Foundation system

Abstract

A foundation system for supporting a structure is disclosed. The foundation system comprises a support member for supporting the structure, at least 2 spaced footings arranged to dispose the support member above ground during use when the footings are founded on the ground, and an anchor member disposable in-ground below the support member during use, the anchor member configured to engage with surrounding ground and resist upward movement of the anchor member relative to the surrounding ground. The foundation system also includes a tension member configured to connect to the anchor member and extend during use between the anchor member and the support member. The tension member is configured to connect to the support member between the at least 2 footings, and the system also includes a tensioning arrangement configured to apply tension to the tension member during use which resists upward loads on the support member, and prestresses the support member which causes an increase of resistance of the at least 2 footings to upward, lateral and moment loads applied to the foundation system.

Description

FOUNDATION SYSTEMField of the Invention

[0001] The present disclosure relates to a foundation system, and more particularly to a foundation system for supporting a structure, such as a mounting structure for a solar PV installation. The present disclosure also relates to a method of deploying a foundation system for a structure, such as a solar PV installation.

[0002] It will be convenient to hereinafter describe the present disclosure in relation to a foundation system and method for use with a solar PV installation. As will be appreciated, however, the system and method of this disclosure are not limited to use with solar PV installations and may find application in a range of mining or civil engineering and / or structural contexts.Background of the Invention

[0003] Any reference to, or discussion herein of, background art, including any documents, is intended to facilitate an understanding of the present disclosure only and is not to be considered as an admission that such background art forms part of the state of the art or is widely known or forms a part of the common general knowledge in the relevant field in Australia or in any other country at the date of this application.

[0004] A typical solar photo-voltaic (PV) installation includes a plurality of solar PV modules, each of which includes at least one solar PV panel, and a foundation system for securely supporting the PV modules during use. Solar (PV) foundation systems and associated support structures provide the structural and geotechnical capacity required to resist the environmental forces applied to the solar PV panels during use. In view of the relatively large surface area of each PV panel, it will be appreciated that the main environmental load experienced by the support structures is wind load. Due to the high ratio of surface area to self-weight of the PV modules, the typical wind load leads to relatively large lateral and axial loads, as well as bending I turning moment loads, being applied to the PV foundation system.

[0005] Two typical foundation systems used to provide support for such structures are (i) shallow spread foundations and (ii) pile foundations. A shallow foundation typically comprises a substantially planar element (that may be round, square or rectangular) positioned at ground level. The material used for the planar element will depend onloading requirements and typically includes timber, steel or reinforced concrete. A shallow foundation is simple to construct and does not require specialist equipment. Shallow foundations are efficient at resisting vertical compression loads and they are commonly used when the loads from a structure are relatively low and can be safely transferred to the soil near the surface. Shallow foundations are however less efficient at resisting moment and lateral loads than deep foundation systems, such as those comprising piles or drilled shafts. Lateral loads, such as those induced by wind or seismic forces, can cause horizontal movement and overturning of shallow foundations. Shallow foundations are also less suitable for resisting uplift or significant moment loads.

[0006] In view of the wind loading typical for solar PV structures, shallow foundations are required to be deeper or heavier than is typical in the construction industry. Their application in remote areas is also limited due to the expense of using concrete.

[0007] Pile foundations typically include prefabricated steel columns that are driven, vibrated, or rotated into the ground. If the strength of the ground or obstructions within the ground hinder the installation process, it is often necessary to pre-drill an open hole and fix the pile in position in the hole using cement-stabilised sand. Bored piles, which involve drilling of holes and replacing the excavated soil with reinforced concrete, are far less common because of their cost and low speed of construction. A single pile foundation is more suited to resisting applied moment loading than a shallow foundation. Its length is controlled by the magnitude of the design uplift and moment wind loads, while the pile diameter and bending stiffness are controlled by the magnitude of the design moment load. Two piles, rather than a single pile, can be employed to resist moment loading in a more efficient manner. Pile foundations are relatively expensive as they require specialized machinery and contractor expertise. Local variations in ground conditions also impact pile capacities and can lead to variable pile lengths and a requirement for additional costly and time-consuming pile testing.

