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Significant infrastructure is required to establish a long-term presence of humans on the lunar surface. In-situ resource utilization (ISRU) is a fundamental approach to ensure the viability of such construction. Here, we investigate the feasibility of constructing blast shields as one example of lunar infrastructure using unprocessed lunar boulders and an autonomous robotic excavator. First, we estimate the volume of unprocessed material required for the construction of blast shield segments. Secondly, we quantify the amount of available boulders in two exploration zones (located at the Shackleton-Henson Connecting Ridge and the Aristarchus Plateau pyroclastic deposit) using LRO NAC images and boulder size-frequency distribution laws. In addition, we showcase an alternative approach that relies on Diviner rock abundance data. Thirdly, we use a path planning algorithm to derive the distance, energy, and time required to collect local material and construct blast shield elements. Our results show that our construction method requires two orders of magnitudes less energy than alternative ISRU construction methods, while maintaining realistic mission time and payload capacity margins. [ABSTRACT FROM AUTHOR]

Complex permeability distribution is frequently encountered in weathered rocks with inherited heterogeneities, such as networks of discontinuities that impact fluid flow and water‐rock interactions. Reactive transport modeling is a powerful tool for analyzing fractured media's chemical weathering dynamics. In this study, two different ways to model the fracture‐matrix interaction were explored. A 1D dual‐porosity simulation of reactive transport is designed to study the global impact of fractures on the weathering progression front, compared with a Single Porosity (S.P.) (unfractured) reference model. Then a 2D discrete model using a Discrete Fracture Matrix (DFM) representation is built to highlight the importance of medium geometry and fracture connectivity on weathering. The relevance of such models was evaluated in the case of weathering processes affecting ultramafic units in New Caledonia. Comparing the average behavior of the dual and S.P. models reveals a similar trend in both global mineralogical evolutions. Yet differences occur when confronting the weathering rates. By extending the weathering over a greater depth, the fractures favor a smoother transition between the saprolite horizon and the oxide ore. Furthermore, a partition of the newly formed phyllosilicates occurs in fractures and matrix: Ni‐phyllosilicates preferentially precipitate in fractures, while Mg‐phyllosilicates remain trapped within the matrix due to differences in residence time and liquid‐to‐solid ratio. The DFM modeling highlights the effect of the connectivity of a complex fracture network on the dissolution‐precipitation processes. Depending on the permeability and geometry, fluid flow is modified, favoring the formation of weathering heterogeneities typically observed on the field. Key Points: Dual Porosity modeling of a fractured rock mass recreates weathering heterogeneitiesWeathering heterogeneities originate from the physico‐chemical differentiation of the fractures and the matrixDiscrete Fracture Matrix modeling reveals the impact of the geometry and permeability of fractures on weathering heterogeneities [ABSTRACT FROM AUTHOR]

Steel baffle installed on footing is commonly used to resist and dissipate the impact energy from boulders carried by debris flow. However, the deformation of a baffle and the resulting energy transfer to the footing during the impact process compound the challenges of predicting the impact force and size of the footing required. In this study, full-scale experiments were conducted to simulate a boulder impacting a steel baffle installed on a square footing. The experimental data were back-analyzed using a three-dimensional (3D) finite element model, which was then used to conduct a parametric study to examine the effects of a range of impact energies and footing sizes. New design charts are developed to assess the required size of a square footing, embedded up to 2 m depth, for a steel baffle subjected to boulder impact with energy in the range of 10–100 kJ. [ABSTRACT FROM AUTHOR]

Local scour holes are erosional bed structures that are related to different scientific disciplines in Earth science and hydraulic engineering. Local scouring at naturally placed boulders is ubiquitous, but many competing factors make it difficult to isolate the effects of a given variable. This is especially true for local scouring at natural instream obstacles that are exposed to unsteady flow conditions in the course of flood hydrograph experiments. Experimental investigations in laboratory flumes offer the advantage that boundary conditions can be systematically varied. We present novel experimental data on the impact of the submergence ratio, hydrograph skewness, and flow intensity on local scouring at boulder-like obstacles during unsteady flow and evaluate the effect of discharge chronologies. In total, 48 flume experiments on subcritical clear-water conditions and channel degradation were performed. The experimental results reveal that local scouring dominantly occurred at the rising limb when flow depth was comparable to the obstacle size, so the obstacle was unsubmerged. The steeper the rising limb, the quicker the local scour hole matured. The experimental results are relevant for the hydraulic interpretation of local scour holes found at boulders in the field. They may be utilized as a proxy for the minimum duration of the beginning stage of a flood. [ABSTRACT FROM AUTHOR]

