A new shopping centre extends over a surface area of 27,000 m² and comprises five storeys (2 basements + ground floor + 2 floors). For the construction of the basement storeys, the construction pit was protected by reinforced-concrete bored piles having a diameter of 80 cm, a length of 15 m and spaced 1.50 m apart. Jet-grouting columns having a diameter of 70 cm are arranged between the piles. The pile wall is strutted apart by steel struts arranged at every 6 m, supported into the foundation of the new building. Where permitted by the distance from the boundaries of the plot, excavation of batters in a slope of 2 : 1 and 3 : 1, protection with a 15 cm thick shotcrete and passive soil anchors having a length of 8 m in a grid 2.0 x 2.0 m or 1.5 x 2.0 m were foreseen. The construction pit is 11 m deep. The soil is composed of sandy gravel stones and gravel stones that are already slightly lithified at greater depths and turn into poorly bound conglomerates. Below the gravel layer, there is a layer of clay having a thickness of 3 to 5 m with gravel stones.
An execution design for construction pit protection was prepared for the client. 2D structural and stability analyses were performed for this purpose based on the finite element method.