[0008] In view of the above, it would be useful to provide a new or improved foundation system and associated method, particularly for use with solar PV modules. In addition or alternatively, it would be desirable to optimise the construction speed and / or the cost-effectiveness of foundation systems used in solar PV installations.Summary of the Invention

[0009] According to a first aspect of the present invention, there is provided a foundation system for supporting a structure, the foundation system comprising: a support member for supporting the structure; at least 2 spaced footings arranged to dispose the support member above ground during use when the at least 2 footings are founded on the ground; an anchor member disposable in-ground below the support member during use, the anchor member configured to engage with surrounding ground during use and resist upward movement of the anchor member relative to the surrounding ground; a tension member configured to connect to the anchor member and extend during use between the anchor member and the support member, the tension member configured to connect to the support member between the at least 2 footings; and a tensioning arrangement configured to apply tension to the tension member during use which: resists upward loads on the support member; and prestresses the support member which causes an increase of resistance of the at least 2 footings to upward, lateral and moment loads applied to the foundation system during use.

[0010] In an embodiment, each footing includes a surface engaging portion that contacts a surface of the ground during use, and wherein the tension applied to the support member during use causes an increase of friction between the surface engaging portion and the ground.

[0011] In an embodiment, the surface engaging portion includes a surface engaging flange.

[0012] In an embodiment, each footing includes an in-ground portion that extends into the ground during use.

[0013] In an embodiment, the in-ground engaging portion includes an elongate stud member that extends into the ground during use.

[0014] In an embodiment, the support member comprises an elongate beam.

[0015] In an embodiment, the support member comprises a substantially planar member.

[0016] In an embodiment, the tensioning arrangement is configured such that the tension applied to the tension member by the tensioning arrangement is adjustable.

[0017] In an embodiment, the tension member comprises a cable or a rod for transmitting a tensile load between the anchor member and the support member.

[0018] In an embodiment, the anchor member is configured such that the anchor member is disposable in-ground by rotating the anchor member.

[0019] In an embodiment, the anchor member includes at least one lateral projection arranged to increase resistance between the anchor member and the surrounding ground.

[0020] In an embodiment, the at least one lateral projection comprises at least one helical blade or fin.

[0021] In an embodiment, the at least one lateral projection includes at least one lateral expansion element movable from a compact position to an expanded position in response to application of tension to the tension member and associated application of an upward force to the anchor member.

[0022] In an embodiment, the system comprises a cementitious grout or polymer resin disposed during use adjacent the anchor member.

[0023] According to a further aspect of the present invention, there is provided a solar photo-voltaic (PV) installation comprising at least one solar PV module supported by at least one foundation system as claimed in any one of the preceding claims.

[0024] According to a second aspect of the present invention, there is provided foundation system for supporting a structure, the foundation system comprising: a support member for supporting the structure; at least 2 spaced footings that are founded on the ground and dispose the support member above the ground; an anchor member disposed in-ground below the support member, the anchor member configured to engage with surrounding ground and resist upward movement of the anchor member relative to the surrounding ground; anda tension member that connects to the anchor member and extends between the anchor member and the support member, the tension member connecting to the support member between the at least 2 footings; and a tensioning arrangement configured to apply tension to the tension member which: resists upward loads on the support member; and prestresses the support member which causes an increase of resistance of the at least 2 footings to upward, lateral and moment loads applied to the foundation system.

[0025] In this way, the foundation system of the disclosure can address a limitation of shallow foundations by providing improved resistance to applied upward and moment loads on the support member.