Toe and boulder due to blasts in the open pit mines reduce the production efficiency and increase extraction costs. In this study, these phenomena were reduced to correct the blast parameters of the ore blocks in the Sirjan Golgohar-2 Mine. For this purpose, the values of seven effective parameters including, an average of depth holes, burden, sub-drilling, powder factor, spacing, rock quality designation, and blastability index were collected for 19 blasting blocks in the studied mine. In this research, the values of Geo-mechanical properties of rock mass were obtained by the photogrammetric method and discontinuity set extractor software. Subsequently, the experimental models were created to predict the volume of boulder and toe relative to the volume of blasting block by nonlinear multiple regression. The predicted ability related to each of the created models by statistical indicators was investigated, and it was determined that the polynomial model to product boulder and the exponential model for toe are more accurate with 94.43 and 98.13 coefficients of determination respectively. Then, the minimization process of these phenomena was performed to access optimal values of controllable parameters and their coefficients in each of the created two models simultaneously by the combinational algorithm of Particle Swarm Optimization-Genetic algorithm. Finally, to evaluate the predicted ability of two optimized models, four blasts based on the optimized information were performed on the mine. The results showed that the models predicted the volume of boulder and toe relative to the block volume with the Root Mean Square Error 0.47 and 0.08 respectively. [ABSTRACT FROM AUTHOR]

To arrest rockfall boulders, baffles are constructed as steel members affixed on top of a concrete footing. Existing designs aim to prevent any footing rotation and steel member bending. As such, existing baffle designs require massive reinforced concrete footings and complex bolt and weld connections. Such designs have limited constructability and result in complex failure mechanisms (i.e., tensile failure of concrete foundation at connections). In this paper, we introduce a new baffle design concept that optimizes the balance between steel member bending and footing rotation to enable a compact design. Full-scale pendulum experiments are conducted to evaluate the proposed easy-to-construct and design baffle under successive boulder impacts of 50 kJ. It is demonstrated that by considering the effects of steel member deflection and concrete foundation rotation, the maximum impact force on baffles is reduced by up to two times when compared with those on a rigid barrier and the failure modes are simplified to either overturning failure of the footing or buckling failure of the steel member. A ratio that defines the flexural capacity of the steel member to the overturning capacity of the shallow concrete foundation is proposed to control the failure mode. The optimized baffle configuration for an impact energy of 50 kJ, with minimum residual deflection, has a target capacity ratio of 2.0. • A capacity ratio (flexural capacity of steel member to overturning capacity of footing) is proposed for baffle design. • A new baffle design concept is proposed and evaluated using full-scale pendulum experiments. • A failure criterion based on baffle rotation is proposed considering the residual boulder velocity. [ABSTRACT FROM AUTHOR]

When constructing subway tunnels in coastal cities, boulders with high strength and large volume are often encountered. A large number of engineering practices have shown that the existence of boulders will destroy the unity and homogeneity of the stratum. If the tunnel is not properly handled during crossing construction, it will lead to the collapse of surrounding rock; in serious cases, it may induce ground collapse, damage the surrounding buildings, and endanger the safety of people’s lives and property. Firstly, with the help of similar material simulation test, this paper reproduces the phenomenon of vault collapse and surface collapse when the tunnel passes through the boulder stratum, explores the law of stratum collapse and surface settlement caused by the boulder in the process of tunnel excavation, and puts forward the “weightlessness weak surface effect” of the boulder stratum disturbed. Then, taking the Liu-Bai inter-district tunnel project of Shenzhen Metro Line 13 as an example, Midas GTS NX numerical simulation software is used to compare and analyze the influence characteristics of surrounding rock deformation and surface settlement caused by the presence or absence of boulders in the tunnel through the stratum and verify the “weightlessness weak surface effect” of the boulder stratum disturbed. Finally, the engineering treatment measures for the Liu-Bai inter-district tunnel project of Shenzhen Metro Line 13 crossing the boulder stratum are given. The research results are of great significance to guide the prediction and treatment of collapse and surface settlement when crossing the boulder stratum in the tunnel construction project.

