Grouting Ground Treatments
By virtue of proximity of marine conditions (in plan and elevation) and the excessive hydraulic conductivity of the native soil and rock stratigraphy (sand and weak, highly fractured rock ground masses), ingress of water and build-up of pore pressures beneath and around construction, and the inherent low density and strength of ground masses, construction on and underground is laden with issues related to excessive water ingress, and weakness that often beg the need to deploy groundwater exclusion and strengthening methods.
These measures counteract these tendencies. Soil and rock injection with carefully selected grout materials is one of the many available practical applications available address these difficulties.
- Injection Mechanism :
- Permeation Grouting in which the injection material is thrusted through drilled grout holes, under pressure to impregnate with selected grout materials the primary and/or secondary pore space of the ground; thereby densifying, strengthening and rendering less permeable the ground mass to be injected. Permeation grouting is normally applied through grout tubes and grout holes are sealed off and pressurized using a combination of manchettes and packers.
- Frac Grouting; Also known as "claquit" or hydro-fracture grouting, in which the grouting pressure in the grout holes are raised to beyond the hydro-fracturing pressure of the ground mass injected; associated with the creations and propagation of newly induced fractures that would be impregnated by the strengthening and possibly densifying grout and with the result that the mass injected is thus improved. Frac grouting is applied through grout holes installed with grout tubes and sealed off and pressurized using manchettes and packers.
- Fill Grouting; in which large sub-terrain voids are penetrated by injection holes and vent holes and the grout is placed at the bottom of the void and allowed to fill the void under gravity or low pressure flow regime in an upward displacement process until the grout emerges from the vent holes. Free-flowing micro-concrete often is used as the injection material for practical and economic considerations. Fill grouting is carried out normally through gravity or pressure tremies.
- Compaction Grouting; is applied to weak soil to achieve lateral compaction along with creation of a strong grout mass column which when applied on a grid results in an increase in the overall strength & stiffness and reduction in soil compressibility. Normally either a stiff mortar-like cement grout is applied to the drilled grout hole or else free-flow grout is applied inside a strong, expandable geo-membrane tube that expands inside the soil laterally.
- Grouting Materials :
Injection materials range in material composition combinations to a wide range of components with the purpose of achieving the intended results with the least time, effort and cost. These material are:
- Cementitious Materials: Such as Portland cement (all types; including ultra fine cement), slag cement (GGBS), fly ash, silica fumes etc with different combinations and additives.
- Muds; including all types of bentonite slurries; in combination with cements or alone with water and additives. Proper hydration of bentonite to mobilize its colloidal behavior is key in its preparation for injection.
- In-organic (normally Silicate)-Based Chemical Grouts; in combination with cements or other chemical systems like reactors, accelerators, catalyst etc. these materials can be controlled in consistency and setting time to achieve what slurry grouts fail to do and are applied at controlled pressures and quantities. They are introduced through tubes installed on grout holes that have been sealed off by using manchettes and packers. Cost of chemical grouts are higher than their cementitious or mud slurry counterparts.
- Organic-Based Chemical Grouts : These are based on a range of organic co-polymer materials like acrylics, epoxies, elastomeric chemicals (foaming and non foaming). They are characterized with low viscosity and thus high penetrability, and are quick setting (or quick foaming) in nature. Their main disadvantage is their high cost compared to all other counterparts mentioned above and thus the case for their application must be carefully considered and justified.
- Applications :
Grout Injection in particular is one of SGFC's main portfolio activities and has been applied to serve a variety of purposes in several sectors such as;
- Subsoil densification and strengthening of rock masses to improve bearing capacity and counteract compressibility and settlement for buildings, infrastructure and facility foundations.
- Sub-terrain void and cavity filling of ground masses ( natural and filled areas) underlying areas proposed for development.
- Construction of curtain walls and other local seepage cutoffs purposed to combat excessive water ingress into excavations, underground works and basements and to facilitate effective dewatering on difficult sites.
- Strengthen and render less permeable rock masses around underground excavation and tunneling.
- Intercept influx of gas under high pressure, originating at depth and extruding into deep excavations and drillings.
- Fixing and strengthening of tie-backs (anchors, soil nails and rock bolts).
- Abandonment works for wells, pipelines, abandoned underground structures and drillings.
- Alternative shoring systems combining grouted curtain walls, tie-backs and shotcrete, in combination with modest intensity of dewatering.
