Karst Exploration Research Articles

Application of Elastic Wave CT in Geotechnical Investigation of Suning Square

Elastic wave CT technology, also known as elastic wave tomography technology. It is on the premise of not destroying the internal structure of the rock and soil medium in the test area, according to the basic principle that elastic waves propagate at different speeds in different rock and soil media, the travel time and wave velocity of the elastic wave in the rock and soil between two points are obtained through the experiment, and through a special inversion method, a large amount of elastic wave velocity information is used to obtain the distribution law and the elastic wave velocity chromatogram of the medium in the test area, in this way, the lithology, structural development and velocity parameters of the rock-soil medium in the test area can be inferred. This article briefly introduces the basic theory of elastic wave CT, including Radon transform and inverse transform, forward ray tracing method and inversion iterative image reconstruction technology. Then combined with the engineering survey example of the Suning Plaza project, it briefly introduced the field work method, data parameter collection, geological interpretation and result analysis. The analysis shows that the results of the three-dimensional velocity map obtained by the elastic wave CT method are intuitive, the test accuracy is high, and the development state, size and location of the karst in the survey area can be clearly seen. It can describe the spatial distribution characteristics of karst in detail, has outstanding advantages in karst exploration, and has good application prospects.

Application of High Density Resistivity Method in Karst Exploration: A Case Study

Application of High Density Resistivity Method in Karst Exploration: A Case Study

Energy-Efficient Configuration and Control Allocation for a Dynamically Reconfigurable Underwater Robot

A dynamically reconfigurable underwater robot, which can vary its configuration during a mission, would be useful for confined environment exploration and docking because of its versatility. A mission can be performed by choosing among different configurations, and the energy cost may increase, owing to the reconfigurability of the robot. Energy saving is the critical issue in long-range missions with underwater robots. Moreover, control allocation must be considered for a redundant system and input constraints. We propose an approach for an energy-efficient configuration and control allocation for a dynamically reconfigurable underwater robot that is built for karst exploration. The proposed method is based on sequential quadratic programming, which minimizes an energy-like criterion with respect to robotic constraints, i.e., mechanical limitations, actuator saturations, and a dead zone. The optimization problem is solved in each sampling instant. Two popular tasks for underwater robots, i.e., path-following and station-keeping (observation) problems, are simulated, and the simulation results show the efficiency of the method. Moreover, an experiment is carried out to highlight the results.

Near-Surface Views & News: Building bridges between geophysical and engineering communities

Over the last few years, the use of geophysics for engineering purposes has been increasing considerably. Geophysical applications within the engineering industry are quite diverse and can range from geotechnical to transportation purposes and to environmental and geohazards studies. Typical applications include detection of bedrock, landfill delineation, water table detection, karst exploration, dam/levee and seepage evaluation, foundation design, pipeline installation, landslide mitigation, earthquake and seismic design parameters, and pavement analysis, among others.

On-manifold probabilistic Iterative Closest Point: Application to underwater karst exploration

This paper proposes MpIC, an on-manifold derivation of the probabilistic Iterative Correspondence (pIC) algorithm, which is a stochastic version of the original Iterative Closest Point. It is developed in the context of autonomous underwater karst exploration based on acoustic sonars. First, a derivation of pIC based on the Lie group structure of is developed. The closed-form expression of the covariance modeling the estimated rigid transformation is also provided. In a second part, its application to 3D scan matching between acoustic sonar measurements is proposed. It is a prolongation of previous work on elevation angle estimation from wide-beam acoustic sonar. While the pIC approach proposed is intended to be a key component in a Simultaneous Localization and Mapping framework, this paper focuses on assessing its viability on a unitary basis. As ground truth data in karst aquifer are difficult to obtain, quantitative experiments are carried out on a simulated karst environment and show improvement compared to previous state-of-the-art approach. The algorithm is also evaluated on a real underwater cave dataset demonstrating its practical applicability.

A Dynamically Reconfigurable Autonomous Underwater Robot for Karst Exploration: Design and Experiment.