[0026] According to a third aspect of the present invention, there is provided a method of deploying a foundation system for supporting a structure, the method comprising: providing a foundation system according to the first aspect above; installing the anchor member in the ground; founding the at least 2 footings on or below the ground so that the support member is disposed above the ground; connecting the support member to the anchor member by the tension member; and tensioning the tension member to: resist upward loads on the support member; and prestress the support member which causes an increase of resistance of the at least 2 footings to upward, lateral and moment loads applied to the foundation system.

[0027] In an embodiment, installing the anchor member in the ground comprises drilling the anchor member into the ground.

[0028] In an embodiment, installing the anchor member in the ground comprises fixing the anchor member in the ground using a cementitious grout or polymer resin.

[0029] In an embodiment, installing the anchor member in the ground comprises increasing resistance between the anchor member and the ground using at least one expansion element expandable between a contracted configuration and an expanded configuration

[0030] Generally, the present disclosure is intended to cover any and all adaptations or variations of the particular embodiments discussed herein. By way of example, a skilled person will readily appreciate that the system of this disclosure is not limited to being made from any specific material described in the embodiments. Rather, the skilled person will appreciate that a range of suitable materials exist and the skilled person can select a material based upon the known mechanical properties of that material which make it suitable for use in the system. As the present disclosure involves engineering technology from different disciplines, it is expected that the notional ‘skilled person’ may comprise a group or a team of individuals having technical expertise and / or qualifications in one or more of the following fields or disciplines: mechanical engineering, structural engineering, and geotechnical engineering.Brief Description Of The Drawings

[0031] For a more complete understanding of the invention of the present disclosure and the advantages thereof, exemplary embodiments are explained in more detail in the following description with reference to the accompanying drawing figures, in which like reference signs identify or designate like parts and in which:Figure 1 is a schematic side view of a mounting structure for a solar PV module supported on a conventional single column pile foundation;Figure 2 is a schematic perspective view of a row of solar PV modules mounted on a plurality of pile foundations shown in Figure 1;Figure 3 is a schematic side view of a conventional shallow foundation;Figure 4 is a schematic side view of a mounting structure for one or more solar PV modules supported on a foundation system according to an embodiment of the present disclosure; andFigure 5 is a schematic perspective view of a row of solar PV modules mounted on a plurality of foundation systems shown in Figure 4.Description of an Embodiment of the Invention

[0032] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification.The drawings illustrate particular embodiments and together with the description serve to explain the principles of the invention. Other embodiments and many of the attendant advantages will be readily appreciated as they become better understood with reference to the following detailed description.

[0033] It will be appreciated that common and / or well understood elements that may be useful or necessary in a commercially feasible embodiment are not necessarily depicted in order to facilitate a more abstracted view of the embodiments. The elements of the drawings are not necessarily illustrated to scale relative to each other. It will also be understood that certain actions and / or steps in an embodiment of a method may be described or depicted in a particular order of occurrences while those skilled in the art will understand that such specificity with respect to sequence is not actually required.

[0034] With reference to Figures 1 and 2 of the drawings, an example of a conventional pile foundation for solar PV installations is illustrated. This arrangement involves a single column pile P that is driven vertically into the ground, and cantilevers above the ground by a distance yi. As seen in Figure 2, a row of piles P are connected via a torque tube T. The solar PV modules M are mounted in an array A on the torque tube T allowing them to be rotated towards the sun. Wind loads act bidirectionally during use on the solar PV modules M, and the loads are transferred via the torque tube T to the piles P. As such, the piles P are required to resist bidirectional lateral loads Fx, a vertical load FY and a twisting moment Mxacting on the torque tube T. The load case combining the ultimate lateral and uplift (tension) loading is the governing case for the structural and geotechnical design. The soil parameters used in the geotechnical design of a foundation are normally derived using a variety of empirical formulae related to data from Cone Penetration Test (CPTs), Standard Penetration Test (SPTs) and / or Dynamic Cone Penetration Tests (DCPTs), which are obtained during the geotechnical investigation for a site. The CPT is the most common and reliable in-situ test employed internationally.

