Page 293 - Analysis and Design of Energy Geostructures

268 Analysis and Design of Energy Geostructures

vertical distance between the highest and lowest peaks of the structure
asperities over a fixed length, R max [m], the soil mean grain size, D 50 [m].
Depending on the interface materials and conditions, it is possible to
identify a critical value of roughness, R cr [ ], such that if R n , R cr the
interface is considered smooth, and if R n . R cr the interface is considered
rough.
r. Smooth interfaces show a higher shear resistance compared to rough
interfaces:
i. True
ii. False
s. Smooth interfaces with a soil show a higher shear resistance compared to
that of the soil:
i. True
ii. False
t. The main factors that affect the behaviour of soil structure interfaces are
(i) the structure roughness, (ii) the normal stress acting on the structure,
(iii) the soil density, (iv) particle angularity and (v) the soil grain size
distribution.
u. Under constant normal load conditions, the normal effective stress
applied to the interface remains constant upon loading, so that
0
σ n 5 const. Under constant normal stiffness conditions, the normal
effective stress applied to the interface varies with loading as
0
0
0
0
0
0
σ n 5 σ n0 1 Δσ n 5 σ n0 2 K int Δδ n , where σ n0 and Δσ n are the initial
and increment of the normal effective stress [Pa], respectively; K int is the
far-field normal stiffness [Pa/m]; and Δδ n is the variation of displace-
ment normal to the interface [m]. Constant normal stiffness conditions
are representative of the state of restraint characterising interfaces
between geostructures and the surrounding ground.
v. Depending on the structure roughness, three failure modes can charac-
terise soil structure interfaces: mode 1 characterises rough interface
surfaces and involves shear failure in the soil; mode 2 characterises
smooth interfaces surfaces and involves full sliding at the interface;
mode 3 involves shear failure and sliding displacement occurring
simultaneously.
w. The shear strength of interfaces between concrete and coarse-grained
soils is highly influenced by temperature variations:
i. True
ii. False