This paper presents the results of a 3 year monitoring program of the volumetric water content in two clay deposits on Montréal Island. The water content was monitored by means of a neutron depth moisture probe, which was lowered down in a series of 3–6 m deep, permanently installed, aluminium access tubes. These tubes are located at various distances from deep-rooted trees on two experimental sites. On the first site, a two-storey reinforced concrete building, surrounded by four rows of 15–20 m high silver maples, has suffered a differential settlement of over 150 mm. On the second site, a three-storey apartment block, surrounded on two sides by a row of 5–10 m high maples, has suffered a differential settlement of about 50 mm. The paper analyses the volumetric water content variations and compares them with both the rainfall deficits calculated for the period of observation and the elevation profiles of the building foundations. In addition, a comparison is made between the observed damages and a classification proposed by the Building Research Establishment of England. Key words : volumetric water content, trees, settlement, distortions, clay deposits, seasonal variations, damages.
During the exceptionally dry summer of 1983, extensive settlement problems developed in lightweight buildings founded in the clay deposits of the Montréal area. In this paper a modified budget method that keeps a running balance of precipitation (P) and potential evapotranspiration (PET) is applied to the region of study to obtain the soil moisture depletion or rainfall deficit (RD) throughout the period 1930–1988. It is shown that extensive foundation problems have developed whenever the rainfall deficit has exceeded 170 mm of water. Key words: settlement problems, clay deposits, evapotranspiration methods, precipitation, rainfall deficit, dry weather.
In recent years radioisotopes have been increasingly used for determining site values of the density and the water content of soils. Since field measurements obtained by neutron moisture gauges are relative, these instruments must be calibrated. Calibration is usually carried out in the laboratory by plotting neutron counting rates versus known water content values of several soil media, homogeneous as well as heterogeneous. The accuracy of the factory calibration curve of a widely used, commercial neutron depth moisture gauge was evaluated both in the field and in the laboratory by comparing probe readings to measured volumetric water contents of several soil mixtures. The analyses of the laboratory results indicate that the factory linear calibration curve is satisfactory for volumetric water contents not exceeding 40%. However, for volumetric water contents in the range from 40 to 100%, the relationship between probe readings and volumetric water contents is nonlinear. This nonlinear curve was found to be quite different from that obtained in the field calibration campaign carried out in a deposit of sensitive Champlain clay having volumetric water contents which compare well with those of the laboratory-prepared clay mixtures.
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