- Construction of grout columns such as compaction grout columns, frac grout columns, permeation grout columns and jet grout columns for the support of building, facility, infrastructure and earthworks foundations.
- Construction of mini-piles and micro-piles with or without ground improvement.
- Repair of underground structures, improvement of bearing capacity of foundations including pile capacity.
- Under-pinning of building, infrastructure and facility foundations adjacent to excavations.
- re- leveling of foundations and pavements.
- Other project-specific applications; such as construction of catholic protection and earthing wells for oil & gas and other industrial applications.
Pile Boring Systems
Bored piles involve boring a cylindrical hole into the ground (cased if so needed), installing designated steel reinforcement in a centralized manner at the designated level and filling the cylindrical hole with concrete to form a RC columnar element.
Boring is usually carried out to the required depth and diameter by means of purpose-built, crawler-mounted, hydraulic drilling machines of different makes, models and capacities to suite the ground conditions and pile dimensions (diameter & depth) of concern. Bored pile foundations are suitable for all types of ground (soil and rock) and compared with their conventional driven counterparts, bored piles are more productive, less tedious and less disruptive to the surrounding environment in terms of noise and vibrations.
- The range of concrete pile diameters available are:
- - Bored cast in situ piles: 450mm to 1500mm.
- - Micro-Piles /Mini-piles: 100 mm to 250 mm.
Piles Shoring Wall System
Pile shoring systems are walls that are formed in progressive manner within the ground by constructing a sequence of piles along the outline of the site and used to laterally retain ground including soil, rock and groundwater. The design of the shoring varies with depth of excavation and prevailing nature of the ground and potential surcharge loads imposed outside the shoring, the allowable deflections and whether the shoring system is permanent or temporary in purpose.
- Bored Contiguous Concrete Pile Walls
A contiguous bored pile shoring wall is an earth retaining system formed by installing closely spaced (nearly touching), bored concrete piles and thus not suitable when a water-tight wall structure is needed. To improve water tightness of contiguous pile shoring walls, a combination of temporary dewatering, shotcreting, surface mortar seal applications and at times; local grouting may be needed. Piles are constructed alternately to avoid disturbance to freshly casted neighboring piles.
Either all piles are reinforced or else alternately reinforced depending on strength and stiffness requirements of the system. Contiguous pile walls are either designed as a cantilever or else supported by one or more level of supports (braces, props and/or tie-backs). The wall at its top is normally fully encapsulated with a continuous RC capping beam and the piles bay be joined at several levels with steel or RC waler beams (continuously or intermittently as needed).
- Bored Secant Concrete Pile Walls:
A secant pile wall is very similar to its contiguous pile wall counterpart except that adjacent piles are constructed overlapping in plan along the full depth of adjacent piles. And depending on the extent of overlap in plan, the wall is rendered water-tight to different extents. Due to the overlap, normally female (primary) piles are not reinforced and are constructed using modest, strength and well retarded concrete (to be easily over-cut during constructing the male piles), Male (secondary) piles are on the other hand are usually heavily reinforced and constructed using high strength concrete.
Nonetheless, with changing the outline geometry of reinforcement in alternating piles, all piles could be reinforced if strength and stiffness requirements deem so. Water-tightness could also be improved by a combination of mortar repairs, local grouting and shotcreting. Normally secant pile walls are needed for exceptionally deep excavations and high groundwater levels.
- Berlin Walls:
A sequence of I / H steel soldier beams of selected section moduli are normally vibrated (or dropped into pre-drilled holes and gravel backfilled) to the designated depth below excavation level and in a manner that the respective flanges of adjacent soldiers are oriented to line up with each other. The soil is thin gradually excavated as timber lagging or precast concrete panels are sled down the cannels formed between the flanges and webs of mutually adjacent soldiers and the process continues in stages until full excavation depth is reached. Berlin walls may be cantilevered or constructed with supports (braces and/or tie-backs) depending on; the prevailing ground conditions, depth of excavation supported and preferred design/construction details
Depending on the prevailing ground conditions, normally 5.0-7.5m excavation depths seem to be the upper limit in the vicinity supported using this system. Berlin walls are naturally not water tight and therefore can’t be used without extensive external and internal dewatering systems provisioned. Length, section and spacing of the soldiers are determined in the design to ensure strength, stiffness and overall stability of the wall which could be analyzed and determined. Likewise, strength and section properties of the lagging and/or concrete panels must be designed as well, so should the supports, if any (including bearing plates and waler beam sections).
