Local Excavation Research Articles

Is BMU-coupling a strain-regulated phenomenon? A finite element analysis.

Histologically, two types of bone reconstruction are distinguished: modeling and remodeling. Modeling changes the amount of bone and determines its geometrical form in relation to the prevailing mechanical loads and their resulting deformation (strain). Remodeling renews existing bone in a sequence of resorption and formation. However, in both processes the cells responsible for resorption and formation are the same: osteoclasts and osteoblasts. We studied if there is a relation between the activity of these cells and the deformation of the local bone tissue during remodeling. Two finite element models were built on a microscopic, supracellular level: (1) a secondary osteon in cortical bone and (2) a Howship's lacuna in a trabecula. Both models were loaded in the "natural," that is, longitudinal direction. Equivalent strains were determined as a measure for the deformation of the bone tissue. In the first model, the strain field around the osteon showed a region of decreased deformation in front of the tunnel, just where osteoclasts excavate cortical bone tissue. Behind the cutting cone, elevated strain levels appear in the tunnel wall at locations where osteoblasts are active. The second model showed that a local excavation of a loaded trabecula leads to higher strains at the bottom of the lacuna, where resorption is stopped and osteoblasts are recruited to refill the gap. However, in the direction of loading reduced strain levels appear, just where resorption continues to proceed along the trabecular surface. We conclude that at the tissue level, strain distributions occur during the remodeling process that show a relationship to the activity of osteoblasts and osteoclasts. This suggests that BMU coupling, that is, the subsequent activation of osteoclasts and osteoblasts during remodeling, is a strain-regulated phenomenon.

A study of clay tobacco pipes in Tunis. Were they traded to Gozo (Malta)?

A significant number of clay tobacco pipes in the style of the Ottoman ‘chibouk’ can be found in museums and private collections on the islands of Malta and Gozo. Indeed the smoking of these pipes remains a folk memory with the majority of senior citizens. It became obvious that very few of these artefacts were made locally and that the Maltese, being at the geographical centre of Mediterranean culture, might have received their imports from anywhere.In 19th-century Tunisia (Malta’s nearest North African neighbour) three-quarters of the European population were Maltese migrants. Therefore, this study set out to discover whether Tunisia was a source of supply.In Tunis it became obvious that although clay tobacco pipes had turned up in local excavations, little attention had been paid to them and a fuller examination was welcomed. A by-product of this examination was to establish a locally made Tunis pipe, although little evidence was found for trade to Malta in that particular commodity.

The "Early Vaults" of Saint-Etienne at Beauvais

The church of Saint-Etienne (Saint-Vaast) in Beauvais was much discussed in the early literature on medieval architecture, particularly in regard to the vaults over the initial bays of the nave aisles. The vaults have long been considered among the earliest rib vaults in northern France, although their exact date had never been determined. The challenge to date these vaults precisely became critical in the late 1950s when local excavations under the present Late Gothic choir uncovered evidence that the original choir may have been rib-vaulted as well. This paper analyzes these unpublished excavations and their implications for the extant vaults of the nave aisles; it also provides a credible dating for the choir and these vaults. In the absence of constructional documents, the dating of Saint-Etienne must depend on stylistic comparisons correlated with the dates of major historical incidents in Beauvais that would have influenced the construction of the church. All of these factors taken together seem to indicate strongly the existence of a fully rib-vaulted choir at Saint-Etienne and of a unified campaign of construction encompassing this choir, the transept, and the initial bays of the nave aisles. Most significantly, a date as early as the 1070s is suggested for the vaults of the choir, thus making them the earliest known rib vaults in medieval architecture and forcing a re-examination of the structural aspect of medieval style in the 11th century.

A mechanism for the production of lunar crater rays

Observations of high resolution photographs of part of one of the prominent rays of the lunar crater Copernicus show that there is a concentration of small bright rayed and haloed craters within the ray. These craters contribute to the overall ray brightness; they have been measured and their surface distribution has been mapped. Sixty-two percent of the bright craters can be identified from study of high resolution photographs as concentric impact craters. These craters contain in their ejecta blankets, rocks from the lunar substrate that are brighter than the adjacent mare surface. It is concluded that the brightness of the large ray from the crater Copernicus is due to the composite effect of many small concentric impact craters with rocky ejecta blankets. If this is the dominant mechanism for the production of other rays from Copernicus and other large lunar craters, then rays may not contain significant amounts of ejecta from the central crater or from large secondary craters. They may in fact only reflect local excavation of mare substrate material by myriads of small secondary or tertiary impact craters.