This paper presents the design and experiment of an autonomous underwater robot which can change the geometric configuration of its actuators, according to mission requirements or environmental constraints. The robot consists of two subsystems: forward part with three thrusters and backward part with four thrusters. The position and orientation of these thrusters can be dynamically changed during missions. Being different from most of other reconfigurable underwater robots which were designed as linked-modules, our robot has a unified design. It is suitable for specific mission in confined environments (e.g., karst exploration) in which the robot has to modify its shape to go through a narrow section or align the most part of its thrusters in the direction of a strong current, for examples. The design procedure, from hardware to software, of the robot is presented and experimental results are shown to demonstrate the versatility of the robot. Furthermore, the discussion and comparison between our robot and other underwater robots with adaptable actuation geometry are presented to highlight advantages of our design. Finally, the idea of using our robot for classic docking problem, which has some common features with karst exploration requirements in using dynamically reconfigurable robots, is discussed.

Transient Electromagnetic 1‐Dimensional Inversion Based on the Quantum Particle Swarms Optimization‐Smooth Constrained Least Squares Joint Algorithm and Its Application in Karst Exploration

Before the construction of the bridge bored pile in the karst area, geological conditions of the excavation area should be investigated. In order to avoid the karst caves in underground space making adverse impacts on the construction, bearing capacity, and stability of pile foundation, in this paper, we use the transient electromagnetic method to detect the karst development in the bearing layer of the pile foundation, which is different from the traditional karst survey method. To improve the interpretation accuracy of transient electromagnetic detection for karst caves, the quantum particle swarm optimization (QPSO) algorithm was combined with the smooth constrained least squares (CLS) algorithm, and the transient electromagnetic inversion based on the QPSO‐CLS joint algorithm was generated. Better inversion results were achieved by the proposed method in this study. Based on the inversion calculation results of simulation data and field test data, it is further demonstrated that the QPSO‐CLS joint algorithm has high optimization efficiency without manually setting the initial model. The interpretation results are consistent with the theoretical model and drilling logging results, which proves the adaptability of the proposed algorithm.

Joint tomography of multi-cross-hole and borehole-to-surface seismic data for karst detection

Two-dimensional (2D) cross-hole seismic tomography is widely used in karst exploration. However, this method only obtains subsurface geological structures from the profiles of two adjacent wells and cannot acquire geological information from the lateral profile direction. The tomographic imaging area and accuracy are also limited owing to sparse ray density in the near-surface area. This approach is therefore not conducive to the spatial identification and evaluation of subsurface karst structures. To address this problem, we conducted multi-hole combined seismic tomography experiments and obtained high-density and high-quality seismic spatial data using an optimized observation system and acquisition parameters. We propose a new method of joint tomography of multi-cross-hole and borehole-to-surface seismic data. We performed 2D seismic tomography inversion by combining cross-hole data with borehole and surface data based on the theory of seismic tomography, and then used the data fusing from multiple wells based on the theory of kriging method. A pseudo-three-dimensional (3D) spatial velocity field of the experimental site is established. The results show that (1) the combined borehole and surface data provide richer ray-tracing information than the cross-hole dataset alone, (2) the pseudo-3D spatial velocity field and spatial distribution of seismic anomalies (karst) can be obtained using the proposed method, and (3) a comparison with actual borehole logging data verifies the effectiveness and accuracy of the proposed method in obtaining subsurface geological structures and detecting the spatial distribution of karst, which has significant practical and application potential.

Karst exploration: Unconstrained attitude dynamic control for an AUV

This paper introduces a new design for the control of the unconstrained attitude of an underwater mobile robot, dedicated to exploration of karstic environment. The approach followed in this study considers a quaternion formalism and proposes a dynamic control design that copes with the classic two-steps Lyapunov and Backstepping design, that remains within the quaternion formalism. Hence the control expression considers quaternion expressions without (as classically done in literature) requiring the decomposition of the quaternion into vectors and angle, which heavies the control expression and may introduce singularities. This control is then experimented on the Cube robot, showing the performance of the method.

