Geotechnical Instrumentation Research Articles

A Study of Stability Investigation of Immediate Roof for Extraction of Thick Coal Seam in India

This study investigates the strata mechanics and convergence monitoring while depillaring in single lift of thick coal seam by cable bolting method. Based on rock mechanical investigations and geotechnical engineering domain, the use of 19-mm-diameter rope as support system and other necessary consumables has been applied to hold the immediate roof over the coal seam. The field application was made in the Bonbahal (R-VI) seam of the case study mine for extraction of full thickness by single lift considering other techno-science parameters. The cable bolting method has success story, while extraction was done by single lift and load haul dumper with belt conveyor combination. The rate of percentage of extraction found 70.12%, and simultaneously no spontaneous heating was observed during extraction of the pillars. Thus, this paper deals with the suitable methods of depillaring to extract thick Indian coal seams followed by scientific observations of immediate roof. Therefore, the research on convergence behaviour of strata will help to design safe extraction of the depillaring panels. Support system and strict vigil of the geotechnical instruments will help to take corrective measures in advance during extraction in safer and efficient manner.

Permanent sheet pile walls in complex soil conditions Surveillance, monitoring and safety

Kvaernerbyen field F1, also known as Kvaernerdammen, is part of the Kvaernerbyen project in Oslo, Norway. Kvaernerdammen consists of a 7-storey residential complex on an underground parking floor. The south-eastern part of the building cuts into the lower part of a steep slope, with soil conditions consisting of dry crust above firm silty clay, followed by quick clay/sensitive clay above a thin moraine layer over bedrock. Due to existing buildings and constructions further up the slope, the allowable deformations of the building pit during and post construction of Kvaernerdammen had to kept within very tight thresholds. Since the summer of 2017, Cautus Geo AS and Multiconsult Norway AS have been cooperating in “research and development” (R&D) focusing on deformations of sheet pile walls (SPW) in complex ground conditions and all aspects connected to interaction between engineering, monitoring, alerting and safety. Starting with surveillance during the construction period, monitoring a permanent SPW supporting the mentioned slope at Kvaernerdammen, the R&D collaboration was continued between Cautus Geo and Multiconsult with continuous surveillance of the construction for almost 2 years after completion. Throughout the project, all phases of a critical SPW-construction have been evaluated, mainly focusing on the effects of seasonal variations in a “permanent” phase. Observations and experiences made during the project with a comprehensive database derived from geotechnical instrumentation have provided an unusually detailed documentation of the development of the construction after completion. The load cells connected to anchors in two rows on the SPW show a correlation between increasing temperature and increasing anchor force in a permanent phase, most likely due to a volume expansion of the structure. This is an opposite trend to what was observed during the construction phase, where increasing force is recorded in the load cells at decreasing temperature, especially at negative degrees Celsius. The temperature in the load cells is measured to oscillate between positive and negative degrees Celsius only during the construction phase. The load may tend to increase in the upper part of the SPW during heavy rainfall, but of negligible value. Based on a slight change in load and deformation during the permanent phase, the SPW is regarded as a stable and secure construction at Kværnerdammen. For future projects, it is important to be aware that load changes in anchors may be dependent on a well-functioning frost protection.

Reclamation and Ground Improvement of Soft Marine Clay for Development of Offshore Terminal 4, JNPT, Navi Mumbai

