Dilatometer Tests in Sensitive Champlain Sea Clay: Stress History and Shear Strength
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Dilatometer Tests in Sensitive Champlain Sea Clay: Stress History and Shear Strength Alan J. Lutenegger University of Massachusetts, Amherst, Ma. USA 01375: [email protected] Keywords: Dilatometer, clay, field tests, in situ, shear strength, stress history, sensitive ABSTRACT: Dilatometer tests were conducted at nine sites in northern New York and southern Ontario in Champlain Sea clay with sensitivity ranging from about 10 to 500. The results are compared with laboratory one-dimensional consolidation tests on undisturbed samples performed to evaluate the stress history (OCR) and overconsolidation difference (OCD = σ’p – σ’vo) and field vane tests performed to evaluate the undrained shear strength. Results from the sites are shown collectively to develop specific correlations for these deposits and are compared with other previously reported results in sensitive clays and with reported correlations between DMT results and reference stress history and shear strength results. The results show strong trends with several DMT pressure readings and provide the possibility of obtaining redundant estimates of stress history. Undrained shear strength from field vane tests also show good comparison with DMT results. 1 INTRODUCTION The purpose of the work described herein was to The Marchetti Flat Dilatometer (DMT) has gained determine the degree to which the DMT could be popularity within the geotechnical profession for in successfully used in Champlain clay deposits to situ evaluation of geotechnical parameters of soils. provide meaningful results of basic soil engineering This may be partly in view of the fact that the test parameters of interest to engineers, i.e., stress history equipment has proven to be rugged and easy to and undrained shear strength. Field tests were operate and the test may be conducted in a wide conducted at five test sites in northern New York range of materials; from very soft clays and waste along the St. Lawrence River and at four sites in materials to dense sands. However, this may also be southern Ontario. Samples were obtained at each of attributed to the surprisingly good accuracy with the New York sites to provide a laboratory data base which the test is capable of predicting certain for comparing field test results. Results from the pertinent soil parameters and more importantly, field sites investigated in Canada were compared with performance of full-scale structures. field and laboratory data available in the literature Like all in situ tests, the DMT may have for each of the sites. Previous DMT tests conducted limitations to its breadth of applicability. In this in Leda clay were presented by Tanaka & Bauer paper the applicability of the test in sensitive marine (1998) who investigated the upper stiff fissured clay clays in North America was evaluated. These soils at a single site in Ontario. may present special problems for any in situ test The results of the work indicate that the current because of the high sensitivity which they may empirical correlations used for data reduction do not exhibit and the structural dependence of measured give satisfactory predictions of stress history. engineering parameters. Unlike unstructured or Suggestions are made for alternative techniques to rather soils which possess massive structure and evaluate data. therefore lend themselves to normalized behavior, sensitive clays may undergo dramatic changes in structure during testing, which in turn leads to 2 TEST SITES unique behavior. These behavioral problems are well documented for the sensitive Champlain clays of The invasion of the Late-Pleistocene Champlain Sea southern Canada, and need not be elaborated on into the St. Lawrence River Valley left deposits of here. clay along both sides of the river and accounted for a large majority of the surficial materials in the St. about 2 m of loose to medium dense mixed silty Lawrence lowlands of northern New York. In New sand which overlies the marine clay. The clay York, four of the sites investigated are located in the extends to a depth of about 12 m and is underlain by general area around the village of Massena, NY coarse glacial sediments. It appears that because of while the fifth is located near the village of the close proximity of the Racquette River, and the Ogdensburg, NY. The sites in Canada are located in rapid change in slope, the groundwater at the site has the St. Lawrence lowlands from Gloucester, near been depressed in the past throughout the thickness Ottawa, Ontario to Louiseville in Quebec. These of the marine clay. During investigations, the sites have been extensively investigated previously groundwater level was about 3 m below the ground by other researchers in Canada. Only a brief surface. In general, the entire profile of marine clay description of each of the test sites and geotechnical is overconsolidated as indicated by oedometer tests. conditions will be presented. 