There is an increasing need for the development of novel technologies for tunnel construction in difficult geological conditions to protect segmental linings from unexpected large deformations. In the context of mechanized tunneling, one method to increase the damage tolerance of tunnel linings in such conditions is the integration of a compressible two-component grout for the annular gap between the segmental linings and the deformable ground. In this regard, expanded polystyrene (EPS) lightweight concrete/mortar has received increasing interest as a potential “candidate material” for the aforementioned application. In particular, the behavior of the EPS lightweight composites can be customized by modifying their pore structure to accommodate deformations due to specific geological conditions such as squeezing rocks. To this end, novel compressible cementitious EPS-based composite materials with high compaction potential have been developed. Specimens prepared from these composites have been subjected to compressive loads with and without lateral confinement. Based on these experimental data a computational model based on the Discrete Element Method (DEM) has been calibrated and validated. The proposed calibration procedure allows for modeling and prognosis of a wide variety of composite materials with a high compaction potential. The calibration procedure is characterized by the identification of physically quantifiable parameters and the use of phenomenological submodels. Model prognoses show excellent agreement with new experimental measurements that were not incorporated in the calibration procedure.

In this chapter, important research results for the development of a robust and damage-tolerant multimaterial tunnel lining are presented. This includes the production, design and optimization of fiber-reinforced hybrid segmental lining systems based on numerical models and experimental investigations under tunneling loads. In addition, novel tail void grouting materials are developed and optimized regarding their infiltration and hardening behavior while taking the interaction with the surrounding ground into account. In order to expand the applicability of mechanized tunneling regarding soils characterized by significant swelling potential due to water uptake by clay minerals, a deformable segmental lining system is presented. The risk of damage due to high localized loads is reduced by the integration of additional radial protective layers on the lining segments and a compressible annular gap grout, which protect the tunnel structure by undergoing high deformations after reaching a certain yielding load. However, the deformability of such support systems affects the distribution of the stresses around the tunnel which governs the magnitude and buildup of the swelling pressure in the soil. Therefore, the development of damage tolerant lining systems requires a material and structural design which ensures an optimal soil-structure interaction through a synergy of computational and experimental techniques.

Real-time monitoring of additive manufacturing processes is challenging because it requires synchronized layer-wise testing, fast data acquisition and processing, and reliable signal interpretation during the build process. In this work, a process-synchronized monitoring system is presented for layer-wise eddy current testing (ET) of metallic additively manufactured components during fabrication on an industrial SLM 280HL system. The proposed approach integrates the manufacturing process with a synchronized measurement and data acquisition pipeline. Signal acquisition is performed using a giant magnetoresistive (GMR) sensor array. Automated triggering is derived from the progression of the build process, enabling consistent layer-wise measurements during fabrication. The acquired signals are transferred to a processing unit, where signal conditioning techniques, including baseline correction and filtering, are applied to improve data quality. The developed workflow enables automated triggering, data acquisition, and evaluation on a layer-by-layer basis without interrupting the manufacturing process. After fabrication of each layer, ET testing is performed, and once the stop signal is received, the acquired data are transferred via Ethernet, processed, and visualized within approximately 10 seconds per layer. The results show that the developed system enables consistent layer-wise ET testing during the build process and supports layer-wise signal evaluation.

The integrity of tunnel structures deployed in difficult geological conditions such as expansive soils can be improved by incorporating compressible layers in the tunnel lining. Such compressible lining materials can be obtained by embedding weak inclusions (Expanded polystyrene, Expanded glass beads, Air voids) into a cement paste material. The material properties of these individual constituents as well as their geometry affect the overall material behaviour of such cementitious composites. Design of the compressible tunnel lining for specific geological conditions can be improved by choosing optimal characteristics of the composite constituents. This procedure can be enhanced by using a simulation based data driven framework. For compaction simulation of the cementitious composite, a multiscale voxel based model is proposed. To account for the influence of the composite microstructure, the model is enhanced by continuum micromechanics.

Compressible cementitious materials are used in tunnel lining systems deployed in ground conditions characterised by expansive soils. The deformation capacity of a cementitious material can be enhanced by the introduction of weak inclusions (EPS) and/or pores. The overall behaviour of such porous cementitious composite materials is strongly influenced by the material properties of the individual components (EPS, pores, sand particles, aggregates), the geometry of the constituents, their spatial distribution and volume. The compaction behaviour of such composites can be described by a voxel model with a discrete distribution of material properties, where the voxels are compacted by applying an eigenforce. The proposed model is integrated into the framework of the reduced order self‐consistent clustering strategy at the scale of a Representative Elementary Volume [1]. The accuracy of the reduced order strategy combined with the voxel model is analysed by comparing it to the full voxel compaction model