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(+4)021.232.39.20

r.decubleoctagon.com.ro

Str. Smaranda Braescu , nr. 20P, sector 1, Bucuresti
Contact

Geotechnical constructions

OCTAGON has a solid experienced management team, able to offer customers the optimum technical solution, for special foundation works, meeting the budget set in the design stage. Our high performance equipment can execute geotechnical works for the most complex projects. 

DIAPHRAGM WALLS
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Diaphragm walls provide water- tightness, stability and support to deep excavations and can perform the role of foundation. They are made of cast-in-place reinforced concrete. When they perform the role of foundation, diaphragm walls are called barrettes.

Applications:

The execution of diaphragm walls is required within several types of constructions.

Diaphragm walls are used especially when tight, deep underground constructions must be built and the lateral overload, generated by the presence of some buildings in the neighbourhood of the future development, is high. These situations are frequent in urban, crowded areas and the role of diaphragm walls is to provide an adequate retaining system.

Buildings with multiple underground levels, which are generally used for garages and underground parking spaces, are built with the help of diaphragm walls.  

Diaphragm walls may also be present in the construction of metro tunnels or of underground passages.

As they provide water tightness, diaphragm walls can also be executed within hydrotechnical constructions, such as dams.

Execution stages:

Diaphragm walls are constructed from the ground level. The first stage consists in the excavation of a trench. Thickness may range between 40- 120 cm and depth may vary between 15- 60 m, depending on the technical project features.

In the second stage, a reinforcement cage is inserted in the trench. In the third stage, concrete is poured through the tremie pipe and the panel is filled  from bottom to top, through the Contractor method. 

To prevent the collapse of the walls, the execution is performed under bentonite slurry protection. This supports the walls of the excavation, through pressure exercised by the high specific weight.

A PVC waterstop is placed between two adjacent panels, to provide a watertight joint. The waterstops are integrated into the panels, during the concrete placement.

OCTAGON executed diaphragm walls within the following projects:

  • Residential complex Construdava
  • Cathedral Plaza
  • Office building B.O.S. 
  • Residential building Primaverii 
  • Office building UTI
  • Blue House Olympia
  • Residential complex Titeica 206- 208
  • Residential building Fundeni
  • Residential building Sevastopol 9
  • Floreasca City Center- Sky Tower
  • City Tower
  • Hermes Business Campus
  • Residential building Ramnicu Valcea Alley
  • Green Gate.

 

 

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Slurry walls provide a non- structural barrier against water access, also called cut- off wall and they are executed from a mixture of bentonite and cement. The thickness of slurry walls can range between 50 and 120 cm and the depth varies between 15 and 60 m.

Applications:

Slurry walls are generally used to seal dams, landfills or industrial installations that can contaminate underground water.

Execution stages:

Slurry walls are built in the same manner as the diaphragm walls.

The first stage consists in the excavation of a trench. In most cases the excavation penetrates about 1 - 2 m into a low permeability soil, such as  clay, to provide water tightness under the wall.

In the next stage the panel is filled with self- hardening slurry.

OCTAGON built slurry walls within the Residential Complex Titeica 206- 208, located in Bucharest.

The excavation within this residential complex with two underground levels, was supported through a combination of diaphragm walls and slurry walls. On one side of the excavation the wall was adjacent to a previously built retaining system made of secant piles. On that side, the diaphragm wall was replaced with a self- hardening slurry wall, made of cemento- bentonite.

 

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Micropiles are small diameter (between 115 and 350 mm) piles.

Although their diameter is small, micropiles have a significant bearing capacity and can be used to consolidate the existing construction, in areas with low building height and limited access. Micropiles can also form a retaining wall.

Applications:

  • Deep foundations in soil where conventional piles cannot be drilled;
  • Indirect foundations and retaining walls;
  • Consolidations of weak soils;
  • Rehabilitation of constructions and foundations;
  • Building tight premises in water tight soils;
  • Slope stabilization;
  • Temporary or permanent retention for underground excavation.

Execution stages:

There are various micropile drilling methods: percusive drilling, continuous screw drilling etc.

The reinforcement cage of suitable dimensions is placed in the drilling well and  micropiles are ready for grouting. Grouting material is made of water, cement and additives, mixed in a high speed mixer. This material is introduced into the micropiles through controlled grouting with piston pump.

Project:

On Bucharest ring road, the earthworks for access to the bridge over the railway in Chitila are supported with small retaining walls. Their foundation is built of micropiles with the diameter of 178 m (drilling), enlarged to 350 mm at the second grounting.

