JET GROUTING

Underpinning the existing buildings and sheeting of a part of a deep foundation pit; the Penta Hotel in PragueJet grouting is a modern, fast and effective method of creating special foundation elements in soils and possibly in semi-solid rocks. The technology is based on grouting from a hole into surrounding soil carried out under high pressure of 30–55 MPa and with the use of cement and clay-cement mixtures.

A jet of grout mixture flowing through nozzles disaggregates a rock into separate chippings or individual grains, while they are mixed together and after their hardening they create desired elements (column, panel or their combination) and improve the qualities of grouted ground.

After a hole is drilled to a projected depth, cement mixture is pumped underhigh pressure into nozzles above the drilling tool. A jet of cement mixture goes through a nozzle and cuts and mixes the soil to the distance of 40–140 cm, if the method M1 (monophase) is used. With the M2 method (double-phase air) the jet of cement mixture is additionally rectified by a coaxial stream of compressed air to the distance of 120–220 cm.
If the grouting string of rods is turning a foundation element– a column – is created. This is the most common use of this technology. If the grouting string of rods is not turning in the process of pulling out, a plane underground element is created, either as a segment or a wall. Strengths of created elements range between 0,5 to 15 MPa depending on the soil type, permeability coefficient lies within the scope of k = 10−8to 10−9 m.s−1.

Detailed view of a grouting string monitor used with the M2 methodUnderpinning of a foundation foot of an existing building with jet grouting columns;reconstruction and finalisation of building works at the Slovansky House in Prague


 

The principle of jet grouting technology with the use of methods M1 and M2The principle of jet grouting technology with the use of methods M1 and M2Princip technologie tryskové injektáže metodou M1 a M2
1a) grout mixture
1b) compressed air
1c) washed-up material
1d) a jet of grout mixture
1e) a jet of grout mixture and compressed air
1f) grouted column of soil

 

 

 

Area of applicability of jet grouting in individual soils compared with standard and chemical grouting

Grafické znázornění využitelnosti klasických injektáží a injektáže tryskové v závislosti na typu injektované zeminy

Technological process of carrying out jet grouting

3a) Realisation of a medium-profile hole for jet grouting
A drilling set drills a hole to the bottom of a prospective jet grouted column. The drilling and grouting string of rods is equipped with a drilling tool anda monitor.
3b) Realisation of a jet grouted column
The transition from the drilling mode to grouting is done by redirecting grout mixture from the wash-up mode to the grouting one by inserting a steel ball into the drilling set. The ball closes the intake to wash-up openings and the mixture starts flowing into a nozzle-equipped monitor. The drilling set is equipped with a cycling and monitoring system that maintains and controls parameters of adjusted grouting pressure of mixture if the M1 method(monophase) is used, and parameters of air pressure if the M2 method (double-phase air) is used, grout mixture batching, rotation speed and gradual pulling out of the monitor.
3c) Finishing of a jet grouted column
Machine-controlled process of high-pressure grouting is stopped after reaching the upper projected level of grouting. The drilling set is further repositioned to a new hole and the described technological procedure is repeated.

Technological process of carrying out jet grouting

Underpinning of foundations of an existing building with jet grouting columns Sheeting of a foundation pit with a jet grouted anchored wall and concurrent securing of the neighbouring building
Podchycení základů stávajícího objektu sloupy tryskové injektáže Zapažení výkopu stavební jámy kotvenou stěnou z tryskové injektáže a současné zajištění sousedního objektu

 

Carrying out jet grouting courtain to secure the existing buildings within the collector driving works in PragueFinal sealing of a building cofferdam made of sheet piles with a jet grouting cut-off; reconstruction of the pillars no. 8 and 9 of the Charles Bridge in PragueStrutting of deep diaphragm walls with a huge jet grouting block; the technological centre of the Královopolské Tunnels in Brno

Sealing a building cofferdam bottom under a bridge pillar with a jet grouting board; the Apollo Bridge in Bratislava



Securing an underground work driving with a compact envelope made of jet grouting columns under the groundwater level Creating a sealing screen from jet grouting columns
Zajištění ražby podzemního díla celistvou obálkou ze sloupů tryskové injektáže pod hladinou podzemní vody Vytváření těsnicí clony ze sloupů tryskové injektáže

Alternative use of jet grouting columns
8a) jet grouting column
8a) field of jet grouting columns
8c) jet grouting wall
8d) doubled jet grouting wall
8e) jet grouting slab

Alternative use of jet grouting columns

Drilling a hole to secure a service connection stope with a jet grouting envelope; the Centre I.A collector in PragueBecause of the specific qualities of jet grouting, it is used in a wide range of rocks (from soft slushy and fine-grained soils to gravels). It can be rather suitable for underpinning foundations (a change of load as a consequence of building reconstruction, cuts close to foundations)for building impermeable walls preventing spreading of pollution (see Chapter Environment – Soil and Water Protection,Diaphragm walls), for creating envelopes of driven underground works, for casing walls of foundation pits in confined spaces, for sheeting of shafts, for breaking shear surfaces of slides, for consolidation of compressed soils, for carrying out anchor roots in complex geological conditions and for final sealing of sheeting constructions of other systems.

Creating an envelope from individual jet grouting columns for securing the subsequent over break of a tunnel gallery. The securing of tunnel callots and subsequent driving of the gallery is carried out step by step.

 

Vytváření obálky z jednotlivých sloupů tryskové injektáže pro zajištění následného výrubu štoly tunelu. Zajištění kaloty tunelu a následná ražba štoly se provádí po jednotlivých krocích.

Carrying out a jet grouting envelope to secure drivings realised in sections;the Centre I.A collector in PragueSheeting a part of a building shaft with a jet grouting wall