The diaphragm technology is for the construction of maximum 120m deep, 40-150 cm thick reinforced concrete walls or columns in the subsoil. Its primary application are the quasi-watertight deep excavation pit retaining, for example 2- or more-level deep garages or walls of public road underpasses. However, it is also commonly used as great load bearing capacity deep foundation element, so-called ”barrette”.
The essence of the technology is the excavation of the diaphragm that determines the construction of the wall in the soil by means of cable-operated or hydraulic grabs, in special cases by means of so-called Hydrofraiser equipped with counter-rotating drums fitted with cutting teeth. During the soil excavation the diaphragm is supported by bentonite slurry. In order to construct the wall structure, the installation of the reinforcement cage and the subsequent concreting of the diaphragm panel follows the soil excavation of the panel.
These pile walls typically constructed as soldier walls are used for the temporary or permanent support of excavation pits or soil masses of great height or slopes. This technology is applied in cases when the confined or unconfined groundwater is located below the bottom level of the construction pit, or due to the impermeable soil environment, the application of a watertight wall structure is not required. The piles are mostly constructed by means of CFA and occasionally by bored piling technology supported by slurry. For protection against grain flow from the interspaces between the piles and against water built up behind the wall rebar net reinforced shotcrete lagging over a surface drainage layer is installed.
Slurry walls are walls constructed in the subsoil with water sealing capability similar to that of the diaphragm walls, but unlike diaphragm walls, slurry walls do not have any significant retaining capacity. It is a commonly used technology mostly for the improvement of the water tightness of earth dams and the solution of environment protectional issues (e.g. to prevent the spreading of contamination in the ground water). It differs from the construction of the diaphragm wall in that its structural element is not concrete or reinforced concrete but a so-called self-hardening slurry, which has limited strength but at the same time the permeability parameters are practically identical with those of the concrete.
The cement-soil columns that are constructed by means of the jet grouting technology, i.e. mortaring with a high energy liquid jet, are structural elements of limited strength with the capability of reducing water seepage. In case of the need for retaining function as well it can be fulfilled by the application of structural steel bars and/or temporary ground anchors. This method is mainly used for the realisation of construction areas or pits with smaller layout dimensions down to a maximum depth of 4-6m, and also to improve the drainability of the construction area.
Bored Pile with Slurry Support
Bored piles constructed utilising slurry support is a technology for the construction of large diameter, long piles – it is commonly used as a foundation of large-span bridges, silos of great height or other structures of significant load and/or high sensitivity to settlements. The soil is excavated by means of cylindrical drums, while the stability of the excavation is ensured by means of bentonite slurry, in the way identical with the diaphragm wall construction technology. In order to create the final structure of the pile, the installation of the reinforced cage and the concreting of the pile follows the excavation. During concreting the excess support fluid is pumped out of the borehole.
The essence of the so-called CFA piling method is that following the driving of the hollow drilling spiral down to the desired depth, the excavation of the soil stuck on the drilling spiral and the concreting of the pile through the hollow drilling rod takes place simultaneously, thus ensuring the stability of the borehole either by the concrete or by the soil above the tip of the auger. The prefabricated reinforcement cage might be installed into the freshly completed pile by means of jacking or vibration. It is the most popular piling technology in our region, which can be used as a foundation for industrial, office and residential buildings, public and railway bridges of small and medium loads.
In this patented technology of Soletanche Bachy no soil is excavated from the pile. A special conical drilling tool is driven into the soil by rotation, which displaces the soil laterally and thus compacting it. The concreting of the pile and the installation of the reinforcement cage is performed in a way similar to the CFA technology. However, by the rotation of the drilling head during the extraction the pile body will have an external spiral thread, thus increasing the pile load capacity.
Due to the relatively low material usage of the method, fast constructibility and the fact that there is no soil excavated during the construction the disposal of which should be ensured, it has become the most efficient foundation solution for industrial and residential buildings with low to medium loads.
The typical field of application of jet grouting i.e. soil concrete mixture columns created by high energy cement slurry jet is the deepening of the base level of existing buildings or reinforcement of their foundations. Due to its smaller dimensions and weight related to other deep foundation construction plants and the flexibility of the drilling arrangements, it can be applied very efficiently for the fullfillment of temporary constriction requirements in confined spaces (empty plot, closed buildings, basements).
Bored, Grouted Soil Anchor
Bored, injected and typically pre-tensioned soil anchors are the provisional auxiliary structures of earth retaining wall structures, which ensure the stability of the wall in temporary construction phases and limit their expected displacements. The essence of the process is that nearly horizontal borings are completed through the wall, with an inclination of 15-30° into which steel strands are installed. Following the injection of cement mortar into the borehole and the hardening of the grout, the wall structure can be tied back to the soil by tensioning the anchors.
The primary method for the design or quality assessment of pile foundations is the static load testing of the piles. On the basis of the applied piling technology, the required pile bearing capacity, the characteristics of the subsoil and the aspects of economics, pile load tests with 2 or 4 anchoring piles or divided, the so-called VUIS pile load test might be performed for the determination of the compressive resistance of the piles.
Rigid Inclusion Soil Improvement
The Rigid Inclusion soil improvement is a combined foundation method that bears the advantageous characteristics of shallow and deep foundations at the same time: the loads from the structure are transferred through a load transferring bedding to the vertical stiffening elements that are installed in a regular grid and are realised by means of piling technology. The latter are exclusively loaded by an axial load, thus generally no reinforcement is required. This method is an efficient, economic solution mostly used for the protection against excessive settlement of structures with even load disribution, for example storage silos, warehouses and road embankments.
As part of our deep excavation projects, temporal dewatering works are performed, generally with the construction of gravity wells and their operation during the construction.
Construction of Reinforced Concrete Pile Caps and Slabs
As part our deep foundation projects, we also carry out the design and construction of reinforced concrete connecting structures for our deep foundation elements (pile caps, beams and baseslabs).
The primary task of HBM’s Design Group is the technical-design support of the Company’s construction projects, from the Tender Phase, through the Design Phase to the termination of the Construction. The Design Group – independent from the construction activities of the Company – is at the disposition of their Clients for the completion of tasks like the compilation of Soil Investigation Reports in the Authorisation or Construction Phase and of Geotechnical Design Plans.
The soil mixing technology is primarily used for soil improvement, in forms of columns and blocks, e.g. for construction area confinement with smaller depths. During the application of the technology the local soil is improved by the addition of binding material, thus creating a column-like body with improved mechanical characteristics. The great advantage of this technology is that the expensive transport of the fill material onto the site is not required, only binding material shall be added on site. Its productivity and machinery needs are more or less equal with those of the preparation of CFA piles. However, its material costs are much favourable. By means of the Springsol tool 400 to 600 mm diameter soil-cement columns might also be constructed in confined spaces, even with electric machinery. Thus, in case of foundation reinforcement tasks this solution is recommended in general.