[0035] With reference to Figure 3, the design parameters of a typical shallow foundation S will be discussed. The bearing capacity qf of a shallow foundation is the load per unit area that causes the foundation to collapse due to shear failure in the ground (referred to as the ultimate limit state, ULS). A serviceability limit state (SLS) also needs to be determined as this ensures that (differential) settlements do not render the structure unserviceable. The overall ULS and SLS performance of a shallow foundation depends on factors such as the soil strength and stiffness; the foundation size, embedment andgeometry; and the magnitude and characteristics of the applied design loading. Two ULS design checks are commonly performed, namely (i) bearing capacity / overturning and (ii) sliding. The settlement predictions for SLS design require assessment of the ground stiffness. This assessment is often assisted by CPT or other in-situ test data.

[0036] Bearing capacity / overturningThe bearing capacity or collapse stress qf of a shallow foundation is related to the shear strength and compressibility of the ground, and is usually calculated from conventional bearing capacity equations. CPT data can provide the necessary input data to these equations such as the bearing capacity factor NY for shallow foundations in sandy soils and the undrained shear strength suin ‘clayey’ soils. Moment loading affects the bearing capacity significantly as the ground has no tensile capacity. As a consequence, only part of the foundation provides resistance to the applied loading. This is shown schematically in Figure 3 for a shallow foundation subject to a lateral load of Fx, a moment load Mx, and a vertical compression load Fy. In this case, as uplift occurs on one side of the foundation, the width of footing in contact with the ground reduces from B to the equivalent foundation width Beqwhere:Beq= B - 2 (MX / Fy) Eq. (1)

[0037] Accordingly, the effect of moment loading essentially reduces the bearing capacity of a surface foundation by a factor of approximately B / Beq, and for an increasing ratio Mx / Fy, the equivalent foundation width Beqreduces. Overturning occurs when Beq(calculated using Equation (1)) reduces to zero, irrespective of the strength of the ground.

[0038] The bearing capacity qf for a surface strip foundation in sandy soil conditions can be determined using the following equation: c / f=0.5 Nriy Y Beq Eq. (2) where: iY= (1 - a / cpY a = tan'1(Fx / Fy) y’ = submerged unit weight of soil (unit weight in dry conditions) Ny = a bearing capacity factor and function of the angle of friction (p of the soil

[0039] SlidingSliding failure is a particular case of bearing capacity failure and arises when the applied lateral load Fxexceeds the product of the vertical compression load Fyand the coefficient of friction p between the footing and the soil. The upper limit on the value Fxthat can be applied in sandy soil is given by:Fx,maX=M' Fy=tan(6)‘ FyEg. (3) where 5 is the angle of interface friction between the foundation and the soil.

[0040] Returning to a consideration of piled foundation design, for most displacement piles in use, vertical compression support to structures is provided by the friction that develops over the surface area of the pile shaft, and the bearing that exists at the pile base. For piles subjected to uplift, the resistance is provided by the friction on the pile shaft only.

[0041] Another displacement pile used is referred to as a screw pile (also called a helical pile). This provides compression and uplift resistance by virtue of a helical plate welded to a steel shaft near the pile base. The relevant unit ultimate shaft friction ifand ultimate end bearing stress qb are estimated using empirical correlations of the CPT data (or other in-situ test data) obtained during a ground investigation. The shaft resistance Qsand base resistance Qb are then calculated from the following expressions (where C is the pile circumference and L is the pile length, and where Ab is the enclosed area of the pile base or screw pile helix):Qs= C^zfdz Eq. (4)Qb= AbqbEq. (5)

[0042] As the empirical correlations do not have a high level of reliability, site specific pile testing is required to verify their applicability at any given site. An adequate SLS design for a pile is usually achieved by ensuring that the applied unfactored design loads are less than about 50 to 60% of a moderately conservative estimate of the pile’s ultimate capacity. The lateral response of single piles used to support solar PV panels is derived using computer software and load transfer curves (or so-called p-y curves) published in international standards. These curves require input of a profile with depth of the friction angle in a sandy soil or the undrained strength in a clay soils. The structural requirements of the pile are derived from the moments and shear computed in the analyses. Theseanalyses are also used to establish the required pile lengths to avoid a geotechnical failure.

