Paper Keywords Highway Subgrade Pavement Construction Measures

This paper analyzes the problems existing in the construction of highway subgrade and pavement, and puts forward a series of related countermeasures.

In recent years, China's highway engineering has developed vigorously, but there are many common problems in subgrade and pavement construction, which are extremely harmful and stubborn. Therefore, it is an important task for the traffic construction department to strengthen research and put forward corresponding countermeasures for related problems. This paper summarizes my experience in highway construction in recent years and puts forward my own opinions.

1. Analysis of subgrade disease factors

1. 1.

(1) Diseases caused by uncoordinated elastic modulus of subgrade structural layer materials. (2) The route passes through the collapsible loess area, and the foundation treatment is improper and the surface facilities are not perfect, resulting in local water accumulation. (3) There is a flowing soft cushion under the original ground of the embankment. (4) The design of the buried depth of subgrade retaining wall is vague, which leads to subgrade diseases.

1.2 architecture

First of all, the subgrade was not treated before filling. Secondly, subgrade filler should choose soil with appropriate water content, which is easy to compact. If colored and silty soil or clay with excessive water content is not easy to compact, it will also lead to pavement diseases. The speed of filling soil is too fast, and the importance of controlling the critical height of subgrade filling soil is not well understood. When approaching the boundary height of subgrade fill, the observation of subgrade settlement is not strengthened, which leads to the strength of soft soil foundation approaching critical state, and the bearing capacity of subgrade is insufficient, which leads to instability, disease or longitudinal cracks of basement.

1.3 geological data

Poor geological and hydrological conditions will lead to unstable foundation. When the highway passes through areas with poor medical conditions and serious natural disasters, it may lead to large-scale destruction of subgrade. Practice shows that the instability of subgrade slope is largely caused by the damage of retaining wall, and the main reason is the lack of geological data along the road, which leads to the serious damage to subgrade stability.

2. Treatment of foundation diseases

There is no geological data along the line, so we can only rely on experience and judgment to determine the proportional distribution of earthwork in a certain pile number, and subjective misjudgment will lead to design errors. Therefore, due to the fuzzy design of retaining wall buried depth, it will bury the hidden danger of instability for subgrade. In order to ensure the stability of subgrade, it is first required to increase the geological data along the line.

2. 1 Improve construction management

In construction management, technical management is the key. Technical management of subgrade diseases (1) There are two common aspects in the technical treatment of high fill embankment and cutting. (2) Soft soil subgrade treatment, appropriate technical measures must be taken in soft soil subgrade treatment and subgrade engineering construction.

2.2 Several common subgrade diseases treatment methods

The quality of subgrade construction is the key to the whole route project, and it is also the key to whether the subgrade and pavement project can stand the test of time, vehicle driving load, rainy season and winter. To do a good job in subgrade engineering, subgrade filling must be carried out in a down-to-earth manner, especially the treatment of the original ground and slope foundation.

2.3 road filling filler

Generally, gravel and soil whose plasticity index and water content meet the requirements of the specification should be used as embankment filler, and silt, swamp soil, frozen soil, organic soil, soil containing turf, domestic garbage and humus should not be used. Generally, soil with liquid limit greater than 50 and plasticity index greater than 26 should not be used as subgrade filler.

2.4 Compaction of Fill Subgrade

Subgrade construction should be carried out in strict accordance with the requirements of the current Technical Specification for Highway Subgrade Construction. The optimum water content, suitable loose laying thickness and corresponding rolling times of different fillers with different mechanical compaction are determined through test sections, and the construction team with certain quality will provide the best mechanical support and construction organization.

2.5 Special foundation treatment

Soft soil foundation is extremely destructive, but in a broad sense, as long as the external load on the soil foundation may cause harmful problems such as excessive deformation and insufficient strength, we should take it seriously as a soft soil foundation and carry out necessary treatment. Generally, it can be divided into ground bitter treatment and embankment treatment according to the treatment position.

2.6 Improve drainage facilities

In order to keep the roadbed dry, solid and stable, it is necessary to intercept the surface water that affects the stability of the roadbed and exclude it from the roadbed to prevent infiltration, accumulation and infiltration. At the same time, the groundwater that affects the stability of subgrade is intercepted and drained, so as to reduce the water level and guide it out of the scope of subgrade, so that ditches, pipes and bridges along the line form a complete drainage system.

