Pullout Test For Geogrid Reinforced Expansive Rock/Soil For Beijing Western Sixth Ring Highway And Its Numerical Emulation

It was a huge success that flexible supporting technology was firstly used in the Beijing Western Sixth Ring Highway depositional expansive rock/soil cutting slope. The overall strength of cutting slope included the friction between geogrid and expansive soil, the anchoring geogrid using U-shaped nail and the folding connection of geogrid. Pullout test is the best method for studying on this interaction. In order to obtain reinforcement mechanism of expansive soil, interface parameters and optimize the flexible supporting design, the research on pullout tests of the Beijing Western Sixth Ring Highway reinforced expansive rock/soil and numerical analysis were carried out.To gain the interface appropriate testing conditions of reinforced soil, a large-scale pullout test system'CS-LB01'was used. Three expansive soil samples from Beijing Sixth Ring Highway and two kinds of geogrids were utilized to research the influence degree by different factors such as various overlying loads, sample moisture contents, pullout rates of geogrid, consolidation times and types of reinforcement material. Totally, thirty-three groups of pullout tests were performed. Based on the results and actual working conditions, the appropriate testing condition was proposed.In order to research on the relation between geogrid drawing force and its strength and geometric characteristics, five kinds of geogrids manufactured by Hubei Nete Geosynthetics Ltd and expansive soil (sample 2) were utilized to perform the pullout tests. The drawing force was related with not only the strength of reinforcement material, but also the number of horizontal rib with the same length of geogrid in the soil. When flexible supporting technology was implemented, these two factors were synthetically considered when reinforcement materials were selected.In order to simulate the practical situation of flexible supporting, pullout tests were carried out with geogrid tail fixed by two types of reinforcement nails. The results showed that drawing force increased considerably than that without reinforcement nails. U-shaped nail played an important role in increasing flexible supporting body's overall strength.Finally, the pullout test between geogrid and expansive soil was simulated by the finite difference FLAC3D software. Geogrid structure unit built-in FLAC3D was adopted for stimulating reinforcement material and Mohr-Coulomb Model was adopted for the constitutive model of expansive soil. The curve of between drawing force and displacement agree very well with the automatic computer testing graphics. When the geogird was effectively drawn out, these that included displacement field distribution, vertical stress distribution, interface horizontal stress distribution and interface frictional resistance distribution were obtained. These provided reference for analyzing on reinforcement mechanism and interfacial interaction parameters.