2.1 Northern New York Sites 2.1.3 St. Lawrence Seaway (SLS) The sites in northern New York are considered This site is located about 1 km north of the Snell typical of Champlain clay in the region and show the Lock on the St. Lawrence Seaway. The upper 1.5 m diversity of geotechnical properties of the materials. contains highly stratified clay and sand seams Four of the five New York sites have a weathered overlying the marine clay. The clays at this site only surficial crust which is overconsolidated, extend down to a depth of about 10 m and are again presumably as a result of desiccation or freeze-thaw. underlain by gravelly glacial materials. A thin sand Conventional test borings were conducted at each of seam containing abundant shells is present at about 5 the sites and traditional soil parameters were m throughout the site. The groundwater level determined from undisturbed (76 mm dia. piston) encountered during field investigations was and disturbed samples. consistently at a depth of 0.4 m and appears to represent static conditions. 2.1.1 Massena High School (MHS) 2.1.4 Industrial Development Agency (IDA) The site is located along N.Y. State Route 37, directly across from the Massena High School. Test This site, located about 2 km south of the Racquette borings indicate about 1 m of very stiff brown silty River, directly south of Massena appears to be more clay, 3 m of stiff gray-brown mottled silty clay characteristic of the classical Champlain clay overlying about 9 m of soft gray and bluish-gray deposits described in Ontario and Quebec. The site clay. These cohesive materials overlie glacial is located in a broad lowland position between materials, primarily sand and gravelly till. An glacial uplands and is capped by 1.5 m of loose fine overconsolidated crust extends to a depth of about 5 sand. The marine clay has been investigated by in m. While the ground water level at the time of field situ tests down to a depth of about 25 m. The investigations varied from 1 to 2 m below the groundwater throughout the year is located about 0.3 surface, larger fluctuations have apparently occurred m above the ground surface and only fluctuates to a during the past. The undrained shear strength, depth of about 0.3 m below the surface. This site measured from Nilcon field vane generally show a generally shows the highest sensitivities and lowest decrease in undrained strength with depth. undrained strengths measured by the field vane than any of the five N.Y. sites. The characteristics at this 2.1.2 Racquette River Cemetery (RRC) site appear to be most similar to the sensitive Leda clays in Canada. This site is located about 2 km south of the Massena airport adjacent to the Racquette River. Numerous 2.1.5 Ogdensburg (OGB) small landslides have occurred near the site in the past. Test borings and DMT tests were conducted in This site is located adjacent to Route 37 just north of a stable upland landscape position, however the site the village of Ogdensburg. The site is adjacent to a drops off rapidly about 15 m toward the river which railroad overpass which has experienced is located about 80 m away. The site is capped by considerable movement in the past 20 years. The soils consist of very stiff brown and gray brown silty small test embankment. Details on the site and the clays which extend to a depth of about 3 m. These soil properties were presented by Kabbaj et al. 1988. materials are underlain by gray and blue gray silty clays to a depth of 19 m. 2.2.4 Louiseville, Quebec 2.2 Canada Sites The Louiseville site is located about 30 km east of Montreal. According to Leroueil et al. (1983) the The sites in Canada were selected as typical of site is typical of the clay deposits in the basin of the Champlain Sea deposits in Ontario and Quebec. Champlain sea in this area. Site characteristics have Each of the sites has previously been used and been presented by Hamouche et al. (1995). DMT evaluated extensively in terms of the geotechnical investigations at the site extended to a depth of 14 characteristics. Published data from each of the sites m. were used in evaluating the results of DMT tests. DMT tests were performed at each of the sites by the author using the same equipment used at each of the 3 STRESS HISTORY FROM DMT New York sites. Engineers are interested in evaluating the stress 2.2.1 Gloucester, Ontario history of soils at a site for a variety of reasons; typically for estimating consolidation settlements but The location for tests near Gloucester, Ontario was often for evaluating other soil parameters from stress near the site of the NRC test embankment.