A container yard of around 100 Ha area was developed as part of the fourth terminal for Jawaharlal Nehru Port Trust (JNPT) in Navi Mumbai by means of reclamation in sea over soft, compressible marine clay. Ground improvement of the subsoil was warranted in order that the finished reclamation satisfies the stringent serviceability criteria. Extensive offshore geotechnical investigation campaign comprised conventional borehole sampling, laboratory tests and various in situ field tests such as CPTu, field vane shear tests, etc. Investigations revealed clay thicknesses of 4 m–22 m, with top layer showing undrained shear strengths less than 7 kPa and increasing with depth, underlain by weathered basalt. The ground was improved using prefabricated vertical drains (PVDs) with preloading. Radial consolidation and cone dissipation tests were carried out to establish the coefficient of horizontal consolidation (ch). The marine reclamation is confined on all sides by a perimeter bund with revetment, Stability analyses carried out for this bund showed that it was necessary to have overfill beyond the reclamation cope line along with tension geotextiles so as to achieve the prescribed factors of safety against slope failure. After removal of the preloading, the overfill was cut back to the final geometry and revetment was provided along the perimeter. Extensive geotechnical instrumentation and monitoring were conducted using multilevel magnetic extensometers, settlement gauges, inclinometer and piezometers to monitor the behaviour and performance of ground improvement. Field ch and smear coefficients were back-calculated. Around 200 confirmatory boreholes (CBH) were carried out after completion of ground improvement to ascertain the post-improvement and validate the design parameters, thus eliminating the risk of post-construction settlement.

ANALISIS STABILITAS TIMBUNAN (MAINDAM) BERDASARKAN DATA INSTRUMEN GEOTEKNIK PADA BENDUNGAN SINDANG HEULA SERANG BANTEN

The development of science and technology has obtained supporting technology for monitoring the soil shear force and pore water pressure in the dam, the presence of shear forces against the landfill and pore water pressure through small cavities in the embankment soil in the dam body which can be detected by equipment such as inclinometer and piezometer that have been installed at predetermined points. The application of inclinometer and piezometer technology is used as a support tool for monitoring the movement of landfill and pore water pressure against dams. The embankment dam is the most complex of civilian structures and is very dangerous if damaged. When there is damage to a dam, it will cause a big disaster for the areas that are downstream of the dam. Damage or collapse of a dam can occur due to several things, including overtopping, sliding of the dam slopes (internal erosion or "piping"), and the occurrence of structural degradation of each zone. on the dam body. In the analysis of the stability of the embankment (maindam) which is based on geotechnical instrument data, it must be carried out as carefully and accurately as possible. The purpose of this analysis is to measure the early damage in the main dam (maindam). After conducting research and field studies at the Sindang Heula dam, there were several points of decline at the top of the core embankment (maindam). To find out the cause of the decline, data was taken from measuring geotechnical instruments.

Finite Element Modeling of Soil Improvement Using Vacuum Consolidation with Vertical Drain Method (Case Study: Apartment Project, Tangerang)

Construction for infrastructure development in soft clay is often a major issue. The low bearing capacity of the soil can threaten the construction stage due to a large settlement in consolidation process. To overcome this problem, soil improvement is needed. Vacuum consolidation with vertical drain method is used in the Tangerang Apartment Project. The soil condition in construction area is determined from literature study and soil investigation to choose the suitable treatment for the construction area. By using vacuum consolidation with vertical drain method, the settlement process can be accelerated in a shorter time. In this study, the author used secondary data analysis method from the Tangerang Apartmentconstruction project. The settlement result from the geotechnical instrument monitoring will be compared to the result from finite element modeling using PLAXIS 2D. This analysis aims to obtain the amount of time and soil settlement during the process of vacuum consolidation with the lateral distance between vertical drains to accelerate the consolidation process and dissipation of pore water pressure.

GB-InSAR monitoring of vegetated and snow-covered slopes in remote mountainous environments

As a member of the International Consortium on Landslides, the University of Alberta is actively working to improve technologies for monitoring natural hazards. Though ground-based, interferometric, synthetic aperture radar (GB-InSAR) has been successfully implemented for near real-time monitoring of natural and man-made slopes, it has seen limited use in Canada outside of the mining industry. This lack of adoption in the rural areas of Canada is due to difficulties associated with providing continuous power to remote sites, other logistical challenges, and concerns with the impact of snow cover on the data collected. This paper presents the results of a project to install a GB-InSAR system to monitor a 2 to 3 million m3 bedrock landslide with a measured average rate of displacement of ~ 10 mm/year. The site is characterized by long periods of deep snow cover, cold temperatures, no connection to the electrical grid, and a location within a steep valley that limits hours of daylight for solar power. Challenges with, and solutions developed for, the deployment of GB-InSAR equipment at this site are described, and the results of the monitoring program are validated with existing geotechnical instrumentation.

