Temporal behavior of deep-seated gravitational slope deformations: A review

It is possible to monitor slow-moving landslides and assess landslide stabilisation measures over protracted periods using an optical–mechanical crack gauge called a TM-71. This technical note outlines the theoretical background to the gauge and illustrates its practical application through a number of case studies. These studies are drawn from a range of landslide types and stabilisation measures. In terms of monitoring slow-moving landslides, three studies of deep-seated deformations are presented. The Taukliman coastal landslide on the Black Sea Coast is characterised by vertical and horizontal displacements of up to 0.2 mm year−1 and sudden earthquake-induced dilations of up to 6 mm. The Parohy ridge spreading landslide in the Mala Fatra Mountains is characterised by gravitationally induced vertical displacements of 0.7 mm year−1. The slope deformation that formed Cyrilka Cave in the Beskydy Mountains is characterised by very slow sinistral strike–slip movements of 0.8 mm year−1. In terms of assessing landslide stabilisation measures, two studies are presented from Orava Castle in Slovakia and Tetin in the Czech Republic. The data recorded at these sites demonstrate that the constructed stabilisation measures have successfully alleviated the potential landslide hazard in both localities. These case studies clearly demonstrate that the gauge represents an important tool with which to monitor slow-moving landslides and assess landslide stabilisation measures. It is able to provide a precise three-dimensional record of deformation, withstand harsh environmental conditions, and record reliable data over protracted periods.

The monitoring of slow-moving landslides and assessment of stabilisation measures using an optical–mechanical crack gauge

Deep-Seated Gravitational Slope Deformation

The Isle of Portland, southern England, is composed of gently folded Upper Jurassic Beds ranging from the Kimmeridge Clay through the Portland Group to the Lower Purbeck Group which are gently folded to form part of the northern end of the Shambles Syncline. The essential arrangement of the beds is for hard, jointed well-bedded and permeable Purbeck and Portland limestones to overlie the Kimmeridge Clay members. The jointing along NW-SE, NE-SW, N-S and E-W master and conjugate sets closely parallels the axis of the syncline and the NNE-SSW fault pattern of the Purbeck Anticline and is a major regional landform control at all scales from the occurrence and form of individual rock falls to the shape of the island itself. Portland has a large number of landslips, which have been mapped from colour air photography. Their spatial pattern is spectacularly related to the geological conditions of the island and varies in size and type in a systematic manner as the thickness of clay and the orientation of the dip changes with respect to the coastline orientation. The slips, which occur predominantly in the winter months after heavy rainfall, are of frequent occurrence and pose major hazards to engineering structures. The landslide pattern and the overall morphology of the island is used to suggest a tentative model of landscape evolution which emphasizes the process of lateral spreading, loading, clay extrusion and erosional unloading.

The structural geomorphology of the Isle of Portland, southern England

Rock massifs are subject to long-term deformations, as well as to environmental effects. Decades of precise crack gauging have led to a series of qualified results of practical importance to geotechnical engineering. Slow deep-seated rock slope movements have been observed and monitored in cases where long-term stability was anticipated. In addition to movement trends, specific events of acceleration were detected and impulse periods determined. Examples in the field of geotechnics are given, which include an observed rock massif response to prestressed anchors, a history of slope instability affected by human interference, and evaluation of fault-controlled stability in a railway cutting affected by long-term rock weathering.

Deformation effects in rock massifs and their long-term monitoring

In a coastal region of high seismicity a giant block-type slope deformation is being propagated in sliding cycles due to the action of creep in a bed of clay, deep under a brittle rock platform.

Propagation of coastal slope deformations at Taukliman, Bulgaria

A local geodetic observation of block displacements in the Szczeliniec Massif was started in 1972, and later was supplemented by an exact fissure dilatation measurement and extended to cover the whole massif. Special instrumentation has been used and a three-dimensional observation system has been developed. Results reveal fluctuating displacements that can be, to some extent, explained by seasonal temperature oscillations. It is intended to continue the observations to acquire more specific results, since the present results cannot be definitely interpreted in favour of slope movements of blocks due to creep in the bed, which was anticipated.

Displacement registration of sandstone blocks in the Stolowe Gory mountains, Poland

Block-type slope deformation models were investigated using viscous and viscoplastic optically sensitive materials loaded by body weight beyond yield and strength limits.

B. Košťák

Papers

Propagation of coastal slope deformations at Taukliman, Bulgaria

Displacement registration of sandstone blocks in the Stolowe Gory mountains, Poland

Photoplastic slope deformation models.