Adam Chrzanowski

On the strain analysis of tectonic movements using fault crossing geodetic surveys

Abstract A generalized approach to the analysis of deformation surveys has been developed by the authors and utilized in the analysis of tectonic movements. The approach is applicable to any type of repeated geometrical measurements (geodetic and non-geodetic surveys), any type of deformations including rigid body displacements and strain, and geometrical configuration of the observation network. The approach is based on the least squares fitting of selected deformation models to the displacement field obtained from repeated observations of deformations. The approach consists of three basic processes: 1. (1) preliminary identification of the deformation models. 2. (2) estimation of the deformation parameters using a generalized mathematical model for the least squares fitting. 3. (3) diagnostic checking of the deformation models and the final selection of the “best” model based on global statistical tests and on calculated significance levels of the deformation parameters. A numerical example is given using survey data from four epochs of observations of a small geodetic network which was established across an active fault in the Peruvian Andes.

Integration of geodetic and geotechnical deformation surveys in the geosciences

Abstract Ground movement studies can utilize information from conventional geodetic surveying, photogrammetry, and geotechnical measurements of strain, tilt, etc. Each method alone cannot yield a complete picture of the deformation. However, each is complemented by the others. Hence, their integration in a simultaneous analysis in space and in time is advocated. An integrated analysis is readily accommodated by a generalized method of deformation analysis devised by the authors. Any number of measurements of any type can be considered in any fashion of modelling with full statistical assessment of the modelling and of derived characteristics. Such an integration is illustrated using data from a coal mining area in rugged mountainous terrain of western Canada. Conventional terrestrial geodetic methods connected 15 stations. Displacements from an additional 29 points were obtained from aerial photogrammetry. Biaxial tiltmeters continuously measured ground tilts at 3 stations. A surface of subsidence for the whole area was modelled with the graphical depiction in three dimensions.

Modern Surveying Techniques for Mining and Civil Engineering

Publisher Summary Surveying is the field of applied science and engineering that deals with spatial information about positions of points on, above or below the earths surface. This information serves as a base for the establishment of geographic information systems (GIS) for the management of land and marine resources, for monitoring environmental changes, and for planning, designing and setting out engineering works. The spatial information may be displayed in the form of maps, digital terrain models, or just as a list of coordinates of the points of interest in a selected coordinate system. Surveying is needed at all stages of most civil engineering or mining projects: in planning and design, during the construction or mining process, and, finally, in monitoring the stability of the constructed object or surrounding rocks. The accuracy requirements for engineering and mining surveys are usually higher than for any other surveying application. They may range from submillimeter requirements in setting out and alignment of such high precision objects as nuclear accelerators, or in deformation measurements of such sensitive structures as large power dams and underground excavations for the storage of toxic materials, to millimeters and a few centimeters in the alignment of long tunnels and bridges or in ground subsidence surveys.

Analysis of deformations of large earth dams

Safety of earth dams depends on the proper design, construction, and monitoring of actual behaviour during the construction and during the operation of the structure. The most critical factor in the assessment of the safety threshold value of any structure is the acceleration of its deformation. Therefore, the designed accuracy of monitoring surveys must fulfill requirements of detecting accelerations at critical locations of the investigated object. As an example, time dependant behavior of a large embankment dam during filling up the reservoir has been analyzed and verified by comparing monitoring results with the deterministic (prediction) model of the deformation. The geotechnical and geodetic monitoring besides providing a warning system in case of an abnormal behaviour of the dam, may be used as a tool for a verification of design parameters where geotechnical parameters are of the highest importance. Modeling of deformation of earth dams is a complex process in which one should consider the nonlinear behaviour of the construction material, interaction between the structure and the underlying foundation strata, influence of water load on the structure and on the foundation bedrock, and the effects of water saturation. Due to the uncertainty of the model parameters, careful monitoring of the dam and its surroundings are required in order to verify and enhance the model. In addition, with properly designed monitoring surveys, one may also determine the actual deformation mechanism. The finite element method may be useful tool in the proper design of the monitoring scheme by providing information on the locations and magnitude of the expected maximum displacements and velocites of movements. The discussed problems are illustrated by three types of earth dams located in California, U.S.A. and in Quebec, Canada.

New Laser Applications in Geodetic and Engineering Surveys

Large engineering constructions and first-order geodetic control nets often require a relative accuracy of 10(-6)or better in positioning of survey points. A team from the University of New Brunswick has developed new instruments for precision alignment surveys and for engineering and geodetic leveling which satisfy the demands for accuracy. Prototypes of integrating centering detectors have been designed and constructed which allow alignment of laser beams with an accuracy of 0.2 sec of arc in a turbulent atmosphere over distances of a few kilometers. Two types of laser plummets have been developed to set a laser beam in a vertical direction with an accuracy of 0.5 sec of arc or better. A He-Ne laser has been adapted to a conventional self-aligning level giving a standard error of 0.7 mm/km in determination of a difference in elevation. A new type of laser level has been constructed which gives new possibilities for precision leveling.

