Internship report for college students on highway construction sites

Many students in our class did not return home this summer, but stayed at the school, participated in social practice, and exercised their abilities! Especially in the past few days, the classmates left by our class collectively came to the on-site construction site of the expressway construction site, which made us open our eyes and have a lot of insights. As time went on, the situation of our team's construction site gradually became more familiar. After we finished the internship, we could not calm down for a long time!

First, the purpose of the internship:

Through the on-the-spot understanding of Xiqiao Expressway and Yongxian Expressway, we have designed and arranged the roadbed treatment, asphalt pavement construction, road design, highway bridge design and construction, and other highway related facilities. With a comprehensive perceptual knowledge, we have deepened our understanding of the knowledge of the courses we have learned and combined learning and practice.

Second, internship time:

July 27-August 1st, 2019

Third, the internship location:

Part of the construction site of Xiqiao Expressway and Yongxian Expressway

The Xi'an-Lianshui Expressway starts from the Qujiang Interchange in the southern section of the Xi'an Ring Expressway and ends at Jiuli Bay in Lianshui County. The total length of the route is 64.714 kilometers.

Yongshou-Xianyang Highway is an important section of the state-designed western channel Yinchuan-Wuhan Expressway in Shaanxi Province. It is also an important part of the main skeleton of Shaanxi highway. It is one of the 12 typical road survey and design projects in China. The project is an extension to the east of Fengxiang Road to Yongshou Expressway under construction. The completed Xi'an-Xianyang Expressway extends westward through Xi'an Xianyang International Airport.

Fourth, the internship content:

Subgrade part

The subgrade's internship mainly includes foundation treatment, embankment, bridge and culvert in some construction sites of Yongning Expressway.

1. Subgrade treatment:

The road section is located in the collapsible loess area, and the treatment method is to replace the fill method. It is to dig all the excess soil in the above 80 cm road bed, and then layer back and fill the 50 cm plain soil with sand. However, the bad thing about this situation is that after the sand encounters the water, the water will seep into the loess on the roadbed, destroying its stability. So the original design was changed, that is, the original 80 cm of soil was dug, first the whole section was crushed, after crushing, backfilled with 40cm of plain soil, then 40cm of 5% lime soil, and then designed blind ditch on both sides. .

There are two treatment methods for collapsible loess: one is impact crushing, and the other is strong tamping. After comparing the functions of the two, the road sections are all powerfully processed. The processing method is: first clearing the table; then, according to the design requirements, the grid line is used to carry out the earthwork design; finally, the mechanical compaction function is determined.

In addition, the handling of the structure. Since the collapsible loess has a great influence on the structure, the treatment method is to excavate the foundation pit first, and then use a large-ton-class machine to carry out the strong smashing to ensure the safety of the structure.

For the treatment of the embankment, the compaction method is used. The mechanism is: the soil is a three-phase body, the soil particles are the skeleton, and the pores between the particles are occupied by moisture and gas. The purpose of compaction is to recombine the soil particles, squeeze each other, reduce the pores, and increase the unit weight of the soil to form a dense whole, which ultimately leads to an increase in strength and an increase in stability.

The method is to carry out the rolling on the original ground, and measure the compactness by the ring knife method; then carry out layered filling and rolling, and measure the compactness by sand filling method. Compaction means: under the conditions that the machine type, soil thickness and stroke number have been selected, the compaction operation should be light and heavy, first slow and fast, first edge and middle. In real time, the adjacent two wheel tracks should overlap one third of the wheel width to maintain uniform compaction without leakage. For corners that cannot be pressed, it should be supplemented by human or small machine tools. During the whole process of compaction, the water content and compactness are often checked to meet the requirements of the specified compaction.

The process of earthwork construction is: rough flat - lofting - ash line - flat - measure compaction.

The roller compactor is compacted with sheep's foot.

2. Bridge culvert:

Due to the high level of highways, the entire line is closed, interchanges, and cross-river valleys, so there are many bridges. Our internships mainly include the Xianyang Airport Viaduct and the Shuangxinggou Bridge.

The 980-meter full length of the Xianyang Airport viaduct is made of prestressed composite box girder and cast-in-place girder. The single girder span is 25 meters. The tensioning process is used to arrange the prestressed steel corner line in the beam to reduce the deformation and increase the bearing capacity.

The Shuangxinggou Bridge is a 2×85 m t-shaped steel bridge. The upper part of the process uses a hanging basket cantilever casting method. Now the two bridge piers are about 38 meters, the design height is 51.5 meters, and the pile foundation below is 75 meters deep. The pier body is made of box-shaped thin-walled piers, and the upper part is 3 m, which is a closed section. The two piers are rigidly connected together to increase the overall effect. It is a large-volume concrete pouring, and has a heat dissipation design in the pouring.

Pavement part

The internships on the pavement are mainly concentrated on the construction site of the Xiqiao Expressway. This highway uses the construction technology of the hot mix asphalt mixture pavement. The pavement is composed of a surface layer, a base layer and a base layer. The top layer is 5 cm in the upper layer, 7 cm in the middle layer, and 10 cm in the lower layer. The materials include modified asphalt, coarse aggregate and the like. The base layer is a two-ash stabilized macadam; the base layer is a two-ash stabilized soil.

