Experiment plan
Because the semi-rigid subgrade is mainly subjected to both environmental
and loading effects in practical applications, that is, the mechanical properties
of the subgrade materials are decayed mainly due to freeze-thaw damage and
fatigue damage, for this reason, the laws of change of mechanical properties
of the subgrade materials under the action of both freeze-thaw and loading
need to be studied.
Therefore, my program is divided into two major parts, the first part to study the
change law of the subgrade under freeze-thaw cycles, and the second part to
study the coupling effect of freeze-thaw cycles plus the fatigue damage.
1. Define objectives/variables
• Investigate matiral life and mechanical properties of Semi-rigid Base Materials under repeated freeze-thaw
cycles by indoor simulation test.
Variables:
- Expansion ratio
- Thermal strength of the Semi-rigid Base Materials (sensor buried into the soil samples)
- Temperature range -15 50 (The number of freeze-thaw cycles was counted in three levels (-15 5℃, 10 30℃,
30 50℃).
- Moisture (water content): saturated / optimal water content of the semi-rigid base layer
- Salt content 0.4% (when the temp goes up the soil samples will show different shrink)
- Compaction (to be checked in the literature)
- Thermal expansion when the soil samples dry need to be added (future work)
- Which is the optimal salt content according to the standards of Xinjiang province (compare)
2. Planning/designing process steps
The mechanical properties of semi-rigid subgrade materials under freezethaw damage are studied through indoor simulation tests.
1. Analyze the temperature and humidity conditions of the subgrade under
actual use conditions and obtain its reasonable simulation conditions of
freeze-thaw damage; to study the temperature and humidity sensitive
characteristics of the mechanical indexes of the subgrade materials and to
determine the controlling variables in the simulation test. (compaction,
moisture content, salt content, temperature, and expansion ratio)
2. Determine the minimum actual number of freeze-thaws per year in
the seasonal freeze area by analyzing meteorological data and
pavement temperature sensor monitoring data.
3. Propose the freezethaw damage
simulation test
method for subgrade
materials by
comparing with the
freeze-thaw test
method in the current
subgrade material test
specification.
4. Carry out freeze-thaw simulation test of semi-rigid subgrade materials
according to different grades of freeze-thaw test conditions, and propose
the concept of equivalent number of freeze-thaw cycles based on the
principle of equivalent damage. The damage accumulation law of subgrade
materials under the action of freeze-thaw for long years, i.e. the law of
mechanical index change, can be obtained.
5. Study the fatigue characteristics of semi-rigid subgrade materials and
the influence law of freeze-thaw damage on fatigue life through indoor
simulation tests: the law of change of mechanical properties of
subgrade materials under the coupling effect of freeze-thaw and load
is further studied.
3. Preparation and curing process of cylindrical
specimens
• Prepare Φ150mm×150mm cylindrical specimens for compressive strength and rebound modulus test;
prepare100mm×100mm×400mm middle beam specimens for bending and tension test and fatigue loading
test.
• Firstly, according to the maximum dry density and optimum water content determined by the compaction
test, determine the quality of each grade of aggregate and the required water and cement, weigh the
aggregate, add part of the water for preliminary mixing, bore the material. The test piece should not be
smothered for more than 24 h. Add the smothered material to the cement and another part of the water left
for mixing, and load the test material into the test mold. Put the test mold into 200t universal test press with
1mm/min loading rate, pressurization after unloading, remove the test mold, and after 24h, the test material
will be put into the test mold. After unloading, remove the mold, and then use the mold release device to lift
out the specimen after 24h, and then gently hold the specimen and place it on the test bench. The specimen
will be wrapped in plastic bag and put into the standard curing room (temperature is 20±2℃, humidity≥95%)
after demolding. The required age of the specimens was maintained according to the test requirements. On
the last day of the curing period, the specimens were taken out, the mass and height of the specimens were
weighed, and the specimens were soaked in water with different salt content.
Preparation and of semi-rigid base cylindrical
specimens for the experiment