Title of Invention

"ANCHORING MEANS FOR RETAINING WALL SYSTEMS"

Abstract

An anchoring means for a retaining wall system comprising a connector provided on an wall element; an anchor block; and an anchor rod provided with means to be secured to said connector at one end and to said anchor block at the other end. The anchor rod extends through and beyond said anchor block and is terminally provided with an end plate. Means is provided to bias said end plate against said anchor block. Preferably, the end plate is provided with adjustable means to adjust the force of bias against the anchor block. The biasing means may be a coil spring, spring washer or leaflet spring bent accordingly. The anchor rod is prefabricated of predetermined high tensile strength suitable for an increase in the tributary area of load transfer. The anchor block may be a thin block, plate or like configuration.

Full Text

Anchoring means for retaining wall systems Field of Invention This invention relates to means for reinforcing a soil embankment or reinforced earth systems. In particular, it relates to anchoring means for such retaining wall or reinforced earth systems employing rods as reinforcing elements. Prior Art Earth reinforcement systems may be broadly dichotomised into (a) constructed embankment type and (b) in situ soil reinforcement type. Constructed embankment-type earth reinforcement systems may be generally categorised into (i) strip reinforcement, (ii) grid or mesh reinforcement, (iii) sheet reinforcement, (iv) rod reinforcement, (v) fibre reinforcement, and (vi) cellular reinforcement1. This invention is concerned with the constructed embankment - type systems using rods (also known as "tendons") as reinforcing elements whereupon stress from the soil may be transferred to the rod elements along the length of the linear rods. Reinforced soil systems are based primarily on the frictional forces between the soil and the reinforcing elements. On the other hand, anchored earth systems are based on the transfer of stress or tension from the soil to the anchoring elements 1 Per James K. Mitchell and Willem C.B. Villet, Reinforcement of Earth Slopes and Embankments, (Report 290), U.S. Transportation Research Board, ,/ June 1987, p. 10. (i.e. passive resistance) or combination of passive resistance and friction. One example of rod reinforcement is the Anchored Earth system which is patented in U.S.A. under US-4407611 (Murray), in Europe under EP-0047610 by the British Transport and Road Research Laboratory, U.K. In this system high tensile steel rod members are connected to facing panels with nut means. The rods extend laterally from the facing wall into the backfill wherein they terminate with deformed ends. It is assumed that passive resistance is developed only at these deformed ends of the rods. As with other methods relying on passive resistance, the Anchor Earth system relies on the cohesive properties of the soil more than methods that rely predominantly on friction. Hence, the features of the head of the anchor rod, i.e. shape of deformation of the rod end, rod section and spacing, manner of compaction of soil, corrosion protection of the elements, connection to facing and deadman elements, etc. are important for the efficiency of this system. Another type of rod anchorage system for reinforcing retaining wall is the use of concrete blocks or deadman at the end of rod as back anchors to the facing wall. Examples are US-4154554 (Hilfiker) and US-4952098 (Grayson) although the scope of these patents are actually directed to the means of tying the reinforcing rods to the face elements. American Geo-Tech, Inc. has also been mentioned2 as having a system in which its face panels are connected to anchor 2 Barry R. Christopher, et. al., "Reinforced Soil Structures" Vol. II, Summary of Research and Systems Information, U.S. Federal Highway Authority, 1989. blocks or deadman panels by tendons or reinforcing rods. The system relies on passive pressures on the deadman panels for stability. Various improvements to the components of such systems, particularly the rod and anchor block, have been described. This includes the rods being prestressed and fabricated from hot-dipped galvanised steel and the anchor blocks being fabricated from precast concrete elements, rocks or concrete rubbles, metal plates or bent or deformed ends of the rod as in the above-mentioned Anchor Earth system3. As evident from the above-mentioned prior art, anchored earth systems generally use high strength tensile rod members incorporated within the soil to form gravity retaining structures. Anchored block or deadman systems are designed to ensure the load transfer to the soil through the passive earth resistance developed on the anchor block which is installed at the free end of the rod, i.e. distal to the face element. Therefore, these systems do not create a composite reinforced soil body and their behaviour is substantially different from that of the reinforced soil systems (e.g. systems using wire grid or mesh to reinforce soil) which transfer the load to the surrounding soil as a composite mass of material through frictional stress. FIGURE I (Prior Art)4 shows schematically the variations of tensile force along a typical anchored block system. The stress transfer is assumed to be primarily through passive resistance and the frictional stress developing along the steel rod or tendon is neglected. Accordingly, the tensile 3 Barry R. Christopher, et. al., "Reinforced Soil Structures" Vol. I, Design and Construction Design, U.S. Federal Highway Authority, 1990. 