[0043] With reference to Fig. 4 of the drawings, a foundation system 1 for supporting a solar PV installation is shown. In this example, the foundation system 1 supports a mounting structure 10 for a plurality of solar PV modules M.

[0044] In this example, the foundation system 1 comprises a support member 2 upon which the mounting structure 10 is supported. In this example, the support member 2 is provided in the form of an elongate beam, although other configurations, such as a substantially planar member that may be circular, square or rectangular, are also contemplated. The support member 2 includes at least one footing 3 at each longitudinal end, each footing 3 in this example having a ground surface-engaging flange 4, and an in- ground engaging portion 5, in this example in the form of a rod or stud, that extends into the ground G during use. In this example, each ground surface-engaging flange 4 is adjustable to modify the orientation of the support member 2, for example to level the support member 2. The arrangement is such that during use the footings 3 dispose the support member 2 above and adjacent the ground G, with the base member 2 spaced slightly above the ground G, as shown in Figure 4.

[0045] In the present example, the support member is a structural steel member, although it will be understood that any other suitable material is envisaged.

[0046] An anchor member 6, in this example having a helical fin or blade 7 to increase friction and improve engagement between the anchor member 6 and the surrounding ground G, is fixed during use in the ground G below the support beam 2. A tension member 8, for example in the form of a cable or rod, interconnects the anchor member 6 and the base member 2 at connection points 9, 9’. A tensioning arrangement 12 that may include a screw mechanism or turnbuckle facilitates application of controlled tension to the tension member 8 and thereby application of a prestressing force on the support member 2 towards the ground G.

[0047] Since the support member 2 is disposed slightly above the ground by the footings 3, when tension is applied to the tension member 8, the support member 2 is prestressed by the tension member 8 and may bend slightly. This in turn causes the friction resistance mobilised between the footings 3 and adjacent ground to increase and the resistance to upward, lateral and moment loads on the support member 2 to increase.As a consequence, an increased capacity to resist upward, lateral and moment loads on the support member 2 is provided to the footings by the support member. For example, an applied wind load on a solar PV module may cause an increase in the downward force at a first one of the footings 3 and a reduction in the downward force at a second one of the footings 3, but the foundation system 1 will remain stable so long as the resistance to upward, lateral and moment loads at the second footing provided by the prestressed support member 2 remains greater than the upward, lateral and moment loads provided by the wind load.

[0048] The resistance to upward, lateral and moment loads increases because friction between the ground surface-engaging flanges 4 and the ground increases. In addition, by virtue of the slight bend in the support member, in an embodiment wherein the footings include in-ground portions, the friction between the in-ground studs 5 and the adjacent ground may also increase.

[0049] In a PV array context, the foundation system 1 provides effective resistance to uplift, moment and lateral loads that may act on the mounting structure 10 due to wind loads on solar PV modules M in use.

[0050] In the present example, the mounting structure 10 includes a pair of angled legs 11 which converge and are joined by a bracket assembly 13 that accommodates a horizontally extending torque tube T to which the solar PV modules M are mounted. The bracket assembly 13 includes a bearing 14 that rotatably receives the torque tube T so that an orientation of the solar PV modules M can be adjusted depending on a position of the sun.

[0051] It will be understood that the foundation system 1 essentially acts as a shallow foundation, following the design principles outlined above, but with additional resistance to upward, lateral and moment loads.

