GB2367840A - Method of combating soil movement in a foundation trench - Google Patents

Abstract

The method for combating soil movement in a foundation trench filled with poured concrete involves, prior to the filling of the trench with concrete, fixing a compressible fill material to a wall of the trench with one or more fixing elements characterised by the imparting of a turning motion to the or each fixing elements as it is driven into the trench wall. Preferably the turning motion is combined with a linear driving force. The or each fixing elements may comprise a pin 11 formed from a narrow strip that has a longitudinal axis about which a twist has been imparted along its length. The pin may have a pointed end 78 and at least one and a half twists along its length. The pin preferably co-operates with a stationary slot to provide the turning motion and is preferably inserted using an applicator remotely activated from outside of the trench. Also included is a kit of parts for combating soil movement pressures in foundation trenches filled with poured concrete.

Description

2367840 IMPROVEMENTS IN OR RELATING TO COMBATING SOIL MOVEMENT PRESSURE IN

FOUNDATION TRENCHES FILLED WITH CONCRETE The present invention relates to the combating of soil movement pressure in foundation 5 trenches filled with concrete for buildings and more particularly but not exclusively to the combating of clay heave pressure in such trenches.

In the construction of all buildings, it is fundamental that sound underground foundations are first laid. The basic steps in the process of preparing such foundations essentially involve 10 digging a trench in the soil down to a depth at which stable land is reached, laying a compressible fill material against at least one wall of the trench and retaining the compressible fill material in position against at least one wall of the trench whilst filling the trench with poured concrete.

15 The purpose of the compressible fill material is to minimise the risk of the foundations cracking due to soil movements. and settlement of the ground. This problem is especially acute in soils having a high clay content. The compressible fill material acts as a cushioning barrier between the concrete and the walls of the trench, by deforming under the pressure exerted by the swelling and shrinking of the soil. In effect, the compressible fill material 20 absorbs soil movement pressures.

The depth to which the foundation trenches have to be dug depends upon the nature and characteristics of the soil including the depth of any underlying bed rock, which govern the depth at which stable land will be reached at the base of the trench. With, some soils such as 25 dense clay, or where the bedrock is relatively close to ground level, the depth of the trench may be as little as I to 1.2 metres. However, with. more unstable soils, such as those encountered on reclaimed land and those from which trees have been removed, it is not unusual for foundation trenches to be dug to a depth of up to 4 metres before stable land is reached. Typical depths of trench range from about 2.5 to about 3 metres.

To the best of the Applicants' knowledge, compressible fill materials such as expanded 2 polystyrene (EPS) in sheet form have been used for combating soil movement in relation to foundation trenches for some 15 years. For the same period, the Applicants have been involved in the development and manufacture of suitable EPS compressible fill materials.

5 The problem which is routinely experienced with utilisation of EPS compressible fill materials is due to EPS having a density which is considerably less than that of the liquid concrete used for the foundation. The liquid concrete being poured into the trench exerts an upwardly acting force on the EPS sheet as it gradually fills the trench which results in the EPS sheet floating on the concrete and being lifted completely out of its position where it lies 10 on the base of the trench and against the trench wall. This unrestrained movement of the EPS sheet can also result in breakage of the EPS sheet which if left can reduce its ability to combat soil movements with potentially disastrous effects on the foundations of the building. For example, it has been known for clay heave pressure acting on unprotected concrete foundations to move a building supported thereon and cause substantial damage to the 15 building.

Accordingly,. it is essential to restrain the EPS sheet against movements in the trench diiring pouring of the concrete to fill the trench. The construction industry has devised various methods of EPS restraint, almost all of which are in one way or another commercially 20 impractical, and/or do not work, and/or are downright dangerous.

In the past, most methods that have been tried necessitate workmen having to climb down a ladder into the trench, to restrain the EPS sheets by some form of mechanical fixing means.

25 Unfortunately, ever present in foundation trenches is the gave danger of the trench walls collapsing inwards; the deeper the trench and the more unstable the soil the greater the danger. Thus, it will be readily appreciated that this presents a potentially fatal risk to workmen installing EPS fill materials in this way. Indeed, it is not uncommon for injuries and even fatalities to occur. Moreover, the longer the foundation trenches are open to complete a 30 fixing operation, the greater is the danger to the workmen in the trench. This is because on any construction site there is construction equipment such as mechanical diggers moving 3 about the site which engender vibrations in the soil which have caused collapse of the trench walls onto workmen in the trench.