4 Ibid., Figure 47, page 167. forces are assumed to be constant along the rods. The transfer of load from the anchors to the soil is realised through the passive soil pressure mobilised on the deadman. However, the mobilisation in turn depends on the magnitude of soil displacement, i.e. earth pressure distribution on the face elements, location of potential failure surface and structure displacement. Furthermore, in a multi-anchored block system, the facing is primarily a structural element which has to withstand both bending moments and shear forces due to the lateral earth pressure of the retained soil and to transfer tension forces to the rods. Accordingly, it is essential that the rod design be selected or made with adequate tensile resistance with respect to the forces transferable to the anchor block. FIGURE 2 (Prior Art)5 shows the load transfer and associated displacement to mobilise resisting pressure. The local equilibrium of each anchored rod implies that the force transferred by the face panel to the anchor rod for each tributary area of the rod is equal to: (Equation 1 Removed) The force transferred by the rod to the anchor block is equal to: (Equation 2 Removed) Hence, 5 Ibid., Figure 48, page 171. (Equation 3 Removed) where: σpm is the passive earth pressure mobilised on the anchor block; σam is the lateral active soil pressure acting on the facing element; Sface is the tributary area of the facing per each anchor rod; and Sblock is the surface area of the anchor block for each anchor rod. Equation 3 implies that the surface area ratio R = SfaCe/Sblock governs the lateral earth pressure mobilised on the facing elements and on the anchor block and thereby the anchor rod's displacements. For R = 1, the lateral displacements of the backfill material is assumed to be restrained and therefore: (Equation 4 Removed) where: KO = 1 - sin Φ' being the coefficient of earth pressure at rest; Φ' = the internal friction angle of the backfill material; and σv = the vertical stress at the level of the anchor. As R increases, the surface area of the anchor block increases, the passive earth pressure required to maintain equilibrium increases, as well as the anchor rod's displacements which can be determined from pullout tests. The limit passive earth pressure is governed by the bearing capacity of the backfill materials which controls the pullout resistance of the anchor rod. The forces in the anchor rods are calculated from the local equilibrium at each level of anchor (i.e. the force in the anchor is equalized to the lateral earth pressure on the face element multiplied by the tributary face area per each anchor. Conventional anchored earth systems provide for anchor rods having tensile strength of 400 Nmm"2 and below. Pullout tests have also established that a failure or shear zone (10) around the anchor block (12) where the soil cohesion fails. The zone (10) is normally in the shape of a lateral tear drop zone as shown in FIGURE 3 (Prior Art) . Due to the conventional anchored earth systems having anchor rods (14) with such a limited tensile strength, more anchor rods have to be provided per tributary area of the face panel. Thus, the tear drop zones tend to overlap with one another to create a failure or shear fault line with disastrous consequences. Objects of the invention It is an object of the present invention to provide for an earth anchorage system which high tensile reinforcement elements may take on higher load with less strain on said reinforcement elements which are inextensible. Another object is to provide for a larger tributary area so that wider spacing of the anchor blocks may be provided and avoid the overlapping of shear zones or soil cohesion failure zones around the blocks. Yet another object is to provide for means for connecting the anchor rods of the present invention to the face elements. Summary of the Invention; To achieve the foregoing objects, the present invention provides an anchoring means for retaining a wall system comprising a connector means provided on a wall element, an anchor block, and an anchor rod provided with means to be secured to said connector at one end and to said anchor block at the other end; wherein said anchor block extends through and beyond said anchor block and is terminally provided with an end plate and wherein means is provided to bias said end plate against said anchor block. Preferably, the end plate is provided with adjustable means to adjust the force of bias against the anchor block. Preferably still, the biasing means is a coil spring. Alternatively, the biasing means may be a spring washer or a leaflet spring bent accordingly. Preferably, the anchor rod of the anchoring means of the present invention is prefabricated of predetermined high tensile strength suitable for an increase in the tributary area of load transfer. Preferably still, the anchoring means is provided with a connector comprises a loop protruding from said wall element with ends of said loop extends outwardly and laterally into said wall element. In one preferred embodiment, the rod end may be tied to the connector by providing said rod end with threading and inserting said rod end via a hole provided traversing the connector and tying said rod end with a corresponding threaded nut. The anchor block may be, as alternative embodiments, a thin block, plate or like configuration. Among the other aspects of the invention include a precast face panel for a wall retaining system provided with a connector according to the present invention. Another aspect includes a retaining wall comprising one or more anchoring means according to the present invention. Yet another aspect includes an anchor rod with a tensile strength suitable for use in an anchoring means according to the present invention. Still another aspect includes an anchor block with means provided to bias the