Sandbox Experiments Research Articles

Heat transfer rate characteristics of two-phase closed thermosyphon heat exchanger

Two-phase closed thermosyphon heat exchangers (TPCTs) have considerable potential for use in ground source heat pump systems. This paper proposes a new metal-polyethylene TPCT that uses water as the working fluid and is composed of a galvanized steel pipe and a polyethylene pipe. The heat transfer rate characteristics of the metal-polyethylene TPCT were studied using a constant-temperature water bath test bench. The experimental results show that the metal-polyethylene TPCT has the best heat transfer rate when the vacuum degree and filling ratio are 1.00 kPa and 12.5%, respectively. The average heat transfer rate increased as the temperature of the heat source and the flow rate of the cooling water increased. Finally, a sandbox test bench was built, which provided seepage and non-seepage experimental conditions for the metal-polyethylene TPCT. In the sandbox experiment, the heat transfer rate capacity of the metal-polyethylene TPCT was initially studied and compared with that of a single U-tube heat exchanger, and the heat transfer rates were similar. When the evaporation section length was 0.5 m, the heat transfer rates were 34.89 W/m and 111.75 W/m under non-seepage and seepage conditions, respectively. The experimental results show that the metal-polyethylene TPCT is feasible as a new type of ground heat exchanger.

Structural Significance of the Mid-level Décollement Within the Western Sichuan Fold-And-Thrust Belt (WSFTB), Insights From Sandbox Modeling

The WSFTB is located outboard of the eastern Tibetan Plateau, western China. It has received great attention due to high earthquake risks and rich resources of oil and gas. For both issues, the detailed structural configuration and deformation mechanism behind it are of great importance, but remain unclear due to the complexity created by the presence of multiple décollements. The effect of regionally distributed shallow Triassic salt décollement (SD) and the basal one (BD) has been well understood. In this paper, we focus on the third décollement situated between them. We conducted three sandbox experiments by varying this mid-level décollement (MD) from absence to presence, and from frictional to viscous, to test the effect on diversity of regional structural configuration. Our experimental results illustrated that 1) Absence of MD facilitated decoupling on SD, forming the greatest contrast between subsurface deformation front and the blind one beneath SD; 2) Frictional MD itself showed little decoupling, while its weakness reduced the bulk strength of deep structural level, lowering decoupling effect on SD and leading to approximating deformation fronts in the shallow and deep; 3) The viscous MD, along with SD relieved the resistance on their interbed layer. Consequently, the fastest deformation propagation rate and farthest deformation front (in all the experiments) occurred in the middle structural level. The modeled fold and thrust structures are comparable with the southern, central and northern WSFTB respectively, suggesting that varied MD may control the along-strike structural variations presented. The results also indicate that MD can alter the deformation partition in depth of any other multiple décollement system.

Contaminant Spill in a Sandbox with Non-Gaussian Conductivities: Simultaneous Identification by the Restart Normal-Score Ensemble Kalman Filter

The joint identification of the parameters defining a contaminant source and the heterogeneous distribution of the hydraulic conductivities of the aquifer where the contamination took place is a difficult task. Previous studies have demonstrated the applicability of the restart normal-score ensemble Kalman filter (rNS-EnKF) in synthetic cases making use of sufficient hydraulic head and concentration data. This study shows an application of the same technique to a non-synthetic case under laboratory conditions and discusses the difficulties found on its application and the avenues taken to solve them. The method is first tested using a synthetic case that mimics the sandbox experiment to establish the minimum number of ensemble members and the best technique to prevent the filter collapsing. The synthetic case shows that among different techniques based on update damping and covariance inflation, the Bauser’s covariance inflation method works best in preventing filter collapse. Its application to the sandbox data shows that the rNS-EnKF can benefit from Bauser’s inflation to reduce the number of ensemble realizations substantially in comparison with a filter without inflation, arriving at a good joint identification of both the contaminant source and the spatial heterogeneity of the conductivities.

