Soil consolidation by grout injection has many applications, for example for the consolidation of embankment dams, for construction anchor and tendon systems, and for foundations for buildings and other constructions on dry land or on sea or lake beds. Particularly in soft earth and marshíand, a common technique for stabilizing constructions is to inject cement grout by means of a long assembly of perforated steel tube sections, sometimes called"piles", inserted in the earth to the depth required for the foundation. The grout cement injected into the perforated steel tube forms a roughly cylindrical cement column or pillar shaped foundation. The columr shaped foundations can be injected individually, or a plurality of piles may be spaced relatively closely together so that the injected cement columns combine together to form an integral large volume underground foundation. The perforated tubes or piles for injection of the cement grout remain in the foundation and may also be used as reinforcements or tendons.

In conventional soil consolidation grouting procedures, a hole is first bored into the ground to the required depth for the foundation, the drilling tool being subsequently removed and the perforated grouting pile assembly inserted into the hole. In conventional systems, the perforated grouting tube is provided with an outer elastic sleeve that blocks groups of perforations provided at levels along the tube and an injection head is inserted in the grouting tube. The injection head is provided with sealing sleeves either side of the injection nozzles to ensure that grout is injected through the tube perforations only at one of the intervals. The injection head is raised in intervals and aligned with a group of perforations of the corresponding interval to inject cement grout into the surrounding soil. The injection of grout at different height intervals serves to ensure that cement grout is injected first at the lower end of the pile assembly and in stages or increments further up the pile assembly to ensure that a substantially regular and continuous column of cement grout is injected into the earth. In the absence of such a system, cement grout would tend to be injected into the earth at positions of lowest resistance, whereby a discontinuous or very irregular distribution of cement grout in the earth surrounding the perforated pile assembly would ensue.

One of the main disadvantages of the above described conventional method and apparatus is that it is often necessary to first drill the hole into which the perforated pile assembly is inserted, which is time consuming and therefore costly. One of the reasons for a need to drill a hole in advance of inserting the perforated pile is to avoid a damage to the outer sleeve that is used for sealing the groups of perforations against entry of injected grout when the injection head is at a lower height level.

In view of the aforementioned considerations, an object of this invention is to provide a grouting method for injecting grout into soil and a grouting apparatus therefor, that reliably injects a relatively uniform grout foundation, and that is economical, in particular that requires few operations and is not time consuming.

Objects of this invention have been achieved by providing the grouting apparatus according to claim 1, and a method of grouting according to claim 4.

Disclosed herein is a cement grouting apparatus for soil consolidation or building foundations comprising a perforated tube assembly insertable into soil, extending from a lower extremity to an upper extremity, and a grout feed injection device system (also called an"integral packer") insertable in a cavity of the perforated tube assembly, the grout feed injection device system comprising a grout injection head and an expansible conduit for feeding grout to the injection head, whereby the expansible conduit is adapted to expand sufficiently within the perforated tube assembly to block the perforations in the tube assembly at the grout injection pressure. The grout injection head may be progressively moved in stages from the lower extremity towards the upper extremity of the perforated tube assembly, whereby the grout injection feed system may be replaced with a system having a shorter conduit, when injection is temporarily stopped and the pressure in the expansible conduit drops, such that the expansible conduit contracts. Grout injection may then be resumed whereby the injection pressure is applied, such that the conduit expands and blocks the tube assembly above the injection head.

The injection head may advantageously comprise a pressure release valve that opens only after a certain pressure is attained, such pressure being sufficient to expand the expansible conduit to block the perforated tube assembly there above.

Advantageously, the perforated tube may be inserted into the ground by vibration or other techniques without prior boring or drilling of an insertion hole, without the risk of damaging the apparatus, in particular since the expansible conduit and injection head are received in the perforated tube assembly and protected thereby, and there is no need for sleeves around the outside of the tube assembly. Grouting operations are therefore economical in the number of operations required and the time consumed.

Further advantageous features of the invention will be apparent from the following description, claims and drawings, in which : Fig. l a is a partial sectional view of a grouting apparatus according to this invention, comprising a perforated tube assembly and a grout injection feed with an injection head thereof in a lowermost position prior to grout injection ; Fig. 1b is a view similar to Fig. 1a of the apparatus according to the invention, whereby the grout injection head is in a subsequent raised position after a first grout injection step ; Fig. 1c is a view similar to Fig. 1b with the grout injection head in a subsequent raised position in a subsequent grout injection step; Fig. 2 is an exploded view of the grout injection head.

