The Behavior of a Coarse Granular Material under Complex Stress Conditions

Yuefeng Zhou,Jiajun Pan,Zhanlin Cheng,Yongzhen Zuo,Shazim A Memon

doi:10.1155/2021/8832252

Abstract

In recent years, dozens of high rockfill dams are under construction or planning for hydropower exploration in western China. In dam construction, the mechanical behavior of coarse granular material greatly affects the compatible deformation of dam body. In this article, an indirect in situ density prediction approach for coarse granular material is firstly proposed to solve the technical obstacle on prediction of the material density in thick overburden layer of a dam site in southwest China. Adopting a self-developed large-scale true triaxial apparatus with a special friction-reduction technique, four series of true triaxial tests were then performed to investigate the behavior of a coarse granular material with a maximum particle diameter of 60 mm. Test results show that the peak strength of the material increases together with the increasing confining stress and the increasing intermediate principal stress ratio. The material dilatancy is restricted by both the confining stress and the intermediate principal stress ratio. With the increase in intermediate principal stress ratio, the internal friction angle increases firstly and then decreases slightly, but the slope of stress path reduces gradually. The tested peak states were compared with several well-known strength criteria under the framework of generalized stress, showing a good fitness with the Lade–Duncan criterion and underestimation by the Mohr–Coulomb criterion and the Matsuoka–Nakai criterion. The strength envelope in the π plane shrinks with the increasing confining stress.

Highlights

An associated issue in the design of rockfill dam is the compatible deformation of dam body, which should be partially considered for coarse granular material used in construction
The riverbed of rockfill dam is always covered by thick overburden layer from dozens to hundreds of meters, which is commonly composed of coarse granular material, such as sandy gravel and pebble [2]
Mountainous regions with complicated geological conditions lead to complex stress conditions that need to be considered in engineering design. e behavior of coarse granular material under complex stress conditions is vital towards developing and economizing the engineering design method

Summary

Materials and Methods

E true triaxial apparatus adopts tall quadrilateral specimen with 600 mm height and 300 mm × 300 mm equal width in cross section (Figure 5). In the direction of minor principal stress, cell water pressure is applied on the specimen as flexible loading. In the direction of intermediate principal stress, lateral load is applied on the specimen via a pair of friction-reduction plates. Of four series of true triaxial tests (25 tests, as shown in Table 2) were performed to investigate the influences of intermediate principal stresses and isotropic consolidation pressure. The volumetric strain was calculated using the volume of discharged water from the specimen utilizing the inner volumetric deformation measuring system

Results and Analyses

Discussion

Conclusions