Sandbox modelling of interactions of landslide deposits with terrace sediments aided by field observation

The Loess Plateau can be considered as a landslide-prone area in northwest China. The genera consensus about the interaction between landslide deposit and terrace sediments is not well studied; this paper summarised 40 loess landslides in the South Jingyang Platform, Shaanxi Province, China to help understand of this issue. Four of the loess landslides with high mobility have been analysed in detail. Three trenches T1, T2 and T3 dug after the loess landslides LD37, LD11 and LD38 highlighted the landslide-induced changes in geomorphology and internal geometry of geology, respectively. Furthermore, observation of upwards seepage flow on the profile of trench T3 is believed to be the trigger of the high speed, and long runout flowslides in the study area. A newly developed sandbox apparatus is used to reproduce the landslide kinematics due to a mass travelling over an inclined plane. The sandbox experiments show that the sediments are sheared and pushed upwards after the collision with the deposits. The deposits are then wrapped in a space between sediments, which tends to form the ‘sandwich’ structure. The distal sediments are thrust when the loess deposits’ kinetic energy consistently dissipates, developing the accumulated folded strata. These results reveal the deposits’ interactions with the sediments in the study area and provide key guideposts regarding prevention and mitigation of loess landslide hazards.

A New Estimate of Sand and Grout Thermal Properties in the Sandbox Experiment for Accurate Validations of Borehole Simulation Codes

Ground-coupled heat pumps usually employ fields of borehole heat exchangers (BHEs), which must be designed by suitable models. In order to validate a BHE model, it is advisable to compare the computation results with experimental data. A well-known data set was provided by Beier et al. (Geothermics 2011, 40) through a laboratory model usually called “sandbox”. Several authors proposed estimates of the thermal properties of the sandbox grout and sand. In this paper, we present a new estimate of those properties, obtained by means of 2D finite-element simulations that consider all the details of the experimental setup, including the thin aluminum pipe at the BHE boundary. Our results show that the measured temperatures in the fluid and in the sand can be reproduced very accurately by considering thermal conductivities 0.863 W/(mK) for the grout and 3.22 W/(mK) for the sand, volumetric heat capacities 4.6 MJ/(m3K) for the grout and 3.07 MJ/(m3K) for the sand, and a slightly enhanced heat capacity of the water contained in the BHE. The 2D simulations are validated by comparison with an analytical solution and by 3D simulations.

Optimization of the Groundwater Remediation Process Using a Coupled Genetic Algorithm-Finite Difference Method

In situ chemical oxidation using permanganate as an oxidant is a remediation technique often used to treat contaminated groundwater. In this paper, groundwater flow with a full hydraulic conductivity tensor and remediation process through in situ chemical oxidation are simulated. The numerical approach was verified with a physical sandbox experiment and analytical solution for 2D advection-diffusion with a first-order decay rate constant. The numerical results were in good agreement with the results of physical sandbox model and the analytical solution. The developed model was applied to two different studies, using multi-objective genetic algorithm to optimise remediation design. In order to reach the optimised design, three objectives considering three constraints were defined. The time to reach the desired concentration and remediation cost regarding the number of required oxidant sources in the optimised design was less than any arbitrary design.

New Insights into the Lateral‐Strength Variations and Depth to the Brittle‐Ductile Transition Zone in NW Iberia

AbstractThe northwest of Iberia experiences important tectonic activity that has led to several episodes of seismic swarms. Despite substantial knowledge of the surface structures that could be responsible for this activity, their distribution at depth remains unclear. Geophysical research and rheological data display important discrepancies concerning the deep structure of the area. In order to shed light on the processes that control deep seismicity and their relationship with surface structures, we combine the analysis of seismic activity in northwest Iberia with the interpretation of sandbox experiments simulating tectonic structures similar to those observed. The structural interpretation of the modeling results was conducted by analyzing the surface particle image velocimetry field. Additionally, yield strength and brittle‐ductile transition zone (BDTZ) maps were constructed from model sections. The modeling results show a direct relationship between the main active structures developed along pre‐existing weak zones and the observed variations in crustal thickness. Moreover, these thickened zones correspond to the sectors where the BDTZ in the crust deepens. Therefore, the anomalous thickness and lateral variations of the seismogenic zone cannot be solely explained by rheological or structural changes but result from a combination of factors such as fluid pressure and the location of fractures at depth, which controls the fluid migration responsible for the failure of crustal faults. These factors can trigger seismic activity at depth and may control the observed thickness variations in the BDTZ.

