International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 04, April 2019, pp. 99-105. Article ID: IJMET_10_04_009
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=4
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
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MODERNIZATION OF THE CLASSICAL
SCHEME OF THE HANDICRAFT
MANUFACTURE OF SOIL PRESSURE SENSORS
Aleksandr V. Kulikov and Aleksey N. Kraev
Industrial University of Tyumen, Tyumen, Russia
ABSTRACT
This article is devoted to the modernization of handicrafts manufactured to measure
the stress in the ground (messdose). Today, when designing buildings and structures,
an important task is to determine the amount of expected precipitation. The calculated
values are not always objective, especially in the conditions of Western Siberia, where
weak organic-mineral soils are common. Based on the experience of the introduction of
sensors measuring the voltage in the ground, the author identified a number of factors
by which they most likely fail. According to approximate calculations, until the end of
the average natural experiment, about 25% of the messdose remain operable. The
author proposed options for upgrading sensors to minimize the risks of their failure.
The main causes of sensor failure: contact breakdown, depressurization, short circuit.
They are eliminated by inserting fiberglass boards and two-stage sealing into the sensor
body. The body of the sensors was made of titanium. Cyanoacrylate glue was used for
sticking the strain gauges onto the body of the messdose. Sealing was performed with
epoxy resin. As a signal cable used 4-core cable KSPV. Calibration of the sensors was
carried out in an aerostatic tank. Upgraded sensors were tested during a laboratory
experiment. The author tested a sample of weak organic soil in compression conditions.
No total pressure sensor has failed. The convergence of the sensor readings with the
load applied to the sample is very high. The measurement error did not exceed 10%.
The author also attempted to make handicraft sensors to measure pore pressures in the
ground, but during the implementation they all failed.
Keyword head: messdose; compression; soil pressure; cyanoacrylate; sensors;
calibration tests.
Cite this Article Aleksandr V. Kulikov and Aleksey N. Kraev, Modernization of the
Classical Scheme of the Handicraft Manufacture of Soil Pressure Sensors, International
Journal of Mechanical Engineering and Technology, 10(4), 2019, pp. 99-105.
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Aleksandr V. Kulikov and Aleksey N. Kraev
1. INTRODUCTION
One of the significant tasks of foundation design and engineering is determination of the
expected future settlement. However, matching of theoretical evaluation and practical results
shows that it works not as well as it supposed to, especially in conditions of weak soils. Progress
of abnormal settlement, which, might be on occasion, in several times higher than calculated
parameters, it leads to increases in nonuniform deformation of constructions and results in a
breakdown conditions of constructions.
There are two basic reasons of low accuracy. At the one hand, it is immaturity in
technologies of engineering calculation and at other hand is a fault in measuring methods of
deformation parameters in engineering-geological researches.
Methods of settlement calculation and soil characteristics measuring techniques were being
constantly improved. Measuring of stresses that arises under load of construction in soil body
and in the place of contact with foundation, measuring of the deformation space and researches
of deformation due to theirs transmission in foundation base are the great challenges in the field
of creating of new technologies and improving existing calculation methods.
Theoretical frameworks of the strain measurement technologies and deformations in soils,
particularly in the case of metrological aspects, are the least-studied, therefore it requires
particular attentions.
True picture of soil strain is very complicated due to its structure. It is a polyphase system
that includes mineral granules filled with water and gases. The stress state can be considered as
sets of interacting contacting stresses in contact areas of mineral granules or like a stress that
arises in them or like pressure in liquids or gases inside the soil’s pores.
And in this, contact areas of mineral granules have changed due to mutual bias of particles
in soil compaction conditions. Therefore, stresses in particles and stresses in contact areas had
either changed. There are a lot of difference in configurations of particles, sizes and stress-strain
properties that make a big variety and unique stress states. That is why it describes with
statistical methods only.
According the above-mentioned, engineer tasks allow to use the conditions where normal
or shearing stresses on area are equal for mean integral projection of actual stress on a normal
line or the tangent to this area.
Mean integral stress states have a high degree of accuracy and reliability to correlate with
soil’s stress-strain properties and mechanical strength characteristics. Therefore, it is fully
compliant with the requirements of engineering missions.
However, for scientific purposes, this strain makes sense only as a phenomenological model
of soils. Creation of physical model implies the actual stress of soil. Note that, actual stresses
in areas of granules contacts might be two-order magnitude than mean integral stress on area.
If we taking into account the mean integral of stress conditions, then stress-strain condition
of the test point in soil body might be measured with stress tensor, exactly if all six independent
parts are known (e.g. normal stresses in a six differently directed areas).
Based on the above, the goal of experimental works of the soils stress state is to measure
normal stresses in a six differently directed areas. Messdoses (sensors of normal soil stresses)
were used as a main tool of research. Messdoses were put in the soil where they were interacted
with soil grains, pore water and gas through the sensing elements.
The simple messdoses are the cylinders with one or two sides with sensors with contour
sealing (Figure 1).
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Modernization of the Classical Scheme of the Handicraft Manufacture of Soil Pressure Sensors
Figure 1. Messdose1.
Messdoses measured the mean integral value of normal stresses in soils on capsule’s area
that bent under the measured strain (Figure 2).
Figure 2. Scheme of messdose with one side sensor.