Increasing public and environmental safety through integrated monitoring and analysis of structural and ground deformations

Any engineered or natural structure, when subjected to loading, undergoes deformation and/or rigid body movements. Once the deformation, its velocity and/or acceleration exceed critical values, the structure fails. The critical values are determined using failure criteria that are based upon either empirical formulae or principles of continuum mechanics. By providing continuous and properly designed deformation monitoring schemes, one may provide information about the new state of the deformation. This information can then be used to provide advance warning of imminent structural failure.

Design and analysis of a multi-sensor deformation detection system

Abstract Development of new technologies for monitoring structural and ground deformations puts new demands on the design and analysis of the multi-sensor systems. Design and analysis of monitoring schemes require a good understanding of the physical process that leads to deformation. Deterministic modelling of the load-deformation relationship provides information on the magnitude and location of expected critical deformations as well as delineates the deformation zone. By combining results of deterministic modelling with geometrical analysis, one can find the deformation mechanism and explain the cause of deformation in case of irregular behaviour of the investigated object. The concept is illustrated by four practical examples.

Some considerations in designing a GPS pseudolite

Some Considerations in Designing a GPS Pseudolite Pseudolites are transmitters of GPS-like signals placed on the ground. Though pseudolites are well known devices and have already been used in the project where visibility to the GNSS satellites is limited, there are still many issues that need enhancement. A prototype of a low-cost pseudolite is being designed and assembled at the University of Warmia and Mazury. This will allow for conducting tests with various codes, signals and software. The goal of the project is to apply the pseudolite as an augmentation to GNSS positioning tasks in geodetic engineering projects. Some practical considerations crucial for the design are discussed in this paper.

Fully Automatic and Reliable Real Time Monitoring Systems for Steep Slopes, Embankments, and Structures

A major concern involving any steep embankment is its stability. This is the case whether it is the side wall of an open pit mine, a steep slope next to a highway, or a man made structure like a dam or dike used to contain tailings or generate hydroelectric power. In general, for each case there is a slow movement of the formation before a failure actually occurs. With the continuous monitoring of a phenomenon’s creep, particularly its acceleration, critical displacements can be detected before the object reaches its failure point. Among new technological developments, robotic total stations (RTSs) give one possible cost effective solution to creating a near real time monitoring system. Repeated surveys at predetermined time intervals can automatically generate warnings if slope movements exceed a preset tolerance level. In addition, the system can be augmented with GPS or geotechnical sensors to make it a more reliable system. The strengths of each sensor type can be exploited to optimize the cost and efficiency of the monitoring system to ensure pre-failure detection. The latest monitoring techniques apply the principles of Synthetic Aperture Radar (SAR), using both satellite and portable ground based systems, to determine complete surface deformations rather than the few discrete points that are obtained with the current systems. A methodology has been developed at the Canadian Centre for Geodetic Engineering (CCGE), in cooperation with ACA Ltd, for optimizing the design of monitoring systems by combining geometrical and deterministic modeling methods to ensure proper sensors are installed at proper locations and utilized correctly. The methodology has been realized in the creation of a software package that has been successfully implemented at large earthen dams and open pit mining operations around the world.

Modelling of Ground Subsidence from a Combination of GPS and Levelling Surveys

Since 1984, the authors have been involved in ground deformation studies in oil fields along the east coast of Lake Maracaibo in Venezuela. Due to oil extraction, an area of about 50 km × 50 km has been subjected to subsidence which in some places reaches 20 cm/year. Subsidence in the whole area has been monitored since 1929 using conventional geodetic levelling with over 1600 benchmarks connected to some points considered to be outside of the subsidence influence. The levelling network consists of 800 km of primary (main network) and 600 km of second-order densification surveys. The complete survey has been repeated every two years with a portion of the network (about a third of the whole area) remeasured every six months for the purposes of upgrading protective coastal dykes, updating the irrigation system, and controlling the stability of offshore platforms and plants. An evaluation (Leal, 1989) of the last few survey campaigns indicates that the standard deviation of the levelling surveys is about 2 mm/√ km for the main network and 4 mm/√km for the densification survey. The average accuracy of the subsidence determination is about 10 mm at a one sigma level. The levelling survey is a slow, expensive, and labour intensive operation. Several survey crews need about three months to measure the whole subsidence area at a total cost of about US