3D sandbox and numerical modeling of coseismic surface rupture induced by oblique-slip faulting and its interaction with embedded shallow foundation

A series of downscaled physical sandbox experiments are conducted to observe the evolution of the surface rupture induced by the oblique-slip faulting and estimate its impact on a rigid embedded shallow foundation. High-resolution orthoimages and digital surface model of the experiments are generated through the photogrammetry technique to quantify the ground deformation pattern.The distinct element model (DEM) is performed to validate the three-dimensional ground deformation pattern and the fault rupture-soil-foundation interaction (FR-SFI). The surface displacement profile reflects the fault-affected width being approximately 1.10 times the soil thickness. And the deformation gradients reveal the migration of the surface rupture on the ground surface. The distribution of accumulative strain in the numerical model shows the propagation of the fault rupture.The embedded rigid shallow foundation undergoes substantial displacement, inclination, and horizontal rotation with increasing oblique-slip faulting. However, the degrees of damage is strongly related to the spatial geometric relationship between the foundation and the fault rupture. The DEM simulation provides mechanical insights into the propagation of the fault rupture and shows the potential to elucidate the interaction between the shallow foundations and the coseismic surface rupture.

Assessing Human Health Risk to DNAPLs Exposure in Bayesian Uncertainty Analysis

The human health risk (HHR) assessment to dense non-aqueous phase liquids (DNAPLs) exposure has become an important part of groundwater environment management. Usually, DNAPL transport models are applied to simulate the concentration distribution of contaminant for HHR assessment. The present paper studied the influences of model uncertainties on the HHR assessment, and the metric of Incremental Lifetime Cancer Risk (ILCR) was used to quantify HHR. The impacts of permeability’s heterogeneity and the structure of DNAPL transport model (e.g., the constitutive model) on HHR assessment were evaluated based on a synthetical DNAPL transport model. The results demonstrate that, compared with the low heterogeneity, the high heterogeneity leads to lower average ILCR value at the control planes near the source zone, and higher average ILCR value at the control planes far away from the source zone. In addition, the HHR assessments would be inconsistent for the two constitutive models, i.e., Stone-Parker (S-P) and Coreyvan Genuchten (C-v) models. Compared with the HHR assessment depending on C-v model, the mean of ILCR’s probability distribution produced by S-P model is larger at the control planes near the source zone, and smaller at the control planes far away from the source zone. Moreover, based on a sandbox experiment, the impact of parameter uncertainty of DNAPL transport model on HHR assessment was evaluated by Markov chain Monte Carlo (MCMC) simulation. The results show that it is infeasible and risky to assess HHR by the specific parameters of contaminant transport model and ignoring parameter uncertainty. The HHR assessment by incorporating Bayesian uncertainty analysis could provide more flexible information. In addition, the sparse grid (SG) surrogate is an effective way to reduce computation burden caused by the larger number of model executions in the MCMC based HHR assessment.

Simplified power law relationship in the estimation of hydraulic conductivity of unsaturated sands using electrical conductivity

The unsaturated zone is a complex multiphase system, and modelling and prediction of flow and contaminant transport in this zone remain a challenge. In order to understand the mechanisms of fluid flow in unsaturated sands, an accurate and efficient approach to estimate unsaturated hydraulic conductivity (K) is essential. In this study, a power law relationship was derived from a combination of Archie’s law and van Genuchten’s model to relate bulk (apparent) electrical conductivity (ECa) with unsaturated K. The laboratory sandbox experiments were conducted first to delineate the soil water characteristic curves (SWCCs). Time domain reflectometry was used to simultaneously measure volumetric water content (θ) and ECa. Then, the experimental relationships of the effective saturation (S) and ECa and simulated S–K were combined to establish the relationship between ECa and unsaturated K. The developed power law relationships described the relative EC (ECr) and relative K (Kr) very well by just using one parameter, exponent β. When fluid EC was low, the β values for the drainage and wetting processes ranged within 2.09–2.74 and 2.50–3.79 respectively. The variations of β values of homogeneous material were smaller that of heterogeneous material and the effect of hysteresis on the ECr–Kr relationship was observed. When pore space was filled with the high-EC solution, it easily mimicked the S–Kr relationship and resulted in a smaller β value. The β value acted as a lumped factor accounting for pore tortuosity, pore connectivity, shape of pore space, and fluid EC. The power law relationship of ECr–Kr developed in this study could lead to a direct estimation of the spatial and temporal variations of unsaturated K, once the measurements of SWCC are available from estimation of saturated K and combination of time-lapse ECa measurements. Accurate and efficient estimation of unsaturated K could improve the prediction of flow in the unsaturated zone and allow a comprehensive understanding of unsaturated zone processes.