Referring to Figures 1a to 1c, a grout injection apparatus 3 according to this invention comprises a perforated tube assembly 4 and a grout injection feed system 5a, 5b, 5c insertable in the cavity 6 of the perforated tube pile assembly 4. Multiple apparatuses 3 may be inserted into the ground to inject multiple cement grout foundations 2, whether vertically or at an angle. It is also possible to position a plurality of grout injection apparatuses 3 in close proximity to consolidate a large single volume, depending on the soil properties and type of construction to be built on the foundation.

The perforated tube assembly 4 comprises a plurality of perforated tubular piles 7 stacked end to end and held together by means of threaded sleeve fittings 8, the number of piles 7 stacked end to end and depending on the depth of the foundation 2 that is required. In soft earth or marsh) and, the depth of the foundation may typically be in the range of 10 to 20 meters below ground level. The perforated tube assembly 4 may further comprise a pointed and possibly hardened tip 9 at its lower extremity 10 to assist the insertion of the perforated tube assembly into the ground, for example by vibrating the assembly as it is hammered or force inserted into the ground. The tip 9 may also be provided with a non-conical shape, much like a drill bit, whereby the pile assembly may be rotated possibly in combination with vibration and hammering in order to insert it to the required depth depending on the property of the earth.

Advantageously, as the grout feed system 5a, 5b, 5c is provided entirely within the cavity 6 of the perforated tube assembly 4 and is thus protected thereby, insertion of the assembly into ground without prior forage is possible.

The grout injection feed system 5a, 5b, 5c comprises an expansible conduit 11 a, 11b, 11c for feeding cement grout under pressure to a grout injection head 12 connected to a lower extremity of the expansible conduit 11. The expansible conduit may be provided with different lengths, as seen in Figures 1a to 1c, in order to change the depth at which the injection head 12 is positioned.

As can be seen in Fig. 1a and Fig. 2, the injection head comprises a pressure release valve comprising a spring-mounted valve pin 13 receivable against a valve seat 14 in a valve housing 15 of the injection head. A plug 16 provides a seat 17 for the spring 18 and closes the end 19 of the housing 15. The housing 15 is provided with outlet holes 20 for injection of the under pressure flowing past the valve 13. The injection head further comprises a conduit connection tube portion 21 that is mountable to the valve housing 15, and to which the end of the expansible conduit 11 a, 11 b, 11 c may be fixed. The valve serves to prevent grout from being injected until a certain pressure release is attained, for example four bars, whereby at the valve release pressure the expansible conduit, which is preferably made of an elastic material such as vulcanized rubber, expands and plugs the cavity 6 of the perforated tube assembly just above the injection head 12.

Therefore, once the perforated tube assembly has been inserted into the ground to the required depth, the grout feed system 5a with the longest expansible conduit Ha is received in the cavity 6 of the tube, such that the injection head 12 is first positioned in the region of the lowermost pile or piles 7, as shown in Fig. 1a. Cement grout is then fed under pressure through the expansible conduit to the injection head 12, whereby the expansible tube expands against the inner wall of the cavity 6 and the valve 13 subsequently opens at the valve release pressure. Cement grout under pressure is thus injected through the outlet holes 20 into the cavity 6 of the tube assembly below the expansible conduit 11 a and through the perforations 22 in the piles into the surrounding ground. The grout injected under pressure displaces the surrounding soil to form a substantially cylindrical column of grout. Subsequently, once sufficient grout has been injected, which may be controlled by measuring the volume of grout injected and/or the injection pressure, injection is interrupted and the pressure dropped until the expansible conduit 11 a contracts, whereby the grout feed system 5b may be raised through the top extremity 23 of the tube assembly 4 and replaced by the grout feed system 5b having a shorter expansible conduit 11b. The injection procedure may then be recommenced.

The height H that the injection outlet device is raised at each successive injection cycle, which corresponds to the difference in length between successive conduits 11a, 11b, 11c, may be determined empirically, and will depend on parameters such as the injection pressure and soil conditions, the objective being to produce a relatively uniform distribution of grout over the depth of the tube assembly.