[0052] With reference to Figure 4, a vertical load FY,G is applied to the support member 2 at a location between the footings 3, for example at a central location of the support member 2, by the ground anchor 6 and tension member 8. In response, the footings 3 work in compression (i.e. , via forces AR,Y, BR,Y), and the support member 2 bends slightly, which causes lateral forces AR,X, BR,X to be mobilised that resist uplift, lateral and moment loads, for example caused by the wind. The (pre-stressing) load FY,G applied to the support member 2 by the ground anchor 6 and tension member 8 is introduced during installationof the foundation system 1 , with the characteristics of the pre-stressing force selected and the ground anchor 6 installed to a sufficient depth to provide the necessary reaction for the ground conditions and application.

[0053] Static equilibrium under design wind loading Fx,w and FY,W implies the following for the footings 3: R, Y = FY, G —FY, W — (Fx, wy + Mx) / x 1 Eq . (6)BR, Y = FY,G —FY,W + (Fx,wy + Mx) / xi Eq. (7)

[0054] Equation (5) implies that the applied pre-stressing force has a minimum value:FY,G > FY,W+(Fx,w-yi + Mx) / xi Eq. (8)

[0055] The design lateral load from the wind Fx,w is resisted by friction (or adhesion) under the shallow footings so that:Fx,w < I~I ( R,X + BR,X) Eq. (9)

[0056] Application of the Equations (6) to (9) for typical wind loading applied indicates that a foundation system 1 used in typical sand or clay conditions will require less than 50% of the material employed for a typical single pile solution in similar ground conditions. The particular soil conditions of the site will influence and / or dictate the final shape or configuration of the ground beam 2 and anchor 6. Loose sand sites may require larger footings 3 on the ends of the base member 2. Harder soils might not require any footings 3 at all (e.g., base member 2 positioned directly on the ground). The mechanical principles, however, remain unchanged. The geotechnical challenges of particular sites may include creep in the fixation of the anchor member 6 and / or the footings 3 over time.

[0057] An implementation to a solar PV array A is shown in Figure 5, the solar PV array A including a row of solar PV modules M mounted on a plurality of foundation systems 1. As shown, the support members 2 of the foundations systems 2 are oriented in a direction generally perpendicular to the row of PV modules M.

[0058] As discussed above, a significant disadvantage associated with the use of conventional shallow foundations as a base support for solar PV modules is the impractically large size required to resist combined uplift, lateral and moment wind loading. In contrast, the foundation system 1 of the present disclosure eliminates this disadvantageand effectively re-establishes the use of shallow foundations as a cost-effective solution, for example in the solar PV industry. The design of the present foundation system 1 of this disclosure is motivated by market demands of significantly reducing construction costs and material costs. Furthermore, by using a shallow foundation system with proof-tested ground anchors instead of foundation piles, the need for specialized geotechnical investigations, for pile testing, and / or for the involvement of specialist piling contractors is essentially eliminated. The foundation system 1 of the disclosure thus achieves reduced construction and material cost whilst providing good stability to wind loads.

[0059] Other advantages and notable features of the foundation system 1 include the following:(i) The installation procedure for a helical anchor is a considerably simpler and more cost-effective solution than for a standard pile.(ii) The cost differential for installing an anchor into deeper soil horizons is negligible.(iii) Creation of a high-capacity anchor allows the support member and footings to be prestressed to much higher levels than required in service.(iv) The anchor may be proof loaded during construction or erection such that there are no subsequent load testing requirements. The ability to proof load the foundation system reduces risk of foundation failure and also reduces the extent of ground investigation required.(v) The system can be re-stressed after a very extreme weather event using the tensioning arrangement 12 (whereas repair of other existing solutions may not be possible).

[0060] Although specific embodiments of the disclosure are illustrated and described herein, it will be appreciated by persons of ordinary skill in the art that a variety of alternative and / or equivalent implementations exist. It should be appreciated that each exemplary embodiment is an example only and is not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those persons skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in anexemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

[0061] Generally, the present disclosure is intended to cover any and all adaptations or variations of the specific embodiments discussed herein. By way of example, a skilled person will readily appreciate that the foundation system of the disclosure is not limited to being made from any specific material described in the embodiments. Rather, the skilled person will appreciate that a range of suitable materials exist and the skilled person can select a material based upon the known mechanical properties of that material which make it suitable for use in this system. As the present disclosure involves engineering technology from a number of disciplines, it is expected that a notional ‘skilled person’ may comprise a group or a team of individuals having technical expertise and / or qualifications in one or more of the following fields or disciplines: mechanical, structural, and / or geotechnical engineering.