Numerical and Experimental Validation of the Applicability of Active‐DTS Experiments to Estimate Thermal Conductivity and Groundwater Flux in Porous Media

AbstractGroundwater flow depends on the heterogeneity of hydraulic properties whose field characterization is challenging. Recently developed active‐Distributed Temperature Sensing (DTS) experiments offer the possibility to directly measure groundwater fluxes resulting from heterogeneous flow fields. Here, based on fundamental principles and numerical simulations, two interpretation methods of active‐DTS experiments are proposed to estimate both the porous media thermal conductivities and the groundwater fluxes in sediments. These methods rely on the interpretation of the temperature increase measured along a single heated fiber‐optic (FO) cable and consider heat transfer processes occurring both through the FO cable itself and through the porous media. The first method relies on the Moving Instantaneous Line Source model that reproduces the temperature increase and provides estimates of thermal conductivity and groundwater flux as well as an evaluation of the temperature rise due to the FO cable. The second method, based on the graphical identification of three characteristic times, provides complementary estimates of flux, fully independent of the effect of the FO cable. Sandbox experiments provide an experimental validation of the interpretation methods, demonstrate the excellent accuracy of groundwater flux estimates (<5%), and highlight the complementarity of both methods. Active‐DTS experiments allow investigating groundwater fluxes over a large range spanning 1 × 10−6−5 × 10−2 m/s, depending on the duration of the experiment. Considering the applicability of active‐DTS experiments in different contexts, we propose a general experimental framework for the application of both interpretation methods in the field, making active‐DTS field experiments especially promising for many subsurface applications.

A new criterion for determining the representative elementary volume of translucent porous media and inner contaminant

Abstract. Representative elementary volume (REV) is essential for measuring and quantifying the effective parameters of a complex heterogeneous medium. To overcome the limitations of the existing REV estimation criteria, a new REV estimation criterion (χi) based on dimensionless range and gradient calculation is proposed in this study to estimate the REV of a translucent material based on light transmission techniques. Three sandbox experiments are performed to estimate REVs of porosity, density, tortuosity, and perchloroethylene (PCE) plume using multiple REV estimation criteria. In comparison with χi, previous REV estimation criteria based on the coefficient of variation (CVi), the entropy dimension (DIi) and the relative gradient error (εgi) are tested in REV quantification of translucent silica and the inner PCE plume to achieve their corresponding effects. Results suggest that the new criterion (χi) can effectively identify the REV in the materials, whereas the coefficient of variation and entropy dimension (F=-2.01×10-12+12π×1.50e-(REV-4.35)22⋅1.502) are not effective. The relative gradient error can make the REV plateau obvious, while random fluctuations make the REV plateau difficult to identify accurately. Therefore, the new criterion is appropriate for REV estimation of the translucent materials and inner contaminant. Models are built based on a Gaussian equation to simulate the distribution of REVs for media properties, whose frequency of REV is dense in the middle and sparse on both sides. REV estimation of the PCE plume indicates that a high level of porosity leads to a large value of mean and standard deviation for REVs of PCE saturation (So) and PCE–water interfacial area (AOW). Fitted equations are derived from distribution of REVs for the PCE plume related to dm (distances from mass center to considered point) and dI (distances from injection position to considered point). Moreover, relationships between REVs of the PCE plume and So are fitted using regression analysis. Results suggest a decreasing trend appears for So-REV when So increases, while AOW-REV increases with increasing So.

Interactions of landslide deposit with terrace sediments: Perspectives from velocity of deposit movement and apparent friction angle

