Underground Infrastructure - February 2023 - 41

CIGMAT Report
FIGURE 15: SP-CIGMAT mounted on a soil sampling rig
SP-Na. Th e air void ratio showed the second highest percentage
diff erence in the properties investigated between the FC
and SP compacted soils.
New Surface Penetrometer (SP-CIGMAT)
In this study, CIGMAT Down-Hole Penetrometer (DHPCIGMAT)
was modifi ed to CIGMAT Surface Penetrometer
(SP-CIGMAT) and used for measuring the strength and
modulus of compacted soils, as shown in FIGURE 15. Tests
were performed on compacted soils varying from soſt to very
stiff clay, silty soils and sandy soils (CL, CH and SC).
A total of 19 fi eld tests were performed with a Shelby
Tube sampling the soil for the unconfi ned compression test.
SP-CIGMAT fi eld tests were performed to investigate
the relationship between penetrometer defl ection (δmax
compressive strength (σu
) and
), modulus (E) and CBR value of
compacted soil layers, which were 8- and 12-inch depths. In
these fi eld tests CH, CL and SC were the major soils.
SP-CIGMAT was mounted to the sampling rigs, using
3-inch Shelby Tubes (Area ratio < 10%) (FIGURE 5). Th e
location of tests was close enough to have similar properties
with the samples, but far enough away not to be aff ected by
opened hole.
Th e bearing capacity theory with non-linear relationship
between soſt rock/stiff clay unconfi ned compressive strength
(σu
, psi) and ultimate strength (qult
qult = αq (σu
)m
,
where, magnitudes of parameters m and αq
, psi) was used:
(13)
depend on the type
of soſt rock/stiff clay and unconfi ned compressive strength
(σu
).
Th e relationship for penetrometer defl ections (δmax
the shear strength (Su
) is as follows:
Su = 56.4 × δmax1.78 N = 19, R2 = 0.72.
(14)
Present design approaches of subgrades for pavement design
use California Bearing Capacity Ratio (CBR) values to
determine the resilient modulus. Hence, it was of interest to
ABOUT THE AUTHOR: Dr. C. Vipulanandan (Vipu) is the director
of the Center for Innovative Grouting Materials and Technology
(CIGMAT) and professor of civil engineering at the University of Houston.
He is also the inventor of Smart Cement.
UndergroundInfrastructure.com | FEBRUARY 2023 41
, psi = 2Su)). Th is relationship can be used to relate the
undrained shear strength of soil (Su
fl ection (δmax
) to the penetrometer de)
and
FIGURE 16: Relationship between SP-CIGMAT deflections (δmax
).
) and
shear strength (Su
FIGURE 17: Relationship between SP-CIGMAT deflection and CBR value.
determine the correlation between CBR and SP-CIGMAT
penetrometer defl ection.
Compacted fi eld samples were collected in CBR molds and
seven tests were performed in the laboratory. Th e relationship
for penetrometer defl ections (δmax
CBR = 33 δmax
Conclusions
Based on the comprehensive fi eld and laboratory compaction
studies, the following conclusions are advanced:
1. Field compacted (FC) dry density-moisture content
relationship was diff erent from the laboratory compaction
test results. Hence, the laboratory relationships cannot
represent the fi eld compacted relationship.
2. Void ratio (e) showed the highest or second-highest
percentage diff erence in the FC and SP compacted soils.
3. Air void ratio (Na
percentage diff erence in the FC and SP compacted soils.
4. SP-CIGMAT defl ection correlated well with the
undrained shear strength of fi eld compacted soils. Th e
relationship was nonlinear. UI
) showed the highest or second-highest
,
N = 7, R2
) and CBR was as follows:
of 0.78.
(15)
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