When the embankment can not meet the design requirements through stability checking or settlement calculation, the soft soil foundation must be strengthened. There are many methods of reinforcement, and the commonly used methods are:

(1) Plastic drainage board: A plastic drainage board is a plate-shaped object with holes, which is inserted into the soil to form a vertical drainage channel. Because of its simple and quick construction, it is widely used. The maximum effective treatment depth is 18m.

(2) Sand drain: Sand drain is to drive steel pipes with various pile drivers, or to obtain holes arranged according to certain rules in the foundation by high-pressure water jet and blasting, and then fill them with medium and coarse sand to form sand columns. Because this kind of manhole plays the role of drainage channel in saturated soft clay, it is also called drainage manhole The top surface of manhole should be paved with cushion to form a complete foundation drainage system. When the thickness of soft soil layer is more than 5m, it is appropriate to use sand drain for drainage. The maximum effective treatment depth is 18m.

(3) Bagged sand drain: The influence of well diameter on consolidation time is not as sensitive as well spacing. However, if the general manhole is too small, it can neither be constructed nor prevented from breaking due to foundation deformation. Therefore, the mesh bag manhole is widely used now, with a diameter of only about 8cm, which is much cheaper than the ordinary manhole, and will not lose continuity because of construction operation errors or horizontal and vertical deformation of the foundation. The maximum effective treatment depth is 18m.

(4) Drainage sand cushion: Drainage sand cushion is a thin sand layer laid on the ground at the bottom of embankment. Drain the water from the sand layer. The maximum effective treatment depth is twice the limit of embankment.

(5) Geotextile cushion: Laying one or more layers of geotextile on the surface of soft soil foundation can reduce the uneven settlement of foundation after embankment filling and improve the bearing capacity of foundation without affecting drainage. For super-soft foundation with high water content such as silt, geotextile cushion can be used as pretreatment before adopting deep reinforcement methods such as sand drain to improve the possibility of construction.

(6) Preloading: Embankment is built on soft soil foundation. If the construction period is not tight, you can fill in part or all of it first, let the foundation consolidate and settle for a period of time, and then fill the pavement. The maximum effective treatment depth is 30m.

(7) Compacted sand (gravel) pile: Compacted sand pile is a method to force sand, stone and other materials into soft soil foundation by impact or vibration to form a larger compact column, which can improve the overall shear strength of soft soil foundation and reduce settlement. The maximum effective treatment depth is 20m.

(8) Jet grouting pile: the grouting pipe of jet grouting pile is put into a predetermined foundation reinforcement depth by using an engineering drilling rig, and the pre-prepared slurry is sprayed out from the nozzle at a certain pressure by rotating the drill pipe and slowly rising, so that the soil and slurry are stirred into a mixture to form an artificial foundation with a certain strength. The maximum effective treatment depth is 20m.

(9) quicklime pile: quicklime blocks are placed in the pile holes to form a pile body, which is called quicklime pile. The maximum effective treatment depth is 20m.

(10) Soil replacement: All soft soil under embankment is excavated manually or mechanically, and high-strength cohesive soil or permeable materials such as sand, gravel, pebbles and flaky are replaced. The maximum effective treatment depth is 3 meters.

(1 1) Counter-pressure berm: Counter-pressure berm refers to the berm with a certain width and height on both sides of the embankment. It uses mechanical balance to maintain the stability of subgrade.