Sinkholes and subsidence pdf

Geological map and section of the Runjh sector geology slightly modified after R. Locally the lavas show the development of planar schistocity.

The volcanics in general occur as interstratified lava flows within the sediments of the Sundernagar Formation. The volcanic rocks, particularly the amygdaloidal-vesicular type, show considerable deterioration of the physical properties due to mechanical weathering.

As a result the saturation moisture content and porosity of the rocks have increased and the rocks have been reduced to a state which can be described as weakly compact.

The massive non- vesicular type is highly fractured and jointed. They comprise salt also salt grit , gritty marl IGcally referred to as lokhan , dolomite, limestone, shale and quartzite. These sedimentaries occur in a schuppen zone. The majority of rock types of the Shali Formation belong to the category which yield freely to the solvent action of water and they are susceptible to rapid weathering.

In the section between Megal and Runjh, the gritty marl lokhan directly underlies the volcanics along a thrust. Lokhan is a low density 0. However, it also contains sporadic clay bands, occurring as lentils, which have a bearing on the movement of underground water. It was Plan and section o f the sinkhole at Runjh. Before the subsidence occurred, there stood a cluster of bamboo trees of 15 m height. At the time of the authors' visit the bamboo trees were completely engulfed inside and could not be seen in the sinkhole.

This means the depth of the hole is in excess of 27 m. The wall of the sinkhole is standing steep and vertical. Along the southern part of the wall a thin boudin-shaped quartzite band is exposed within the volcanics. The rest of the wall space is occupied by highly fractured and weathered basic volcanic rocks. Along the orifice of the sinkhole there is a thin capping of residual soil over the volcanic rocks.

Local geological study has revealed that the axial plane of the minor synformal downwarp in the volcanics and the quartzite interband almost coincides with the vertical axis of the sinkhole. From the description of the sink- hole it is apparent that the subsidence is of cylindrical type. In the northwestern peripheral zone there are tension cracks roughly paralleling the outline of the sinkhole opening.

They range in length from 2 to 5 cm. Cracks have also developed within the bordering land under cultivation in the southwestern part. The cracks are 6 - 1 0 cm wide with a tendency to continuously enlarge.

They have developed in the wake of subsidence. As an immediate consequence of the subsidence, a building along the northwestern edge of the sinkhole has been damaged with the development of wide fissures on the wall. From all evidences collected, it appears, that the sinkhole at Runjh has followed the same pattern, in its formation, as reported by Prince for sinkholes in general, i.

It belongs to the category of catastrophic sinkholes. Subsidence usually occurs as a slow settling. Shallow, saucer-like depressions 30 m to several km wide are common on the high plains of western United States and they have been attributed to consolidation of sediments and the solution of salt and gypsum Schultz and Cleaves, Subsidence may be rapid and catastrophic resulting in the formation of sinkholes particularly in karst regions.

Such catastrophic sinkholes are formed due to groundwater withdrawal from the unconsolidated debris above carbonate bedrock to a level below the bedrock surface Foose, The subsidence in the Hershey valley of Pennsylvania United States , and the Far West Rand in South Africa are the two outstanding examples of catastrophic sinkhole development.

The sinkholes in both the localities are situated in carbonate country and the main cause of their development was due to excessive lowering of the groundwater table by pumping at nearby mining operations. However, the sinkhole at Runjh is located in volcanic rocks. It is situated in a rugged terrain with a strong relief, where the tendency for rainwater is to gain rapid runoff into the valley stream and for the rock debris to slide downhill along a freeside due to gravity.

Further, in the Himalayas karst topography is almost nonexistent and there are no other reported sinkholes from the carbonate or non-carbonate country and even the underground channels which are normally associated with the carbonate country are not widespread. Many pressure tunnels driven through the carbonate rocks of the Shall Formation, about 50 km south of Runjh, in connection with a local hydro-electric project, have not encountered any caverns of significance.

In the area around Runjh, there was no operation involving the lowering of ground- water table by pumping. The area had not suffered any draught during the period preceeding the subsidence. No change in the rate of flow of spring water in the surround- ing villages was reported. Thus the subsidence at Runjh is a unique phenomenon and it has to be attributed to other causes. In determining the causes of subsidence at Runjh the following geological, geohydro- logical and other background aspects have been taken into consideration: 1 Subsidence is located in a volcanic terrain which is tectonically a part of a subnappe.

As earlier discussed, the volcanic rocks, occurring as a subnappe, are part of ancient lava flows possibly Precambrian and as such the possibility of collapse that is prevalent in regions of active volcanoes is eliminated. Thus, the volcanic rocks though affected by the subsidence are not directly related to it.

The fact that the subsidence occurred during a period when the precipitation was at its minimum suggests that the monsoon rains have not triggered the subsidence. The present phenomenon, therefore, is due to other cumulative factors spread over a long period. The important preludes to a cylindrical subsidence are the creation of void at depth and loss of support. Void can form only if the material underground is removed without replacement.

Among the litho-units encountered in this area the sedimentaries of the Shali Formation are susceptible to the solvent action of water with rock salt being the most soluble. The associated carbonate rocks also fall within the category of soluble rocks. However, the general absence of sinkholes in large tracts of carbonate rocks in the Himalayas and its present occurrence in a known salt-bearing region of the Simla Himalaya directly connects the cause of subsidence with the soluble property of the rock salt.

As a proof for the solvent action of water over the salt there are saline springs in the downhill sector of Runjh along the Megal stream. It is equally significant to note that the occurrence of saline springs along the salt belt is limited and so also of the sinkhole, which points to the fact that the salt is not everywhere accessible to groundwater.

This is also proved by the observation in the shallow underground salt mine at Drang, 10 km north of Runjh, where the salt is absolutely dry. This is mainly due to the capping of clay or shale over the salt bed which makes the latter impervious to subsurface water. In the subsidence at Runjh the subsurface water appears to have played a major role. The presence of springs, which are both sweet and saline, in this area is the only pointer regarding the movement of underground water.

The sweet-water springs dot the volcanic terrain in large numbers, particularly in the area below the level of the situation of the Runjh village.

These springs also seem to be confined to the zone that occurs above the tectonic trace of the Mandi thrust separating the volcanics from the Shali sedimentaries. However, there are also sweet-water springs below the trace of the thrust which are mainly of contact type. The springs serve as the main source of potable water to the inhabitants. There are several saline springs in the downhill sector of Runjh particularly along the course of the Megal stream. These springs are everywhere located below the trace of the Mandi thrust.

It provides a thorough and practical overview of subsidence processes, effects, detection, and remediation. The book is remarkably compact …. The presentation is seamless and well organized …. Classifications are meaningful and easily applied …. We recommend this book enthusiastically to anyone involved in the engineering aspects of karst ….

In presentation and utility it is in a class by itself. Palmer and Margaret V. Photographs are of high quality, and related directly to the text. This is a book that should find a place on the bookshelves of all geotechnical practices, either to act as a warning or as a reference should karst problems be encountered. Pascall, Geotechnique, Vol. To me this seems to be a useful, user-friendly and well-written reference text that carries significant interest for lay readers ….

Skip to main content Skip to table of contents. Advertisement Hide. This service is more advanced with JavaScript available. Authors view affiliations Tony Waltham Fred G.

Bell Martin G. Front Matter Pages i-xxxi. Rocks, dissolution and karst. Pages Sinkhole classification and nomenclature. Rock failure in collapse and caprock sinkholes. Soil failure in subsidence sinkholes.