| dc.description.abstract | This research study set out to evaluate the
pe rrorrnanoe o f some six road test sections locat.ed
on in-service bitumen standard roads in and around
Nairobi, Kenya. The selected road test sections
were:-
(L) Thika road test. site ES1, w i t.h a s':;.rface
dressing, 305·rom s t ab Ll Lzed mu rram base
and 457 mm murram sub-base;
(ii) Langata road test site ~S2, with a surface
dressing, 229 ~~ crushed stone base and
229 n~ murram sub-base;
Mombasa road test site ES
asphaltic concrete surfacing, 130 mm
crusher-run base, 200 mm crushed stone
sub-base and 300 mm improved subgrade;
(L v) 1-1ombasaroad test site ES4 I with a 100 mm
asphaltic concrete surfacing, 165 mm
crusher-run base, 165 nun crusher-run sub-
/ ~ 150 r.~improved subgrade;
(v) Mombasa road test site.ESS, with a lQO mm
packed stone base, 200 rom soft stone subbase
and 300 mm improved subgrade;
(vi) Mombasa road test site BSf,; •.,.;•.th a H)O r.'.;".
asph aLtic concrete surf ac ing, 200 nun hand
packed stone base, 200 mm soft stone subbase
and 300 mm improved subgrade.
The study also included a laboratory investigation
of the strength characteristics of some of the
subgrade soils used in the construction of the roads
covered in this study.
Also included is an analytical study of the
influence of flexible pavement geometry and material
characteristics on various pavement distress parameters,
using variational techniques and a digital
computer. Finally, a basis upon which flexible pavement
design could be developed in Kenya was also
considered.
Flexible pavement performance evaluation was done
using data collected periodically over a period of
16 months from the following field studies:-
(a) pavement rebound deflection measurements
using Benkelman deflection beams and 3175
kg dual wheel loads,
(b) pavement deflection profile measurements
using the same apparatus as in (a) above,
(c) pavement settlement measurements using a
Wild Ni 3 precise level,
(d) cracking measurements and
(e) rutting measurements
The subgrade soil strength characteristics were
investigated using California Bearing Ratio (C.B.R)
and controlled strain triaxial compression tests.
The analytical study of the influence of
pavement geometry and material characteristics on
pavement deflections, stresses and strains in various
layers was carried out using the following computer
programs, based on the finite-element technique:-
(a) PAVE - a program based on a triangular
element mesh formulation,
(b) PAST - a program based on isoparametric
element mesh formulations,
(c) ROAD - a triangular element program
capable of pavement fatigue
cracking simulation,
(d) UNIV - a triangular element program
capable of elastic modulus
variation as a function of stress.
The study found that considering the design
standards of the road test sections and the traffic
traversing them, the t'st sections were in general
performing satisfactorily. Pavement. age, traffic
and climate were found to be some of the major
factors affecting pavement performance. Evidence
was found to suggest that for cracked pavement
sections',.rebound deflections provided reliable
/
indications of pavement weakness. This relationship
was however not found to hold in the case of rutting.
The tangent moduli of the subgrade soils tested
were found to be a linear functio~ of confining
pressure. The soils were found to exhibit a peaked
CB~ - moist~re cc~tc~t relationship. =vi2enc~ ~~~
found to suggest that the resilience (deformation
moduli) characteristics of the subgrade soils tested
i~lluenced the performance of the pavemcn~s fou~ded
on them, irrespective of the magnitudes of CBRs of
thesesoi.ls, thus rendering CBR alone inadequate as
a measure of subgrade soil strength.
The use of·the finite-element technique in
predictive analysis in the field of flexible pavement
design and performance monitoring relies heavily on
how accurately the behaviour-and strength parameters
of the pavement materials can be determined. The
technique as used in the analysis presented in this
thesis was found to habour great potential as a:l
analytical tool for pavement analysis . | en |
