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Four research models made in different material technology were tested on a natural scale. The main purpose of the research was to compare the displacement and stress values of structures under failure load. Tests were carried out on the station for static, dynamic and fatigue tests, which consists of a reinforced concrete foundation with a length of 80.0 m and a width of 20.0 m together with a hall and a steel frame constituting a retaining construction for hydraulic load-inducing devices.
Research models were constructed in all technological steps of the buried structure based on the applicable transport engineering standards and regulations, included additionally geometric control of the test models, mounting sensors and gauges on the structures and soil backfilling with mechanical compaction with 30.0 cm thick layers. Displacement and stress measurements were carried out using sensors and induction gauges in characteristic points of the structures. The applied loads were in accordance with the Polish transport engineering standards. The load variant replacing the railway load was used in the laboratory tests. Failure tests of culvert models were carried out for several different values of load forced by hydraulic actuators and for different values of backfill layer over the structures. The article describes the results for maximum loads and backfill layer equal 0.3 m. The backfilling material was well-graded soil with a maximum grain size of 32 mm. The basic parameters of soil backfill are summarized in Table 1.
Table 1 Properies of soil backfill.Full size table
The aim of laboratory tests on a natural scale was to create a knowledge base on the behavior of buried structures under various types of loads. This database, in its assumption, allows the verification of calculations performed by a numerical method such as FEM.
The research covered two culverts with a diameter of 0.80 m and a length of 13.70 m. The first research model was made of a PE plastic pipe. The second model was a flexible corrugated steel pipe. The soil conditions for both models were similar due to constant monitoring of the degree of compaction of soil backfill layers and of the lateral zone of the structures. Figure 2 shows a cross-section of the research models.
Figure 2Cross-section of the research models: PE plastic pipe and steel corrugated pipe.
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Figure 3 present general view of test model for research.
Figure 3General view of the research models after soil backfill.
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The basic parameters of PE plastic pipe are summarized in Table 2. Table 3 contains the list of the basic parameters of pipe made of corrugated steel sheets.
Table 2 Parameters of the pipe made of PE plastic.Full size table
Table 3 Parameters of the pipe made of corrugated steel sheets.Full size table
The laboratory failure tests were carried out for the following maximum loads:
maximum pressure force: Fmax = 1960 kN.
maximum force per actuator:Fmax / 2 = 980 kN.
Failure tests of research models were carried out according to the diagram shown in Fig. 4.
Figure 4Diagram of the failure load.
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Displacement measurements were carried out using induction gauges located in the vertical axis (in the crown) and in the horizontal axis (on both opposite side walls). Stress measurements were carried out using electric resistance strain gauges located in the vertical axis and in the horizontal axis (on both opposite side walls). The arrangement of the induction sensors and strain gauges is shown in Fig. 5.
Figure 5Arrangement of induction sensors and strain gauges for the testing models.
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The next stage of research concerned Box Culvert model under failure load. The research covered a culvert with a span of 3.55 m and a height of 1.42 m. The steel structure was additionally reinforced by special ribs made of steel plates located on the top section of perimeter—in the crown. Figure 6 shows a cross-section of the research model.
Figure 6Cross-section of the research model: Box Culvert.
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A general view of the steel structure for testing is shown in Fig. 7. Figure 8 presents a general view of the research model after soil backfill.
Figure 7General view of the tested steel box structure.
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Figure 8General view of the research model after soil backfill.
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Type of the model profile is a box with open cross-section. Other basic parameters of the tested structure are summarized in Table 4.
Table 4 Parameters of the Box Culvert research model.Full size table
The laboratory failure tests were carried out for the following maximum loads:
maximum pressure force: Fmax = 1990 kN,
maximum force per actuator: Fmax/2 = 995 kN.
The speed of the load was 40 kN/s with the time of the maximum load T = 600 s.
The data collecting equipment consisted of 22 electric resistance strain gauges in 11 locations, with a strain gauge on the top and bottom of the corrugation and 3 inductive sensors used for vertical and horizontal displacement measurements.
Figure 9 presents a schematic layout of strain gauges and induction sensors around the corrugated Box Culvert model1.
Figure 9Arrangement of induction sensors and strain gauges for the Box Culvert model1.
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Another research model in natural scale was Multi Plate structure made of corrugated steel sheets. The research covered a culvert with a span of 2.99 m and a height of 2.40 m. Other parameters of the research model are shown in Table 5. Figure 10 shows a cross-section of the Multi Plate model.
Table 5 Parameters of the multi plate research model.Full size table
Figure 10Cross-section of the research model: multi plate.
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General view of the steel Multi Plate structure for testing is shown in Fig. 11. Figure 12 presents a general view of the research model ready for testing.
Figure 11General view of the tested steel Multi Plate structure including the two pipes from the chapter 2.1.
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Figure 12General view of the complete research model.
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Described laboratory failure tests were carried out for the backfill layer over the structure equal 0.3 m and for the following maximum loads:
maximum pressure force: Fmax = 2000 kN,
maximum force per actuator:Fmax / 2 = 1000 kN.
Displacement measurements were carried out using three inductive sensors located in the vertical axis (in the crown) and in the horizontal axis (on both opposite side walls). Stress measurements were carried out using 28 electric resistance strain gauges in 14 locations, with a strain gauge on the top and bottom of the corrugation. The strain gauges were located on the perimeter of the research model at equal distances of 631 mm. The arrangement of the induction sensors and strain gauges is shown in Fig. 13.
Figure 13Arrangement of induction sensors and strain gauges for the multi plate model.
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According to the Polish Standards in the case of buried structures made of PE plastic, an important parameter is the allowable deflection, which is equal to 3%. When designing this type of structure, it is necessary to estimate the value of the maximum deflection during use of the object and compare it with the permissible value. Deflection of the structure results from the displacement and the span ratio17.
During the implementation of culverts made of corrugated steel sheets, compliance with the permissible values of wall stresses must be checked. The allowable stress value in this case is equal to the tensile strength of the steel from which the buried structure was made.
This article does not contain any studies with human participants or animals performed by any of the authors.
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