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The paper presents the results of a numerical analysis (FEM) describing the effect of the undercutting head angle on the formation of the rock mass failure zone during the initial stages of failure propagation. The research was carried out in the context of developing a technology for rock extraction by controlled pull-out of undercut anchors installed in the rock mass. The focus was on the initial stage of crack propagation and its trajectory for anchors embedded at an assumed constant depth and a value of the friction coefficient of the rock against the anchor head. It is shown that smaller angles favor smaller stripping angles and an increased radial impact of the head on the rock material (in the plane perpendicular to the head axis), while the impact of heads with larger angles is found to favor larger fracture penetration angles and faster penetration towards the free rock surface.

Anchors are widely used today to join or support metal structures to concrete. In this union, there is a transfer of forces both in the elements that are joined (concrete and the metallic element) and in the transmitting elements (bolts). Detachment may occur in concrete and shear failure or shear failure may occur. Currently there is a wide variety of anchors and fastening systems, including gas fastening and adhesive technologies. This investigation will offer a comparison of the values of the resistant load of an anchor using the current regulations respect to the experimental values of the failure load made to the post-installed adhesive anchors. In order to achieve it, an experimental program was proposed in which the behavior of post-installed anchors in lightweight structural concrete will be analyzed, for this, 27 solid concrete slabs were built, on which 201 threaded bars were anchored, where 162 of these anchors were tested at tension loads, while the remaining 39 were tested at shear. The results obtained will be compared with the equations that determine the resistance of the anchors through the formulation established in the current normatives, as well as the expected failure mode of the anchors before different geometric configurations. A program was proposed to determine the tensile and shear capacities of adhesive post-installed anchors with threaded rods in high strength structural lightweight concrete with 1.82 T / m3 specific weight, using AnchorFix300 epoxy provided by Sika, for this purpose 27 slabs were cast (9 for tension-confined tests, 9 for tests not confined to tension and 9 for shear tests) of thicknesses of 10 cm, 15 cm and 20 cm where threaded rods with diameters 3/8 ", 1/2" and 5/8 "anchored at 5cm, 10 cm and 15 cm; the anchors have separated threefold depth of the anchor. The results of the tests were compared with the data calculated using the ACI 318-19 equations and it was concluded that 1) For post-installed anchors with anchor depths greater than 100 mm, the equations of the American regulation ACI 318-19 well predict the fails to use 3/8”, 1/2” and 5/8” threaded rods anchored in lightweight concrete, 2) In unconfined anchors in lightweight concrete for 1/2” and 5/8” threaded rods, the predominant failure is the removal of the concrete, regardless of its anchorage length, however, the values obtained from the tensile force differ from the results of the equations but are not far from these values, 3) The greater the diameter and the greater the depth of the anchorage, the less variation there is in the theoretical results vs. the experimental results., Los anclajes son bastante usados en la actualidad para unir o apoyar estructuras metálicas a las de concreto. En esta unión se presenta una transferencia de esfuerzos tanto en los elementos que se unen (concreto y el elemento metálico) como en los elementos transmisores (pernos). En el concreto puede ocurrir desprendimiento y en el perno puede ocurrir falla por tracción o por corte. Actualmente existe una amplia variedad de anclajes y sistemas de fijación, incluidas la fijación por gas y las tecnologías con adhesivos. Esta investigación ofrecerá una comparación de los valores de la carga resistente de un anclaje empleando la normatividad vigente respecto a los valores experimentales de la carga de falla realizados a los anclajes postinstalados adhesivos. Con el fin de lograr lo expuesto anteriormente, se planteó un programa experimental en el que se analizará el comportamiento de anclajes postinstalados adhesivos en concreto liviano estructural, para lo cual se construyeron 27 losas macizas de concreto liviano, en las que se anclaron 201 barras roscadas, 115 de estos anclajes fueron ensayados a cargas de tensión y 39 se ensayaron a cortante, para un total de 154 ensayos. Los resultados obtenidos se compararon con las ecuaciones que determinan la resistencia de los anclajes mediante la formulación establecida en la normativa vigente, al igual que la modalidad de falla esperada de los mismos ante diferentes configuraciones geométricas. Se planteó un programa para determinar las capacidades a tensión y cortante de anclajes postinstalados adhesivos con barras roscadas en concreto liviano estructural de alta resistencia con peso específico 1.82 T/m3 usando epóxico AnchorFix300 proporcionado por Sika, para ello se fundieron 27 losas ( 9 para ensayos confinados a tensión, 9 para ensayos no confinados a tensión y 9 para ensayos a cortante ) de espesores de 10 cm, 15 cm y 20 cm en donde se anclaron varillas roscadas de diámetros 3/8”, ½” y 5/8” ancladas a 5cm, 10 cm y 15 cm; los anclajes se separaron a 3 veces la profundidad del anclaje. Los resultados de los ensayos se compararon con los datos calculados mediante las ecuaciones del ACI 318-19 y se concluyó que 1) Para los anclajes postinstalados con profundidades de anclajes superiores a 100 mm, las ecuaciones del reglamento americano ACI 318-19 predicen bien la falla al usar las varillas roscadas de 3/8”, 1/2” y 5/8” ancladas en concretos livianos, 2) En anclajes no confinados en concreto liviano para varillas roscadas de diámetros 1/2” y 5/8” la falla predominante es arrancamiento del concreto, independiente de su longitud de anclaje, sin embargo los valores obtenidos de la fuerza a tensión difieren de los resultados de las ecuaciones pero no están lejos de estos valores, 3) A mayor diámetro y mayor profundidad del anclaje se presenta menor variación de los resultados teóricos vs los resultados experimentales.

Knowledge of the in situ stress state of rock mass is fundamental for engineering, geological and geophysical applications. In situ stress state determination requires in principle the evaluation of the three principal stresses and the related principal directions, but it is widely recognized in the literature that the maximum horizontal stress is the most difficult component to accurately estimate. In the context of borehole methods, this paper proposes a step-by-step analytical procedure to estimate some bounds to the maximum horizontal stress, starting from a geomechanical description of the rock and relying on information generally available in the engineering practice. The procedure is divided in substeps, each one requiring additional information about the mechanical properties of the rock and on the geometrical properties of the failed portion of rock: more information available implies a lower uncertainty on in situ stress estimate. Furthermore, since the proposed procedure is analytical, it allows a complete and very easy implementation in a spreadsheet. The aim of the work is thus to provide a rigourous but simple analytical tool that can be used in engineering practicte to estimate some bounds to the maximum horizontal in situ stress state. The approach is finally validated by means of both numerical simulations, performed with a sophisticated numerical tool, and experimental field data coming from the literature.