(1) The undisturbed foundation soil at the bottom of the groove shall not be disturbed, and 200~300mm soil layer shall be reserved at the bottom of the groove during mechanical excavation, and the soil layer shall be leveled from manual excavation to the design elevation.
(2) the bottom of the trough shall not be soaked in water or frozen, when the bottom of the trough is partially disturbed or soaked in water, it is advisable to use natural graded gravel or lime soil backfill;
(3) When the soil layer at the bottom of the groove is miscellaneous fill soil and corrosive soil, it should be excavated and the foundation treatment should be carried out according to the design requirements
1. [Single Selection] Under the same construction conditions, the slope method is used to excavate the trench, and the soil with the steepest slope slope is ( ).
A. Hard-plastic silt B. Hard-plastic clay C. Old loess D. Soft soil after precipitation at the well point
2. [Single Choice] Regarding the relevant provisions of trench excavation and support, the correct one is ( ).
A. Mechanical excavation can be dug to the design elevation at one time, B. The depth of each manual excavation trench can reach 3m
C. When the soil layer at the bottom of the tank is corrosive soil, it should be replaced according to the design requirements
D. After the bottom of the tank is soaked in water, it is not suitable to backfill with lime soil
(1) Larsen steel sheet pile construction technology:
The pile driver is in place→ the Larsen sheet pile is laid→ trench excavation and support installation → is applied for pipeline foundation→ pipeline installation→ trench backfill and support demolition→ Larsen sheet pile uprooting → pile hole backfill.
(3) Trench excavation and support installation:
Steel supports should be made and installed according to the size of the design drawings. The steel support end is provided with a movable head, and the steel support is assembled and hoisted by a crane, and prestress is applied.
After the support system is completed, the trench earthwork excavation operation can be carried out, and the trench excavation meets the requirements of the design and construction plan, and anti-fall measures are taken. After digging to the design elevation, the cushion paving and pipeline hoisting construction are carried out.
(4) Dismantling of the support system:
The support system should be dismantled in layers and sections, and the corresponding support can only be removed after the trench is backfilled to a certain height.
(5) Sheet pile uprooting:
a. According to the soil conditions, water can be poured into the edge of the pile before pulling the pile to reduce friction resistance.
b. The pores that appear after the pile is pulled should be filled with sand or grouting immediately to reduce the impact on adjacent structures and roads.
c. The pulled piles are placed neatly and stacked on solid ground, and the height should not exceed 1.0m.
5. Ground treatment and safety management
2) Ground treatment
(2) when the bottom of the groove is partially over-excavated or disturbed, when the over-excavation depth does not exceed 150mm, the original soil of the trench can be backfilled and compacted, and its compaction degree should not be lower than the compactness of the original foundation soil;
(3) When the foundation soil is disturbed due to poor drainage, the disturbance depth is within 100mm, and it is advisable to fill in natural graded sand or gravel; when the disturbance depth is within 300mm, but the lower part is hard, it is advisable to fill pebbles or stones, and fill the void with gravel to level the surface.
(5) Composite foundations such as sand piles and mixing piles should be used for the treatment of flexible pipeline foundations.
(7) When the rock foundation is partially over-excavated, all the base slag should be cleaned up, and the low-strength grade concrete or backfilled sand and gravel with a particle size of 10~15mm should be backfilled and tamped.
(8) When the undisturbed foundation is rock or hard soil, a sand cushion should be laid under the pipeline.