[0001] The object of the present invention is a method for preventive stabilisation of the
soil forunderground minings by means of the so-called techinique of the protective
umbrella, in particular for unstable kinds of soil.
[0002] Among the present techniques for the preventive stabilisation of underground minings
in particularly unstable soil, there is one known as the "protective umbrella", which
consists of inserting into the soil arrays of steel tubes provided with nonreturn
valves for executing injections of stabilising and consolidating mixtures, mainly
cement grout.
[0003] The tubes are disposed like an umbrella, protecting the vault of an intended tunnel
excavation so as to allow excavation of parts of it within a limited length. The excavation
of the parts of the tunnel is alternated with the execution of said umbrellas of steel
tubes that is combined with the soil stabilising injections.
[0004] The technique that is normally used comprises a phase in which the soil is drilled
with a temporary and recoverable steel tubular casing; in a second phase a steel tube
is fitted inside the casing. This tube is provided with holes at regular intervals
and has elastic sleeves, in correspondence of each hole, that act as nonreturn valves
when the stabilising mixtures are injected through the tube. A following phase is
that of the recovery of the provisory casing, after which a grout sheating is formed,
having a controlled maximum compressive strength, for sealing the injecting tube into
the soil. In the end, the stabilising mixtures are injected into the soil, through
the holes of the tube, breaking the sheating.
[0005] An alternative technique is to execute the provisory casing with the techiniques
used for carrying out jet-grouting columnar treatments, that form columns of consolidated
soil by injecting high pressurized grout mixtures by means of a tubular rod provided
with nozzles for letting the mixture out and with a piercing bit that is made to rotate
and is extracted and pushed into the ground with a controlled speed.
[0006] Traditional jet grouting is used to execute substantially vertical columns by drilling
the soil by means of a hollow drill pipe having a piercing bit at its bottom end and
a plurality of nozzles proximate thereto. After drilling operations are completed,
grout injection is carried out in an ascending phase, beginning from the bottom of
the borehole. The jet grouting technique cannot be employed conveniently for executing
substantially horizontal columns because problems arise if the grout feeding is interrupted
due to drill pipe damages or substitution of parts. The walls of the hole tend to
collapse rather easily, owing to the fact that the grout in a substantially horizontal
borehole cannot sustain the walls as it does in vertical boreholes.
[0007] Moreover, as the function of the consolidated columns is to temporarily sustain the
soil above them while a tunnel is dug out underneath, the columns must be reinforced
to resist shear and bending stresses that occur when archings are placed underneath
them.
[0008] According to the known technique of drilling first and then injecting from the bottom
of the borehole, the metal reinforcement can be fitted only when the column is formed.
Two alternative methods can be used:
- a reinforcing steel tube is inserted as soon as the column is completed, therefore
the tube will tend to move, because if its weight, to the lower part of the semi-solid
column and it will not be coaxial with respect to it;
- the reinforcing tube is inserted in the column when this is already stiff, after
having drilled the centre of the column; then it should be sealed by injecting additional
grout.
[0009] All of the above identified inconveniences, that render horizontal jet grouting impractical,
expensive, slow or even dangerous, are avoided by using a method according to this
invention, in which the grout injection is executed advancing, simultaneously with
drilling operations. In this case an outer hollow tube protects hollow grout delivering
rods and guarantees an annular space therebetween through which the grout can flow
out. Borehole wall collapses have therefore no influence on the operations, whatever
kind of soil is being drilled.
[0010] Moreover, to reinforce the column it is enough to extract only the rods, leaving
the outer tube inside the column and exactly in the centre of it.
[0011] Document JP-A-58-228558 discloses a method in which a borehole is excavated first,
and after that, a planking pipe is installed in the hole. Then, a grout pipe with
packings is inserted inside the planking pipe. The packings are then inflated and
a grout is injected at low pressure through the grout pipe and discharge holes of
the planking pipe so as to fill the space between the excavated hole and the planking
pipe. Finally, the grout pipe is pulled off, and the planking pipe is filled with
mortar. This method suffers from the above drawbacks, and is not suitable for high
pressure grout injections.
