The dilatancy and contraction phenomena exert a significant influence on the strength properties of soils. As Bishop has noted [3], the effect of shear stresses on saturated loose sands may cause their catastrophic breakup in the absence of drainage. Corresponding phenomena are not well understood for clayey soils. To fill this gap to some degree, we conducted research on clayey soils under conditions whereby lateral expansion (compression) and subsequent shear (torsion) were impossible under compaction on M-5 devices [4]. The author, in conjunction with Arshakyan [5], tested disturbed samples of a clayey toam (Ps = 2640 kg/m3), W L = 0.299, Wp = 0.217, and Ip = 0.082) sampled from a construction quarry for the Egvardsk Reservoir (Republic of Armenia) to determine the dilatancy and contraction of clayey soils as a function of their initial state: density, moisture content, consistency, and structural strength. We tested four series of twin specimens 101 mm in diameter and 24-ram high with an initial moisture content W 0 = 0.263. Of the 17 specimens in each of the four series, 13 were precompacted under az.O = 0.05, 0.15, 0.30, and 0.60 MPa to complete stabilization of deformation, and then unloaded to crz, f = 0.05 MPa and tested in torsion. Four control specimens were used to determine the physical characteristics corresponding to the start of their twisting (Table 1). The specimens were twisted by a torsional moment Mr0 r applied in one-minute steps of 200 N.cm each. The test results corresponding to the next-to-last step of the application of twisting moments are presented in Table 2, from which it follows that the specimens of fluid and highly plastic consistency, which were precompacted under Oz,O = 0.05 and 0.15 MPa experienced additional compaction - contraction - while those of highly plastic and semi-hard consistency compacted under ~ = 0.4 and 0.6 MPa experienced dilatancy under torsion. Moreover, we tested 16 specimens of a disturbed clayey loam (Os = 2640 kg/m 3, o0 = 1940 kg/m 3, W 0 = 0.215, W L = 0.350, Wp = 0.225, and [p --- 0.125) of hard consistency (I L = -0.08) [4]. All soil specimens were precompacted for 100 days at ~ = 0.8 MPa, and eight of the specimens were then unloaded to 0.2 MPa, four to 0.4 MPa, and four to 0.6 MPa. The specimens were tested at two torsional rates V = 2 and 0.2 mm/min, which were maintained approximately constant throughout the entire experiment, with the exception of the initial stages; this was associated with the design of the device [6]. The tests were repeated twice at O-z, f = 0.4 and 0.6 MPa, and four times at ~z.f = 0.2 MPa. Indicators of the physical properties of the specimens prior to their twisting are presented in Table 3. Test charts of the twin specimens in the three soil states are presented in Fig. ta, b, and c.
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Jan 1, 2008
Bin Xin + 3
Open Access