2.7 Preventive measures

In addition, the prevention measures of subgrade diseases are also a treatment method for early treatment. Preventive measures taken before subgrade filling are also important preventive measures for maintaining subgrade diseases. Before subgrade filling, the basement should be thoroughly cleaned, weeds and roots should be dug out, and the organic soil, planting soil and garbage soil on the surface of the basement should be removed. Cultivated land and soft soil foundation should be compacted to achieve the required compactness of roads of all grades and ensure the safe use of subgrade.

This road is not smooth.

The main reason for the unevenness of the road surface is that the smoothness of the grass-roots level is not strictly controlled, and even wave-like ups and downs occur. Poor pavement construction control, low level of paver and roller operators, and out of control of reference line or slipper. Judging from the current situation of pavement construction, sliding shoes have basically replaced the baseline, but they still have their limitations. Therefore, the elevation and smoothness should be strictly controlled step by step from the subgrade during construction. On the basis of ensuring the degree of compaction, the microstructure and appearance smoothness of pavement surface are reasonably controlled.

4. Bridge expansion joints and bump at the bridge head

Due to the difference between abutment settlement and abutment settlement, and the poor expansion joints, bridge end transition slab formed steps at the abutment, which affected the comfort and safety of driving and had a great impact on the bridge. During the construction, it should be noted that the backfill material with good water permeability and compaction performance (1) should be selected for the abutment back, so as to achieve the best compaction degree and reduce the settlement of embankment fill. (2) For the pile-column abutment, fill the soil first, and then build the pile-column abutment after the fill is completely settled, so as to reduce the settlement difference between the structure and the fill. (3) Choose expansion joints with good performance and carefully construct them to ensure the smoothness and integrity of bridge deck expansion joints. (4) Take effective measures to minimize the cracks in the grille pavement. (5) Do a good job in bridge end transition slab or adopt new technologies such as geogrids for transition.

5. Early damage of asphalt pavement

The main reason for the early damage is that pavement engineering unilaterally pursues smoothness and ignores compactness, requiring materials to arrive at the site with low final pressure temperature. Even at low temperature, the mixture ratio of materials is improper, the asphalt at the base is unqualified, the bearing capacity of pavement base and even subgrade is poor, and the deflection value is too large. In addition, the reflective cracks of asphalt pavement caused by the shrinkage of pavement base materials will also cause early damage, and the preventive measures are (1). Don't pursue individual indicators unilaterally. (2) When paving and rolling asphalt mixture, the paving quality of asphalt mixture on site should be strictly controlled, and the paving and initial pressure should be strictly controlled. The final pressure temperature of asphalt mixture shall be carried out in strict accordance with the rolling operation procedures to prevent the occurrence of transverse cracks. (3) Make vertical and horizontal joints in strict accordance with Code for Construction and Acceptance of Asphalt Pavement. (4) Control the ductility of asphalt used in asphalt mixture, or use modified asphalt to prevent overheating and avoid asphalt mixture when mixing asphalt mixture? Burned? . (5) The new asphalt mixture should be used in particularly humid, cold and high temperature areas.

6. High fill settlement

The main causes of subsidence are: on the one hand, construction factors, such as poor compaction control, thick stratification, improper construction measures in winter, etc. On the other hand, it lies in material factors, such as incorrect maximum dry bulk density and optimum water content, too large material compression coefficient, and the use of open soil with high plasticity index. According to the road contour line, take corresponding measures (1) to control the fill elevation in layers. According to the thickness of subgrade filler of test road, the deposition amount of filler in scale construction is controlled. (2) At the junction of new and old fill, strictly control the minimum step length of planting fill in summer to avoid excessive planting and insufficient compaction in summer. (3) Prevent partial ramming or insufficient ramming, and it is forbidden to overstock the stuffing. (4) Where it is difficult for machinery to compact, supplement compaction with appropriate small machines and tools. (5) During construction in winter, the soil shall be backfilled and compacted, and shall not be frozen, so as to avoid serious uneven compaction density of the filled soil and soil subsidence. (6) When backfilling several kinds of soil, the density standard obtained from the compaction test of one kind of soil should not be used as the compaction standard of all fill soil, but several groups of compaction tests of corresponding soil should be done according to different types of fill soil, and the values should comply with the corresponding regulations.