[0012] Document JP-A-55-64395 relates to a method for executing vertical reinforcing concrete
pillars by means of an apparatus that comprises a hollow grout delivering shaft having
a bottom excavating blade. The shaft is located inside a cylinder having a bottom
agitating blade and both the shaft and the cylinderare rotated in opposite directions.
This method is not suitable for executing substantially horizontal columns that are
required for tunnelling with the protective umbrella technique.
[0013] Document DE-A-3447872 discloses a soil stabilising method for tunnelling in which
a plurality of boreholes are obtained in the soil about an arc of a circle outlining
a tunnel that has to be dug out. A tube provided with valves and surrounded by a jute
bag is slipped in each borehole, and an injection packer is inserted in each tube
for injecting a fluid mixture that fills the bag, presses the walls of the borehole
and infiltrates in the surrounding soil. The fluid mixture in the bag and the portion
that has penetrated in the soil consolidates and stabilises the soil. Also this method
suffers from the same inconveniences as JP-A-58-228558, and is incompatible with high
pressure grout injections.
[0014] It is an object of this invention to provide a method for stabilising the soil for
tunnel excavations capable of overcoming the above inconveniences.
[0015] These and further objects and advantages, which will be more apparent hereinafter
are attained by using a method according to Claim 1.
[0016] The details of this invention will appear more clearly from the detailed specification
of a favourite form of execution of the process for tunnel excavations that is illustrated
in the enclosed drawings, in which:
fig. 1 shows a phase of the present process;
fig. 2 shows a phase following the phase of fig. 1.
[0017] With reference to figs. 1 and 2, for carrying out the process, a straight metallic
hollow tube 1, preferably made out of steel, and a straight hollow rod 2 are used.
Said rod has a diameter that is smaller than the one of the tube 1 and a double rotary
drilling unit, which is not shown in the figures, is used to rotate both the tube
1 and the rod 2.
[0018] The rod 2 is provided at one end with a boring tool indicated as a whole with 3 which
comprises a traditional piercing bit 4 and near this there are nozzles that are distributed
radially on the rod and that communicate with the outside. The tools that are hereby
mentioned are not described in details, as they are traditional and already known.
[0019] In operating conditions, the rod 2 is slipped into the tube 1 and is kept coaxial
with respect to the tube by the rotary drilling unit.
[0020] The boring tool 3 is positioned and kept outside the front end of the tube 1 and
is directed perpendic- ularto the soil that has to be stabilised. The rod 2 and the
tube 1 are both rotated by the rotary drilling unit for piercing the soil and proceed
this way. The rotary drilling head forces the rod 2 and the tube 1 to rotate at the
same time but in the opposite directions of rotation. For example the rod 2 is rotated
clockwise while the tube 1 is being rotated counter-clockwise.
[0021] The material that is excavated by the drilling operation is conveyed towards the
outside through the annular hollow space 5 between the rod 2 and the inner annular
surface of tube 1.
[0022] Simultaneously to the proceeding of the tube 1 and the rod 2 in the soil, high pressurized
liquid mixture is injected through the rod, removing the finest part of soil. The
mixture flows through the nozzles forming a column 6 of soil and grout mixture around
the tube 1 that later on will stiffen.
[0023] When the right length of the column 6 is obtained, the rod 2 has to be pulled out
of the tube 1 and taken away whereas the tube 1 may be left in the soil so to form
columns of reinforced soil.
[0024] In a preferred form of realization of the first phase of the piercing process, the
tube 1 and the rod 2 are forced to advance and spin according to prefixed parameters
in a direction substantially oblique compared with the level line so that columns
are formed in such a way that they partially lie one over the other like the scales
of a fish.
[0025] As it can be observed, the process that has been described cuts off some phases of
the traditional process establishing a column of consolidated soil in a shorter time.