One such method involves the use of steel shuttering which is applied to the trench walls with 5 the EPS sheets being held against the shuttering by means of screw props. This method may require as many as 20 workmen in the trench at any one time. Moreover, even with screw props in position, the concrete being poured may still find its way between the steel shuttering and the sheets resulting in splitting of the sheets. Once the poured concrete has set, the expensive steel shuttering has to be removed which is not easily achieved and the gap left by 10 the removal of the shuttering has to be back filled.

Sometimes the shuttering cannot be removed 'Mthout damaging the recently set foundations. This method is not without danger, is expensive in manpower, time and materials and is therefore no longer in use.

Because of the difficulties and expense encountered with the aforementioned method, up until comparatively recently, a common method was one that involved workmen entering the trench and manually. holding the EPS sheets in position against the trench wall whilst hammering fixing elements, such as metal pins, through the EPS sheet and into the trench 20 wall.)NUlst this method is relatively simple, considerably less time consuming and effective in providing a positive restraint, it still puts the lives of workmen continually at risk because they are forced to enter the trench.

Applicants have experimented with wood en fixing poles which were not viable because they 25 split and with steel T-shaped fixing pins which were discarded because they did not avoid workmen having to climb into the foundation trench.

The rising concern for the safety of workmen in foundation trenches has recently been recognised by the National House Building Council (NHBC) and Government Health & 30 Safety Office which latter were in process of preparing and may, by now, have prepared a directive banning workmen from climbing down into foundation trenches to fix the 4 compressible fill material to the trench walls Accordingly, attention has been directed to overcoming the problem from outside the foundation trench which avoids workmen having to enter the trench. Thus, in another known 5 method, which has not found acceptance because of its time consuming expense and potential for damaging the foundations and the EPS sheets, the concrete is firstly poured into the trench. Then, after the concrete has set a supplemental trench is dug on at least one side of the foundation into which the EPS sheets are inserted, followed by the backfilling of any remaining gaps between the EPS sheets and the wall of the supplemental trench.

These failures led Applicants to research into devising ways of using positive fixing elements such as metal pins to restrain the EPS sheets in foundation trenches without necessitating workmen entering the trench. Applicants investigations have led to the invention described in the specification of Applicants' own earlier specification GB-A-2311081A which discloses a

15 method of combating soil movements, such as clay heave, in a foundation trench filled with poured concrete, in which prior to filling the trench with poured concrete, a compressible fill material, such as an EPS sheet, is fixed to a wall of the trench using fixing elements which are passed into the trench wall to fix the compressible material to the trench wall by means of an applicator which is actuated from outside the trench.

The main advantage of this invention is that workmen do not have to enter the trench positively to restrain the fill material against the trench wall. By means of the remotely actuated applicator, the compressible fill material is simply, easily and quickly fixed by the fixing elements to the trench wall so that the workmen are never exposed to the potential risk 25 of injury presented by collapsing trench walls.

The Applicants invention has been carried into effect under site conditions and has met with a great deal of commercial success, not only fulfilling a long felt want in the construction industry but also meeting the safety requirements may have already been imposed by the 30 NHBC and Health and Safety Office.

However, under certain specific conditions during the use of Applicants' earlier invention, difficulties have been experienced in fixing the EPS sheets because of the composition and condition of the ground fortning the trench walls.

5 With increasingly long dry spells of weather allied with hot summers, it has been found, in some instances, that the ground becomes very hard because the water content is very low and/or has become baked by the sun; this is especially marked with soils having a high clay content. Hard ground is also encountered where the soil includes flint rocks. This means that the trench walls are sometimes too hard adequately to receive the fixing elements, if at all,, 10 and satisfactorily fix the EPS sheets to the trench wall.

An alternative scenario to the trench walls being too hard to take fixing elements, is where the trench walls are too yielding, i.e. they are not sufficiently firm to retain the fixing elements, such as for example in earth having a high sand content.

Accordingly, Applicants have been experimenting with alternative ways of fixing - still from outside the trench - an EPS sheet against a trench wall which does not necessarily require fixing elements.

20 One method which does not need fixing elements is disclosed in the specification of GB-A-2 287 730, in which weights, such as concrete blocks, are lowered to the bottom of the trench on flexible straps and are placed against one side of, and at suitably spaced intervals along the length of, the trench. The straps are then held taut by attaching them to ground anchors in the ground surface outside, and on the same side of the trench. Next, concrete is poured into the

25 bottom of the trench to forin a so called concrete 'toe' which is sufficient to embed the blocks and the junctions between their respective straps in poured concrete. Then the concrete toe is allowed time to stabilise.