Determining the productivity of excavating rocks with water jets

1. Local caving of a rock or soil when acted on by a water jet begins at the moment when the ratio of the head to the jet diameter at its zone of impact on the face reaches a certain value which depends on the characteristics of the material being worked, i.e., its porosity (permeability), particle diameter, and tensile strength (Formula (2)). 2. The productivity of local washing excavation depends on the hydraulic characteristics of the water jet (power and diameter) and the water-strength characteristics of the rock being worked (the permeability in the direction of the jet and the tensile strength). 3. The productivity of local caving by various water jets (m3/h) is proportional to the jet power, to the square root of the permeability, and to the size of the particles broken away by the jet, and inversely proportional to the jet diameter at its zone of incidence and the tensile strength of the rock (formula (14)). 4. The rate of undercutting of the face (the undercut area per unit time) is independent of the jet diameter. It is proportional to the dynamic jet head (at the point of impact) raised to the power 3/2, to the square root of the permeability of the rock (in the direction of action of the jet), and to the diameter of the particles broken off, and is inversely proportional to the tensile strength of the worked material (formula (15)). In addition, it depends on correct management of the jet.

REBOUND IN THE BEARPAW SHALE, WESTERN CANADA

The Bearpaw formation (Upper Cretaceous) which occurs over large areas of Western Canada presents problems in connection with engineering works. These clay shales were consolidated under high pressures, but the load has been removed. A rebound occurred which is a maximum at the shale surface and decreases with depth. The rebound is made up of elastic rebound which occurred immediately upon removal of load and a “time rebound” which is still occurring slowly and involves a softening of the material. The characteristics of the shale and the depth of the rebound zone are being studied by soil-mechanics methods. Routine tests were made for water content, density, and Atterberg limits; water content is the best indicator of consistency. The results of laboratory strength tests do not correlate well with observed field behavior, and this has led to the conclusion that observations of existing slopes will supply more reliable strength data for long-time stability studies. Field investigations involve piezometric measurements and observations of slides, particularly creep. The softened surface zone is unstable, and slides have occurred on flat slopes. Slickensides are common in this zone, but their intensity appears to decrease with depth. The underlying shale is firm and stable. Rebound is also caused by local excavations for structures. Observations are being taken on light concrete structures to correlate predictions from laboratory swelling tests with observed heave.

Local Archæological Studies in Nottingham

PUBLICATION of the first annual report of the Excavation Section of the Thoroton Society of Nottinghamshire falls opportunely at a moment when attention has been directed in Parliament to the opportunity open to local archaeological and scientific societies to educate their neighbours, the local authority and the local public generally, as to the desirability of preserving for posterity buildings and erections of historical or aesthetic interest and places of natural beauty (see NATURE, Feb. 27, p. 345). The Excavation Section of the Thoroton Society has been formed as an outcome of the enthusiasm of a small number of students of the past history of the city of Nottingham, but more especially through the efforts of Mr. G. F. Campion, who was anxious that the work of local excavation carried out by himself and his father before him over a number of years should be placed on a permanent footing. Very wisely it was decided not to form a new society for this purpose, but to join forces with the Thoroton Society, the long-established centre of archaeological and antiquarian interest in the county. Thus the activities of the newly established section will be directed not only to continuing the work of excavation, but also to the expert examination and record of the numerous evidences of the city's past cultural history which are being brought to light with increasing frequency in the building operations in progress in connexion with the improvement and enlargement of business and other premises in Nottingham. It should at least be able to ensure that nothing worthy of note is overlooked a matter of much importance in an area like Nottingham which is honeycombed with underground caves. The record of the first year's operations covers not only the excavations in Nottingham's Norman and Plantagenet castle, and a Roman fortress, but also the supervision of excavations for building operations on eight sites, which produced some interesting samples of medieval pottery, including a fabric unknown from any other area and thought to be an exclusive product of Nottingham.