Rocky reefs provide complex structures in the otherwise largely sand-dominated coastal North Sea. Therefore, these reefs are highly important natural habitats for the functioning of coastal ecosystems, as they provide shelter, refuge and nursery grounds for various mobile and sessile species. In the North Sea, the spatial distribution of these habitats has been intensively investigated over recent years. However, these studies generally provide static accounts of the current state of these reef systems, but limited data exist on the temporal variations in sediment dynamics at and around natural rocky reefs. In this study, we provide observations from a multiannual time series of hydroacoustic seafloor surveys conducted at an isolated rocky reef in the North Sea. We use multibeam bathymetry and side-scan sonar backscatter data in combination with video observations, sediment sampling, and sub-bottom profiler data to assess the long-term variations of the rocky reef system. The reef is located in water depths between 11 and 17 m with an areal extent of ~0.5 km2 and is surrounded by mobile sands. The topography of the rocky reef appears to create a distinct hydrodynamic system that permits mobile sands to settle or move into bathymetrical deeper parts of the reef. Our results suggest a very dynamic system surrounding the reef with large scale scouring, sediment reworking and transport, while the shallower central part of the reef remains stable over time. We demonstrate the importance of hydrodynamics and current scouring around reefs for the local variability in seafloor properties over time. These small-scale dynamics are likewise reflected in the spatial distribution of sessile species, which are less abundant in proximity to mobile sands. The hydroacoustic mapping and monitoring of seafloor dynamics at higher spatial and temporal resolutions presents an important future direction in the study of valuable coastal habitats. [ABSTRACT FROM AUTHOR]

Local scour holes are erosional bed structures that are related to different scientific disciplines in Earth science and hydraulic engineering. Local scouring at naturally placed boulders is ubiquitous, but many competing factors make it difficult to isolate the effects of a given variable. This is especially true for local scouring at natural instream obstacles that are exposed to unsteady flow conditions in the course of flood hydrograph experiments. Experimental investigations in laboratory flumes offer the advantage that boundary conditions can be systematically varied. We present novel experimental data on the impact of the submergence ratio, hydrograph skewness, and flow intensity on local scouring at boulder-like obstacles during unsteady flow and evaluate the effect of discharge chronologies. In total, 48 flume experiments on subcritical clear-water conditions and channel degradation were performed. The experimental results reveal that local scouring dominantly occurred at the rising limb when flow depth was comparable to the obstacle size, so the obstacle was unsubmerged. The steeper the rising limb, the quicker the local scour hole matured. The experimental results are relevant for the hydraulic interpretation of local scour holes found at boulders in the field. They may be utilized as a proxy for the minimum duration of the beginning stage of a flood.

Boulder falls are an archives of recent surface activity on Mars, however, determining how recently they fell remains elusive. Our multitemporal HiRISE image analysis shows that new tracks are characterized by a herringbone‐like ejecta pattern at each boulder bounce that we call boulder fall ejecta (BFE). First systematic survey of BFE revealed ∼4,500 tracks whose total integrated track length is ∼900 km. Our BFE longevity analysis reveals that these tracks likely formed in the last few decades. From few examples we also observed slope streaks originating from BFE tracks, providing additional evidence favoring a dry origin theory. BFE fade in as little as ∼2 to 4 Mars years, whereas, others can persist >6 Mars years suggesting differential weathering. Nearly 30% of BFE are observed in the Cerberus Fossae region, which suggests it is one of the most seismically active regions. Thus, BFE can be used to recognize very recent surface processes on planetary surfaces. Plain Language Summary: High‐resolution images of Mars have revealed numerous boulder falls on the surface. Here, we systematically surveyed images from 2006 to 2020 to find recent boulder falls which have ejecta. The images of the same place taken at different times, revealed that all new boulder falls have ejecta which we call boulder fall ejecta (BFE). We searched all the images and found BFE present in large numbers suggesting recent falls are common and widespread. Our results revealed that on Mars it takes ∼2 to 4 Mars years (4–8 Earth years) for BFE to disappear, whereas on Earth BFE are rarely preserved. We found that the Cerberus Fossae region adjacent to NASA's InSight lander landing site hosts nearly 30% of BFE, suggesting it is a currently active regions on Mars. Key Points: Comprehensive multitemporal HiRISE image analysis revealed all new boulder falls have ejecta along the track termed as boulder fall ejecta (BFE)Approximately 4,500 tracks with total integrated length of ∼900 km formed in last few decades, 30% BFE located in Cerberus Fossae suggests active regionSome BFE fade within 2–4 Mars year and few persist >6 Mars year, evidence for slope streaks originating from BFE tracks support dry theory [ABSTRACT FROM AUTHOR]

