Inclinometer Probe Research Articles

A fiber Bragg grating-based inclinometer probe with enhanced sensitivity for a higher slope profiling resolution

A fiber Bragg grating (FBG)-based inclinometer probe with enhanced sensitivity has been developed for slope or ground movement monitoring. The inclinometer probe utilized six FBGs for the tilt measurement and a strain-free FBG that provided the temperature compensation factor. The inclinometer probe was fabricated entirely using a 3D printer and can fit into the standard inclinometer casing, which can be placed into the boreholes. The dimension of the probe is similar to the conventional inclinometer probe, with a total length of 70 cm. Additionally, this design was equipped with three highly compact tilt sensors within the same probe length, providing a better resolution of the inclination profile. Each tilt sensor possesses a flexible middle shaft fabricated using thermoplastic polyurethane (TPU) and was equipped with two FBGs for bi-directional tilt angle measurement (+x and -x). Initially, the tilt sensor was calibrated in the laboratory, which yielded a sensitivity value of 0.0215 nm/°. This value is higher than most previous designs by a factor of two because of the middle shaft's elasticity, which can induce a more significant strain on the FBG. The horizontal displacement of a conventional inclinometer casing could be observed during the field test, which proves the device's functionality. The results have indicated that the inclinometer can be applied in several geotechnical applications, particularly ground movement monitoring.

Slope Monitoring of a Road Embankment by Using Distributed Optical Fibre Sensing Inclinometer

Distributed Optical Fibre Sensor (DOFS) is a versatile sensor considering that it can be used to measure various parameters, such as detection of small strains over large areas and long distances. The application of DOFS is currently being explored as an early warning system, particularly for slope movement detection. In this paper, an embankment slope at Sungai Rual, Jeli, Kelantan, Malaysia was selected to determine the best monitoring layout for landslide detection. Two methods of installation for vertical Fibre Optic (FO) inclinometers (using conventional casing with a special grove) were installed to monitor subsurface horizontal ground movements. The first method of FO inclinometer installation uses concrete (grade 35) grouting, and the second method uses a bentonite mixture. It was found that the first method was unsuccessful due to the fibre breakage during the hardening process of concrete and hence not recommended. However, the measurement was successfully taken for the bentonite mixture method. The displacement reading was taken using both the FO and conventional inclinometer probe. The reading for the 9.5 m depth of the inclinometer casing were recorded for the comparison between FO and conventional inclinometer probes. A comparison between FO and conventional systems showed almost similar results to the conventional method. The FO inclinometer developed in this project shall provide vital information to assist designers and operators, as well as inform stakeholders on the integrity of their structures.

Distributed fibre optic inclinometer with cloud-based monitoring system

Geotechnical instrumentation and monitoring are important aspect of controlling subsurface ground movement, particularly in deep excavations and forewarning of geological disasters such as landslides, land subsidence, ground fissure, and surface collapse. A borehole inclinometer is an example of the established method to monitor such ground movements. For real-time data, a series of in-placed inclinometer probes are installed inside the borehole casing to provide the lateral displacement response over time. The limitation of the conventional system is the high cost and the practicality of inserting a high number of sensing probes into the casing for better measurement accuracy. Recent advancement in Distributed Optical Fibre Strain Sensing (DOFS) enables the incorporation of DOFS as a fibre optic (FO) inclinometer with lateral displacements to be plotted at centimetres spacing and is unaffected by the gauge lengths between the probes. This study enhances the FO inclinometer by developing a web-based application (SmartGeopipe©) to automate data acquisition which also includes complex data processing for the final pipe deflection profile visualisation. The FO inclinometer comprised of optical cables attached externally onto a remodified inclinometer casing and connected to a Brillouin Optical Time Domain Analysis (BOTDA) strain analyser. A standard installation procedure was established to safely secure the sensors during the casing installation process inside the borehole. SmartGeopipe© software is written using a predominantly monolithic Python / Cython backend and a multi-page frontend built with HTML, CSS, and JavaScript ES5 languages. All the computation work and data storing are done in a cloud server and SQL database, respectively. A case study of a station box excavation as part of the Mass Rapid Transit (MRT) tunnelling project was chosen to validate the performance of the FO inclinometer and the web application. Data from the FO inclinometer corroborated well with the manual measurements of the inclinometer probe. This ability supports the realization of an early warning system as an engineering control for hazard management in civil engineering infrastructure projects.