[0062] It will also be appreciated that the terms "comprise", "comprising", "contain", "containing", "have", "having", and any variations thereof, as used in this document are intended to be understood in an inclusive (i.e. , non-exclusive) sense, such that the process, method, device, apparatus, or system described herein is not limited to the features, integers, parts, elements, or steps recited but may include other features, integers, parts, elements, or steps not expressly listed and / or inherent to such process, method, device, apparatus, or system. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, unless indicated to the contrary, the terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose numerical requirements on, or to establish a ranking of importance of, their objects. In addition, reference to positional terms, such as “lower” and “upper”, used in the above description are to be taken in context of the embodiments depicted in the figures, and are not to be taken as limiting the disclosure to the literal interpretation of the term but rather as would be understood by a skilled addressee in the appropriate context.

[0063] Drawing reference signs1 foundation system 2 support member3 footing4 ground-engaging flange 5 rod or stud6 anchor member 7 helical fin or blade8 tension member 9 lower connection point9’ upper connection point10 mounting structure11 legs 12 bracket assembly13 bearing 14 torque tube P pile T torque tube M solar PV module A array G ground levelS shallow foundation

Claims

Claims1. A foundation system for supporting a structure, the foundation system comprising: a support member for supporting the structure; at least 2 spaced footings arranged to dispose the support member above ground during use when the at least 2 footings are founded on the ground; an anchor member disposable in-ground below the support member during use, the anchor member configured to engage with surrounding ground during use and resist upward movement of the anchor member relative to the surrounding ground; a tension member configured to connect to the anchor member and extend during use between the anchor member and the support member, the tension member configured to connect to the support member between the at least 2 footings; and a tensioning arrangement configured to apply tension to the tension member during use which: resists upward loads on the support member; and prestresses the support member which causes an increase of resistance of the at least 2 footings to upward, lateral and moment loads applied to the foundation system during use.

2. A foundation system as claimed in claim 1, wherein each footing includes a surface engaging portion that contacts a surface of the ground during use, and wherein the tension applied to the support member during use causes an increase of friction between the surface engaging portion and the ground.

3. A foundation system as claimed in claim 2, wherein the surface engaging portion includes a surface engaging flange.

4. A foundation system as claimed in any one of claims 1 to 3, wherein each footing includes an in-ground portion that extends into the ground during use.

5. A foundation system as claimed in claim 4, wherein the in-ground engaging portion includes an elongate stud member that extends into the ground during use.

6. A foundation system as claimed in any one of the preceding claims, wherein the support member comprises an elongate beam.

7. A foundation system as claimed in any one of claims 1 to 5, wherein the support member comprises a substantially planar member.

8. A foundation system as claimed in any one of the preceding claims, wherein the tensioning arrangement is configured such that the tension applied to the tension member by the tensioning arrangement is adjustable.

9. A foundation system as claimed in any one of the preceding claims, wherein the tension member comprises a cable or a rod for transmitting a tensile load between the anchor member and the support member.

10. A foundation system as claimed in any one of the preceding claims, wherein the anchor member is configured such that the anchor member is disposable in-ground by rotating the anchor member.

11. A foundation system as claimed in any one of the preceding claims, wherein the anchor member includes at least one lateral projection arranged to increase resistance between the anchor member and the surrounding ground.

12. A foundation system as claimed in claim 11 , wherein the at least one lateral projection comprises at least one helical blade or fin.

13. A foundation system as claimed in claim 11 , wherein the at least one lateral projection includes at least one lateral expansion element movable from a compact position to an expanded position in response to application of tension to the tension member and associated application of an upward force to the anchor member.