1. A method for stabilising the soil for tunnel excavations by inserting into the
soil arrays of steel tubes with valves for the injection of grout into the soil about
an intended tunnel excavation, characterised in that it comprises the steps of:
- locating a hollow tube (1) at an excavation site;
- positioning a hollow rod (2) coaxially within said hollow tube (1) wherein an annular
space (5) is defined between the rod (2) and the tube (1), the hollow rod being fitted
with boring means (3) on one end thereof;
- rotating the hollow tube (1) and the hollow rod (2) for excavating material from
said excavation site by means of said boring means (3);
- injecting a high pressurized fluid mixture through said hollow rod (2) into said
excavation site proximate to the boring means (3) during rotation of the hollow tube
(1) and the hollow rod (2) wherein a portion of the finest part of the excavated soil
is removed from the excavation site via said annular space (5) and said fluid mixture
admixes with the remaining portion of the excavated material for forming a solidifying
column (6) of soil and fluid mixture; and
- removing said rod (2) from the hollow tube (1).
2. A method according to Claim 1, characterised in that during excavation the tube
(1) and the rod (2) are forced to proceed simultaneously and are rotated in opposite
directions.
1. Verfahren zum Stabilisieren des Bodens zur Tunnelausschachtung durch Einbringen
von Gruppen von Stahlrohren mit Ventilen in den Boden zum Injizieren von Zement in
den Boden um die beabsichtigte Tunnelausschachtung
dadurch gekennzeichnet, daß
- ein hohles Rohr (1) an einer Ausschachtungsstelle angeordnet wird;
- eine hohle Stange (2) koaxial in dem hohlen Rohr (1) angeordnet wird, so daß ein
ringförmiger Zwischenraum (5) zwischen der Stange (2) und dem Rohr (1) gebildet wird,
wobei in die hohle Stange eine Bohreinrichtung (3) an deren einem Ende eingesetzt
wird;
- das hohle Rohr (1) und die hohle Stange (2) gedreht werden, um Material aus der
Ausschachtungsstelle mittels der Bohreinrichtung (3) auszuschachten;
- ein Hochdruck-Fluidgemisch durch die hohle Stange (2) in die Ausschachtungsstelle
nahe der Bohreinrichtung (3) während der Drehung des hohlen Rohres (1) und der hohlen
Stange (2) injiziert wird, so daß ein Teil des feinkörnigsten Anteils des ausgebaggerten
Bodens aus der Ausschachtungsstelle über den ringförmigen Zwischenraum (5) entfernt
wird, und das Fluidgemisch mit dem verbleibenden Anteil des ausgeschachteten Materials
vermischt wird, um eine Verfestigungssäule (6) des Bodens und des Fluidgemisches zu
bilden; und
- die Stange (2) aus dem hohlen Rohr (1) entfernt wird.
2. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, daß
während des Ausschachtens das Rohr (1) und die Stange (2) gleichzeitig vorgerückt
und in entgegengesetzten Richtungen gedreht werden
1. Procédé pour stabiliser le sol dans des excavations de tunnels, dans lequel on
enfonce dans le sol des rangées de tubes d'acier équipés de vannes pour injecter du
mortier dans le sol autour d'une future excavation de tunnel, caractérisé en ce qu'il
comprend les phases consistant à :
- placer un tube creux (1) dans un site d'excavation ;
- positionner une barre creuse (2) coaxiale- ment dans le tube creux (1), un espace
annulaire (5) étant défini entre la barre (2) et le tube (1), et ledit tube creux
étant muni à une de ses extrémités de moyens de forage (3)
- faire tourner le tube creux (1) et la barre creuse (2) pour creuser le matériau
du site d'excavation à l'aide desdits moyens de forage (3)
- injecter un mélange fluidique sous haute pression dans le site d'excavation, par
ladite barre creuse (2), à proximité des moyens de forage (3) pendant la rotation
du tube creux (1) et de la barre creuse (2), une partie de la fraction la plus fine
du sol creusé étant évacuée du site d'excavation par ledit espace annulaire (5), et
ledit mélange fluidique se mélangeant avec la partie restante du matériau creusé pour
former une colonne (6) de sol et de mélange fluidique qui se solidifie ; et
- extraire ladite barre (2) du tube creux (1).
2. Procédé selon la revendication 1, caractérisé en ce que, pendant l'excavation,
le tube (1) et la barre (2) sont contraints à avancer simultanément, tout en étant
mis en rotation en sens inverse l'un de l'autre.