Analysis of landslide kinematics integrating weather and geotechnical monitoring data at Tan Son slow moving landslide in Ha Giang province

Rainfall infiltration on the slope increases pore-water pressure in the soil/ rock mass and may cause landslides. Therefore, the precipitation, pore-water pressure and displacement show the kinematic variation of a landslide. In recent years, several approaches have been proposed to investigate the kinematic behavior. Among them, the combination of time series data and geotechnical model has demonstrated its effectiveness in stage classification of landslide kinematics. This paper aims to analyze and classify the stages of landslide kinematic variation with integrating weather and geotechnical monitoring data of Tan Son market landslides. The real-time monitoring station for Tan Son slow-moving landslides were equipped with fixed-in-place inclinometer probes and standard pore-water pressure sensors. The results show that landslide kinematics consist of three stages: stabilization, accumulation, and displacement. The displacement of the landslides was heterogeneous process. The velocity of the landslides significantly increased when the pore-water pressure ratio (ru) at the sliding surfaces > 0.53. While it is almost impossible to notice any displacement when the ratio r­u < 0.45. During the displacement state, the trend of inverse velocity variation gradually decreases to near zero hour/mm. In addition, early warnings of landslide can be released based on the kinematic stages and changes in inverse velocity in this study.

Advances on Measuring Deep-Seated Ground Deformations Using Robotized Inclinometer System.

In the field of geo-hazards and geo-engineering, monitoring networks represent a key element for the geological risk assessment and the design and management of large infrastructures construction. In the last decade, we have observed a strong development on remote sensing techniques but just small changes in the subsoil observations. However, this type of measurement is very important to have a three-dimensional representation of the studied area, since the surface measurements often represent a sum of deformations that develop in a complex way in the subsoil. In this paper, we present a robotic inclinometer system developed to acquire deep-seated ground deformations in boreholes. This instrumentation combines advantages offered by manual inclinometer measurements with a robotized approach that improves the results in term of accuracy, revisiting time, and site accessibility. The Automated Inclinometer System (AIS) allows one to explore automatically all the length of the monitored borehole using just one inclinometer probe with a semi-wireless system. The paper presents the system and a detailed dataset of measurements acquired on three inclinometer tubes installed for the monitoring of the construction phase of the new Line C Metro of Rome. The dataset was acquired in real monitored site and undisturbed conditions and can represent a benchmark for modern inclinometer measurements.

Seismic and Rainfall Induced Displacements of an Existing Landslide: Findings from the Continuous Monitoring

“La Sorbella” is a deep-seated existing landslide in a Miocene clayey formation located in central Italy. Given the interaction with a national road, this landslide has been monitored for a long time with inclinometers and hydraulic piezometers. Recently, the monitoring system was implemented by adding pressure transducers in the Casagrande cells and by equipping the old inclinometers with in-place probes, to allow a remote reading of the instruments and data recording. This system allowed to identify that the very small average rate of movement observed over one year (1.0–1.5 cm/year) is the sum of small single sliding processes, strictly linked to the sequence of rainfall events. Moreover, data recorded by in-place inclinometer probes detected the response of the landslide to the seismic sequence of 2016 occurring in central Italy. Such in situ measurements during earthquakes, indeed rarely available in the scientific literature, allowed an assessment of the critical acceleration of the sliding mass by means of a back-analysis. The possibility to distinguish the difference between seismic and rainfall induced displacements of the slope underlines the potential of continuous monitoring in the diagnosis of landslide mechanisms.

FIELD TRIALS ON THE SOIL CEMENT MIXING TECHNOLOGY TO REINFORCE EARTH LEVEES IN THE MEKONG DELTA, VIETNAM

The effectiveness of seepage cutoff and sliding stability of an earth levee reinforced by soil cement deep mixing technology (SCDM) was evaluated by field monitored data. Groundwater observation was conducted via nine ground water wells installed in the research site. Lateral displacement of the whole earth levee was measured by the 15-m inclinometer casing and a 0.5-m inclinometer probe. The research assessed effects of soilcrete reinforcement by comparing with simulations before applying widely in the Mekong Delta, Vietnam. The results indicate that the soilcrete walls can effectively prevent the seepage through the earth levee’s body and improve the factor of safety about 1.2 times.

Design and Testing of a Flexible Inclinometer Probe for Model Tests of Landslide Deep Displacement Measurement.