end plate against said anchor block for use in an anchoring means according to the present invention. Preferably, the anchor block further comprising one or more of the following: a biasing means; an end plate; and adjustable means for fastening biasing means to said end plate. Brief description of the drawings The features and other advantages of the invention mentioned above will be more easily understood from the following detailed description of the preferred embodiments as examples of the invention with reference to the accompanying drawings of which: FIGURE 1 (prior art) shows schematically the variations of tensile force along a typical anchored block system; FIGURE 2 (prior art) shows the load transfer and associated displacement to mobilise resisting pressure; FIGURE 3 (prior art) shows the side elevation of the pullout shear or failure zone around the anchor blocks; FIGURE 4 shows the side view of the anchorage system of the present invention; FIGURE 5 shows an embodiment wherein the biasing means of the anchor block is a leaflet spring; FIGURE 6 shows the biasing means being a spring washer; FIGURE 7 shows in detail a preferred embodiment of the connector for the anchorage system; FIGURE 8 shows the spaced apart rods of the invention which prevents the overlapping of shear zones around the anchor blocks; FIGURE 9 shows in isolation an anchorage lug being a preferred embodiment of the connector; and FIGURE 10 shows a face panel in spatial arrangement with the various components of the anchorage system of the invention. Detailed Description of Specific Embodiments The invention will now be described in detail with respect to specific embodiments of the anchoring means according to the present invention. As shown in FIGURE 4, the anchorage system (20) according to the invention comprises of a connector (22) provided embedded partially on a face or wall element (24), an anchor block (26) and an anchor rod (28). The rod (28) is provided with means (30) to secure to the connector (22) at the proximal end (32) by having said end (32) penetrating through a hole (34) provided traversing the connecting loop (36) of the connector (22). The means to secure the proximal end (32) of the anchor rod may be any conventional means such as shown in the present example as a bolt and nut means. The proximal end (32) of the rod may be threaded so that a complementarily threaded nut (30) may be affixed thereonto to prevent said proximal end (32) from being withdrawn from the connector (22) , thus securing one end of said anchor rod to the face or wall element (24) . The distal end of the anchor rod is provided to extend through and beyond an anchor block (26) . The terminal end (40) of the rod that extends beyond the anchor block (26) may be provided with an end plate (42) which is biased away from the anchor block (26) by a spring biasing means (44). The end plate (42) is prevented from being pushed away further by a nut (46) fastened to the threaded end of the rod. It will be appreciated that any other forms of adjustable fastening means to secure the end plate (42) against the biasing means may be used. While the conventional anchor rod's tensile strength is about 400 Nmm-2 or less, the rod employed in the present invention is of a much higher tensile strength, i.e. in the range from 400 Nmm-2 to 2000 Nmm-2. High tensile rod is generally inextensible, i.e. it may take higher tensile load with insignificant strain. With the spring-bias mechanism (44) employed at the anchor block (26) or deadman of the present invention, the yield stress developed on the rod (28) may be controlled or absorbed by the spring mechanism (44) which bias strength may be adjustable by turning the nut (46) holding in the end plate (42) against the spring mechanism (44) . Therefore, the anchor rod's yield stress or tensile failure due from anticipated stress or strain loading on the structure may not be reached as the spring mechanism (44) is able to govern the maximum tensile stress within the anchor rod (28). This is especially when unexpected high stress develops on the wall structure or soil which is then transferred to the reinforcement rod, e.g. when an overweight vehicle passes the road built on the embankment. With the spring-bias mechanism absorbing the additional stress, the ultimate stress that may develop on or transferred to the rod is thus limited; otherwise the rod might fail leading to the failure of that section of the embankment with catastrophic results. The invention thus ensures greater safety of such anchor earth embankment system to the general public. It will also be appreciated that various other means or elements for mechanically biasing against the anchor plate may be improvised. While FIGURE 4 shows the preferred biasing means embodied as a coil spring, FIGURE 5 and FIGURE 6 show alternative embodiments of the biasing means being a leaflet spring (44A) bent accordingly and a spring washer (44B) respectively. It will further be appreciated that the anchor block (26) or deadman may be alternatively improvised as an anchor plate, thin block or like thinner elements provided that the surface area Sblock of such anchor plate is adequate with respect to the tributary area of the face or wall element in the foregoing equations or relationships. In one aspect of the invention, as shown in FIGURE 7, the connector (22) for securing the proximal end of the anchor rod to the face or wall element is fabricated in substantially Ω or like shape wherein a loop portion (50) is provided to protrude from the back surface of the wall or face element in the manner of an anchorage lug. FIGURE 9 shows a 3-dimensional view of a preferred anchorage lug in isolation. The protruding lug