The straps are released temporarily from the ground anchors, sheets of compressible fill 30 material are placed in the trench against the trench wall on the same side as the, blocks with their bottoms resting on the concrete toe and the straps are pulled tight and re-secured to the 6 ground anchors to hold the sheets in place. The point at which the lower ends of the straps emerge from the concrete toe is spaced from the trench wall by a distance which is approximately equal to the thickness of the sheets so that each strap applies a force against the exposed surface of the respective sheet from the bottom and top edges of the exposed 5 surface and around the top edge of the exposed surface to hold each sheet against the trench wall during the next pour of concrete onto the concrete toe to fill the trench.

After the trench has been filled with concrete the portions of the straps extending out of the poured concrete are untied from the ground anchors and are cut off flush with the surface of 10 the concrete and the ground anchors can be used again.

When Applicants experimented with this method, they found that the holding force applied to the exposed surface of the sheet by the flexible straps was not always positive enough to prevent poured concrete from forcing its way between the EPS sheets and the trench wall 15 which caused the EPS sheets to split. Hence, Applicants carried out finther experiments and research with a view overcoming the problem of splitting of compressible fill material (EPS sheets) in a method of combating soil movements, such as clay heave, in a foundation trench filled with poured concrete, in which prior to filling the trench with poured concrete, a sheet of compressible material is held against a wall of the trench.

These experiments and research have led to an invention that in one aspect is characterised by applying a force around the bottom and top edges of the exposed surface of a compressible fill material, such as an EPS sheet, in the direction from the bottom edge to the top edge in a foundation trench, to hold the fill material against a wall of the trench, prior to filling the.

25 trench with concrete.

Expressed in another way the invention resides in a method of combating soil movement in a foundation trench filled with poured concrete characterised in that, prior to pouring concrete into the trench, a sheet of compressible fill material is held.against a wall of the trench by 30 applying a force around the bottom and top edges and in the direction from the bottom edge to the top edge of the said compressible fill material.

By applying a force around the bottom edge, as well as around the top edge of the exposed surface of the fill material in the direction from the bottom edge to the top edge of the exposed surface, there is sufficient positive force exerted on the fill material to hold it firmly 5 enough against the trench wall to guard against poured concrete forcing its way up between the fill material and the trench wall. With the method disclosed in the specification of GB-A2,287,730, it is impossible to apply a force around the bottom edge of the exposed surface of the fill material because the bottom of the fill material rests on the concrete toe.

10 In addition, and with soil conditions permitting, fixing elements can be used further to secure the or each sheet of compressible fill material to the trench wall, for example by hammering in fixing elements along the top of the or each sheet in a conventional way, using the remotely actuated applicator described in the Applicants specification GB-A2311081A, or by using an alternative applicator to be described.

In a preferred way of carrying out the method, the holding force extends between the bottom and top edges of the exposed surface of the compressible fill material.

The holding force may be applied by means of a length of any suitable flexible material such 20 as a strap or band, e.g. a length of 75mm wide building contractor's tape which may advantageously also be used to lower the fill material into the trench so that it lies against a trench wall with its bottom edge spaced from the bottom of the trench by a distance of 500mm or 600mm. (BS 6031 1581) so that the requisite "toe" of concrete will, be formed between the trench bottom and the bottom of the sheet when the trench is filled with poured 25 concrete.

An advantage of the invention is that the concrete can be poured in one continuous operation, without having to pour an initial toe which has to be allowed to stabilise before the final pour, as with the method disclosed in the specification of GB-A-2287730. The effect of this is that

30 ready-pour concrete trucks are not kept waiting for as long as the concrete toe needs to stabilise. This waiting time can be up to two hours or more thereby increasing the cost of 8 laying the foundations.

In one way of carrying out the invention, an end region of the or each flexible length is conveniently attached to the bottom of the fill material from outside the trench before the fill 5 material is lowered into the trench and then by pulling on the free end region the length is pulled around the lower edge of the exposed surface, against the exposed surface between its bottom and top edges and around the top edge of the exposed surface to apply the holding force and the free end region is anchored to the ground outside the trench with the flexible length held taut to maintain the force.

Alternatively, the or each flexible length may be in the form of a sling that supports the fill material in the trench with the two sides of the sling extending along the exposed and unexposed surfaces respectively being drawn around the top edges of the exposed and unexposed surfaces respectively and secured together as by knotting on top of or adjacent to 15 the top of the fill material and then the free ends of the sling are anchored to the ground outside the trench with the flexible length held taut to maintain the force.