Monitoring of Strain and Temperature in an Open Pit Using Brillouin Distributed Optical Fiber Sensors.

Marble quarries are quite dangerous environments in which rock falls may occur. As many workers operate in these sites, it is necessary to deal with the matter of safety at work, checking and monitoring the stability conditions of the rock mass. In this paper, some results of an innovative analysis method are shown. It is based on the combination of Distributed Optical Fiber Sensors (DOFS), digital photogrammetry through Unmanned Aerial Vehicle (UAV), topographic, and geotechnical monitoring systems. Although DOFS are currently widely used for studying infrastructures, buildings and landslides, their use in rock marble quarries represents an element of peculiarity. The complex morphologies and the intense temperature range that characterize this environment make this application original. The selected test site is the Lorano open pit which is located in the Apuan Alps (Italy); here, a monitoring system consisting of extensometers, crackmeters, clinometers and a Robotic Total Station has been operating since 2012. From DOFS measurements, strain and temperature values were obtained and validated with displacement data from topographic and geotechnical instruments. These results may provide useful fundamental indications about the rock mass stability for the safety at work and the long-term planning of mining activities.

High Water Ingress during TBM Tunnelling under Andheri Kurla Road, Marol Naka, Mumbai, India.

For surface space limitations in metro cities, tunnel is the best option worldwide for the development of modern transport system, utilities and other infrastructures. But tunnelling is full of surprises depending on geological and hydrological factors. Underground Mumbai Metro line -03 is also full of surprises. In this paper we are going to discuss the encountered high water pressure during the Up line mining underneath the Andheri – Kurla road & elevated Mumbai Metro line -01 at Marol Naka. Pressure of water was observed to be 4.5 bars to 5 bars, geotechnical instruments showing no settlement but tunnel always filled with muck and progress were affected badly apart from taking precautions during the mining. As per geology, grade III basal and breccia were encountered. Team tried to find out the source/causes of this high water ingress but even after searching various options such as utility damage, recharging with water body, geological & geophysical investigation options, it was unable to conclude the confirm source. It was very astounding that no high water ingress was observed during the down line TBM mining. In this paper, all options have been discussed in details and also suggesting for taking high precautions during construction of cross passage in this area.

High Water Ingress during TBM Tunnelling under Andheri Kurla Road, Marol Naka, Mumbai, India.

For surface space limitations in metro cities, tunnel is the best option worldwide for the development of modern transport system, utilities and other infrastructures. But tunnelling is full of surprises depending on geological and hydrological factors. Underground Mumbai Metro line -03 is also full of surprises. In this paper we are going to discuss the encountered high water pressure during the Up line mining underneath the Andheri – Kurla road & elevated Mumbai Metro line -01 at Marol Naka. Pressure of water was observed to be 4.5 bars to 5 bars, geotechnical instruments showing no settlement but tunnel always filled with muck and progress were affected badly apart from taking precautions during the mining. As per geology, grade III basal and breccia were encountered. Team tried to find out the source/causes of this high water ingress but even after searching various options such as utility damage, recharging with water body, geological & geophysical investigation options, it was unable to conclude the confirm source. It was very astounding that no high water ingress was observed during the down line TBM mining. In this paper, all options have been discussed in details and also suggesting for taking high precautions during construction of cross passage in this area.

Monitoring subsurface ground movement using fibre optic inclinometer sensor

The monitoring of subsurface ground movement is important for the prevention and control of geological disaster including land subsidence, ground fissure, surface collapse, and landslides. Inclinometer and extensometer are examples of the conventional geotechnical instruments for monitoring the subsurface ground movement. However, most conventional geotechnical instruments for subsurface monitoring are limited to discrete sensing, high cost, and susceptible to various reading errors. This paper presents the advancement of technology mechanism to monitor horizontal ground movements as well as the data processing technique involved. Distributed optical fibre inclinometer is developed through laboratory pipe bending tests whereas the data is corroborated with conventional instruments. This system was installed on site, measuring the performance of the sensors as well as to monitor the associated ground movements. A simple cost comparative study between fibre optic inclinometer and conventional geotechnical instrumentation indicates the new technology is cost-effective for applications in ground monitoring particularly when monitoring a large number of borehole points and measurement arrays.