Hot mix asphalt mix is ​​suitable for asphalt finishes on all grades of roads. The upper, middle and lower layers of the asphalt surface layer of expressways, primary roads and urban expressways and trunk roads shall be paved with asphalt concrete mix. The type of hot mix asphalt mixture material should be reasonably selected according to specific conditions and technical specifications. Should meet the requirements of durability, anti-rutting, anti-cracking, water damage resistance, anti-sliding performance, etc., but also need to consider the actual situation of construction machinery, engineering cost.

The asphalt pavement of the plant mixing method includes asphalt concrete and asphalt gravel. The construction process can be divided into two stages: mixing and transportation of asphalt mixture and paving on site.

1. Mixing and transportation of asphalt mixture

There are two types of stationary mixing equipment for mixing the mixture in the factory, both batch and continuous. The former measures the weight of various materials of the mixture during each mixing, while the latter is continuously fed into the mixer after metering various materials. The mixing station uses a 3000 batch mixer.

Before mixing the asphalt mixture, the test mixture should be tested according to the determined mixing ratio. The various minerals and asphalt used should be strictly measured during the trial mixing. Determine the heat of each plate by trial mixing and sampling test

Second, the mixing ratio of the mixture and its total weight, or the opening of the feed opening of various mineral materials and the speed of the feed of the asphalt and mineral materials, the preparation and stakeout of the base layer

Before the surface layer is paved, the base layer and the roadbed should be inspected to ensure that the base layer and the surface layer of the road are well bonded and the water is immersed in the base layer.

In order to control the paving thickness of the mixture, the measurement stakeout is performed after the base layer is prepared, and the sample pile is set along the centerline of the pavement and the width of the quarter road to mark the looseness of the mixture. When paving with an automatic leveling paver, the control baseline that guides the running direction of the paver and the elevation should also be released. The test section shall be paved before the construction of the expressway and the primary road. The length of the test section shall be determined according to the purpose of the test and shall be 100 to 200 m. The test section should be laid on a straight section. If paved on other roads, the conditions of the pavement structure should be the same, and the test of each structural layer of the pavement can be arranged on different test sections.

Paving

Asphalt mixes can be paved manually or mechanically, and high-grade road asphalt pavements should be mechanically paved.

Asphalt mix pavers are available in both crawler and tire versions. The construction and technical performance of the two are roughly the same. The main components of the asphalt paver are the hopper, chain conveyor, spiral spreader, vibrating plate, spread plate, exercise part and engine.

Rolling

After the asphalt mixture has been paved flat, it should be rolled in time. The temperature of the rolling should meet the specified requirements. The compacted asphalt mixture should meet the requirements of compaction and flatness. The thickness of the asphalt mixture should not exceed 10cm.

The asphalt mixture rolling process is divided into three stages: initial pressure, double pressure and final pressure. The initial pressure is first rolled twice with a 60-80kn two-wheel roller at a speed of 1.5 to 2.0 km/h to make the mixture initially stable. Then use a 100 ~ 120kn three-wheel roller or tire roller to repress 4 to 6 times. Rolling speed: 3 km/h for three-wheel roller and 5 km/h for tire roller. During the re-pressing phase, it is compacted until it is stable without significant wheeling. Recompression is the most important stage of the rolling process. Whether the mixture can reach the specified compactness is the key to the rolling in this stage. The final pressure is crushed by a 60-80kn two-wheel roller at a rolling speed of 3 km/h after recompression for 2 to 4 times to eliminate the wheel tracks generated during the rolling process and to ensure the smoothness of the road surface.

When roller compaction, the direction of the roller should be parallel to the centerline of the road, and the edge of one side of the road should be pressed into the road. When rolling with a three-wheel roller, each time should overlap 1/2 of the width of the rear wheel; the two-wheel roller overlaps 30cm each time; the tire roller should also be overlapped and crushed. Since the tire roller can adjust the internal pressure of the tire, the required contact pressure can be obtained.

Third, the aggregates are inseparated into each other, easy to obtain uniform compactness, and the density can be increased by 2 to 3%. Therefore, the tire roller is most suitable for rolling in the recompression stage.

3. Seam construction

Various construction joints of asphalt pavements are often due to insufficient compaction, which are prone to problems such as steps, cracks, looseness, etc., affecting the flatness and durability of the pavement, and must be paid attention to during construction. The half-section mechanical construction used in this section is divided into sections in the middle. In the construction, there are two machines in synchronous paving, and the longitudinal joints between the machines should be treated with care.

4. Drainage facilities

The whole road surface is an arch type, so the general road surface adopts the slope to face the two sides and flows into the side ditch on both sides of the road; in the section of the road curve, the outer side of the road is super high, using single-sided drainage, and the central separation belt is set. There is a rainwater pipe to collect rainwater from the road outside the curve, and then a horizontal drain pipe laid under the roadbed flows into the side ditch.

V. Internship summary

Through this road internship in the field, we have a more comprehensive understanding of the design and construction of the highway's subgrade and pavement, and further understand the knowledge in the classroom, so that the theory can be used in actual production. In recent years, China's highway industry, especially highways, has developed rapidly and its demand is increasing. This is both an opportunity and a challenge for workers engaged in roads. As students who are going out of school, they should master more professional knowledge and strengthen their practical and design skills in a limited time. This will be more conducive to future development and enable them to make a difference in this field.

This internship has enabled us to see the rapid development of the country. This is what we have been constantly asking for. I really want to say that this internship, I have learned a lot, but as time goes by, the project will sooner or later. At the end, the new project will start again. I will continue to work hard. I will insist on the internship and find the direction of life in the internship. I will!