Strains of internal face of capsule (with extension in the middle and shortening in support)
were transformed from resistive-grain sensors into an electric signal that was sent to secondary
device of measuring system. Then, signal was decrypted with the calibration chart as a normal
stress that has an impact on messdose.
To date, researchers do not have the methods and tools for direct stresses measuring. All
known tools and techniques, including the messdosess, can record only stresses of environment,
where they were installed. Then, data processed with calibration chart or with formulas that
correct for model of environment (e.g. theory of elasticity formulas) as a stress in environment.
2. EXPERIMENTAL PART OF THE RESEARCH
More than 500 sensors [1, 2, 3] had used during the assembly works and experiments. The
sensors were made in a ‘classic scheme’ (that was made by D.S. Baranov [4] and upgraded by
A.V. Golly [5]) The main reasons of failure and defective sensors works have been identified
during the researches:
 break of contact stress transducer;
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 ingress of moisture and air inside the sensor body;
 break of signal cable;
 transducer short-circuit to messdose body;
 transducer ungluing;
 messdose body rejection.
The following recommendations will reduce the level of rejections:
 applying of fiber-glass plastic board for rigid fixation of cable inside the messdose
body (Figure 3, Figure 4);
 two-stage body capsulation;
 applying of cyanoacrylate adhesive instead of BF-2 (phenol-resin glue);
 Applying of a new signal cable type KSPV (indoor signal cable) instead of UTP
cable.
Figure 3. Upgraded messdose inside view.
Figure 4. Upgraded messdose scheme.
Two-stage body capsulation process was made with epoxide resin in a two steps. The first
stage includes the fixing of messdose body and cables to plastic molds with the clamp (Figure
5) with the subsequent epoxy injection for the top of the sensor’s body. Second stage starts with
clamp removing after complete epoxide resin consolidation (for better adhesion effect). Then
second layer of epoxide resin was injected with complete covering of the sensor. In short, the
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Modernization of the Classical Scheme of the Handicraft Manufacture of Soil Pressure Sensors
above-mentioned technique allows to protect the messdose body from air and water. As a result,
messdose has a full sealed and cable has a rigid fixation.
BF-2 glue [6,7] (that first used for strain gage sensor pasting on a messdose body) requires
oven heat treatment that made assembly process more difficult and increased probability of
rejection rate. Cyanoacrylate adhesive (‘super Moment’ ® glue) was used instead of BF-2 to
simplify pasting of strain gage sensors. Cyanoacrylate adhesive had not impact on sensors
functionality but it reduced probability of unstucking to zero.
Figure 5. First stage of capsulation process.
The upgraded messdoses were applying in set of lab tests at interdepartmental scientific
experimental laboratory of Industrial University of Tyumen [8,9]. The upgraded membranetype sensors of normal pressure gauge (Figure 6) were set in soil sample. The sensors were used
for verifying of conditions of compression and sample loading control. Sensors were assembled
at the laboratory, had a circular shape and body made of titanium. Strain gage sensor was gluing
on sensor’s work surface.
Work surface incurved with increasing of general pressure, through this; the contact length
has been changed as a resistance. Unit record equipment (secondary transducer ITC-03p-40)
was used for data collecting. Messdoses calibration tests were made in rating tank [10].
Figure 6. Diagram indicating the placement of sensors in sample (M1,3,4,5 is for general pressure
messdoses, M2,6 – pore pressure messdoses).
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In additions, author tries to handcraft pore pressures measuring sensor. In this case,
upgraded messdose have a perforated extra half of body with glycerine soaked sponge inside
(Figure 7).
At the start of experiment, messdose naturally showed changes of pore pressures with its
typical dissipation after load application. However, increasing of pressure had resulted in
ingress of soil into the measuring capsule through the holes of sensor’s body (it was detected at
the end of experiment). Messdose had shown the pressure increment like general pressure
sensor.
3. RESULTS
Pressure had been applying on soil sample with console-lever system during the experiment by
steps with the laboratory determining of the strength and strain characteristics according State
Standard1. Strain was 30 kPa (such slight pressure explained by organo-mineral soil sample
that characterized small soil strength), after that step soil had becme conditionally-stable.
Figure 7. Messdose prototype for soils pore pressures measuring
The experiment has been lasting for 30 days. During the experiment, none of general
pressure sensors had a failure and proved itself. Measurement errors had not passed 10 % which
is a good indication for handcrafted sensors. The soil pressure of sample pressure under presstool diagram (Figure 8) was made according results of experiment.
Figure 8. Soil pressure of sample pressure under press-tool diagram (1 is for sensor at 20 mm depth, 2
is for sensor at 200 mm depth, 3 is for sensor at 380 mm depth).
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Pore pressure sensors were broken down at 15 kPa due to the big diameter of holes in
sensor’s body. Probably, it is impossible to handcraft pore pressure sensors.
Upgraded scheme eliminated all defects in ‘classic’ scheme of sensors that have been
revealed during the experiments. Break of resistive strain sensor was prevented with soldering
to hard fixed board. Resistive strain sensor short circuit to sensor’s body was prevented too.
Two-step sealing excludes ingress of moisture and air inside the messdose body. Break of signal
cable was prevented with high quality of soldering.
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