In the case of temporary Berlin walls, and once the permanent construction is completed and the excavation backfilled, the beams are normally extracted by conventional vibratory pile extracting methods.
- Sheet Pile Walls:
Sheet pile shoring wall systems are flexible, hot rolled structural steel retaining wall sections; coming in different shapes, dimensions, strength and stiffness. The sections are driven by conventional vibrating or hammering systems into the soil or else pre-bored and driven into rock. The common-most of sheet pile types used in the area are Larsen, Z, U, straight, angled and other standard sections. Normally, sheet piles are rolled in mild steel version or in their high tensile counterparts. They are also rolled in a range of alloying elements to suite the environment in which they serve. Traditionally, sheet piles come in 12m long sections and may be either cut to shorten or spliced to lengthen as needed. Sheet pile sections come with strong interlocking clutches to join adjacent sections of piles together to compose a wall that is rather water tight. Clutches could be mortar filled or grouted with different materials to be made fully water-tight. Sheet pile walls may be combined with other structural steel sections or concrete piles for added strength, stiffness and attain the outline shape required as needed.
Sheet piles walls are constructed by establishing a steel guide frame ensuring the wall is controlled in alignment and verticality and that the sections do not declutch during driving. Driving is normally achieved by standard hydraulic vibrating hammers systems fixed to the booms of a rig or suspended from heavy crawler cranes. Sheet piles when well clutched and penetrate sufficiently below excavation levels form water tight shoring wall systems. Sheet pile walls may be designed as cantilevers or may be tied-back, propped and waled. And all these elements need to be designed for strength and stiffness and dimensioned carefully.
- The range of concrete pile diameters available are:
Bored piles involve boring a cylindrical hole into the ground (cased if so needed), installing designated steel reinforcement in a centralized manner at the designated level and filling the cylindrical hole with concrete to form a RC columnar element. Boring is usually carried out to the required depth and diameter by means of purpose-built, crawler-mounted, hydraulic drilling machines of different makes, models and capacities to suite the ground conditions and pile dimensions (diameter & depth) of concern. Bored pile foundations are suitable for all types of ground (soil and rock) and compared with their conventional driven counterparts, bored piles are more productive, less tedious and less disruptive to the surrounding environment in terms of noise and vibrations.
The anchorage is formed of a dial plate resting on a bearing plate fixed at the wall surface and strands transfer load to the dial plate and hence to the bearing plate through steel wedges. Strands are normally pre-stressed to different designated degrees. Anchors are either supported on waler beam systems or in capping beams of shoring walls or in cases directly bearing onto the pile concrete surface.
- Soil Nails & Rock Bolts
These are a form of tie-backs involving a central reinforcing element centrally positioned in a borehole grouted in place using a high strength grout material along its full length and externally tightly bearing on an anchorage plate through a form of stressing element (nut or other). Design, detailing and material selection depends on the service purpose, time and environment.
- Propped Systems:
Due to non-accessibility of adjacent space, anchorage may not be permitted for supporting shoring walls and then internal strut (prop) systems are to be provided. A prop is a horizontal (or inclined) strut that supports in between two shoring wall or at an inclined on the ground (or a lower bearing surface) and using a form of load distributing element like a waler beams etc. The design, detailing and material selection of propped support systems depend on purpose and spatial constraints.
Shoring is a term used to describe a system that functions to retain earth, water, and adjacent existing assets when an excavation is required. Shoring design can be a very complicated matter. The designer has to reckon with many unknowns and factors that influence the behavior of the shored excavation and surroundings. Typically, there are two systems in excavation shoring that must be designed:
- - The earth retention System that restrains the earth i.e. the shoring wall and;
- - The supports (i.e. the internal or external bracing such as tie-backs, struts, waler beams…etc) and that brace up the earth retention wall system.
Performing detailed analysis & design calculations for both systems can be a time consuming process; especially when governing parameters have to be changed. Also many current software packages do not offer an integrated platform for geotechnical and structural analyses required to properly design shored excavations. As a result, the designer is forced to use numerous software programs to analyze the system separately. With the exception of the finite element analyses method, there are limited theoretical solutions for analyzing shoring systems in an integral manner. As a result, the whole process can become unnecessarily complicated and time consuming. Shoring can be designed with both traditional linear and non-linear methods of analyses. For while it is realized that traditional methods of analysis have obvious limitations in accurately predicting shoring behavior, they are important for framing the problem and providing a check on the more rigorous numeric modeling methods.
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