Causes and treatment of road frost boiling

Qi city is located in the plain, with high groundwater level and poor drainage. In particular, the multi-section silty soil on the surface and the multi-section cohesive soil with poor water permeability in the lower layer have long annual freezing time, and the initial freezing changes alternately with cold and warm, which promotes water accumulation under the action of negative temperature, and the change process of frost boiling sections in the same season is different.

Autumn is the period of subgrade moisture accumulation. With the increase of rainfall in autumn, the ground moisture seeps down and the groundwater level rises, which makes the subgrade moisture increase and even reach the state of supersaturation, which is the prerequisite for frost boiling.

When the temperature drops in winter, the upper soil of subgrade begins to freeze, while the lower soil of subgrade is still in a high temperature state, and water moves from high temperature to low temperature in the soil. The moisture in the upper soil of subgrade increases with the decrease of temperature and freezes into ice. Frost heave or heave occurs on the pavement. The temperature rises gradually in spring, and the upper soil of subgrade melts first, but the lower soil has not been thawed, which makes the strength of soil foundation decrease rapidly or even lose its bearing capacity, and the phenomenon of frost boiling appears under the action of driving. Qishi Culture Street is located in the northwest of the city, with relatively low terrain. Before the reconstruction, the subgrade was soaked in water all the year round, and the excessive water content of the soil foundation often caused the phenomenon of boiling in Wenhua Street.

2. Factors affecting road surface boiling The main factors affecting road surface boiling are:

(1) soil quality. Silty soil boils easily. The capillary water of this kind of soil rises quickly, and under the action of negative temperature, the water flow is serious, the strength of the soil drops quickly and loses stability. Although the capillary water of cohesive soil rises very high, it is very slow, and only when there is enough water can it form frost boiling. Generally speaking, the lower part of sand will not be boiled. When the boiling phenomenon of Wenhua Road was rectified, the form of changing soil was adopted.

(2) temperature. A certain freezing depth and cooling capacity are important conditions for boiling formation. Under the condition of the same cold junction depth and refrigeration capacity, the negative temperature characteristics and thawing speed in winter have great influence on the formation of frost boiling. The initial setting temperature in our city is warmer and appears alternately. The temperature stays between 0 ~ 5℃ for a long time, and the freezing line stays in a shallow place under the road for a long time. A large amount of water gathers and flows near the road surface, which is easy to boil. On the other hand, if the weather is very cold in early winter, the freezing point will soon drop from the road surface to a deeper place, and there is less ice accumulation on the upper part of the soil foundation, which is not easy to frost. In addition, the changing characteristics of spring water temperature and thawing speed also have an influence on boiling. If the spring thaws quickly, the weather is warm and the soil base melts quickly, the boiling degree will be aggravated.

(3) moisture. The process of boiling is the process of water transfer and change in soil foundation. The surface water and shallow groundwater near the low-lying subgrade in Qi city can provide sufficient water sources. This is an important condition for the formation of boiling in this area. In addition, too much autumn rain, the increase of soil alkali content and the rise of groundwater level will all lead to boiling.

(4) Pavement structure. The phenomenon of boiling is closely related to the pavement structure. Pavement structure has certain influence on frost boiling. If black pavement is laid on the wet ground. Because of the poor air permeability of pavement structure, the moisture in subgrade can't evaporate from the surface smoothly, which reduces the strength of subgrade and causes serious frost boiling under the action of traffic load.

(5) Driving load. The action of traffic load exposes the phenomenon of road boiling. Other things being equal, the greater the traffic volume in the boiling season and the boiling section, the heavier the vehicle and the more boiling.