portion (50) allows the anchor rod end to be tied thereto via a traverse hole (34) . Embedded within the face element (24) is a pair of base flanges (52) which extend outwardly and laterally to be securely embedded within the precast face element (24) . With such extended base, the anchorage area of the anchorage lug (22) is increased in order to meet the pull-out stress requirements of the anchor rod of the invention which is expected to take on increased bearing. As a preferred embodiment, the anchorage lug (22) may be provided more securely embedded in the precast face element (24) by a pair of rods (54) transversing the base flanges (52) . The transverse rods may be provided horizontally to transverse the base flanges if the anchorage lug is provided to extend vertically and vice versa. FIGURE 10 shows one of the most preferred embodiment of the invention with all the components of the system of the present invention in spatial arrangement. The face panel (24) is shown with the anchorage lugs (22) embedded therewithin and in connection with the anchor rods (28) at the proximal ends while the distal ends are shown connected to the anchor blocks (26) with biasing means (44). It is apparent that many of the prior art connectors, such as those embodiments disclosed in US-4929125 (Hilfiker) may be adapted to be pre-cast in concrete as the wall or face elements for use with the anchorage system of the invention. With the increased in predetermined high tensile anchor rods being fabricated for use in the present invention, the tributary area of load transfer for each rod is also correspondingly increased. With the (i) increase in the tensile strength of the rod and (ii) spring-biased mechanism, the tributary area of reinforcing rod element may be increased. Thus, fewer rod elements per face elements may be designed. Accordingly, the rod reinforcements may now be spaced out further apart from one another as shown in FIGURE 8. This in turn reduces the "tear-drop" shearing zone (10) from overlapping and soil fault due to such phenomenon may be avoided. Accordingly, this enables the presently proposed anchor earth system to have increased safety due to increased failure tolerance of both the reinforcing elements as well as soil failure. It will be apparent to a person skilled in the art that the methods of the present invention and its various specific embodiments and configurations, or parts or components thereof may be varied or modified without departing from the methods or principle of working described herein. It will also be apparent to a skilled person that a number of the anchor earth wall embankment systems and their associated tying method and anchor means or deadman may be adapted for use with the spring-biased anchor block of the present invention. These and other such embodiments not specifically described herein are not to be considered as departures from the present invention and shall be considered as falling within the letter and spirit of the following claims. We claim: 1. An anchoring means for a retaining wall system comprising: a connector means provided on an wall element; an anchor block; and an anchor rod provided with means to be secured to said connector at one end and to said anchor block at the other end; wherein said anchor rod extends through and beyond said anchor block and is terminally provided with an end plate; and wherein means is provided to bias said end plate against said anchor block. 2. An anchoring means as claimed in Claim 1 wherein the end plate is provided with adjustable means to adjust the force of bias against the anchor block. 3. An anchoring means as claimed in any one of Claims 1 and 2 whereiri the biasing means is a coil spring. 4. An anchoring means as claimed in any one of Claims 1 and 2 whefein the biasing means is a spring washer. 5. An anchoring means as claimed in any one of Claims 1 and 2 wherein the biasing means is a leaflet spring bent accordingly. 6. An anchoring means as claimed in any one of Claims 1 to 5 wherein the connector means is fabricated as an anchorage lug and comprises a loop protruding from said wall element with ends of said loop extends outwardly and laterally into said wall element. 7. An anchoring means as claimed in Claim 6 wherein the ends of the anchorage lug are provided as a pair of base flanges which are precast embedded in the wall element. 8. An anchoring means as claimed in Claim 7 wherein retaining rods are further precast to transversely secure the base flanges in the wall element. 9. An anchoring means as claimed in Claim 6 wherein the rod end is tied to the connector by providing said rod end with threading and inserting said rod end via a hole provided traversing the connector and typing said rod end with a corresponding threaded nut. 10. An anchoring means as claimed in any one of the preceding claims wherein the anchor block is a thin block, plate or like configuration. 11. An anchoring means as claimed in any preceding claim wherein a precast face panel is located on said wall element. 12. A retaining wall comprising whenever comprising one or more anchoring means according to any preceding claim. 13. An anchoring means for a retaining wall system substantially as hereinbefore described with reference to the figures 4 to 10 of the accompanying drawings.

Documents:

1021-del-2001-abstract.pdf

1021-del-2001-claims.pdf

1021-del-2001-correspondence-others.pdf

1021-del-2001-correspondence-po.pdf

1021-del-2001-description (complete).pdf

1021-del-2001-drawings.pdf

1021-del-2001-form-1.pdf

1021-del-2001-form-19.pdf

1021-del-2001-form-2.pdf

1021-del-2001-form-3.pdf

1021-del-2001-form-5.pdf

1021-del-2001-gpa.pdf

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