Near-surface site investigation and imaging of karst cave using comprehensive geophysical and laser scanning: a case study in Shandong, China

The karst development of Jiao Dong Peninsula in Shandong Province has formed a unique karst landform, and has become one of the typical karst areas in the north of China. Karst collapse occurred during the construction of high-speed railways and caused many environmental problems. To reveal the development situation of karst area in Shandong, the conventional surface geophysical techniques were used for karst exploration and location of key area. And the results of drilling verification were in good agreement with the results of geophysical exploration. At the same time, the new technology in the field of surveying and mapping 3D laser scanning technology, is cited in the engineering geophysical exploration, and the key issue is the shape and size of the karst. It makes up for the shortcomings of traditional geophysical exploration technology that can only be qualitative and cannot be quantitatively analyzed. It realizes the transformation of karst exploration from regional detection to single cave exploration, and better implements the concept of information construction. It has contributed to the smooth progress of the project and environmental protection.

Application of Cross-borehole Integrated Geophysical Methods for the Detailed Investigation of Karst in Urban Metro Construction

With the significant development of China's metro construction, the development of urban underground karst poses a serious threat to related tunnel construction and public safety, with frequent occurrences of mud and water inrushes during tunnel construction and urban ground subsidence events. Because of the complex, urban, and shallow geological conditions and construction environments, conventional geophysical methods cannot meet the requirements for high-precision detection of small-scale and inhomogeneous complex geological bodies. Based on numerical simulation, herein we comprehensively applied both cross-borehole electrical resistivity tomography (ERT) and cross-borehole seismic computed tomography (CT) to urban underground karst surveys of the Hangzhou-Fuyang intercity railway. The results showed that: 1) under limited urban construction conditions, the use of advanced geophysical monitoring equipment greatly improved construction efficiency; 2) utilizing drilling geological results to calibrate the abnormal geophysical field attribute parameters (including wave velocity and resistivity) improved the accuracy of karst exploration and reduce defective geophysical multi-explanation effects; 3) applying the joint comparative explanation of both velocity and resistivity profiles can distinguish and explain karst and fracture development zones; 4) 550 pairs of velocity and resistivity profiles were obtained which revealed 258 karst cave anomalies and 5 fracture development zones which integrated detection accuracy exceeded the 1 m level. Thus, the high-precision joint cross-borehole tomography technology was shown to be useful for guiding intercity railway construction.

Search for an artificially buried karst cave entrance using ground penetrating radar: a successful case of locating the S-19 Cave in the Mt. Kanin massif (NW Slovenia)

The S-19 Cave was with its explored depth of 177 m one of the most important caves of the Mt. Kanin massif, but after its discovery in 1974, a huge snow avalanche protection dyke was constructed across the cave entrance. To excavate the buried cave, the accurate location of the cave had to be determined first. Since the entrance coordinates were incorrect and no markers were available, application of geophysical techniques was necessary to do this. A Ground Penetrating Radar (GPR) with special 50 MHz rough terrain antennas was selected as the single suitable geophysical method for the given conditions where thick debris overlay a rugged limestone surface. Nevertheless, it was not possible to directly detect the relatively narrow cave entrance itself due to data resolution limits. However, a historical photo of the area showed that the cave entrance was located in a local depression, which therefore represented the main target of the GPR survey. Seven GPR profiles were measured across the rough and steep surface causing difficulties in traversing the area with sensitive research equipment. In all recorded radargrams a small depression was clearly imaged under debris, and recognized as a topographic feature with the cave entrance. Based on the GPR data interpretation, the exact location for digging was determined and the thickness of debris assessed at 6.5–7 m. A massive excavation by a dredger resulted in a successful opening of the cave entrance, confirming both its geophysically determined location and its estimated depth. The application of an advanced geophysical method was therefore proven successful in providing a solution to this specific case in karst exploration and an important cave was saved.

Fuzzy-based spatial modeling approach to predict island karst distribution: a conceptual model

Previous studies have shown that island karst could successfully indicate paleoclimate change in the Quaternary Period. However, because of the relative inaccessibility of carbonate islands and their rural settings, the exploration of island karst features has been limited. To enhance future research, remote sensing and geospatial modeling were used in this study to improve the island karst exploration record. The results showed that fuzzy-based spatial modeling could successfully predict the island karst distributions on a simple carbonate island. The accuracy of the model was above 90 %. This method could apply to other coastal karst regions and carbonate islands in the future.

