Experimental and finite element assessment of stabilizing configurations for underground heritage sites

Heritage sites in Alexandria, Egypt, are some of the UNESCO world heritage sites at high risk from geo-environmental hazards, in particular caused by sea level rise and heavy rain due to the climate change. Recently, safeguarding UNESCO world subterranean and built heritage draws more attention. After recent environmental catastrophies in Alexandria, sustainable conservation materials and stabilizing configurations of underground monumental structures has also become urgent and highly demanded. Based on typical damage due to the heavy weathering caused by the ground water table and salt, this paper offers a guide for engineers and conservators, where rock structures consolidation and stabilizing configurations to protect these structures in the static state and against strong seismic events is presented. In this paper, typical geotechnical problems and damage to the Catacombs of of Kom El-Shoqafa are presented first, followed by an experimental evaluation methodology that includes spectroscopic and morphological characterization in addition to the mechanical testing of untreated and treated rock samples with synthetic organosilicone and acrylic compounds. The effectiveness of the new silica-based consolidants was evaluated in terms of the amount of solid adsorbed, mechanical properties (e.g., surface hardness, ultrasonic velocity, modulus of elasticity and modulus of compressive strength), and resistance to salt crystallization. The treated groups showed better mechanical strength than the control group. The ability of the treated samples to resist climate change negative impact was also greatly improved. According to laboratory tests, new silica-based hardeners and hydrophobic materials have great potential for strengthening weathered Calcarenitic rock structures. It was observed that the rock samples containing the modified binder (MTMOS + Wacher BS 15) reach higher mechanical strength parameters. After the experimental study (testing procedures), FEM analysis was performed using PLAXIS 2D code to validate the silica-based consolidants and verify their efficiency in improving the response of rock structures in static and seismic states against strong earthquake events. The results of this work confirm the high potential of low-cost injection techniques and stabilizing configurations (pre- stressed anchors and concrete friction piles) technology, confirming the possibility of achieving significant improvement in the geotechnical properties of Calcarenitic rock structures and enhancing the seismic performance of underground archaeological structures using low-cost injection technology that is easy to manufacture.