The marine acoustic techniques are powerful tools to investigate and identify the seabed objects by applying different processing and interpretation steps. Two types of marine acoustic imaging techniques used in this study; Side Scan Sonar (SSS) that mapping seabed features and identifies the objects on it, and Sub-Bottom Profiling (SBP) that providing information about sediment thicknesses and stratigraphic structure. The integration between these two marine acoustic techniques, as well as, ground truth data obtained from an underwater camera, was used to distinguish seabed objects; coastal boulder accumulations that are documented along the western Mediterranean coast of Egypt. The study and analysis of the collected data demonstrated that: the combination between side scan sonar, chirp sub-bottom profiling systems, and ROV images can successfully distinguish different types of objects. Generally, objects observed from SSS are indicated in the SBP as weak backscatter curves. The case study results, from analysis of SBP with ROV image to the object detected by SSS utilized three objects making a shadow in SSS seabed: boulder, hard substrate, and seagrass. The integration of these techniques resulting specifies the location of the geo-hazards area. [ABSTRACT FROM AUTHOR]

Among several subgrade stabilization alternatives, the improvement with oversized material (boulders of approximately 10-inches in size) has traditionally been used. The Boulders form a thick mineral skeleton that supports the structure and favors moisture control. Nowadays, this technique is not included within the design protocols of Colombia. In this research, the mechanical properties of the pavement are quantitatively evaluated through 2Dnumerical-elastic modeling employing the improvement of soft subgrades with boulders. Comparative studies of performance and analysis of the fundamental variables in pavement design are carried out through 2D-numerical modeling. This way, guidelines to sketch a design protocol are suggested to improve mechanical properties in soft subgrades through the inclusion of oversized material. [ABSTRACT FROM AUTHOR]

Abstract Corals at Ishigaki Island, Japan, are characterized by their high species diversity. Not only are they struck by storm waves generated annually by typhoons, the corals, especially the massive ones, in the fringing reef were buffeted by huge tsunami waves with a run-up height of ca. 30 m in 1771 Meiwa tsunami and its predecessors at few hundred-year intervals. We present field survey and numerical results demonstrating that such near-field large tsunamis could have reset the growth of massive corals, a phenomenon which large typhoons have not caused. Our field survey revealed that the massive corals in the lagoon are not attached to the bedrock but are instead located on the sandy sea bottom. Therefore, those are movable of sufficiently large wave inundated in the lagoon. Our numerical results further showed that the maximum velocity of the tsunami at the reef edge, calculable as

To date, cases of severe ground subsidence or abrupt cave-in failure of roadway without warning after crushing and removing boulders in the sand matrix by tunneling have been frequently reported in practice, which jeopardize the safety of pedestrians and vehicles and even cause casualties. Despite the severe consequence, it is still difficult for engineers to give reliable estimations on the ground subsidence hazards and then take suitable countermeasures or remedial measures in advance to prevent or mitigate relevant risks. In this study, failure mechanism of ground subsidence due to removing large isolated boulder in the sand matrix by tunneling and its adverse effects on tunnel performance were explored using numerical modeling. It is discovered that after removing the boulder, the soil stratum above the cavity maintained stability momentarily, and no clear sign of subsidence could be immediately observed at ground surface. With more and more sand particles falling off into the cavity over time, the soil particles nearby were mobilized which finally led to subsidence or cave-in of ground surface. Removing the boulder also incurred redistribution of bending moments and increase of axial stresses in the tunnel lining. In the end, the effects of tunnel cover depth and position of boulder along the tunnel circumference on ground subsidence and tunnel performance were also investigated. The findings in this study can serve as references for evaluating the risk of ground cave-in failure due to future tunneling work in similar geological conditions. [ABSTRACT FROM AUTHOR]

Boulders are spheroidal and weathered rock fragments that exist in softly weathered granite strata. Boulders can cause severe damage to the cutter heads of shield machines and can even lead to the failure of shield tunneling during the excavation of metro tunnels in granite strata. However, there is no effective method to safely and rapidly cope with this problem on a large scale. This study proposes a method to detect and to pretreat boulders during shield tunneling within granite strata. The detection method is a combination of microtremor surveying and supplementary drilling exploration to ensure both rapid, large-scale detection and high detection accuracy. Based on the microtremor survey results, principles of interpretation are developed to predict the presence of boulders and evaluate the safety status of shield tunneling. Furthermore, the predicted boulders are precisely confirmed by supplementary drilling exploration. After the boulder locations are detected, a combined surface drilling and preblasting technique are adopted to pretreat the boulders. This method was successfully applied in the shield tunneling of Fuzhou Metro Line 5 in China. The application shows that this method is effective for the prediction and pretreatment of boulders during shield tunneling. The prediction of boulders has high accuracy. The preblasting of boulders improves the tunneling efficiency, which significantly reduces the total thrust and torque on the cutter head, and markedly increases the tunneling speed. [ABSTRACT FROM AUTHOR]

