Retaining walls are rigid supporting structures built to ensure that natural or filled floors at different elevations stand more upright in terms of natural slope or prevent collapse.
- Keeping the ground at a steeper angle than the natural slope in order to benefit from the land in sloping lands,
- Preventing the potentially collapsing floors from slipping,
- Creating building basement walls,
- Preventing coastal erosion or protecting it from floods,
- Channels and eclipses
- To act as an edge foot in bridges,
- In deep excavations,
- To use it while arranging the slope on the road route,
- Using stabilized and coal storage,
- On roads that require filling and splitting,
- On the slope roads,
It consists of two parts, the retaining walls , the body and the foundation. The rear body portion drainage crushed to / stabilized filling and drainage pipe for discharging the water in the junction between the body portion and the foundation portion Barbakan which is formed. There is also filling material between crushed stone / stabilized filling and natural ground.
Types of Retaining Walls
In addition, retaining wall types can be classified differently according to the materials from which they are made.
Flexible Retaining Walls
In flexible retaining walls , they do not rotate from their lower ends underground thrust, and their own weights are neglected in stability calculations. We can list this group as rock filled walls, wire mesh walls, lattice type and reinforced floor walls.
Rock fill walls
Rock fill walls are built from large rock fragments. They are used to ensure the stability of the slopes moving according to the suitability of the heel location.
Gabion (Wire mesh = Chest) Walls
Gabion walls are walls built with steel cages, filled with various filling materials.
Lattice Retaining Walls
Lattice walls are very flexible against lateral and vertical movements, they have an important function in keeping slopes and slopes in balance. Constructed of concrete, galvanized sheet steel and sometimes wooden elements for architectural purposes in other countries, these walls could not be widely used in Turkey.
They have an important potential because they are economical and can be manufactured quickly. These lattice walls that can be manufactured without any expertise in the field function in the form of cells by filling stone chips and hearth debris into them. These walls can make 4 m horizontal and 70 cm vertical movements without any damage.
The manufacturing of the locking elements and beams is done easily and quickly at the construction site. While the single or double row box cells to be formed in manufacturing are filled with large stones, making the back filling in parallel prevents the wall from falling over. If the wall height is less than 2 m, it must be built on solid rock or a reinforced concrete foundation must be built under the wall. Since the rockfill is permeable, the water coming from the slope to the backfill can easily be drained. In order to prevent the coarse-grained ground in the cage box from clogging over time, it is recommended to lay geotextile between the filled ground.
Earth Retaining Walls
Earth retaining walls ; These are galvanized steel, aluminum alloy metal, synthetic fiber strips or reinforced wall systems using geosynthetic cover material placed in the reinforced ground infill floor, which have been used in highways in recent years. The reinforcement should have sufficient length (0.8-1.2 times the height of the structure) and width to provide the required ground friction. In order to obtain the friction, the internal friction angle of the fill floor used must be min 25 ° and the 25% part must pass through the No. 200 sieve. It is designed in the form of grounding with mechanical strip reinforcement and geotextile cover.
Rigid retaining walls
Rigid retaining walls; They are retaining walls that can rotate a little less than the ground thrust.
Weight (Solid) Retaining Walls
Weight retaining walls made of stone and concrete materials meet the active and passive ground pressures with their own weight. Since the tensile stress of stone and concrete is low, it is not preferred at heights of more than 4-5 m, as tensile stress occurs as the height increases.
Concrete Retaining Walls
7-8 m. They are retaining walls that are economical up to the height and manufactured as L or inverted L, T shaped reinforced concrete depending on the location of the land. If a cantilever retaining wall higher than 7-8 m is built, a reduction console can be made to reduce the horizontal load and moment distribution affecting the body.
- Sometimes the area where the wall will be placed may be narrow and insufficient. The required size and weight cannot be given to the stability of the wall sections. In this case, a shoe is made on the back or front of the wall.
- If this shoe is in the front, it increases the resistance moment of the wall against the tipping by increasing the distance from the center of rotation of the resistance forces.
- If the shoe is at the back, it increases the resistance movement against toppling by adding the filling loads behind the wall on the shoe.
- Putting the shoe forward or back depends on which direction the space is narrow.
- With the insertion of the shoe, bending moments will occur in the wall foundation masses.
- These moments are prevented by making the wall foundation reinforced concrete.
- Due to the small size of the wall sections, the pressure line in the wall sections will go beyond the section core, and eccentric force will create tensile stresses in the sections.
Reinforced concrete ribbed retaining walls
If it is higher than 7-8 m, the cantilever retaining wall sections are too large and ribbed retaining walls are preferred because it is not economical . As the height increases, the moments coming to the heel point increase. Ribs are made at regular intervals to accommodate these moments. Ribs are formed in front of or behind the retaining wall, depending on the situation of the land.
Prefabricated Retaining Structures
These loads should be determined in the most accurate way during the projecting phase of retaining walls exposed to various loads according to the place and purpose of their construction. Loads / loads that are not taken into account in the project may negatively affect the stability of the wall, and an unnecessary load will prevent the retaining wall from being economical. Loads acting on the retaining wall; self weight of the wall, active thrust behind the wall, passive effect in front of the wall, groundwater effect, earthquake effect and surcharge loads. Depending on the condition of the land, the effects of railway, road vibrations or frost effects can also be counted.
In terms of the building material and system used, retaining walls can be divided into the following types:
- a – Masonry retaining walls.
- b – Concrete retaining walls.
- c – Reinforced concrete retaining walls.
- d – Lattice retaining walls.