In another alternative, the or each flexible length may be in the form of a sling that supports the fill material in the trench with the end region on that side of the sling adjacent the trench 20 wall being anchored to the ground outside the trench and then by pulling on the free end region on that side of the sling adjacent to the exposed surface of the sheet, the length is pulled around the lower edge of the exposed surface, against the exposed surface between its bottom and top edges and around the top edge of the exposed surface to apply the holding force. The other free end region of the flexible length is then anchored to the ground outside 25 the trench at a location that is at a greater distance from the trench than the anchoring of the free end region on the side of the sling adjacent the trench wall with both sides of the sling being held taut to maintain the force.

Application of the holding force is facilitated by anchoring the fill material to the trench 30 bottom at a predetermined spacing from the bottom of trench, to provide the requisite toe when the concrete is poured. Alternatively, the predetermined spacing may be maintained by 9 propping the or each sheet from the bottom of the trench.

Anchoring and/or propping are particularly advantageous because they overcome the dangers encountered by workmen entering the trench to provide the spacing necessary to form the toe 5 in methods used prior to the advent of the invention described in the specification of applicant's aforementioned Patent Application No.9605143. 8.

Whatever the form of the flexible lengths, e.g. a single length, a sling or a knotted sling, the anchoring and/or propping action can advantageously be utilised to attach the flexible lengths 10 to the bottom of the fill material.

In such a case the flexible length is tied or otherwise attached to an anchoring or propping member that anchors the fill material to, or supports the fill material from, the bottom of the trench.

Applicants have found, however, that the fill material holding forces are applied, i.e. whether by means of fixing elements or flexible straps, the provision of anchoring the fill material to the trench bottom at a predetermined spacing from the bottom of trench is extremely advantageous because when the concrete is poured in one operation, not only is the requisite 20 toe obtained but also, when the concrete is poured, the anchoring provides resistance to the sheet being forced upwardly under the pressure exerted by the concrete. Indeed it is conceivable that in some instances, anchoring in itself will provide a sufficient holding force.

Accordingly, from another aspect, in a method of combating soil movements, such as clay 25 heave, in a foundation trench filled with poured. concrete, in which prior to filling the trench with poured concrete, a compressible material is held against a wall of the trench, the invention consists in anchoring the fill material at a predetermined spacing from the bottom of the trench.

30 For ease of installation and simplicity of use, the anchoring may be achieved by means of pins having one pointed end (lower in use) which can dig into the soil at the bottom of the trench (upper in use) and its other end also pointed that can penetrate into the relatively soft material of the fill material through its bottom to secure the pin to thereto. In order to ensure that the pin does not readily become loose in the relatively soft fill material and fall out of the fill material, e.g. when being lowered into the trench, the upper end of region of the pin is 5 preferably provided with retaining means such as serrations, a screw thread or the like which facilitates entry into the sheet but resists detachment.

To resist detachment, the serrations may be of saw tooth configuration and in a preferred construction encircle the upper end region of the pin in a number of annular rows.

The pointed lower end of the pin may be provided with suitable reinforcement against bending when the pins are pushed into the bottom of the trench, e.g. by the provision of a series of longitudinally extending fins or ridges which taper in the direction of the pointed lower end. Thus the fins or.ridges are conveniently of triangular form.

is In order to guard against the pin pushing up into the relatively soft material of the fill material for a greater distance than is consistent with maintaining the bottom of the fill material at the predetermined distance form the trench bottom to provide the requisite toe, a spacer means such as a collar e.g. of circular form, is disposed between the upper pointed end and a location on the pin which corresponds to the predetermined distance to abut the bottom of the fill material and support the fill material on the pin.

The pins are conveniently of light-weight axially rigid construction, e.g. of a suitable plastics, and are capable of being gripped by the rising concrete being poured into the trench to hold 25 the pins in position in the trench. And even in the absence of any fixing elements or holding means for holding the fill material against the trench wall it is conceivable that the retention means are capable of exerting a sufficient hold on the sheet to guard against the rising concrete forcing the sheet off the upper pointed end and out of the trench.

30 However, for completeness and to avoid any risk of failure, the practice of the. invention ideally involves the use of the holding force or remotely applied fixing elements referred to hereinabove.