Rocky reefs provide complex structures in the otherwise largely sand-dominated coastal North Sea. Therefore, these reefs are highly important natural habitats for the functioning of coastal ecosystems, as they provide shelter, refuge and nursery grounds for various mobile and sessile species. In the North Sea, the spatial distribution of these habitats has been intensively investigated over recent years. However, these studies generally provide static accounts of the current state of these reef systems, but limited data exist on the temporal variations in sediment dynamics at and around natural rocky reefs. In this study, we provide observations from a multiannual time series of hydroacoustic seafloor surveys conducted at an isolated rocky reef in the North Sea. We use multibeam bathymetry and side-scan sonar backscatter data in combination with video observations, sediment sampling, and sub-bottom profiler data to assess the long-term variations of the rocky reef system. The reef is located in water depths between 11 and 17 m with an areal extent of ~0.5 km2 and is surrounded by mobile sands. The topography of the rocky reef appears to create a distinct hydrodynamic system that permits mobile sands to settle or move into bathymetrical deeper parts of the reef. Our results suggest a very dynamic system surrounding the reef with large scale scouring, sediment reworking and transport, while the shallower central part of the reef remains stable over time. We demonstrate the importance of hydrodynamics and current scouring around reefs for the local variability in seafloor properties over time. These small-scale dynamics are likewise reflected in the spatial distribution of sessile species, which are less abundant in proximity to mobile sands. The hydroacoustic mapping and monitoring of seafloor dynamics at higher spatial and temporal resolutions presents an important future direction in the study of valuable coastal habitats.

Jezero crater is the landing site for the Mars 2020 Perseverance rover. We report 63 boulder fall tracks within the crater using High‐Resolution Imaging Science Experiment (HiRISE) images. The boulder tracks have both fresh and faded morphologies similar to those reported elsewhere on Mars, but reported for the first time in Jezero crater. We combine observations from 16 boulder‐tracks on the western delta deposit with 47 in the surrounding regions to infer possible process(es) of boulder destabilization, which can be tested with rover observations. This newly found hazard should be taken into account for rover operations. Boulders associated with tracks are geologically "recent falls," so it is possible that the surfaces of these boulders may provide an opportunity to sample material less exposed to radiation than other rocks at the martian surface and could be ideal targets to analyze for organics. Plain Language Summary: We have found tracks left by falling boulders within Jezero crater on Mars, which is the landing site of the Mars 2020 Perseverance rover. The boulder tracks are observed on the slopes of the delta deposits that the rover will explore, on the wall of Jezero crater and on the wall of an ~2 km diameter crater on the floor of Jezero crater. Boulders of a few meters in size have fallen down moderately steep slopes, moving distances from a few tens of meters to nearly a kilometer. The boulder tracks appear both fresh and degraded. The positions of the boulders and the appearance of the tracks have not been observed to change, but the simple existence of the tracks suggests that the boulder falls are recent and could be ongoing. Our results reveal a new location on Mars where boulder fall activity is observed and indicate a new hazard to be taken into account by the rover team. These recently fallen boulders may also have surfaces less exposed to radiation and could be ideal candidates for obtaining samples that could be analyzed for signs of ancient life. Such signs usually degrade rapidly with exposure to radiation. Key Points: We report on previously unrecognized boulder fall activity in Jezero crater—landing site of Mars 2020 Perseverance roverHazardous boulders bigger (length >2.7 m) than the rover have recently fallen on the front of the western delta deposits within the craterRecently fallen boulders may have freshly exposed surfaces, which can be ideal targets for astrobiological investigations by the rover [ABSTRACT FROM AUTHOR]

