1365
Influence of Mechanical Indices for Soil Basement on Strength of Road Structure
Influence des paramètres mécaniques de la couche de fondation sur la résistance d’une structure
de chaussée
Teltayev B.
JSC “Kazakhstan Highway Research Institute”, Almaty, Kazakhstan
ABSTRACT: It has been observed that at present insufficient attention has been paid to the consideration of moisture and mechanical
indices variety for soil basement while designing of highways. Peculiarities have been analyzed for moisture variety of soil basement
for the highway “Astana-Burabai”. Peculiarities for indices variety of stress-deformed condition of road structure with cement
concrete pavement have been calculated and determined.
RÉSUMÉ : Il a été observé que les variations de teneurs en eau et des paramètres mécaniques des couches de base sont généralement
insuffisamment prises en compte lorsqu’on dimensionne des chaussées. Des particularités ont été analysées pour différentes teneurs
en eau du sol de fondation de la route "Astana-Burabaï". Des variations des paramètres de comportement contraintes/déformations de
la couche de fondation ont été également prises en compte et analysées lors du dimensionnement de la chaussée en béton de cette
route.
KEYWORDS: highway, soil basement, cement concrete pavement, moisture, deformation, stress.
1. INTRODUCTION
Main elements for modern highways are pavement and soil
basement. They have been operated jointly in the highway.
Therefore while designing of highways calculation for
pavement and soil basement strength has been carried out
jointly (SN RK 2005).
As mechanical impact from car wheels, as well as
climatic factors (temperature, moisture and so on) has been
made over longevity and strength of road structures. Moisture of
soil basement can be one of the main climatic factors,
influencing greatly over highways with cement concrete
pavement.
The following assumptions have been made in
Kazakhstan present standard provisions for calculation of rigid
pavements for strength (SN RK 2005):
- maximum moisture of soil basement has been observed
in spring, when its complete thawing occurs, and the weakest
condition of road structure complies with that time moment;
- theoretically soil basement has constant moisture value
during overall service period for road structure (from 16 to 20
years for highways of I-III technical categories).
Fundamentals of present method of road structures for
strength (SN RK 2005) were established in 60s-70s of the last
century. At that time the above assumptions were accepted to
simplify calculations. At present there are high performance
computers and powerful software’s, which allow to carry out
very complicated calculations, considering seasonal moisture
varieties, therefore, deformation and strength characteristics of
soil basement.
2. HIGHWAY “ASTANA-BURABAI”
Express highway “Astana-Burabai” connects the capital of
Kazakhstan, Astana city, with resort zone Burabai, and is a part
of international automobile route “Atana-Kokshetau-
Petropavlovsk-border of Russian Federation”. Total length of
the road is 224 km. It has 6 lanes with the width of 3.75 m each.
Start (50 km) and final (47 km) road sections have cement
concrete pavement, road section in the middle of the road (127
km) is pavement from crushed stone mastic asphalt concrete.
Reconstruction of the road was fully completed in November
2009.
Pavement structure consists of: cement concrete, 25 cm;
crushed stone optimum mix, 25 cm; coarse-grained sand, 30 cm.
To investigate the peculiarities of temperature and
moisture variety temperature and moisture sensors were placed
into soil basement of that road section in October 2010. Depth
for placement of those sensors from the surface of cement
concrete pavement was 80, 115, 150, 185 and 220 cm.
Soil basement of the road consists of light pulverescent
clay loam: moisture at the border of rolling W
р
= 15.0 %;
moisture at the border of fluidity W
т
= 25.4 %. Granulometric
content of soil has been shown in the Table 1.
Table 1. Granulometric content of light pulverescent clay loam
Full residue (%) in sieves with size of cells (mm)
2.0
1.0
0.5
0.25
0.1
0.05
6.8
8.4
10.9
17.3
28.2
29.4
Underground waters lay in the depth (below than 3.0 m
from the land surface).
3. MOISTURE OF SOIL BASEMENT
Diagrams have been represented in the Figures 1 and 2,
showing moisture variety during time period in different points
of soil basement. Analysis of the mentioned diagrams has
shown that character of moisture variety in various depths of
soil basement is different. The surface of soil basement (80 cm)
has proved to be very sensitive to seasonal climate variety: the
biggest values of moisture (21-23 %) have been observed in
spring and autumn seasons of the year, and in summer, due to
the dry weather moisture reduces to 8-8.5 %, which can be
explained by transferring of part of the liquid moisture into soil
condition (ice) with negative temperatures.