The anchoring pins have another function in accordance with yet another aspect of the method of the invention in that they may be used to lower the fill material into the trench to 5 avoid workers standing at an edge of the trench and/or leaning over the excavation, This is achieved by pushing their pointed upper ends into the top of the fill material and then holding onto the pins whilst lowering the fill material into the trench. Once the anchoring pins extending from the bottom of the fill material have been pushed into the trench bottom to anchor the fill material, the pins sticking out of the top of the fill material can be removed.

Applicants also considered devising a "universal", as it were, applicator which could be used whatever the soil conditions to pass the fixing elements into the trench wall and thereby adequately fix the compressible fill material to the trench wall and, to this end, carried out further experiments. In the course of these fiirther experiments, applicants overcame the 15 difficulties experienced under certain soil conditions with the applicator described in the Applicants specification GB-A-2311081.

Accordingly, from a further aspect the invention provides a method of combating soil movements, such as clay heave, in a foundation trench filled with poured concrete, in which 20 prior to filling the trench with poured concrete, a compressible fill material, such as an EPS sheet, is fixed to a wall of the trench using fixing elements which are driven into the trench wall from outside the trench, characterised by imparting a turning motion to each fixing element as it is being driven into the trench wall.

25 By combining a turning motion action with the linear driving force which is directed towards the trench wall, applicants have found that there are few, if any, soil conditions that cannot be catered for. If there should be any problems encountered, then these may be expeditiously dealt with by applying a holding force around the bottom edge, as well as around the top edge, of the exposed surface of the sheet and on the exposed surface of the fill material 30 between the top and bottom edges of the exposed surface, such as by the use of a flexible length of e.g. builder's tape in any of the ways in accordance with the invention as mentioned 12 hereinabove.

In a preferred way of imparting the turning motion to the fixing elements, each fixing element is preferably a pin in the form of a narrow strip (i. e. of rectangular cross-section), having a 5 longitudinal axis to which a twist has been imparted along its length. When the pin is of metal the strip is conveniently twisted along its length and is provided with at least one pointed end. Preferably both ends are pointed so that the pins can be driven into the t;Dch wall with either end leading which saves construction time. The twisting provides what is in effect a very coarse screw thread and occupying the whole body of the pin, preferably 10 throughout its length. The pin preferably has a minimum of one and a half twists but two, two and a half or three or more twists may be used depending upon the length of the pin. The greater the number of twists the greater the degree of turning.

As an example, the twisting is such that the pin can co-operate with a stationary slot to 15 provide the turning motion as the pin is driven along a linear path towards the trehch wall.

The pin may be mechanically driven, e.g. by a jacking action, hydraulically e.g. by a suitable piston and cylinder device or electrically as by a solenoid or an electric motor. Both the turning and linear driving motions may be effected hydraulically and electrically.

However, a mechanical drive such as that provided by a jacking action is preferred for cost effectiveness, robustness of construction with less likelihood of breakdown and ease of application under the conditions which prevail on building sites.

25 The twisting and linear driving motions are conveniently provided by means of an applicator which may be of any appropriate construction consistent with remote actuation outside the trench to provide the combined linear and twisting motions.

An advantage of twisted pins is that they bite more firmly on the relatively soft material of the 30 fill material so that the holding force is greater and the same applies to the soil of trench wall which is a particular advantage with sandy soil.

Sheets of compressible fill material which have hitherto been used in preventing clay heave 'in foundation trenches filled with concrete have been of generally flat rectangular shape and are industry standards. Such sheets are abutted against each other at the comers of the trenches-.

5 This can give rise to problems such as concrete seeping behind the sheets which can force the sheets away from the trench walls at the comers and cause splitting of the sheets at the comers despite the use of remotely applied holding forces and fixing elements in accordance with the invention.

10 With a view to solving this problem and in accordance with a still finther aspect of the invention, there is provided a compressible fill material that is designed for use in relation to comers of or adapted for use in, a comer region of a foundation trench.

Such comer compressible fill materials may be made up of two sheets, preferably of smaller 15 size than trench wall sheets for ease of installation and handling.- One of these sheets may be of a width which is larger than that of the other by the thickness of the sheet and laminated or otherwise fixed as by an adhesive substantially at right angles to each other to produce a comer unit having both sides of substantially the same width.

20 Alternatively, the comer unit is made in one piece.

Whatever comer unit is used, in a preferred embodiment, the comer unit includes a plastics containment system such as a plastics bag in order toguard against seepage of concrete at comers, which can blow the sheet off the trench wall, and impr ove strength at the comers.

25 The plastics containment system also helps the flow of concrete at the comers which are the most vulnerable points of this materials installation and improves strength.