Stability Assessment of Old Underground Coal Mine Openings for the Safety of Overlying Railway Tracks

This paper presents the stability assessment of a century old coalmine situated under a railway track. The mine openings may lead to the surface subsidence which can endanger the track safety. To assess the stability, this paper presents a unified approach of observational, empirical, and analytical methods. Observational approach monitored the immediate roofs with geotechnical instruments during a period. In empirical approach, the coal pillar safety factors were assessed using rock mass classification. Finally, the analytical study was performed using numerical simulation. All these studies found that the openings and the coal pillars are stable for the track safety.

Development of a model to estimate strata behavior during bord and pillar extraction in underground coal mining

Instrumentation and monitoring is undertaken aiming at evaluation of changing values of rock mechanic parameters, namely, dilation, load, convergence, and stress, during mining for a safe strata control. It enables the mining practitioners to anticipate roof fall–related dangers in advance and taking subsequent preventive measures while depillaring. The coal measure formations consist of relatively weaker stratified rock masses. Bed separation occurs in the overlying strata due to induced mining stresses, which cause the rock mass in its surrounding to displace. These occurrences can be monitored by installing geotechnical instruments at judicious locations to avoid occurrence of any dangerous condition due to roof fall. Improper anticipation of strata movement during extraction in coal mining is one of the principal causes of accidents due to roof and side collapses. Also, the installed instruments can help in prediction of any apprehensive condition during depillaring. Preventive measure can be taken if the strata movement is monitored and roof fall is predicted in advance. The study is aimed to develop a conceptual model roof fall warning index, based on critical strata movement during underground coal extractions. Numbers of mining aspects, such as analysis of instruments’ reading, geo-mining parameters, physico-mechanical properties roof formations, and induced stress, are taken into considerations for development of the model. This study is mainly focused to predict a critical strata movement value for safety of the bord and pillar method of mining, perticularly depillaring.

Performance of a coal pillar at deeper cover: Field and simulation studies

Exhaustion of coal reserve, extractable by conventional longwall method of working at Czech mines, provided an opportunity to try modified Room and Pillar (R&P) method to extract high grade coal locked-up in larger shaft protection pillar at around 900 m depth. The shaft pillar is divided into various R&P panels and the development process in a panel followed a constant gallery width of 5.2 m and 3.5 m height. This development in the shaft pillar by bolter miner resulted oblique and inclined pillars of 860–1225 m2 area. Stability of these pillars is realised to be vital for optimum recovery of high-grade coal from these panels. No empirical formulation is found suitable for the design of pillars at such a depth. Therefore, an attempt is made to select a better representing one through comparative study of the available formulation. CMRI formula is found to be an alternative solution for designing pillars at this depth as it contains depth of cover as a design parameter. This parameter in the formulation is included to take care of the in situ stress conditions and compactness of the material at higher depth of cover. Further, a number of geo-technical instruments are installed in two pillars of Panel V for an analysis of their stability during the development. An attempt is made to develop a strain-softening based numerical modelling approach, calibrated by field studies and CMRI empirical formulation, to assess pillar performance at deeper cover. This development is found to be helpful in pillar stability analysis, when the installed instruments ceased to work. Further, an apprehension of pillar failure by extrapolation of field results is not confirmed on simulated models. This paper briefly presents a discussion of difficulties involved in pillar design at higher depth followed by results of field and simulation conducted for the deep Czech mine.