14. A foundation system as claimed in any one of the preceding claims, comprising a cementitious grout or polymer resin disposed during use adjacent the anchor member.

15. A solar photo-voltaic (PV) installation comprising at least one solar PV module supported by at least one foundation system as claimed in any one of the preceding claims.

16. A foundation system for supporting a structure, the foundation system comprising: a support member for supporting the structure; at least 2 spaced footings that are founded on the ground and dispose the support member above the ground;an anchor member disposed in-ground below the support member, the anchor member configured to engage with surrounding ground and resist upward movement of the anchor member relative to the surrounding ground; and a tension member that connects to the anchor member and extends between the anchor member and the support member, the tension member connecting to the support member between the at least 2 footings; and a tensioning arrangement configured to apply tension to the tension member which: resists upward loads on the support member; and prestresses the support member which causes an increase of resistance of the at least 2 footings to upward, lateral and moment loads applied to the foundation.

17. A foundation system as claimed in claim 16, wherein each footing includes a surface engaging portion that contacts a surface of the ground, and wherein the tension applied to the support member causes an increase of friction between the surface engaging portion and the ground.

18. A foundation system as claimed in claim 17, wherein the surface engaging portion includes a surface engaging flange.

19. A foundation system as claimed in any one of claims 16 to 18, wherein each footing includes an in-ground portion that extends into the ground.

20. A foundation system as claimed in claim 19, wherein the in-ground engaging portion includes an elongate stud member that extends into the ground.

21. A foundation system as claimed in any one of claims 16 to 20, wherein the support member comprises an elongate beam.

22. A foundation system as claimed in any one of claims 16 to 20, wherein the support member comprises a substantially planar member.

23. A foundation system as claimed in any one of claims 16 to 22, wherein the tensioning arrangement is configured such that the tension applied to the tension member by the tensioning arrangement is adjustable.

24. A foundation system as claimed in any one of claims 16 to 23, wherein the tension member comprises a cable or a rod for transmitting a tensile load between the anchor member and the support member.

25. A foundation system as claimed in any one of claims 16 to 24, wherein the anchor member is configured such that the anchor member is disposed in-ground by rotating the anchor member.

26. A foundation system as claimed in any one of claims 16 to 25 wherein the anchor member includes at least one lateral projection arranged to increase resistance between the anchor member and the surrounding ground.

27. A foundation system as claimed in claim 26, wherein the at least one lateral projection comprises at least one helical blade or fin.

28. A foundation system as claimed in claim 27, wherein the at least one lateral projection includes at least one lateral expansion element movable from a compact position to an expanded position in response to application of tension to the tension member and associated application of an upward force to the anchor member.

29. A foundation system as claimed in any of claims 16 to 28, comprising a cementitious grout or polymer resin disposed adjacent the anchor member.

30. A solar photo-voltaic (PV) installation comprising at least one solar PV module supported by at least one foundation system as claimed in any one of claims 16 to 29.

31. A method of deploying a foundation system for supporting a structure, the method comprising: providing a foundation system as claimed in any one of claims 1 to 13; installing the anchor member in the ground; founding the at least 2 footings on the ground so that the support member is disposed above the ground; connecting the support member to the anchor member by the tension member; and tensioning the tension member to: resists upward loads on the support member; andprestress the support member to cause an increase of resistance ofthe at least 2 footings to upward, lateral and moment loads applied to the foundation system.

32. A method as claimed in claim 31 , wherein installing the anchor member of the ground comprises drilling the anchor member into the ground.

33. A method as claimed in claim 31 or claim 32, wherein installing the anchor member in the ground comprises fixing the anchor member in the ground using a cementitious grout or polymer resin.

34. A method as claimed in any one of claims 31 to 33, wherein installing the anchor member in the ground comprises increasing resistance between the anchor member and the ground using at least one expansion element expandable between a contracted configuration and an expanded configuration.

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