Kagir Retaining Walls
Masonry retaining walls are walls made of stone. If mortar is used between the stones, it is called “retaining walls with mortar”, if no mortar is used, it is called a “dry masonry retaining wall” or “drywall”.
Building material and masonry of masonry walls
- The joints between the stones in the wall should be staggered from bottom to top. The stones on the visible face should be interlocked by entering at least 25-30 cm with the stones behind.
- In mortared walls, the joints should be filled with mortar. In dry walls, stones should be clamped to the substrate at at least three separate points.
- Another material of the masonry wall is mortar. Mortar is a mixture of sand and cement.
- It is usually 300 kg / m3 dose.
- Sand consists of solid minerals or stone particles, it should not contain soil or vegetal substances.
- The water content in the mortar and whether the mortar causes excessive shrinkage cracks are very important.
- The mortar should be uniform.
- Care should be taken to avoid degradation during transport and placement.
- Wall foundations should be checked frequently during excavation.
- General conditions should be sought in terms of bearing capacity in wall foundations.
- Excavation work is continued until it is certain that it is sufficient.
- The foundation should have a uniform bearing strength throughout the wall.
- However, if this cannot be achieved, a «dilatation joint» is placed on the wall between sections with different bearing strength.
- In landslides, the foundation of the wall must penetrate to a certain depth below the sliding surface. The wall whose foundation is at the level above the sliding surface moves from its place with the sliding mass.
- The depth of the foundation should go below the depth of the carving in the walls built in places where water can gouge.
- After the excavation work is completed on the wall foundation, 10 cm. It would be better to make a leveling concrete from lean concrete.
Shaping the Wall:
- Before starting the wall construction, wooden molds are made in the shape, size, measure and elevation of the wall cross-section. These are called “Templates” in practice.
- During the construction of the wall, a rope is pulled between the front faces of these molds, the rope direction is horizontal. These threads are called «Twigs». Wall faces are made tangent to these ropes.
- A dilatation joint is formed in the wall structure by placing templates in the sections where the height and width of the wall height and width change points or bearing strength change points on the wall. Wall sections between these joints are called “ANO”.
- Joint sections are called “Ano heads”. Anos should be at most 10 meters tall, even if there are no reasons we have stated.
Barbakan Holes in Walls and Drainage Precautions:
- A measure for drainage in retaining walls is 0.20 × 0.20 m with a square or circular cross-section perpendicular to the wall. “Barbakan” in size is to leave holes.
- These are placed at suitable intervals. They come in several rows to change according to the height of the wall. The holes of the rows are staggered according to those of the previous and next row.
- At least 15 cm from the surface in the barbecue holes. Protruding stones to serve as troughs should be used for protruding glaciers or barbecues with excavation sections.
Filling Back Walls:
- Filling behind walls is very important. The active lateral soil pressure that these fillings will give to the wall should not exceed the values specified in the wall calculations.
- In practice, floors with stone filling and granular and non-cohesive, easily compressible floors are good back-wall filling materials.
- Back of the wall fillings should be made by layer, layer and compression.
- In the walls built in front of the infill, the back side of the back wall infill is generally in a form that creates an inclined surface from the head of the wall. If possible, these fillings should be made in steps.
- Joints are made at the joints between the stones on the wall faces. In these joints, the roughness, small protrusions and indentations of the stone edges are removed with «Chisels and Chips».
- It opens to a certain depth. Thus, the slots opened are called “Fuga”. Then the gaps are filled with mortar.
- Eventually the face of this filing is left a few centimeters (1.5 cm.) Deep from the surrounding stone faces.
- The mortar on the edges of the groove is continued from the edges to the faces of the perimeter, creating a strip of several centimeters parallel to the line on the stone faces.
- Rather than being made from the stone faces of the joints in the pit, those protruding from the stone faces forward are called «Fluffy joints». These bumps break off from the wall over time.
CONCRETE RETAINING WALLS
For concrete retaining walls, we can repeat the same rules we have given for masonry retaining walls on places of use, foundations, backfill, drainage.
Comparison of Masonry and Concrete Retaining Walls
- The following criteria should be taken into account in the construction of masonry or concrete walls.
- a – Material provisioning status
- b – Economy
- c – Time savings
- d – Appearance (Aesthetics)
In some regions, it is not possible to provide stones of the desired quality. It may be easier to provide sand, gravel, and cement. Accordingly, it is preferred to make a concrete wall. Naturally, it could be the other way around. For example, it is very easy to provide stones in the business district. Sand is abundant, even if it is difficult to provide cement, a masonry wall does not need as much as a concrete wall, then a masonry wall is built.
There may also be situations in which the facilities for both concrete and masonry are equal in providing materials. In fact, since the concrete wall formwork issue is also at play, it requires one more construction material than the masonry wall.
- Concrete surfaces are very uniform in terms of their appearance and enthusiasm, masonry building faces are more beautiful.
- This should be considered where the image is important.
- In addition, stone coatings can be applied to concrete faces that enhance the image. Or color and pattern can be given to concrete.
- Moreover, some evergreen ivy plants can be grown to cling to wall faces.
CAGE SYSTEM-GABION RETAINING WALLS
- The lattice retaining walls are prepared by filling the inside of the cages made of bars made of some materials with stone. These bars are mostly reinforced concrete as well as metal.
- Stability calculations of lattice retaining walls are like other walls. It is possible to quickly build them into walls and place them where they want support.
- Especially in front of an active landslide, when a wall is required, the landslide skirt is cleaned as short anos and cage holders are immediately placed on these anoes. Thus, landslide clearing teams do not wait long to switch to other slabs.