The physical model test of landslides is important for studying landslide structural damage, and parameter measurement is key in this process. To meet the measurement requirements for deep displacement in landslide physical models, an automatic flexible inclinometer probe with good coupling and large deformation capacity was designed. The flexible inclinometer probe consists of several gravity acceleration sensing units that are protected and positioned by silicon encapsulation, all the units are connected to a 485-comunication bus. By sensing the two-axis tilt angle, the direction and magnitude of the displacement for a measurement unit can be calculated, then the overall displacement is accumulated according to all units, integrated from bottom to top in turn. In the conversion from angle to displacement, two spline interpolation methods are introduced to correct and resample the data; one is to interpolate the displacement after conversion, and the other is to interpolate the angle before conversion; compared with the result read from checkered paper, the latter is proved to have a better effect, with an additional condition that the displacement curve move up half the length of the unit. The flexible inclinometer is verified with respect to its principle and arrangement by a laboratory physical model test, and the test results are highly consistent with the actual deformation of the landslide model.

Testing of laterally loaded piles in natural sandy gravels

In this paper, the authors present the results of field tests on a single laterally loaded pile and two piles in line. Bored reinforced concrete piles with a diameter of 0·25 m and a depth of 5 m were constructed in natural sandy gravels. The lateral loading on a head of tested piles is applied using a hydraulic press with a maximum force of 500 kN. A single pile and two piles in line were incrementally loaded with a controlled head displacement of 2 mm until the ultimate capacity of the pile was attained. The deflections of the piles were measured using an inclinometer probe through inclinometer casings installed in the axes of the piles. The results are analysed and approximated using the Fourier series and the Cesáro sum technique. The measurements are compared using a three-dimensional finite-element method and Rocscience RS3 software, whereas the modelling soil and pile material are compared using simple constitutive laws. The comparison results of the measured and computed deflections of the piles correlate, which indicates that granular materials, such as sandy gravels, provide acceptable approximation and can be modelled using simple constitutive laws.

Quantifying Errors in Manual Inclinometer Field Measurements

Inclinometer systems are commonly used to measure horizontal ground displacements at landslides, pile wall construction, tunneling, and excavations. These systems have been in widespread use since the late 1960s (Dunnicliff, 1988). My primary goal with this research was to determine the accuracy and precision achievable with an inclinometer. I also sought to determine the variables that contribute to or reduce accuracy. Inclinometer systems consist of an inclinometer casing (with four vertical grooves spaced 90 degrees apart), a portable traversing probe, a control cable, a readout/data recorder, and monitoring accessories (a pulley and wheel). One groove is selected as the A0 direction, which is typically oriented toward the expected direction of movement. The inclinometer probe used in this research is an English-style probe, with a wheelbase of 24 in. (61 cm) between the upper and lower spring-loaded wheel assemblies. The inclinometer probe is typically run down the casing with the wheels oriented in the direction of anticipated movement. Two accelerometers are mounted within the body of the probe to measure tilt (deviation from vertical). The two accelerometers are perpendicular to each other, with one in-line with the wheel assemblies. The direction 90 degrees clockwise from the A0 direction is designated as B0 (Figure 1). The probe measures its vertical tilt in the A0 and B0 axes. Two sets of readings are taken by lowering the probe to the bottom of the casing and taking readings every 2 ft (0.61 m) as the probe is pulled back up. The probe is then turned 180 degrees, and the process is repeated. These readings are then compared to generate an average orientation value. When the casing is set up, an initial set of readings is taken. Baseline measurements are then documented for the casing, and subsequent readings are compared to these readings to identify changes in conditions. …

Cold Region Applications for In-Place Inclinometers Based on Microelectromechanical Systems Technology

Inclinometer probes are an industry standard for measuring ground movement; however, this technology has drawbacks, including costly trips for manual measurements, operator error, and limited measurements caused by casing deformation. Relatively new in-place inclinometers based on microelectromechanical systems (M-IPIs) consist of microelectromechanical systems accelerometer segments separated variously by flexible joints or field connection systems and encased in a watertight housing. M-IPIs provide nearly continuous ground movement measurements, accommodate greater ground movement because of their flexibility, and may contain temperature sensors, useful for applications in frozen ground. Two M-IPIs from different manufacturers were evaluated at four research sites in Alaska (a) to monitor creep in frozen ground (vertical installation), (b) to identify and monitor a slide shear zone (vertical installation), (c) to monitor thaw settlement under a newly constructed embankment (horizontal installation), and (d) to identify movement mechanisms within a slide and to evaluate the M-IPIs functionality through large amounts of shear (vertical installation). Each M-IPI was evaluated for ease of installation and subsequent retrieval, durability, and functionality in frozen ground. Measurements from both devices compared well with those from the inclinometer probe; this feature indicated that these devices were suitable for use in cold regions. However, field experience indicates that the installation procedure for each instrument is better undertaken at temperatures above freezing because of the manual dexterity required. For horizontal installations over permafrost, it is recommended that casing ends be secured to posts anchored below the permafrost table and any cold-affected plastic components be replaced between installations to avoid unwanted breakage during reinstallation.