Preferably, in order to connect the comer unit to another sheet, coupling means may be provided such as pegs or dowels, e.g. of plastics. Optionally, the comer units can be provided 30 with their own anchoring or propping members such as hereinbefore described.

It should be appreciated that the various aspects of the invention not only provide safe methods of installing compressible fill materials in foundation trenches but also provide a system or kit of parts for carrying out any of the methods according to the invention as defined hereinabove.

Accordingly, from yet another aspect, the present invention comprises a system or kit of parts for use in combating soil movement pressures in foundation trenches filled with concrete, said system or kit of parts comprising a compressible fill material having, in use, a top edge, a bottom edge and an exposed surface, for positioning against a wall of a foundation trench, 10 and holding means adapted to apply from outside the trench a force around the top and bottom edges of the exposed surface and in the direction of and preferably between, its top and bottom edges to hold the fill material against the trench wall.

In an alternative aspect, the present invention comprises a system or kit of parts for use in 15 combating soil movement pressures in foundation trenches filled with concrete, said system or kit of parts comprising a compressible fill material, a plurality of fixing elements constituted by pins having a twist along their lengths and an applicator for driving the pins along a linear path and effecting a turning motion to the pins for use in holding the compressible material against the trench wall.

Optionally, the system or kit -of parts additionally includes any of the anchoring or propping members and/or comer units such as defined hereinabove.

The invention also comprehends a system or kit of parts, comprising a compressible fill 25 material and any of the anchoring pins such as defined hereinabove.

In order that the invention may be more readily -understood, reference will now be made, by way of example, to the accompanying drawings, in which:

30 Fig. I shows an anchoring member in the form of a pin for anchoring sheets of compressible material in a foundation trench and for spacing the fill material at a predetermined distance from the trench bottom in accordance with one embodiment of the invention, the pin having part broken away to reduce its length for convenience of illustration; Figs. 2 to 6 show the steps in a method of combating soil movement pressure in a foundation 5 trench, prior to filling the trench with poured concrete in which sheets of compressible fill material are held by means of flexible straps against a trench wall in a foundation trench using the pins of Fig 1, prior to filling the trench with concrete, and in accordance with another embodiment of the invention; 10 Fig 7. shows a similar method to that of Figs. 2 to 6 but using a comer unit of compressible fill material positioned around a trench wall comer between two sheets of compressible fill material held by flexible holding straps against adjacent foundation trench walls; Fig. 7a shows the same view as Fig. 7, without the flexible holding straps; Fig. 8 shows the same view as Fig 7, but with an alternative form of comer unit; Fig. 8a shows the same view as Fig 8, without the flexible holding straps; 20 Fig. 9 shows a sheet of compressible material supported against a wall of a foundation trench and anchored to the trench bottom. by means of two anchoring pins as illustrated in Fig. 1, with the sheet having been lowered into the trench by an alternative method; Fig. 10 shows a sheet of compressible material supported against a wall of a foundation 25 trench and anchored to the trench bottom by means of two anchoring pins such as illustrated in Fig. I in accordance with yet another method of the invention; Fig. I I shows a fixing element in the form of a twisted pin for use in holding a sheet of compressible fill material such as is shown in Figs. 7a, 8a, 9, 10 and 16 against a trench wall 30 in an alternative method according to the invention; 16 Fig. 1 la shows an alternative fixing element in the form of a twisted pin; Fig. 12 is a perspective view of an applicator for mechanically driving the pin of Fig. 11 through a sheet of compressible fill material and into a trench wall, with a pin driving head 5 thereof in a retracted position; Fig. 13 is a detail perspective view to an enlarged scale of the applicator of Fig. 12 showing a magazine forming part of the pin driving head, for receiving a plurality of the fixing pins such as is shown in Fig. 11, with one such pin being shown to show the direction of entry of the 10 pins into the magazine; Fig. 14 is a detail perspective view to an enlarged scale of the applicator of Fig. 12 showing the magazine containing fixing pins, with the pin driving head within an extended position with one pin projecting out of the magazine; Fig 15 is a detail perspective view of a fixing pin driving harnmer forming part of the pin driving head shown in Figs. I I to 14; and Fig. 16 is a perspective view of the applicator of Figs. 12 to 15 in operation in a foundation 20 trench, driving a fixing pin through a sheet of compressible fill material and into the trench wall.

