Shear Strength and Compression Coefficient for Conditioned Sand Subjected to Earth Chamber Stress Levels

Abstract

Ground conditioning agents are often needed when performing earth pressure balance shield tunneling in sand soils due to its high internal friction, low plastic ductility, and low compressibility. In this work, vane shear and compression tests for standard sand were performed using a homemade test device, and three types of conditioning agents composed of foam, bentonite slurry, and polymer were used in the tests. The effects of the agents on shear strength and compressibility of the conditioned soils were investigated under a typical earth chamber stress level as high as 2 bar. The measured results show that foam does better in reducing shear strength and improving the compressibility of the conditioned soils than bentonite slurry and polymer. Significant increases in the compressibility of foam-conditioned soils can be achieved using foam, and the shear strength of the conditioned sand can be decreased by more than 30% with an initial injection ratio of 40% foam. The bentonite- and polymer-conditioned sands have similar compressibility. The HPMC (hydroxypropyl methylcellulose) polymer does better in decreasing the shear strength of the conditioned soils than other liquid soil conditioners. The influences of the device shear rate on the shear strength of the conditioned soils are also presented.

Compression Characteristics and Microscopic Mechanism of Coastal Soil Modified with Cement and Fly Ash

“…Compared with the prevalence of studies on unconstrained compressive strength and direct shear strength, there have been fewer studies on the consolidation characteristics of cement soil, especially modified cement soil. However, it is worth noting that due to the high compressibility of coastal soft soil, the issue of excessive deformation should not be underestimated [20,21,22,23,24]. Therefore, it is of great significance to further study the consolidation characteristics of coastal soft soil and modified coastal cement soil.…”

Experimental Study on Mechanical Behavior of Lean Cemented Sand and Gravel Material in Unloading and Reloading Paths

“…Advances in Materials Science and Engineering LCSG [8,9]. e specific gravity of the medium-sized sand was 2.62 with a fineness modulus of 2.48 and a bulk density of 1450 kg/m 3 .…”

“…e Portland cement was obtained from Anhui Digang Hailuo Cement Co., Ltd. e fineness of the cement was 2.26%; the contents of SO 3 and MgO in the cement, which are harmful mineral contaminants, were 2.56% and 1.78%, respectively, and did not exceed the prescribed content levels. e mix proportions of each group of LCSG specimens are given in Table 1 [8,9]. e mix materials are shown in Figure 1.…”

“…Each specimen was 700 mm high and had a diameter of 300 mm, as shown in Figure 1. e material composition, curing, and preparation methods of the specimens were the same as those of the conventional triaxial test specimens prepared using the LCSG material [8,9]. e LCSG specimens for the unloading and reloading triaxial tests were prepared, and the tests were conducted according to the relevant regulations stated in SL237-1999 [23].…”

“…rough triaxial shear tests, Younes et al analyzed the characteristics of their stress-strain curve, including the strength, initial elastic modulus, and dilatancy by changing the confining pressure and cementing agent content [6][7][8][9][10]. Although there have been some reports of static triaxial shear tests on LCSG materials, most of these tests were carried out under complete loading conditions.…”