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XVI Pan-American Conference on Soil Mechanics and Geotechnical Engineering (XVI PCSMGE) Geotechnical Engineering in the XXI Century: Lessons learned and future challenges, Cancun, MEXIQUE, 17-/11/2019 - 20/11/2019; The use of helical anchors has expanded in recent years although the understanding of its behavior is still unsatisfactory. The uplift capacity of multihelix anchors in sand has been estimated using breakout factors, which vary with the sand friction angle and embedment ratio. These factors are affected by the disturbance produced by screwing the helices into the sand mass, which is more significant in the soil above the upper helices than above the bottom helix. However, the number and position of the helices (upper, intermediate or bottom) is not taken into account in the prediction of the uplift bearing capacity of the individual helices of helical anchors. The current investigation reports the effect of the number of helices on the breakout factor of helical anchors, measured from centrifuge tests in sand. Twenty-six tensile load tests were performed on different model anchors installed in sand samples with two different relative densities. The findings show that for helical anchors in dense sand, the values of breakout factor of the upper helices are lower compared to the bottom helix; however, for the looser sand case the values are similar.

Pull-out has been proved to occur more often for bonded anchors under tensile loads at high temperatures than at ambient temperature. The existing evaluation method of bonded anchors under fire only covers steel failure mode. Due to the absence of guidelines for evaluating the pull-out of bonded anchors directly exposed to fire, only the evaluation method for mechanical anchors (without resin) is applicable. This paper presents an experimental study on the influence of different parameters linked to the existing evaluation method by means of pull-out fire tests. Additional unloaded fire investigation tests were conducted to compare different configurations of pull-out fire tests. This paper highlights the level of accuracy of load prediction using the resistance integration method based on temperature profiles of bonded anchors directly exposed to a standard ISO 834 fire. Results showed that parameters such as the existence of metallic fixtures on the rod barely influence the predicted load-bearing capacity and failure time. However, parameters such as adopting concrete element temperature along the thickness instead of steel temperature along the embedment depth, and the existence of insulation around the fixture have a greater influence and may result in a false estimation of the load-bearing capacity and failure time.

Classical techniques for backfilling of trenches use unbounded materials. Unfortunately, they have always been presenting several drawbacks: difficulty of compaction, noise disturbance and time of implementation... Controlled Low Strength Materials (CLSM) could be a good alternative thanks to their fluidity and cementitious setting, provided that they remain excavatable, even with a pick. In fact, it is essential to ensure a rapid and easy permanent access to the underlying networks, in case of emergency or maintenance. Modular concrete pavements were developed during the last years for that purpose. The concrete elements are laid on a base of cement treated material to keep their stability. They are designed to be easily removed but the base material must be excavated with a light facility as well. Yet, until recently, the excavatability was not well defined, nor well measured. Recently, a new approach based on a simple laboratory punching test was developed at Ifsttar to provide a quantitative characterization in laboratory of cement treated materials excavatability. This paper first details the general approach. Then a large parametric experimental campaign conducted with the punching test on mixes with various compositions is presented. From the results obtained, a model linking the mix proportions to the pick penetration depth is proposed. Finally, excavations are realized on real scale trenches to confirm that the optimization of the penetration leads to a better excavatability of the material.