The study is related to determine the influence on local hydraulic conditions of a group of boulders carried out in 2016 in the context of a restoration project in the Wisłoka river channel. After the boulders deposition in 2013, the study aims to determine whether there is a local impact of the cluster on the microhabitats distribution. The studied hydraulic features were: velocity, velocity pulsation, discharge, water depth and topographical measurements from three field sessions at three different discharges (31.2, 19.3 and 10.4 m3 • s–1). A study of the velocity profiles as well as pictures and videos allowed to determine the microhabitats distribution. Calculation method presented by Byczkowski were used to get mean velocity values. The boulders create different kinds of velocity profiles: „logarithmic”, „uniform”, „reverse logarithmic” and even with „negative velocities”. The cluster influences on the creation of different microhabitats. Distribution of them depends on discharge value. „Fast run”, „turbulence zone”, and „recirculate zone” have been observed around boulders at higher discharge. This influence is not so strong for the lower discharges, but the creation of several microhabitats can still be observed: „shallow water”, „turbulent”, „ripples”.

In tropical and subtropical granite regions, quantities of boulders were encountered by the tunnel boring machine (TBM) threatening construction safety. The detection of potential boulders in the driving path of a TBM before construction begins in this region has always been a critical issue. However, boulder detection seems to be aimless owing to a lack of recognition of the boulder distribution law. In this study, the process by which boulders form and evolve is analyzed on the basis of the weathering mechanism of the strata. From this, a general law is hypothesized: on the vertical axis, boulder frequency decreases exponentially with increasing of vertical distance from the bedrock. Data from the literature prove the reasonability of this hypothesis. Subsequently, on the basis of this law, a simple approach for forecasting high-probability zones of boulder occurrence in TBM tunnel engineering was proposed, which was then applied to two newly built tunnels. The field data showed that all boulders were spotted in the forecasted high-probability zones, which verifies the effectiveness of this approach. Significant cost-savings will occur when more boreholes or geophysical prospecting are used in the forecasted high-probability zones rather than all over the tunnel line aimlessly. [ABSTRACT FROM AUTHOR]

Granitic boulders are widespread geomorphological elements, particularly found in humid granitic areas. Although they seldom represent a hazard for people or infrastructures, sometimes their location in steep or natural slopes may jeopardise their stability and potentially affect people or infrastructures. In addition, their complex geometry makes the instability mechanisms difficult to identify, so it is even more difficult to compute factors of safety regarding their stability. In this paper, the authors analyse potential failure mechanisms of granite boulders based on analytical mechanic calculations and physical tilt tests, permitting understanding the phenomena under scrutiny. Then, they study the stability of one of these boulders: the Pena do Equilibrio or equilibrium rock. To do that they resort to standard geotechnical characterization and advanced geometrical characterization derived from UAV photogrammetric and 3D Laser Scanning of the boulder. The presented results exemplify how the application of these recently available topographic technologies, in combination with rock mechanics approaches, enable a rigorous analysis of the stability of granite boulders. • Failure mechanisms of granite boulders have been analysed through analytical calculations and tilt tests in laboratory. • Pena do Equilibrio boulder, located in NW Spain, has been selected for the presented analysis. • UAS and Terrestrial Laser Scanner have been resorted for geometrical calculations like volume and position of the centroid. • The stability of the granitic boulder has been assessed through rock mechanics approaches combined with remote sensing techniques. • A 3D-printed 1:50-scale plastic replica of the boulder has been utilized for analyzing results in laboratory. [ABSTRACT FROM AUTHOR]

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The essential requirements of a successful tunnel boring machine (TBM) tunnelling operation are complete characterization of the ground and thorough identification of geological and geotechnical risks. This paper predicts the geological and geotechnical risks of Tabriz Urban Railway Line 2 (TURL2) in Iran. The railway consists of a 9.5-m-diameter, 22-km-long tunnel and 20 stations. The tunnel passes through a soft alluvial sedimentary combination of clay (CL), silt (ML), sand (SM, SP) and gravel (GP). The tunnel alignment has been divided into three parts subject to the geological and geotechnical conditions that might be encountered during construction. The investigated geological-geotechnical risks of the soft ground along the TURL2 are oversize grains, soil abrasiveness, liquefaction potential, differential permeability and clogging. The results show that all of the investigated geological-geotechnical risks are present in the TURL2 route and that improvement of the tunnel route soils is essential. For example, to reduce the liquefaction potential, it is necessary to decrease the water table level or else improve the soft soils by injecting cement grout. In addition, in order to reduce clogging of the tunnel route soils, the use of foam as a soil conditioner is appropriate. [ABSTRACT FROM AUTHOR]