First, the characteristics of soil subgrade subgrade laid on natural foundation, its load is larger, the foundation should have sufficient bearing capacity, in order to maintain the stability of subgrade, also should make some natural factors (such as groundwater, collapse pits, etc.) will not produce harmful deformation of subgrade and pavement. The cause of soft soil roadbed is mainly the content of soil and water. Soil is a three-phase body, soil particles as the skeleton, the pores between the particles for water and gas. So the soil between the particles and compression relative mobility and permeability, the characteristics of soil and the soil particle re combination in the process of compaction, each other tightly, narrow pore, unit weight of soil increased, the formation of dense, ultimately resulting in an increase in strength to improve stability. But in the case of large water content, under the action of load, the soil grain is not easy to form a whole, then it forms the spring soil. The deformation characteristics of the deformation characteristics of two, soft soil subgrade of soft subgrade has three main features: large deformation; compression stability requires a long time; lateral deformation. Large deformation: as long as the soft soil silt or silt soil, its own water content is large, the water is not easy to come out. Compression stability requires a long time: soft soil mainly clay, although the pore is relatively large, but the single pore is fine, hole in the water is difficult to flow, low permeability, saturated soil after loading, water can not be excluded as soon as possible, but slowly deformation, the deformation should be through a few years or even dozens of years. Lateral deformation: larger than normal soil, and the ratio of lateral deformation and vertical deformation is larger than that of general soil. Three, weak subgrade treatment method according to the deformation characteristics of soft soil, and combining with the construction of weekdays, focuses on the treatment of soft soil roadbed of several of the following highlights several applicable scope, construction method and effect. 1, jackstone scope: embankment located on the pond, fish ponds, sand or mud is not easy to drain the water or to desilt silt or deep water or not their place. Approach: in the above direct dumping large size is not easy to be water soaked to soften rocks and stones block diameter between 50 ~ 80 cm, and 20 cm ~ 50 filling is not easy to be water softening small stones in the crevice in the gap, throwing and filling height control in water

More than 50 centimeters, paving after wheeled roller vibration compaction, until the sludge is out of the embankment slope, and no obvious subsidence phenomenon, if filled with deep depth, must be filled with layered compaction, the thickness of each layer is controlled in 50 ~ 80 cm, the whole processing after the shop a 10 cm thick layer of gravel in the above, it is necessary to add a layer of geogrid, then filling earthwork. : because of large diameter cast in stone, the mud road squeezed out most of the substrate, forming a hard skeleton in the subgrade bottom, and in the stone filling between small rocks, by roller vibration compaction, the rocks and stones between the more closely, increase the load to bear the whole. A good effect on the whole in the future under the pressure of embankment. 2, laying blind ditch use: paddy field or mud at a depth of 2 meters below the rice or not easy to dry the water flowing. : by laying the blind ditch, can greatly reduce the soil water level, can be a lot of water in the soil into the blind ditch, and is discharged through the blind ditch Road, the sun, the soil reached a relatively dry state. Treatment methods: first, along the road every 10 meters horizontally by manual or machine dug into rectangular (trapezoid) of blind ditch ditch, 150x150 cm by 1.5 meters above the soft soil layer of soft soil under 1.5 meters according to the other form. Secondly, along the highway longitudinally arranged blind ditch, the distance control in 10 meters; filling block size at 30 ~ 50 cm is not easy to be water soaked stones in the blind ditch dug, filled with 10 cm after laying gravel thereon, and laying a layer of Geotextile in rubble, prevent blind ditch water overflow, dust leakage, plugging blind ditch, drainage effect influence. 3, change the scope of for filling embankment height less than 3 meters and the soft soil layer is not thick (less than 1.5 meters). Treatment methods: the depth of soft soil within 1.5 meters dug out, and then cut out by one or compacted backfill layer to pass from one field to get borrow. Special attention to the changes in the weather during construction, the requirements of each section must be completed in a working day, the large area or length of the road segment must be replaced by paragraph. : by changing the fill in fill material, roadbed by compaction to meet the requirements of bearing capacity, can effectively bear the vehicle load force and embankment weight. 4, scope: Gravel Pile in soft soil within 15 meters in depth and embankment in high embankment. : compaction, pressure from the two directions of the soil. Dissipation of pore water, to speed up the consolidation of the foundation. Treatment methods: used for drilling machine of gravel pile diameter of the same or similar drilling according to layout a good position in advance, and remove the mud or water in the air, and poured into the gravel to vibrate, the dense. At the top of the gravel, a layer of 50 ~ 30 cm of the gravel layer is provided to transfer the additional stress to the composite foundation.

Five, the soft soil foundation has great harm, if not treated or handled properly, it will cause instability of foundation settlement, the road is too large or small settlement, the harm of different process on the road, described above is only several at the site。