The Loess Plateau has been deemed as a landslide-prone area in northwest China because of the unique platform geomorphology and the wetting-induced loess collapse. The interactions of landslide deposit and terrace sediment have been under-explored in the literature. This lack of research has inhibited the prevention and mitigation of loess landslide. This study summarises a total of 40 loess landslides in the South Jingyang Platform, Shaanxi Province; 4 out of the 40 loess landslides are investigated in detail, with an emphasis on the geomorphology feature and the internal geometry of geology. While the sandbox experiments and the discrete element modelling primarily aimed to reproduce the kinetic process of landslide deposit falling from the platform edge and colliding with terrace sediments. The field observation distinguished three domains that represent varying degrees of interaction between the landslide deposit and the terrace sediments, namely push forward domain, shear up/out domain and original terrace sediment domain. The push forward domain is defined as an area completely contained the loess deposit, with most distinct surface upheaval, while the shear up/out domain is defined as an area that significantly interacts with the push forward domain and possesses remarkable evidence of interactions. The original terrace sediment is defined as an area that is thoroughly not disturbed by the interactions. The internal geometry change and the geomorphology features, induced by the interactions of the deposit with the sediments, are reproduced using the sandbox experiments and the discrete element modelling. The sediments shearing upwards and the occurrence of shear liquefaction are interpreted from perspectives of the velocity of deposit movement and the apparent friction angle. The results are deemed to be useful in enhancing our understanding about the interactions of the landslide deposit with the terrace sediments and countermeasures against loess flowslides in the study area in future.

Float-laser device for measuring the water table and freshwater–saltwater interface in laboratory-scale experimental systems

Processes in coastal aquifers involving variable-density fluids are often investigated using laboratory sand tanks. However, experimental monitoring of the interface between liquids of different densities is challenging, typically requiring dye tracers and photographic analysis. These are susceptible to problems of tracer adsorption and image inhomogeneity, and experiments are often limited to two-dimensional cross-sections. In addition, the water-table position is an important factor, but its accurate measurement is often difficult. A device has been developed for sand-tank experiments to obtain high-frequency, high-precision measurements of both the freshwater–saltwater interface (inferred from density) and the water-table depth, using a float and a laser sensor in a monitoring well. The proposed device was tested using a two-column experiment, allowing for the estimation of measurement errors, which were generally less than 1 mm. The measurement device can be modified to allow for the monitoring of multiple salinity values, and is well suited to sand-box experiments where salinity dynamics are otherwise difficult to visualize.

Effect of hydraulic and mechanical characteristics of sediment layers on water film formation in submarine landslides

Through two lab-scale experiments, we investigated the hydraulic and mechanical characteristics of sediment layers during water film formation, induced by elevated pore pressure—considered one of the triggers of submarine landslides. These involved (1) sandbox experiments to prove the effect of water films on mass movement in low slope gradients and (2) experiments to observe the effect of the tensile strength of semi-consolidated sediment layers on water film formation. Portland cement was used to mimic the degree of sediment cementation. We observed a clear relationship between the amount of cement and pore pressure during water film formation; pressure evolution and sediment deformation demonstrated the hydraulic and mechanical characteristics. Based on the results of these experiments, conditions of the sediment layers during water film formation are discussed in terms of pore pressure, permeability, tensile strength, overburden pressure, and tectonic stresses. The results indicate that the tensile strength of the sediment interface provides critical information on the lower limit of the water film formation depth, which is related to the scale of potential submarine landslides.

Insights into lava dome and spine extrusion using analogue sandbox experiments

Lava dome formation is a common process at stratovolcanoes involving the shallow intrusion or extrusion of viscous lava and may lead to the rise of spines. Spines are protrusions observed to extrude episodically during lava dome growth, yet the structural and mechanical factors controlling their formation are only partially understood. Here, we provide new, detailed insight into lava dome growth and the production of spines using a novel set of analogue experiments extruding sand-plaster mixtures from a fixed-diameter conduit under isothermal conditions. We trace displacement and strain with photogrammetric methods for precise and detailed monitoring of the extrusion process. Results show initial dome growth forming a steep-sided and flat-topped shape through extrusion of new material, leading to slumping of oversteepening slopes, forming a talus. Spines are found to protrude at a later stage through the dome surface along discrete circular faults that originate from the conduit walls, starting a cycle of spine growth and collapse. As our spines only appear after prolonged extrusion, we relate their appearance to the compaction and strengthening of material within the conduit. We find that spine diameter, height and volume are positively correlated with increasing cohesion and therefore material strength. The spine diameter was also observed to be smaller or equal to the diameter of the underlying conduit, as shear extrusion occurs along vertical to outward-dipping fault planes. For natural domes, our findings imply that spine growth may be the consequence of compaction and densification via porosity loss, shearing and/or outgassing of conduit magma during ascent. More efficient compaction will yield wider and taller spines as a result of increasing rock strength. Our study further highlights the relevance of analogue experiments in the study of lava domes and spines, which remain one of the most hazardous and unpredictable features at dome-forming volcanoes worldwide.

