EP0437262A1

EP0437262A1 - Method for preventive consolidation of the soil for underground minings

Info

Publication number: EP0437262A1
Application number: EP91100265A
Authority: EP
Inventors: Davide Trevisani
Original assignee: Trevi SpA
Current assignee: Trevi SpA
Priority date: 1990-01-11
Filing date: 1991-01-10
Publication date: 1991-07-17
Anticipated expiration: 2011-01-10
Also published as: IT9003306A0; DE69103027D1; DE69103027T3; ATE109234T1; IT9003306A1; EP0437262B2; DE69103027T2; EP0437262B1; IT1238428B

Abstract

A method for the preventive consolidation of tunnel excavations by using the protective umbrella techinique, exploiting an equipment comprising: a metallic tube (1) of reinforcement, a tubular rod (12) provided with nozzles, a piercing bit (4) and a double rotary unit. The process comprises the following phases:

a) mainly sub-horizontal drilling of the soil with the piercing bit (4) coaxially contained inside the tube (1), said tube (1) and said rod (2) being rotated one opposite to each other by a rotary unit;
b) injection of pressurized liquid mixtures through the nozzles of the rod (2) with the removal of the finest part of the soil that is being consolidated;
c) extraction of the rod from the inside of the tube.

Description

The object of the present invention is a method for preventive consolidation of the soil for underground minings by means of the so-called techinique of the protective umbrella, in particular for unstable kinds of soil.
Among the present techniques for the preventive consolidation of underground minings in particularly unstable soil, there is one known as the "protective umbrella", which consists in slipping a line of steel tubes provided with nonreturn valves for executing injections of stabilizing and consolidating mixtures, mainly cement grout.
The tubes are disposed lime an umbrella, protecting the vault of the tunnel under construction so as to allow to dig parts of it wiht a limited lenght. 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 consolidating injections.
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 consolidating 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 consolidating mixtures are injected into the soil, through the holes of the tube, breaking the sheating.
As an alternative to such technique, the provisory casing can be executed with the techiniques used for realizing jet-grounting columnar treatments, that form columns of consolidated soil by injecting high pressurezed concrete 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.
A purpose of the present invention is to propose a method for the preventive consolidation of tunnel excavations that can be executed in a simple and quick way.
This aim is obtained, according to this invention, by using the protective umbrella techinique, exploiting an equipment comprising a metallic tube of reinforcement, a tubular rod provided with nozzles, a piercing bit and a double rotary unit, characterized in that it comprises the following phases:

a) mainly sub-horizontal drilling of the soil with the piercing bit coaxially contained inside the tube, said tube and said rod being rotated by a rotary unit;
b) injection of pressurized liquid mixtures through the nozzles of the rod with the removal of the finest part of the soil that is being consolidated;
c) extraction of the rod from the inside of the tube.

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 that follows the one shown in fig. 1.

With reference to figs. 1 and 2, for the realization of the process, a straight metallic tube 1, preferibly made out of steel, and a straight tubular rod 2 are used. Said rod has a diameter that is smaller than the one of the tube 1 and a double rotary head, which is not shown in the figures, is used to rotate both the tube and the rod.
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.
In operating conditions, the rod 2 is slipped into the tube 1 and is kept coaxial with respect to the tube by the rotary unit.
The boring tool 3 is positioned and kept outside the front end of the tube 1 and is directed perpendicularly to the soil that has to be consolidated. The assemble formed by the rod 2 and the tube 1 is rotated by the rotary unit for piercing the soil and proceed this way. The rotary 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.
The material that is produced by the drilling is conveyed towards the outside through the annular hollow space 5 between the rod 2 and the inside annular surface of tube 1. 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. When the right lenght 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. In a favourite 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.
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.

Claims

A method for the preventive consolidation of tunnel excavations by using the protective umbrella technique, exploiting an equipment comprising a metallic tube (1) of reinforcement, a tubular rod (2) provided with nozzles, a piercing bit (4) and a double rotary unit, characterized in that it comprises the following phases:
a) mainly sub-horizontal drilling of the soil with the piercing bit (4) coaxially contained inside the tube (1), said tube (1) and said rod (2) being rotated by a rotary unit;

b) injection of pressurized liquid mixtures through the nozzles of the rod (2) with the removal of the finest part of the soil that is being consolidated;

c) extraction of the rod from the inside of the tube.
The process defined in claim 1 wherein said rod (2) and said tube are forced to rotate at the same time in the opposite rotating directions.
The process defined in claim 1 wherein said injection of pressurized mixtures causes the formation of a column (6) of treated soil surrounding said tube (1) and that stiffens after being mixed up with the injected mixtures.
The process defined in claim 1 wherein said tube (1) in which the rod (2) is slipped during the drilling is then left inside the column (6) of consolidated soil as a reinforcement.
The process defined in claim 1 wherein said tube (1) is removed from the treated soil so that a column (6) of non reinforced soil is formed.
The process defined in claim 1 wherein said rod (2) is maintained in the inside of said tube (1) coaxially and with the piercing bit (4) sticking out of the front end of the tube (1), said rod (2) having a plurality of nozzles disposed radially near the piercing bit (4).