International Journal of Corrosion

Volume 2018, Article ID 9870673, 11 pages

https://doi.org/10.1155/2018/9870673

## Embankment Filling Loads on an Assembled Concrete Culvert beneath High Embankment

Technology Research Center of Ecological Road Engineering, Hubei University of Technology, Wuhan 430068, China

Correspondence should be addressed to Qiang Ma; moc.361@729gnaiqam

Received 19 March 2018; Revised 9 June 2018; Accepted 20 June 2018; Published 1 August 2018

Academic Editor: Yi Zhang

Copyright © 2018 Qiang Ma et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

A culvert with prefabricated and assembled structural components is introduced to speed up the progress of highway construction in China. In order to clear the behavior of the prefabricated and assembled slab culvert, the center line section and the shoulder section of the embankment are selected for field tests. In the tests, the distribution and the growth of the earth pressures on the top slab and the lateral walls and the displacements and the deformations of the top slab and lateral walls are investigated, thereafter, the tested earth pressures are linearly fitted, and the formulas of fitting lines are obtained. The results show that the deflections of the lateral walls and of the cover slab are very small, and the variation of distribution and growth of the earth pressures presents significantly nonlinear characters, which is totally different from the linear earth pressure theory proposed by the current Chinese code. The vertical pressure is much smaller in the middle part of the top slab than that on both ends, and it is much larger than the linear theory results. The distribution curve of the lateral earth pressures on the lateral walls is approximately “3” in shape, and the maximum earth pressure locates at the junction of the cap and the lateral wall. The formula of the fitted line obtained from the primary stage pressure can be employed to estimate the earth pressure of embankment completion. The results of the field tests can provide references for the calculations of the components and the strength in the junctions of the assembled culverts.

#### 1. Introduction

The stress state of culvert beneath embankment fill in mountainous area is very difficult to determine, as there are many influences on pressure distribution [1]. It is very important to correctly clear the distribution state of the surrounding earth pressures, which is of great significance to the design and construction of assembled concrete culverts [2].

