In recent years, with the rapid pace of urban development and old city reconstruction, the resulting number of construction waste is also increasing. Construction waste mainly comes from urban village reconstruction projects, municipal projects and real estate projects. The repeated generation, dumping and removal of construction waste have formed a vicious circle, which not only consumes a lot of construction funds, but also pollutes the environment and occupies land, which will have a great social impact. If these construction waste can be reasonably utilized, it will produce huge economic and social benefits. Therefore, the reuse of construction waste is imminent and has a broad application prospect.

First of all, the impact roller is used for the paving and compacting of construction waste, which can not only make full use of waste resources and is conducive to environmental protection, but also reduce the costs of large-scale removal from the existing pavement surface (removal and transportation of ground construction materials) and construction, and promote the reconstruction progress. It has been proved that the yield is up to 60% of the cost savings and time compared with the traditional method, Therefore, it represents a new technological development direction for the upgrading and transformation of construction waste.

A large amount of construction waste produced by urban construction on the other hand, construction waste has excellent characteristics such as high strength, high hardness, strong impact toughness, high wear resistance, good water resistance, etc. at the same time, it has good physical and chemical stability, and its performance has exceeded that of clay, silty soil, sandy soil and lime soil. Because construction waste has good water permeability characteristics, such as no frost rise and shrinkage when encountering water, large particles, less film water, small specific surface area, and no plasticity, and construction waste also has excellent characteristics of good quality, large quantity, and low cost compared with other construction materials, it is wise to use it as subgrade construction materials with high strength and water stability in the construction of roads, squares, and urban roads.

As for the requirements of subgrade backfill material, the code for design of building foundation states in the terms of soft foundation treatment that "if the homogeneity and compactness of construction waste or stable industrial waste are good, it can be used as a bearing layer." that is to say, construction waste can be used as backfill material under certain conditions, which depends on whether the difference in building shape determines whether it is easy to compact, The second is to see how to compact after backfilling and whether the compactness can meet the engineering requirements.

The potential of the impact roller in the field of compaction has been recognized by many parties. Next, I will take the construction project of Xi'an East Third Ring Road as an example to discuss the performance of the impact roller in the compaction operation after construction waste filling.

With a total length of 71.4km, the main line of Xi'an Third Ring Road system project is a key project in Xi'an during the Tenth Five Year Plan period, and also an urban road project with the largest investment scale and the highest design grade in Xi'an so far. The total length of the East Third Ring Road is 14.7km, and the main line is designed as a two-way eight lane road. According to the urban expressway standard, the design load is 100kN, and the width of the standard road section is 100m. In the road design, there are four ponds at stake k7+998~k8+046, k8+124~k8+231, k8+239~k8+309, k8+650~k9+094, which are respectively about 4.5m deep, about 5.3m deep, about 5.5m deep, and about 5.2m deep. It is necessary to remove the sludge and backfill the road subgrade materials, To meet the requirements of subgrade strength and pavement settlement.

Due to the construction of the Third Ring Road in the middle section of the East Third Ring Road of the project, centralized demolition was carried out in the early stage. After the demolition, a large amount of construction waste was left in the k9+550~k10+250 section. The average thickness of construction waste on the surface is about 4.0m. According to the design requirements of the construction drawings, the project needs to be disposed of. On the one hand, the treatment of construction waste needs to consume a lot of construction funds such as land acquisition and garbage removal and transportation. On the other hand, the problems such as scattering, dust and flying ash in the process of removal, transportation and stacking aggravate environmental pollution and cause great pressure on the environmental governance of the city. Based on the principle of "resource utilization, energy conservation and emission reduction", after expert argumentation, It is decided to adopt the subgrade construction method of impact compaction and layered rolling, and backfill the subgrade of pits and ponds with construction waste.

Main construction processes of roughly flattening construction waste impact rolling:

1. Roll fill: after lowering the excessively deep water level in the pit and pond, transport the construction waste to the area to be backfilled, roll the construction waste along the edge of the pond with a backhoe into the sludge of the pond, so that the sludge is extruded by the construction waste, and part of the sludge is filled in the gap of the construction waste. After impact rolling, it plays a role in filling the construction waste, making the strength and stability of the treated foundation better. 2. Roughly flattening: the construction waste is paved in a backward manner, that is, the compacted upper subgrade surface is backfilled and unloaded by the material truck, and the dense fill pile formed is leveled by the bulldozer, and the higher pile is treated by manual leveling, so that the thickness of the loose layer reaches the required 25cm;

3. Surcharge preloading: pile soil on it as a load to preload the backfilled construction waste, so as to compact, settle and consolidate the subgrade soil, so as to improve the subgrade strength and reduce the settlement after the completion of the road construction. Construction waste and soil are mixed, with poor grading, and the proportion of coarse and fine aggregates is unstable. It can be effectively used in subgrade backfill engineering by adjusting its mixing proportion with benign soil.

Impact compaction of construction waste 4. Impact compaction: after the completion of surcharge preloading, the backfilled construction waste shall be impact compacted to further improve the compactness and stability of the subgrade. Before impact compaction, it shall be leveled, and the height difference shall not exceed 200mm.

5. Geocell: after the impact rolling, fill lime soil above it and add a layer of geocell to increase the overall stability of the subgrade, improve the dynamic load bearing capacity of the general subgrade and enhance the subgrade protection capacity.

Construction waste impact rolling construction scheme:

1. After the pit and pond are properly drained, the construction waste shall be rolled and filled according to the requirements of the specification. The particles exceeding 1m shall be broken, and the bottom shall be backfilled with the construction waste hard material to squeeze the silt and pave the bottom, and then be properly compacted;

2. Roll and fill 1.5m of construction waste, properly level and compact, stack pre compacted soil for pre loading and pre compaction, until there is no obvious settlement, remove the pre compacted soil, and impact and roll the backfilled construction waste.

3. The impact roller with impact energy above 30kj shall be used for impact rolling, and the average settlement of the last two times shall not be greater than 5mm;

Impact rolling effect 4. Repeat the above procedures until the pit and pond are flush with the surrounding road surface;

5. Fill the wavy lines, and then use the vibratory roller to compact the loose surface;

6. Lay a layer of geocell, fill it with lime improved soil under it, and add a layer of 15cm thick 5% lime soil on it.

Construction waste is the solid waste generated in the process of building construction, reconstruction, expansion or demolition. According to the different sources of construction waste, it can be divided into construction waste and demolition waste. As the name implies, construction waste is the solid waste generated in new construction, reconstruction or expansion projects, and demolition construction waste is the construction waste generated in the demolition of buildings.

Construction waste has a widespread corrosive effect on our living environment. If the attitude of ignoring construction waste for a long time is implemented, it will have a bad impact on urban environmental sanitation, living conditions and land quality assessment. First of all, after a large amount of land is stacked with construction waste, the quality of soil will be reduced and the production capacity of soil will be reduced; Construction waste is stacked in the air, affecting air quality, and some dust particles will be suspended in the air, which is harmful to human health; During the stacking process of construction waste, the long-term accumulation is that the harmful substances of construction waste infiltrate into the underground waters and pollute the water environment; If the construction waste is stacked in the city, it will be detrimental to the urban environment and aesthetics; There may be some potential safety hazards in the stacking of construction waste, and some accidents may occur at any time.

Impact compaction effect the crushing and stabilizing technology of the impact roller reduces the working area of the plate by cracking and crushing the construction waste, and fully releases the internal stress. The crushed construction waste is compacted to form an embedded structure to solve the stress concentration and reduce the occurrence of reflection cracks. It has irreplaceable advantages in terms of environmental protection, performance and cost saving.

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