Surface displacements of two landslides evaluated by GPS and inclinometer systems: a case study in Southern Apennines, Italy

This paper reports experimental data on surface and deep displacements evaluated by means of GPS stations and inclinometers in two rototranslational deep landslides in a clayey slope of the Italian Southern Apennines. The displacements of the landslides cause continuous damage to buildings and infrastructures. To study these phenomena and control their effects, the local public administration provided financial support for a geotechnical investigation that started in 2004. Laboratory tests, in situ pore pressure and inclinometer measurements were carried out. In July 2006, systems of fixed-in-place inclinometer probes with continuous data acquisition were installed in two of the eleven guide casings, in correspondence to the slip surfaces detected by previous periodical measurements. In the meanwhile, a GPS network was installed, consisting in six permanent stations and ten non-permanent ones. Among the latter, five were installed on the top of five inclinometer casings. The experimental results show that, in the case under study, the surface displacements evaluated by means of the GPS stations are consistent with the surface displacements evaluated by means of the inclinometer measurements. This implies mutual data validation, availability of considerable amount of continuous data, as well as monitoring continuity when, for some reason, one of the instruments goes out of use.

Development of a fibre Bragg grating sensored ground movement monitoring system

Monitoring ground movement manually by lowering an inclinometer probe (IP) in a grouted-in-place casing has been in practice for decades. It is possible to install multiple IP units at various depths in an inclinometer casing to allow automated data logging. The high cost and other problems associated with transmitting signals electrically make an automated IP rather impractical for long term and/or massive deployment. In addition to its small size, available technologies allow optical signals to be transmitted over many kilometres and not be affected by electromagnetic interference. The optical fibre Bragg grating (FBG) is one of the many available fibre optic sensor technologies. The authors used FBG as a sensing medium and developed a ground movement monitoring device referred to as the FBG segmented deflectometer (FBG-SD). The FBG-SD, designed to be inserted into the conventional inclinometer casing, measures the relative deflection between the segments. The amount of lateral movement is computed on the basis of the distribution of the segmented deflections. To verify the effectiveness of the new system, the authors performed indoor as well as field experiments where results from FBG-SDs were compared with conventional IP readings. This paper introduces the design principles of the FBG-SD and describes the performance of the system in their indoor and field applications.

The interpretation of pendulum-type inclinometer readings

The conventional method of inclinometer data analysis computes the displacement components in two mutually orthogonal directions separately by using corresponding readings measured in individual directions. It is shown in this note that calculation errors, although insignificant, are induced when this method is used to interpret data measured by pendulum-type inclinometers, which are widely used as probe inclinometers in engineering practice. The inclinometer readings measured in the two directions are correlative, and they are dependent on both the angle of the inclinometer probe axis inclined to the gravity vertical and on the azimuth angle at which the probe movement direction deviates from one of the two directions. The displacement component in each direction can be interpreted more accurately by simultaneously using the tilt angles in both directions measured directly by the inclinometer probe. Relationships between the actual displacement components, the resultant displacement, the azimuth angle, and the tilt angles are derived and verified by laboratory experiments. A refined calculation procedure is proposed for interpreting the pendulum-type inclinometer readings, and the errors induced in the conventional method are analyzed.Key words: deformation, field instrumentation, ground movements, monitoring.

Borehole logging with an eight-arm caliper–inclinometer probe

AbstractA newly designed eight-arm caliper–inclinometer probe for borehole logging is presented. The caliper sounding gives eight points of cross-sections of the borehole at 1 cm intervals along its axis. Regression circles and ellipses are calculated and used as obvious hypotheses to be tested in order to obtain information on strain rates in the horizontal planes and isotropic or anisotropic borehole closure. The scratching of identifiable marks into the wall of the borehole enables material displacement to be tracked, in particular in the vertical direction, thus providing information for determining vertical strain rates along the borehole. Measurements in two boreholes drilled on high-altitude glaciers in the Swiss Alps are used to demonstrate both the potential and the limitations of the probe and of the mathematical methods presented.