Segmental Block Reinforced Structure Applied for the Highway Interchange Project, Middle East

This project is a highway interchange construction in the Middle East. The northern part of the interchange is adjacent to a developing industrial park, the densely populated city is located to the west of the job site, and the east is a planned residential area.

Before the construction, the road in surrounding cities and industrial parks are always congested. Interchanges are needed to lighten the traffic loading from north to south on the existing highway and connect the urban areas on the east and west sides of the highway. But the elevation of the east and west sides of the job site is about 10 meters higher than the existing highway, a series of 3 to 10 meters height mechanically stabilized earth walls (MSEWs) are needed to construct an interchange system to smoothly lower the elevation of the urban road and connect to the highway.

The job site is crossing agriculture and fish farms, and therefore MSEWs are located on the soft soil of high plasticity clay (CH) with a thickness of about 8 meters. For reducing the total settlement of the foundation soil, the construction installed prefabricated vertical drainage (PVD) with 30 cm sand drain layer before geogrid wrapping faced MSEWs construction. 2 to 3 layers of 600kN/m ACETex^® geotextile were laid at the bottom of MSEWs so as to make the load evenly applied to the foundation, the geotextile can restrict the lateral deformation as well. In this case, the self-load of the MSEWs and soil-filled tone bulk bags stacked on top of MSEWs were used as preloading to accelerate the clay consolidation.
It was also required landscape and safety design for MSEWs, so the segmental blocks facing located on anti-slide piles foundation was chosen. Since the settlement of geogrid wrapping MSEWs structure used for preloading and the block faced piling structure are very different. If two structures are constructed at the same time, the large differential settlement will occur at the interface between the segmental blocks and MSEWs, and then rupture the geogrid. Therefore, MSEWs were designed with a special two-stage construction method to ensure the sustainability, safety, and stability of the overall structure. When constructing the first stage of the geogrid wrapping MSEWs, within 2 m of the geogrid wrapping MSEWs face, an extra layer of geogrid with strength 200 kN/m is pre-embedded, and 0.7 to 0.9m length geogrid is reserved outside the MSEWs face. Once the preloading is completed and achieves expected total settlement, the geogrids reserved outside MSWEs were connected with the segmental blocks of the second stage to complete the construction of whole MSEWs structures.

Due to the special construction of two-stage MSEWs, it requires the geogrid with ultra-durable characteristics with lower creep, the high tensile strength geotextile was demanded as well.

The particular design is the modular block facing system which was not installed until the main consolidation and lateral deformation of MSEWs fully developed so as to effectively control the deformation of the future whole retaining structure. Furthermore, the construction is rapid with a lower construction cost, achieving both economic and safety benefits.