Spatial mapping of submerged cave systems by means of airborne electromagnetics: an emerging technology to support protection of endangered karst aquifers

ABSTRACTKarst aquifers represent important but very vulnerable sources for water supply to a significant part of the Earth’s population. For sustainable use of these resources, development of integrated management tools based on numerical groundwater models is required. In principle karst aquifers are characterized by the presence of two distinct flow domains: the limestone matrix fractures and the conduits. A flow model of karst aquifers requires detailed, spatially distributed information on the hydrologic characteristics of the aquifer and flow paths. Geophysical methods determining the distribution of the electrical resistivities within the subsurface could provide such information. An international scientific research project was initiated to explore the potential of airborne electromagnetic mapping for providing such innovative information for improving groundwater modelling of karst aquifers. The project study area is located in the Sian Ka’an Biosphere Reserve located in Yucatán, Mexico, a coastal wetland of international importance. As a first step ground geoelectric and ground electromagnetic measurements were performed in March 2006 to determine the electrical properties of the Sian Ka’an Biosphere Reserve subsurface environment. These results were used for 3D forward modelling to calculate the expected airborne electromagnetic response. Based on these promising results, an airborne pilot survey was performed in 2007 to evaluate the applicability of airborne electromagnetic methodology. This survey covers an area of 40 square kilometres above the well‐mapped Ox Bel Ha cave system. The results showed that the signature of the cave system could be clearly detected. The pilot survey offered as well the chance to define the limits of current state‐of‐the‐art airborne data acquisition and inversion. The study helped to define the needs for further developments and improvements to establish the frequency domain electromagnetic method as a practical karst exploration method.

Improved karst exploration by VLF‐EM‐gradient survey: comparison with other geophysical methods

ABSTRACTThe knowledge of size, density and both orientation and vertical distribution of fractures as well as their opening and filling material or overburden thickness is a valuable contribution to estimating hydraulic conductivity and to evaluating the vulnerability and protection strategy of karst aquifers. To obtain some of these parameters and to ascertain high‐permeability zones, the Very Low Frequency‐Electromagnetic Gradient (VLF‐EM GRAD) method was applied, together with Radio Frequency‐Electromagnetics (RF‐EM), Radiomagnetotellurics (RMT), Geoelectrical Tomography and refraction seismics, over a karstic terrain in the Swiss Jura Mountains. In this area, karst springs infiltrate a porous aquifer. This survey investigated the highly permeable karst structures, which provide fast water‐infiltration pathways into the karstic flow network. A dye tracer test validated the geophysical results. The results show the efficiency and reliability, particularly of the VLF‐EM GRAD method, for high‐resolution investigation at shallow depths and for its potential for fast data acquisition over large surfaces at catchment area scale without ground contact.

Shallow karst exploration using MT-VLF and DC resistivity methods: R. Guerin & Y. Benderitter, Geophysical Prospecting, 43(5), 1995, pp 635–653

Shallow karst exploration using MT-VLF and DC resistivity methods: R. Guerin & Y. Benderitter, Geophysical Prospecting, 43(5), 1995, pp 635–653

Shallow karst exploration using MT‐VLF and DC resistivity methods1

AbstractA geophysical test was carried out over a well‐located and fairly embedded karstic conduit. The MT‐VLF method was selected because of its high resolution and its ability to provide a resistivity parameter sensitive to water and Clay. This method was used together with DC resistivity methods which allow vertical adjustment of the VLF data and show consistency between the investigation and target depths. After correcting the deformations due to the polarization of the primary field, the MT‐VLF data show clearly, in the Central part of the site, that the conduit does not coincide with an anomaly axis but coincides with the boundary between a conductive area and a resistive area. 2D modelling confirms that direct detection of the conduit is not feasible and that the conduit is located close to a conductive zone corresponding to a completely Clay‐filled fractured zone. This situation was observed on the whole site and the conduit seemed systematically to thread its way between the conductive zones to join the outlet. The distribution of the conductive fractured zones and the direction of the hydraulic gradient were two important elements in predicting the location of the conduits. A 3D approach would increase the probability of finding the conduits in such a case.

Karel Absolon as a Geographer and a Great Personality of Czech Natural Science

Karel Absolon as a Geographer and a Great Personality of Czech Natural Science