In Figs. 2, 3, 4, 5, 6, 7, 7a, 8, 8a, 9, 10 and 16 of the drawings, there is shown a compressible fill material in the form of a rectangular EPS sheet 1, (two sheets 1 in Figs. 7, 7a, 8, 8a,) 25 positioned in a foundation trench which is indicated by the reference 2 in Figures 6, 7, 7a, 8, 8a, 9 and 16 prior to filling the trench 2 with poured concrete. The sheet I is anchored to the trench bottom 3 against one trench wall 4 at a predetermined spacing of 500mm or 600mm from the trench bottom 3 to provide the requisite concrete toe by means of two anchoring pins 5 of which one is shown in more detail in Fig. 1. The trench 2 has an opening 6 defined 30 by edges 7 and the ground outside the trench level is indicated at 8.

The sheets I function to combat soil movement pressures, such as clay heave, when the foundation trench 2 is filled with poured concrete and forms the foundation of a building.

Referring more particularly to Figure 1, the anchoring pin 5 is of elongate form and is of 5 light-weight axially rigid construction, e.g. of a suitable plastics. The anchoring pin 5 is made in four parts, a tubular shaft member 10, a pointed lower end member 11 made of tapered triangular reinforcing ribs 12 terminating in a point 13 and which friction fits into the lower end of the shaft member 10, an annular collar member 14 and a pointed upper end member 15 which friction fits into the upper end of the shaft member 10 to hold collar 14 onto the shaft 10 member by means of an annular flange 16. Intermediate to its ends, the pointed end member 15 has several rings of saw tooth serrations 17 for a purpose to be described.

As will be understood from Figure 2, the pins 5 are mounted to the sheets I by pushing the upper pointed end members 15 into the relatively soft plastics material of the sheets through 15 their bottoms 20 to secure the pins 5 thereto and retain the pins therein by the engagement of the rings of saw tooth serrations 17 with the sheet material. The collars 14 abut the sheet bottoms 20 (see Figs. 2 and 3) to ensure that the pins do not go any further into the sheets beyond necessary to provide the predetermined spacing of 500mm or 600mm, shown in Figs. 6, 7, 7a, 8, 8a, 9, 10 and 16 from the bottom 3 of the trench 2 in which the pointed lower end 20 members have dug into the bottom 3 of the trench 2. To guard against the pin 5 going too far into the soil of the trench bottom 3, the pointed lower end member 11 is provided with a soil abutment member 18.

In Fig. 10 the sheet I has been lowered into the trench 2 by hand without external assistance 25 and the same applies to the embodiments of Figs. 7a and 8a which illustrate integral and two sheet comer units 50 and 50a respectively between sheets 1. But in Fig. 9, the pointed upper end members 15 have been pushed into the top 19 of the sheet 1. By holding onto the pins 5 the sheet can be lowered into the trench 2 without workers standing too close to the edge 7.

Once the anchoring pins 5 extending from the bottom of the sheet 1 have been pushed into 30 the trench bottom 3 to anchor the sheet, the pins 5 sticking out of the top of the sheet 1 can be removed.

When the concrete is poured into the trench 2 illustrated in Figs. 9 and 10, 7a and 5a, the anchoring pins 5 are gripped by the rising concrete being poured into the trench to hold the pins in position in the trench.

%ilst even in the absence of any fixing elements or holding means for holding the sheets I against the trench wall 2, it is conceivable that the retention means are capable of exerting a sufficient hold on the sheet to guard against the rising concrete forcing the sheet off the upper pointed ends and out of the trench, the use of a holding force or fixing pins to hold the sheet I 10 against the trench wall is preferred.

In Figs. 3 to 6 a holding force is exerted against the sheet 1 in the following way. Flexible straps 30 are tied to the pins 5 adjacent the sheet bottom 20 by means of knots 31 leaving two side lengths 32 and 33 of strap (Fig.3) which form a sling and which extend over the exposed 15 surface 34 and unexposed surface 35 respectively of the sheet 1 to the top 19 of the sheet where they are tied into knots 36 leaving the end regions 37 free. The end regions 37 are then used to lower the sheet 1 into the trench 2 as shown in Fig 5 so that it lies against the trench wall 4 with the anchoring pins digging into the trench bottom 3. By pulling on the free end regions 37 so that sides 32 are drawn taut against the exposed surface 34 between its bottom 20 and top edges 40 and 41 and around the top edge 41 of the exposed surface 34 then held in position outside the trench by ground anchors 38, a holding force is applied around the bottom and top edges 40 and 41 of the exposed surface 34 and in the direction from the bottom edge 40 to the top edge 41, in this case also extending between the bottom and top edges, to hold the sheet against a wall of the trench.