So far, there have been a lot of studies on calculation of earth pressure on culvert crown and influences of earth pressure distribution, in which the stress states of the culvert with different embankment height are focused on. The previous studies on instrumented culverts date form 1919, in the year Marston measured a culvert with height of 1.02 m beneath 6.10 m backfill and found that the pressure on its top was nearly 1.92 times the weight of the overburden soil (Spangler 1968) [3]. Thereafter, Spangler (1947) [4] gave the testing results of two rigid circular culverts, one of the culverts with soft soil placed on the crown, the unit weight of which was 15 kN/m^{3}, and the measured pressure was about 1.9 times the overburden soil weight. For the other culvert beneath gravel filling of 20kN/m^{3}, the measured pressure was about 1.5 times the overburden pressure. And, then, Spangler (1950) [5] reported the load measurements for seven positive projection culverts with the width ranging from 0.61 m to 2.44 m. The average pressure of the culverts was measured and a method for predicting culvert load was developed by observing soil deflection compared to culvert deflection. And it was found that the design pressure should be a function of projection conditions, various soil properties, and backfill height (H) to culvert width (B) ratio(H/B). Based on Spangler’s study, Clarke (1967) [6] pointed out that the growth ratio of the vertical pressure of the culvert was essentially considered constant when the embankment heights were greater than the plane of equal settlement (the plane of equal settlement was defined by Spangler (1947) [4] as the horizontal plane in the embankment at which the settlements of the interior soil prism above the culvert and the exterior soil prism outside the culvert were equal). Woodbury et al. (1926) [7] gave the test report on eight different culverts from the American Railway Engineering Association on the Illinois Central Railway embankment. In the report the pressure reading of the two culverts indicated that the crown pressure was about 1.58 times the cover backfill weight pressure. Braune et al. (1929) [8] reported the tests on the culverts placed on the weighing device, for the cast iron pipes with different H/B ratios and the inner diameters and thicknesses, the pressure was about 1.27 to 1.40 times the overburden backfill weight pressure. Binger (1947) [9] reported a pressure measurement at the center of the box culvert which was 2.74 meters wide and 3.30 meters high and about 15.2 m of sandstone filled above it, and the vertical pressure measured at the culvert center was about 1.8 times the overburden soil unit weight. Trollope et al. (1963) [10] reported on pressure measurements of a culvert in horseshoe shape under the embankment of a dam, there were 8 points with different positions measured and the pressures were 1.6, 2.6, 1.5, 1.7, 1.7, 2.9, 1.9, and 3.2 times the overburden pressure, respectively. Höeg (1968) [11] investigated the behavior of the model cylinders in the test chamber filled with Ottawa sand, there was one or two cylinders of sand at the top of the culvert, and then pressure was applied to the top of the sand with an air bag, the crown pressure was 1.42 to 0.69 times the applied pressure, which depended on the stiffness of the culvert, and these stiff culverts would support greater pressure than overburden pressure. Girdler (1974) [12] reported a 1.73-meter-wide single cell box culver, with overburden 23.5-meter-high backfills, the pressure was very asymmetrical, with one side of the crown pressure 0.90 times and the other side 1.74 times the overlying soil pressure, and the average pressure was 1.32 times the overlying soil unit weight. Penman et al. (1975) [13] reported pressure measurements made on a culvert passing under a 53m high rockfill dam. They found that, with increasing fill heights more than* H*/*B*=9, the ratio of measured pressure to overburden pressure decreased. At the final fill height corresponding to an* H*/*B *ratio of 12.9, the crown pressure was 1.76 times the overburden pressure. Dasgupta and Sengupta (1991) [14] studied 1.35 m×1.35 m model box culvert which was covered with 2.4 m height dry sand as backfill, and the measured pressure values at three positions on the top of the culvert from the edge were 0.09 B, 0.3 B, and 0.5B. The pressure presented a parabolic distribution with a ratio of measured pressure to overburden pressure at each of the three corresponding positions of 1.90, 1.06, and 0.66, and the average pressure was about 1.32 times the overburden pressure. Vaslestad et al. (1993) [15] reported the pressure measurement of a 2.0 m wide by 2.55 m high box culvert, with 9.8 meters’ silty clay on top as backfill; the measured pressure was 1.24 times the overburden pressure. And a series of finite element analysis results given by Katona et al. [16] (1981) and the measured results given by Dasgupta and Sengupta (1991) [14] show that the pressure at the culvert center was usually the lowest on the culvert top plane. Yang (2000) [17] reported the results of pressure measurements on a 9.9 m wide by 3.7 m high double box culvert, with 2m incompact backfill around the culvert. The measured pressure was 1.26 times the soil overburden. As the pressure is commonly bigger than the overburden soil weight, the lightweight and compressible materials such as straw, EPS geofoam, compressible soil, or tire chips are placed on the top of culverts to decrease the vertical load on the crown. Stone et al. (1991) [18] carried out a series of centrifugal model tests to study the effects of load reduction with lightweight and compressible materials filled on the culverts crown. Dancygier et al. (1996) [19] studied the fill-soil interaction mechanism of deep buried structures and obtained an optimum dimension of the soft zone for reducing vertical pressure. Sun et al. (2005) [20] performed a series of finite element analyses to study the stresses and deformations of a slab culvert with lightweight geofoam on the roof. Mcguigan et al. (2012) [21] carried out field tests of a twin 3660 mm inside diameter induced trench culverts installed under 21.7 m of fill, and the monitoring results showed that the average earth pressures measured at the crown and spring line were 0.67 and 0.32 times the overburden. And his centrifuge test results of an induced trench culvert indicated that the base contact pressures were 25%–76% greater than the top pressure plus dead load because of shear stresses mobilized along the sidewalls (Mcguigan and Valsangkar, 2011) [22], and the induced trench culvert partially transferred the earth pressure from interior backfill prism to the lateral prisms, leading to increases of the earth pressure on the lateral walls and the foundation. An investigation was carried out by Turan et al. (2013) [23] of induced trench method using a full-scale test embankment, and the results also showed that the loads on the crown of the induced trench installed culvert were 30% to 60% less than the overburden. Dong et al. (2013) [24] performed a series of finite element analyses to study the variation law of pressure on crown under grid-shaped treatment. Thereafter, Chen et al. (2013, 2014) [25, 26] and Osama et al. (2015) [27] carried out a series of field tests and mechanical analyses, and the results indicated that the differential stiffness between the culvert and the adjacent fill mass caused the differential settlement between the surrounding soil prism and the central soil prism above the culvert. Hence, the shear stress between the surrounding soil prism and the central soil prism resulted in backfill pressure concentration on the culvert. Zhang et al. (2017, 2018) [28, 29] carried out a series of field tests and demonstrated the efficacy of digital photogrammetry as a powerful technique for deformation measurement in the geotechnical model tests. The previous studies mainly aimed at cast-in-place constructed culverts, but, seldom at assembled culverts, the distribution and the growth of the earth pressures on an assembled culvert have not been reported, and hence calculation methods of the strength of the assembled culvert are lacking testing data support.

Therefore, this study introduces the assembled culvert in the construction process of the Huixing expressway located in Guizhou province China. Then the distribution of earth pressure around the assembled slab culvert and the displacement of the culvert are investigated by the field instruments, with particular emphasis on the maximum earth pressure location. After that the tested earth pressures are linearly fitted to obtain the fitting formulas of load on the assembled culvert.

#### 2. Introduction of Assembled Slab Culvert

In mountainous areas, concrete culverts casted in situ cannot conduct follow-up process of the construction until the strength of concrete reaches 75% of the designed strength, which slows the construction progress of embankment frequently. And the mechanical compaction of embankment filling causes additional stress on the concrete culvert structures, which breaks the components of the culvert as the strength is not fully formed during the process of embankment filling. In addition, the construction quality, especially in winter and rainy days, is difficult to guarantee, which has a negative effect on the structure safety. To solve the above problems, an assembled culvert construction method was adopted for the first time in the process of Huixing expressway culvert construction in China.

This method produced the components of a culvert in prefabrication plant, which were prefabricated with C25 concrete. C20 rubble concrete was used to form foundation in the construction field by in situ casting. The prefabricated concrete wall and slab were installed after the strength of foundation concrete reaches 70% of its full strength. A 5.0cm depth groove is preserved at the installation junction of culvert lateral wall on foundation. Double hook gantry crane was adopted to lift the lateral walls and to put them to the groove on foundation, as shown in Figure 1. Two abutment caps were installed on the top of each lateral wall, and the ends of cover slab was placed on each abutment cap to avoid crushing the lateral wall. In addition, C25 self-compacting concrete was used in the junction area to bond the assembled components.