uniform charge distribution with hydraulic charge distribution plow, jolt ramming with high-frequency vibrating bar, vertical vibration of vibrator to press in coarse aggregate, forming template extrusion forming and smoothing and other procedures are adopted to guarantee density of the cement concrete pavement. Especially, the pavement flatness is obviously improved, which can satisfy high-standard quality requirements for high-grade road, airport flight area and other projects.
All paving construction process is automated, and the electro-hydraulic control system and the sensor are adopted to control steering and lifting. It is integrated with the functions of cement concrete charge distribution, paving, compaction, forming, smoothing and so on, realizing primary forming of cement concrete pavement. The reinforcement dowel bar can be automatically driven in the middle or at both sides of the cement concrete pavement according to design requirements. It can adapt to construction requirements for cement concrete pavement with different widths (2.5 to 10m) and different thickness (maximum thickness can up to 45cm).
Highway construction and development in China propose higher and higher requirements for asphalt material performance. In recent years, various modified asphalt with more superior road performance. Modified asphalt from finished product or direct modification at the mixing site are adopted in various physical and chemical modified asphalt, and there are certain insufficiencies in storage stability, finished product uniformity, construction safety and operability. However, rock asphalt is more and more emphasized in the highway technology industry at home and aboard due to good compatibility with matrix asphalt, lasting aging resistance and operability in construction.
The domestic rock asphalt is also successively applied in the highway (including the expressway) since 2001, and certain effects are achieved. Research in such buton rock asphalt, as a new material, has not been popularized in China, and there are no specific regulations for indicators in the currently effective highway standards of the Ministry of Transport. As per such situation and design features of heavy load and high flow of subgrade cofferdam improvement work of Dongjiang Port Area Line 2 of Tianjin Port, raw material performance and mixture ratio design of buton rock asphalt are subject to systematic research.
4）Test and research of the modified asphalt and mixed material.
The renovation and capping work of Tianjin Airport is conducted in three layers with asphalt concrete, and the total thickness is 18cm. The modified asphalt is adopted for the middle surface layer and the upper surface layer. We research road performance of the modified asphalt relying on the project, conducts technical development of the project, and conducts comparative test of high-temperature stability, segregation and rutting test of modified asphalt and mixture ratio design of modified asphalt SMA. We believe that the subject to be researched in the field is very wide through plenty of experimental researches.
For selection of the modifier, Tianjin has the climate conditions of cold winter and hot summer, and there are high requirements for high- and low-temperature performance of the modifier. However, SBS has good thermal stability and low-temperature cracking resistance, which can increase adherence of asphalt and stone material, and good high- and low-temperature performance and elastic recovery. Therefore, we select SBS modifier as the research object.
SBS is the English abbreviation of block polymer of styrene - butadiene - styrene, and it is divided into three kinds of star, line type and mixed type according to the size and structural form of styrene block. We select four kinds of samples in 3 types for test and research.
Judging from conventional indicators of the modified asphalt through test, the overall modification effects are: star ＞ mixed type ＞ line type; it is obtained that changes in conventional indicators of the modified asphalt are not large after the modifier content reaches 5.5％ through comparative test with different parameters. Water stability, freeze-thaw splitting and scattering test of the modified mixture are far better than the regulatory requirements, which can satisfy requirements for pavement at the special conditions of the airport.
5）Optimization of mixture ratio design of the asphalt mixture
There is the momentum of rapid development in expressway of our county in recent years, and there is also diversified development for the pavement structure with high grade, high performance and high requirements. Hangzhou-Jinhua-Quzhou Expressway is located in the south and at the place with abundant rainwater throughout the year, high traffic flow and high annual average air temperature. The pavement shall not only satisfy vehicle load requirements, but also be provided with the high temperature resistance and anti-seepage performance. Therefore, graduation design of asphalt concrete must be strictly controlled, so as to guarantee that various performance satisfy requirements. Through optimization of the asphalt mixture, we finally satisfy the design requirements.
6）Application of micro-surfacing control of early disease at the asphalt pavement
With rapid development of expressway in China, the time when the early disease appears at the asphalt pavement is mostly 1 to 3 years, even only several months, which seriously influences high efficiency, safety and comfort of travel on the expressway. How to rapidly recover pavement service performance and improve durability has become the main problems to be solved for highway management.
Micro-surfacing technique is applicable for repair of various asphalt concrete pavement, and is completely applicable for maintenance of high-grade pavement. Compared with other pavement construction and maintenance measures, the micro-surfacing technique has the advantages of rapid and convenient construction, greatly shortening traffic time, energy conservation, low cost and so on. Therefore, it has better economic benefits and social benefits. It is widely applied by our company in multiple expressways in the south.