The concrete is then poured in one pour to fill the trench with concrete, the ground anchors 3 1 are removed and the free end regions cut off.

The embodiments of Figs. 7 and 8, which illustrate integral and two-sheet comer units 50 and 30 50a respectively between sheets I differ from that of Figs. 2 to 6 in that single strap lengths are knotted to the pins 5 against the sheet bottoms 20 and then pulled taut around the 19 bottom edge 40, the exposed surface 34 and the top edge 41 of each sheet and the free end regions 61 are secured by ground anchors 3 8 outside the trench to exert the holding force.

Alternatively to using a holding force as described say with reference to Figs 2 to 6, an 5 applicator 70 such as is illustrated in Figs. 12 to 16 using twisted fixing pins such as illustrated in Figs 11 and 11 a may be used to hold the sheet 1 in Figs 9, 10 and 16 against the trench wall 4. The twisted fixing pin 74 has two pointed ends whereas one end of the pin 74a is rounded for engagement by a hammer to be described.

10 The applicator 70 comprises a frame 71 fixed against sliding to a long pole 72 and carrying a magazine 73 for receiving twisted fixing pins 74 or 74a, The magazine has front and rear walls 75 and 76 respectively with there being a stationary vertical slot 77 in the front wall 76 in which a pointed free end 74b of the lowermost fixing pin 74 is located. An elbow linkage 78 is pivoted to the fi-ame and to the pole 72 and carries a hammer 79 pivoted at its upper end 15 which engages in a slot 80 in the bottom of the magazine 71. When a handle 81 at the upper end of the pole 72 is actuated with the applicator 70 lowered into the trench 2, as shown in Fig 16, the chain 82 connected to the link 83 actuates the elbow linkage 78 to cause the hammer 79 to drive a pin 74 along a linear path with the co-operation of the pin 74 in the slot 77 causing turning motion of the pin 74 to drive the pin through the sheet 1 and into the 20 trench wall 4.

By loosening the fixing, the frame 71 can be slid to any desired location along the pole to drive in fixing pins at different depths.

Claims (14)

1. A method of combating soil movement in a foundation trench filled with poured concrete in which prior to filling the trench with poured concrete a compressible fill material is 5 fixed to a wall of the trench by one or more fixing elements characterised by imparting a turning motion to the or each fixing element as it is driven into the trench wall.

2. A method according to claim 1, wherein the turning motion is combined with a linear driving force which is directed towards the trench wall.

3. A method according to claim I or claim 2, wherein the fixing element is a pin in the form of a narrow strip having a longitudinal axis to which a twist has been imparted along its length.

15

4. A method according to claim 3, wherein the pin comprises at least one pointed end.

5. A method according to claim 3 or claim 4, wherein the pin has at least one and a half twists along its length.

20

6. A method according to any one of claims 1 to 5, wherein the pin cooperates with a stationary slot to provide the turning motion.

7. A method according to any one of claims I to 6, wherein the twisting and linear driving motions are provided by means of an applicator which is remotely activated from outside 25 the trench.

8. A method of combating soil movement in a foundation trench filled with poured concrete substantially as hereinbefore described with reference to, and as shown in, Figures 11 to 16 of the accompanying drawings.

9. An applicator for use in carrying out the method as claimed in any one of claims I to 8.

10. An applicator for use in a method in combating soil movement in a foundation trench substantially as hereinbefore described with reference to, and as shown in, Figures 12 to 15 of the accompanying drawings.

11. An applicator for use in a method in combating soil movement in a foundation trench substantially as hereinbefore described with reference to, and as shown in, Figures 12 to 16 of the accompanying drawings.

12. A kit of parts for use in combating soil movement pressures in foundation trenches filled with concrete, comprising a compressible fill material, a plurality of fixing elements constituted by pins having a twist along their length and an applicator for driving the pins along a linear path and effecting a turning motion to the pins for use in holding the compressible material against the trench wall.

13.A kit of parts for use in combating soil movement in a foundation trench filled with poured concrete substantially as hereinbefore described with reference to, and as shown in, Figures I I to 16 or 11 a to 16 of the accompanying drawings.

14. A kit of parts for use in a method of combating soil movement in a foundation trench filled with concrete and comprising an applicator as claimed in any of claims 15 to 17 and pins substantially as hereinbefore described with reference to, and as illustrated in, Figure 11 or Figure I I a of the accompanying drawings.