 

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Bored piles with large diameter, ranging between 60 and 200 cm, are circular columns made of reinforced concrete, installed in the soil. Depending on the role they perform in a construction, bored piles are divided into three categories: secant, tangent or independent.

Applications:

Bored piles discharge high structural loads into lower soils (indirect foundation). Tangent bored piles can act as a retaining wall for an excavation pit or a step in the terrain. If water tightness is also required, the retaining wall is built of secant piles.

In the case of walls built of secant piles, all the piles can be reinforced, if the walls are submitted to high loads, which require higher resistance or secondary piles can be reinforced, if the walls are not submitted to high loads.

Depending on the role the wall must perform, bored piles can be executed of material that only provides water tightness (mixture of bentonite slur and cement) or simple concrete, with higher resistance.

Due to the multiple joints, the walls made of secant piles provides weaker water tightness than diaphragm walls.

Execution stages:

There are several methods that can be used to build bored piles. Their selection depends on the soil conditions, diameter and depth. The most usual construction methods consist in drilling the piles under bentonite slurry protection or under the protection of a casing.

Drilling under bentonite slurry protection increases productivity and allows the execution of larger diameter piles at great depth. Drilling is performed using buckets adjusted to the ground. The stability of the bore hole is maintained by the bentonite slurry, which prevents hole collapse and underground water infiltration.

When drilling is finished, the bentonite slurry is recirculated to the bentonite plant for desanding. The reinforcement cage is installed  and concrete is casted, through the tremie pipe Contractor method.

Projects:

OCTAGON built the foundation of the superior passage over the railway in Otopeni (part of Bucharest ring road) with the help of bored piles with a diameter of 200 cm and 23 m depth.

  • Cathedral Plaza
  • B.O.S. office building
  • UTI office building
  • Blue House Olympia
  • Maresal Averescu 159 residential complex
  • Residential complex Tineretului Hills
  • Residential building Pangratti
  • Combined cycle power plant 867 MW- OMV 
  • Bucharest ring road - DN 7- DN 1 A
  • City Tower
  • Hermes Business Campus
  • Green Gate

 

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Sheet piles are elements used to support the vertical walls of deep excavations, which goes bellow the level of ground waters.  

The presence of sheet piles within a construction has a double role: support the excavation walls and build a water- tight wall, which does not allow water infiltration. 

Applications:

Sheet piles can be made of wood,plastic, metal or reinforced concrete. Metal sheet piles are most frequently used in constructions.

Metal sheet piles are used for deep excavations, performed under the level of ground waters. They can be used with both temporary and permanent role. Sheet piles can easily be recovered from the construction. The disadvantages consist in the fact that their installation causes noise and vibrations, which can be disturbing for the inhabitants in the constructionm area. Metal sheet piles are also more expensive than wood or reinforced concrete sheet piles. This is the reason why, the use of metal sheet piles within buildings located in urban areas, is limited.

Execution stages:

Sheet piles are placed in the ground, in vertical position. Temporary guide walls insure that the sheet piles are placed and pressed to the correct alignement. 

Sheet piles have keys on their length that help them interlock and provide thus continuity to the structure and a certain degree of water tightness. Sheet piles’ locks can be supplementary sealed to improve the water- tightness of the retention, if necessary.

 Sheet piles are installed and extracted with vibratory hammers.

Projects:

  • Combined Cycle Power Plant 867 MW- OMV Petrom;
  • Bridge over Mures river.

 

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Grouting with cement suspension is used for soil improvement, by filling the existing gaps and cracks, with material injected under pressure.  

Applications:

Grouting is used on dams and tunnels to improve the connection between the structure and the soil, seal deep excavations and improve the bearing capacity of bored piles’ base.

Execution stages:

Drilling is performed through a method chosen depending on the soil characteristics. Injected suspension usually made of water, cement and additives is mixed in a high- speed mixer.

Grouting is usually performed under high controlled pressure, using packers to control the injected area.

The quantity and pressured of the grout are permanently monitored to observe the grouting efficiency.

Projects:

  • Cathedral Plaza;
  • Bucharest ring road DN 7- DN 1 A. 
ANCHORS
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Ground anchors are retention elements. Their role is to carry and transmit the load into the ground.  

An anchor is made of steel strands, inserted into in the drilling and has two parts: the free length and the bond lenght. 

Applications:

Ground anchors are most frequently used to support the retaining wall of a deep excavation and can play a permanent or temporary role. When they are no longer necessary, temporary anchors are extracted or de- stressed.

Anchors can be used to perform works for the stabilization of slopes.

It is not recommended to use anchors in certain types of grounds: wet sensitive soils, muddy soil and soils that contain organic matter.