Research on the acceleration of settlement by installing vertical drain and preloading with sand

The container yard, which facilitated the Container Terminal of the Jakarta International Container Terminal (Terminal Peti Kemas Koja), at Tanjung Priok Jakarta is located on a land which the subsurface soil is predominated by a compressible clay layer, from 5.00 to 22.00 m depth. The load from containers quite high and will stay for a long period. Without soil improvement, the estimated consolidation settlement is 1.418 m, which will take place in a very long time. Soil improvement has carried out by accelerating consolidation, by installing vertical jute fiber-drain, and loading the soil by a preload of sand to elevation of +8.50 m. To investigate the effectiveness of the installed vertical jute fiber-drain, geotechnical instruments also installed, which are settlement plate, standpipe piezometers, pneumatic piezometers, magnetic extensometers, and inclinometers. Vertical jute fiber-drain is a Prefabricated Vertical Drain (PVD) made of natural jute fiber and coconut coir designed to accelerate consolidation of soft clayey soil. It has high tensile strength to withstand installation stresses and excellent water discharge capacity. The cross section of natural fiber PVD measures 80-120 mm in width and 8–12 mm in thickness and have a tensile strength of above 7 kN. The present drain differs from the others drain is that its manufactured in existing jute mills machinery, the manufacturing process entails low energy consumption, and has capability of varying the width, thickness and weight per linear meter to suit different soft clayey soil conditions. An important feature of the jute burlap is its swelling nature that allows it to function as filter without clogging and it's biodegradable, hence environmentally friendly.

Settlement Evaluation of a Concrete Face Rock-Fill Dam (CFRD) Using a Back-Analysis Method Based on Measurement Results (A Case Study of Siah-Bisheh Dam)

The behavior of the Siah-Bisheh concrete face rock-fill dam in Mazandaran, Iran was investigated. Numerical analyses were performed before construction to evaluate the stability and predict the deformation of the dam. The material properties were chosen based on the results of geotechnical investigations. The amounts for deformation and settlement of the concrete surface were also calculated with the numerical model. The information from a number of geotechnical instruments was collected after construction and analyzed to measure settlement at different sections of the dam. The locations of the different deformations and their values are presented with various contours. The data were analyzed and used to revise the original numerical model of the dam. Following that, the long-term stability of the dam was evaluated, using parameters that were modified based on the measurement data. A comparison of the results from the numerical analysis and the values obtained from the dam settlement measurement showed that the initial results from the numerical model were much higher than the real values. It also showed that the number of construction layers used in the modeling of the dam had a significant effect on the obtained maximum amount of deformation.

Evaluasi Kinerja Perbaikan Tanah Lunak Dengan Menggunakan Preloading dan Prefabricated Vertical Drain (PVD)

The settlement of soil consolidation is geotechnical problem which is often found in soft soil accumulation. It is therefore, Preloading and Prefabricated Vertical Drain techniques are used to accelerate consolidational settlement. The problem which often appeared in using Preloading and Prefabricated Vertical Drain (PVD) is the failure of design. It causes the consolidationtime cannot run in accordance with the planning. In order to have soil improvemet method which has high effectiveness it is necessary to evaluate the use of geotechnical instruments. In this study, the evaluation covers 3 (three) geotechnical instruments, where Settlement Plate is used to evaluate theoretical settlement, to calculate final settlement prediction with Asaoka observation method and consolidation degree in the field. Consolidation degree also can be evaluated using Pneumatic Piezometer instrument. The inclinometer is used to evaluated the stability of embankment. The failure of design in using Preloading and Prefabricated Vertical Drain (PVD) can be accured because of the mistake of planner in determaining soil design parameters, therefore this study also discusses soil design parameters in actual condition using back analysis method. The results obtained in this study are comparison of actual and theoretical settlement on average of 0.862. To predict final settlement it can be obtained the value 2191,08 mm with the rest of settlement which will be accured about 100 – 450 mm. In this study the actual consolidation degree from Piezometer reading is 85,36% and Settlement Plate reading is 88,42% with the difference of 3,06%. From Inclinometer reading lateral shift which is accured below the soil there is no land slide so that the embankment which is used remains safe The result of back analysis method is Ch value where the new Ch value is 1,914Cv.

