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The problem of axially symmetric loading of a spheroidal rigid inclusion embedded in bonded contact with an isotropic linear viscoelastic infinite medium is investigated. This particular problem is of interest in connection with the analysis of the time-dependent anchorage efficiency of deep ground anchors and rock anchors embedded in soil and rock media susceptible to creep. The solution to the spheroidal rigid anchor problem pertaining to a linear viscoelastic medium is facilitated by the application of the Laplace transform-based correspondence principle. The transformed viscoelasticity problem is then solved by the use of Boussinesq's three-function approach developed for the solution of three-dimensional problems in classical elasticity. For the purposes of illustration, the particular viscoelastic material behavior is restricted to one which exhibits a dilatational response which is elastic and a deviatoric response which is that of a standard linear solid. Explicit analytical results are presented for anchors of both prolate and oblate spheroidal shapes which are subjected to either loads or displacements which vary as step functions of time. Numerical results are presented for cases where the rigid anchor embedded in typical geological materials is subjected to a step function of displacement. These results illustrate the manner in which the tension in the anchor rod can be influenced by the creep of the geological material in the vicinity of the anchor region.

Research into the bahaviour of groups of inclined ground anchors is described. Results of laboratory tests are presented and discussed. The effect of anchor spacing and inclination was investigated in a test rig in which metal discs simulating the underreams were embedded. These were connected by a steel tendon to an instrumental linkage and a motor driven pull-out head. The instrumented linkage containing strain gauges and transducers was connected to a 20 channel bridge and digital voltmeter which produced direct punching of results on tape as the pull-out progressed. The article gives results in graphical form of many tests on groups of three and five anchors covering a range of inclinations and spacings. Differences were found in the loads taken by the 'leading' and 'trailing' anchors which were always compared with the performance of a single control anchor. Using stereo-photogrammetric techniques to record movements within the leighton buzzard sand in which the anchors were embedded, a picture of the 'pressure bulb' around the anchor group was obtained. The change in shape of this bulb with changes in other variables is discussed.

Ground anchors essentially comprise a high strength tendon which is fixed in the ground by means of grout, and in general they are used to resist pull-out forces such as occur with transmission towers, dry dock floors such as tied-back retaining walls. The authors discuss the effect of prestressing such anchors to stiffen the system, and suggest that in the past little or no attention has been given to the effects of repeated loading of both prestressed and dead (zero prestress) anchors. This paper presents the results of a study into static loading effects related to the repeated loading of foundations - in such cases inertia forces are very small and therefore negligible. A review of previous relevant work is presented. The test equipment illustrated and described consisted of six identical test rigs constructed to fulfil the basic requirements of (1) that any sand density could be achieved, (2) that any sand stress history could be maintained, (3) that the plate-shape anchors used could be subjected to both uplift and compressive loading in a cycle of loading if necessary, and (4) that very small changes in load could be applied. Information is provided on the materials used, and the test sequences adopted, and the results of static load tests and repeated load tests are presented in graphical form and discussed. It is suggested that despite limitations inherent in the tests, trends and conclusions can be drawn from the results. First, dead anchors when subjected to load repetitions sustain non-recoverable movements, the movement per cycle of load decreasing with the number of loadings. A family of curves exist for a particular anchor system and the life of an anchor will depend primarily on the load range for a particular limiting deflection. Secondly, alternating loads cause much more severe loading conditions and the life of an anchor is markedly reduced. /TRRL/

In this article the author describes 40mm diameter mechanical anchors that have been designed specifically to function in the weaker rocks similar to the chalk encountered at Chinnor. The self-under-reaming reversed expanding (SURE) rock anchor has segments which expand over a cone in the reverse direction to a conventional anchor until locked between the cone and a cup. The radial force applied to the ground by the SURE anchor acts inwards, the rock is drawn into the path of the anchor and its ability to resist the load applied is enhanced. The SURE Anchor was designed for use in soft or high fissured ground where existing anchors may not develop adequate loads. The anchor was originally developed for chalk, however its use could be extended to other weak rocks as well as in artificial materials such as poor concrete. In very bad ground it is possible to distribute the load applied to the ground as does a resin anchor, by stacking anchors. Although the SURE anchor was designed with a nominal 40 mm retracted diameter, the design could be adapted to a greater diameter. A larger version can be designed to open to a proportionately greater span and withstand a 90kn load before failure of the steel. The cost of the SURE anchor is more than the conventional mechanism anchor, however the SURE anchor is designed to function in weak rock, alternative methods of suport in such circumstances, using concrete or steelwork would be more expensive.