The site is underlain by a deep soft Connecticut Valley varved clay (CVVC) deposit extending approximately 120 ft (37 m). The CVVC deposit is comprised of alternating silt and clay layers with an occasional very fine sand layer. The deposition of these layers is directly related to glacier retreat and the passing of the annual seasons, during the last ice age. The total thickness of each varve is typically on the order of 0.1–0.25 in (2–8 mm) and the varves generally lie in a horizontal position.
An overconsolidated CVVC crust exists at the test site extending approximately16 ft (4 m) below grade (See Figure 1 below). Within the crust, the overconsolidation ratio ranges between 4 and 10. The CVVC is overlain by about 5 ft (1.5 m) of loose fill, composed of a mixed fine grain and granular soil.
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The groundwater table (GWT) at the site fluctuates within a depth of 10 ft (3m) from grade with an average of 5 ft (1.5m) below grade . The GWT was approximately 2 ft (0.6m) below grade during the load tests.
The undrained shear strength of the CVVC deposit, obtained from field vane tests, is approximately 300 kPa (43.5 psi) in the over-consolidated crust and about 35 kPa (5 psi) in the lower soft clay. The locations of the test shafts were sounded with a miniature cone penetration test prior to shaft installation (see Fig. 2 below). Overlain on these data are CPT data previously recorded at the NGES Amherst site using a standard (10 cm2) cone penetrometer. This data confirm that the soil conditions at the drilled shaft locations are uniform, and that the test location is representative of the remainder of the NGES site.