Corrigendum to “The influence of a weak upper ductile detachment on the Longmen Shan fold-and-thrust belt (eastern margin of the Tibetan Plateau): Insights from sandbox experiments” [J. Asian Earth Sci. 198 (2020) 104220

Corrigendum to “The influence of a weak upper ductile detachment on the Longmen Shan fold-and-thrust belt (eastern margin of the Tibetan Plateau): Insights from sandbox experiments” [J. Asian Earth Sci. 198 (2020) 104220

Application of a genetic algorithm to groundwater pollution source identification

The accurate identification of groundwater pollution sources is the key to site remediation and management, which directly relates to the cost and effect of remediation during later periods. Studying the identification of some small-area site pollution sources by using a small amount of groundwater monitoring data is difficult and is currently a hot topic in the field of groundwater management. In this study, a method combining the Advection-Dispersion Equation (ADE) of contaminants in groundwater with Genetic Algorithm (GA) was proposed to identify groundwater pollution sources, that is, the location of the pollution source, the time of pollution release, and the intensity of pollution release. A sandbox experiment for the migration and transformation of deterministic petroleum hydrocarbons in groundwater is designed to verify the method. The results show that the method code program has basically the same identification parameters as the deterministic experimental pollution source parameters. The ADE-GA method was applied to an actual site polluted by a gas station in Beijing, China. The parameters of the pollution source obtained from the detailed site investigation are basically consistent with the calculated values. Therefore, the source code established in this work is a reliable tool for identifying the parameters of groundwater pollution sources in small areas.

Experimental and numerical investigation of saltwater intrusion dynamics on sloping sandy beach under static seaside boundary condition

Two-dimensional sandbox experiments were conducted to investigate the variable-density circulation and flow patterns in sloping beach configurations. The experiments provide new benchmark results for validating the sandbox models based on quantitative and qualitative measurements. Previous studies have considered density dependent flow in porous media, vertical beach face saltwater boundary, and multilayered hydrogeology ignoring a sloping beach face, which is a much more common phenomenon in real world. The present study considers sloping beach face under both homogeneous and low-permeability strata configurations. The geohydraulic processes encountered were quantified through pore-water pressure measurements and image analysis techniques. Moreover, validations were performed with numerical simulations (FEFLOW). A simple image analysis procedure is proposed with respect to two-dimensional laboratory scale benchmark experiments. Experimental results provided a detailed circulation flow path within and outside the saltwater wedge with sloping beach face. Fingering effect in porous media was also observed for both the experiments during initial time periods. Stability analysis shows the existence of a stationary convective flow pattern followed by gravitational instabilities under the quasi-steady state condition.

Influence of the orientation of cohesive blocks upon the structural grain of fold-and-thrust belts: An appraisal by means of analogue modeling

Analogue sand-box experiments have been set up to illustrate and analyze the control exerted by lithological heterogeneities on the evolution of a model fold-and-thrust belt (FTB). The structural architecture within many FTBs is highly sensitive to pretectonic obstacles (e.g., basement highs or intrusive bodies). To address FTB evolution with emphasis on the latter, we perform a series of experiments that include tabular cohesive blocks surrounded by a layered sandpack of negligible cohesion. Two degrees of cohesion are tested (low vs high cohesion) as well as different geometrical boundary conditions (longer axis parallel vs oblique relative to the main far-field stress). Modeling results show a tendency of sequential faults to avoid rigid obstacles, enhancing frontal accretion and propagation of the deformation front. Structural traces have arcuate patterns in map-view, strongly consistent with the geometry of the underlying block/obstacle. High-cohesion models show major deviations on the structural pattern with respect to models with low-cohesion blocks. We find that the rheological contrasts between rock types have an important effect on the structure of the upper crust, controlled by the degree of the contrast and the geometry (orientation) of the discordant block. An interesting aspect of our results is that orientation of the block plays a considerable role on whether new thrusts cut the block or stresses propagate towards the foreland through the cohesive body. Block obliquity also influences the generation of back-thrusts. These features are compared to natural cases as well as to other physical models of FTBs. We suggest that irregular structural patterns in FTBs may shed light on the presence of buried rock bodies (intrusive bodies, metamorphic complexes or crystalline basement highs) within the components of the deformed rock sequence.