**Abstract**

The article shows the analysis of the behavior at long-term deformation of geocells for a set time period, due to its importance on the modulus improvement factor (MIF), which is considered in the design stage of a reinforced pavement structure with geocells. When inquiring into the research about the structural behavior that exists in the geocells, as well as the distribution of stresses that this generates, in order to determine how important the existence of a deformation in the geocell is. We proceeded with the sampling and execution of the test "modified stepped isothermal method (SIM) for geocells." The test was carried out under the comparison of the materials and thicknesses of the sample, with the purpose to analyze the influence on the behavior of a pavement structure. The stresses generated at the level of the granular subbase layer of a pavement are taken into account as load effects.

**Keywords:** creep, geocells, modulus improvement factor, stepped isothermal method

#### **1. Introduction**

One of the most common problems in road geotechnics projects is encountering subgrade soils of low carrying capacity. Multiple solutions are proposed to improve the unfavorable conditions of this type of soil; however, a large part of them can be harmful to the environment. In this sense, alternatives based on design with geosynthetics are important and allow for adequate reinforcement of the unsuitable soft subgrade as a supporting layer of the pavement structure.

However, with the implementation of geosynthetics, problems associated with the stresses experienced by the material were observed, such as UV degradation and long-term plastic deformation. These effects occur in almost all geosynthetics, even in geocells, which will be analyzed in detail in this article.

The first need to reinforce highly compressible soils arose during wartime at the beginning of the twentieth century, when the transport of heavy machinery was required. For this reason, the US Army Corps of Engineers was the first to use and

develop the cellular confinement system in the late 1970s, as a means to help build roads, runways, platforms, and others; all these solutions were made on very soft soils and under humid conditions.

The main large-scale use of this system of cellular confinement was during the Gulf War, in "Operation Desert Storm", where it transported heavy military material with speed and efficiency. For the purpose of mobilizing large troops, according to the company Geoceldas SA, the defense department of the United States "acquired 6.4 million square feet (600,000 square meters) of cellular geosynthetics for use in various military applications [1]."

In terms of its implementation in design tasks, pavement structure with geocells uses a coefficient of increase for the modules of the materials (MIF), which depends on several factors. Among these is resistance to long-term deformation of the material that makes up the panel of geocells. This generates a mechanism of confinement, which creates an apparent cohesion of the material incorporated therein. If the geocells yield, it is susceptible to losing its properties and begins to deform causing a settlement in the pavement structure, in addition to providing a deconfinement in the geocell filling material [2, 3].

Therefore, some consequences of deformation in the geocell are the reduction of the apparent cohesion in the filling material due to the loss of confinement, according to which there is a high decrease in the MIF coefficient taken into account during the design of the structure.

For these reasons, it is important to know the properties of the materials that are involved in the pavement structures and the veracity of the calculations that are made in the analyses. Therefore, when calculating the MIF, it is important to know the long-term deformation of material to give support and certainty in the analyses. Consequently, a modified test based on the SIM for geocells was developed. A test program was carried out using different samples of geocells, exposing results for each one of them.

The definition of the MIF factor refers to the material modulus with reinforcement vs. the material without reinforcement. This value is obtained at the moment of designing a structure with geocell, applying five characteristics of the materialgeocell set, among which is the long-term deformation of geosynthetic. The MIF value depends on the analysis of the creep in the geocells, because if the material becomes deconfined, the increase of the modulus considered in the design will be reduced. For this reason, a safety factor is applied to the MIF, due to the creep in the geocells.

The samples were analyzed under load effects, which contemplate those generated at the level of the granular subbase layer of pavement, thus showing the feasibility of use in this layer and the possible behavior of these over its usable life.