Construction stages:

The first stage consists in drilling the hole for the anchor installation, at the suitable diameter and length. The anchorage is then installed and grouting suspension is performed under high controlled pressure, to provide a strong link between the strand and the soil, while the free length of the anchor is protected, to allow the strand to remain free.  

After grout curing time the anchor is stressed according to design specifications.  

Projects:

OCTAGON executed anchorages within the project Bucharest ring road DN 7- DN 1 A.

 

 

TOP- DOWN CONSTRUCTION
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Top- down construction is one of the best solutions for buildings with multiple underground levels, that require large excavations. This construction method was adopted at the beginning of the '60s and it is currently used, in general, for the construction of buildings located in crowded urban areas.

Construction stages:

The underground levels and the superstructure are built simultaneously. In the first stage the retaining walls (diaphragm walls) and the bearing elements, which will support the superstructure (bored piles or barrettes) are built. 

The underground floors are supported by steel columns, inserted into the piles, until the slab foundation is built. The steel columns are built in the first construction stage.

In the next stage, an excavation to the level of the floor is performed. This is built on the ground, on a leveling concrete layer, used as formwork.The slab has technological holes. After attaining the suitable resistance, the excavation under the floor continues, through the technological holes, to the level of the next floor, which is built through the top- down method.

The procedure is repeated until the last underground level is reached.

The superstructure is built simultaneously with the underground levels.

Advantages and challenges of top-down construction method:

An advantage of this construction method consists in the fact that the infrastructure and the superstructure can be built simultaneously, the delivery term being reduced significantly. The excavation is supported by the underground floors instead of by temporary retaining elements, which saves the cost for retaining system.

Due to increased stiffness of the slabs, compared with the stiffnes of temporary support elements, the strains of retaining walls are smaller, so the excavation is safer.

The top- down construction can also be challenging for constructors, as it is difficult to excavate under the floor.

 Octagon used this construction method for the projects:

  • Cathedral Plaza
  • Floreasca City Center – Sky Tower
  • Hermes Business Campus

 

PRECAST CONCRETE PILES
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Driven piles are classified as displacement piles, and where the soil can enter during driving as small displacement piles. These piles may be used for all types of structures and foundations, from housing, through other forms of domestic building, to commercial and industrial buildings and installations. The piles can also be used for all types of civil engineering applications from bridges to embankment support, power and transmission towers and rail-related structures. The precast piling system is quick to install and very cost effective in most ground conditions. This pile is environmentally attractive as no spoil or arisings are generated from pile installation.

Installation:
Precast concrete piles are usually constructed in a casting yard and transported to the job site. They are either regularly reinforced or pre-stressed to resist handling and driving stresses. Both types come in a variety of cross sections (square, cylindrical, octagonal etc.).

Precast concrete piles may be manufactured full length or in sections which can be spliced during installation. The precast concrete piles are usually top-driven using hydraulic drop hammers. Low noise, low vibration hammers and can be mounted on a variety of tracked or wheeled rigs, depending upon Methods of protecting the head of the pile from shattering must be decided before commencing the driving process. This can be determined from the end bearing requirements and driving conditions, project location, type, access and headroom constraints. 

ADVANTAGES OF PRECAST CONCRETE PILES:
• Reinforcement used in the pile is not liable to change its place or get disturbed
• The defects in pile can be easily identified after the removal of forms, and these defects (such as presence of cavity or hole) can be repaired before driving the pile.
• The cost of manufacturing will be less, as a large number  of piles are manufactured at a time.
• Precast concrete piles can be driven under water. If the subsoil water contains more sulphates, the concrete of cast in situ piles would not set. Thus precast concrete piles have added advantage in such a circumstance.
• Precast concrete piles are highly resistant to biological and chemical actions of the sub soil.
• Better quality control can be implemented as compared to bored cast in situ piles.
• These piles can be constructed in various crosssectional shapes such as circular, octagonal or square.

DISADVANTAGES OF PRECAST CONCRETE PILES:
• These piles are usually very heavy. So, special equipment is required for handling and transportation.
• Sufficient care must be taken at the time of transportation, otherwise piles may break.
• For embedding these piles in field heavy pile driving equipment is required.
• These piles are costly as extra reinforcement is required to bear handling and driving stresses.
• The length of the pile is restricted since it depends upon the transport facility.
• Once constructed, it is not possible to increase the length of the pile (as per the site demand)
• If the pile is found to be too long, during driving, it is difficult and uneconomical to cut. Also, cutting of extra length results in the wastage of material.
• Driving these piles created a lot of noise pollution.