Wide-area excavations, part 3

tmp813e-1The figure shows the structure of the sheet piling, wooden, consisting of driving piles, logs hammered and ticks. The steering piles and all the logs have longitudinal cutouts that allow for a single plane of the wall and greater tightness.

The logs are cut at an angle of 10-30 ° at the lower end, what causes, that when they are hammered, they are pressed more tightly against each other.

At trench depths above 3,0-5,0 m there is a high pressure of earth and water, and then it is necessary to use a steel sheet piling. These walls are made of various profiles produced by steel mills. The German type of Larssen is widely used in Poland (rys.b) about width 400 mm and height 247-290 mm.

tmp813e-2Support of the excavation walls with steel sheet piling: a) section through the wall, b), c), d), e), 0 cross-sections of the steel profiles used.

A widely used method of securing the walls of wide and deep excavations on construction plots with a small area and in the immediate vicinity of existing buildings, there are concrete diaphragm walls in the ground.

Diaphragm walls are made around the perimeter of the planned excavation with sections with a length from 2,5 do 10,0 m and depth to 50,0 m.

tmpeb42-1Reinforced concrete diaphragm wall protecting the excavation: a) cross-section, b), c), d) cross sections of guide walls, e) horizontal section of the wall; 1 - guide walls, 2 - wall in the ground, 3 - strut, 4 - reinforcement.

Concrete diaphragm walls can be used in any soil, regardless of its cohesion and the level of the groundwater table..

The slots in the ground are made with excavators of a given bucket width, which is inserted into the ground between the guiding walls (rys.d, c, d). The guide walls give the bucket the correct position in the ground when sinking the trench. In the process of selecting soil and deepening the fissure, a thixotropic slurry is poured into the trench, e.g.. bentonite, which exerts pressure on the fracture walls and keeps the ground in a state of equilibrium.

After making a slot in the ground to the desired depth - filled with bentonite - steel pipes called alloy pipes or other steel profiles are inserted at its ends., which end the gap and form the joint between the individual wall segments. Between the "alloy" pipes, the reinforcement skeletons with the required cross-sectional area of ​​the bars are set - in bentonite, and then proceeds to concreting, starting to fill with concrete mix from the bottom of the trench with a feed pipe, which is pulled up as the concreting progresses. The bentonite displaced by the concrete mixture is removed from the joint and can be reused for the next wall segment. The next segment should be executed in every other adjacent field, and the segment made earlier.

After the two segments have been made, you can only proceed to make the segment gap between them, and after removing the soil and filling with bentonite, the "alloy" pipes are removed, places reinforcement skeletons and concretes.