Stone blowing as a remedial measure to mitigate differential movement problems at railroad bridge approaches

Railroad track transitions such as bridge approaches often experience recurrent track geometry problems due to differential settlement between the bridge and the adjacent track. The resulting “bump at the end of the bridge” leads to significant passenger discomfort and causes rapid deterioration of the track as well as vehicular components. In general, railroad managers address recurrent track geometry defects through track resurfacing methods, such as tamping that involve raising the track through mechanically induced vibration and rearrangement of particles within the ballast layer. Although widely used for track resurfacing, the tamping process tends to destabilize the ballast layer, and the track may rapidly return to its former deteriorated state based on the traffic flow. The method of “stone blowing,” on the other hand, which was developed as an alternative to tamping, relies on the principle of injecting fresh ballast particles into gaps underneath ties and raising the track level rather than disturbing the packing condition of the existing ballast. In a recently completed research study in the United States, stone blowing was successfully implemented as a remedial measure to mitigate the problem of differential movement at a problematic bridge approach along Amtrak’s Northeast Corridor. Advanced geotechnical instrumentation was used to monitor transient deformations within individual track substructure layers before and after stone blowing. Moreover, tie support conditions and track geometry data were also analyzed to quantify the effectiveness of stone blowing on the improvement of track performance.

Integrated fuzzy decision approach for reliability improvement of dam instrumentation and monitoring

Dams constitute a potential hazard to downstream life and property. Therefore, it is necessary to detect any signs of abnormal behaviour in structural safety. Monitoring of an embankment dam plays a key role to increase dam safety and to prove performances. Appropriate instrument selection is one of the most important steps of a monitoring plan. Inappropriate instruments may cause irreparable damages in critical situations. The lack of a method to analyse the instruments, and to select an appropriate one is one of the shortages of a monitoring plan. Nowadays, decision-making methods have been widely used to optimise the selection process. In addition, due to uncertainty in decisions, fuzzy methods are applied. The present study aims to establish an integrated decision model based on FAHP-FTOPSIS methods, by taking into account 9 influential criteria and 42 alternatives as geotechnical instruments. The model has been applied for a clay core embankment dam. Results showed that group decision-making can reliably be used to prioritise the instruments. For instance, the best instrument for monitoring stresses was hydraulic pressure cell while its closeness coefficient was .55. The possible choices were reliably selected and prioritised due to their adjacency to the ideal solution.

Optimal monitoring instruments selection using innovative decision support system framework

Structural monitoring is the most important part of the construction and operation of the embankment dams. Appropriate instruments selection for dams is vital, as inappropriate selection causes irreparable loss in critical condition. Due to the lack of a systematic approach to determine adequate instruments, a framework based on three comparable Multi-Attribute Decision Making (MADM) methods, which are VIKOR, technique of order preference by similarity to ideal solution (TOPSIS) and Preference ranking organization method for enrichment evaluation (PROMETHEE), has been developed. MADM techniques have been widely used for optimizing priorities and determination of the most suitable alternatives. However, the results of the different methods of MADM have indicated inconsistency in ranking alternatives due to closeness of judgements from decision makers. In this study, 9 criteria and 42 geotechnical instruments have been applied. A new method has been developed to determine the decision makers\' importance weights and an aggregation method has been introduced to optimally select the most suitable instruments. Consequently, the outcomes of the aggregation ranking correlate about 94% with TOPSIS and VIKOR, and 83% with PROMETHEE methods\'results providing remarkably appropriate prioritisation of instruments for embankment dams.

Lesson learned from retaining wall failures: a geotechnical disaster

This article presents five failure cases of retaining wall which is obtained from literature and some personal documentation. One case is located in Singapore, two cases are located in Taiwan, and the other two cases are located in Indonesia. Among those five cases, four cases were the unloading problems and one case was the loading problems. The objective of this article is to summarize the causes of those failures, according to the literature study and to provide some recommendations to prevent similar events happened in the future. The failure of retaining wall is categorized as a geotechnical disaster because it is not only causing major economic losses but also some casualties also been reported. The main reason for the failure was the improper design of the retaining and supporting system. One of the good indication before failure would occur was excessive movements induced by excavation or fill. Hence, it was recommended to install a proper geotechnical instrumentation in the construction and the nearby area. Moreover, an excavation or fill project should be strictly operated and controlled by a safety management to avoid any casualties. The safety regulations should be supported and understood by all of the people involved in excavation or fill projects.