چكيده به لاتين
Nailing is one of the common methods of stabilizing slopes and excavations (slopes with an angle of 90 degrees). One of the main reasons for the popularity of this method is its quick construction and also its cost-effectiveness. In order to mobilize the bond stress between the soil and the grout in the nailing method, deformation must occur in the excavation wall, but next to residential buildings in urban areas, stabilization of deep excavations is done with the anchoring method. In this thesis, it is intended to investigate the behavior of nailed excavation next to neighboring buildings. In this thesis, using the laboratory method and simulating the dimensions and characteristics of the specific excavation in the centrifuge in order to achieve the real conditions, 10 tests were designed to determine the effect of surcharge, nail density pattern, soil type and excavation depth on failure surfaces, lateral deformation and settlement of soil behind the facing and lateral pressure distribution in nailed excavations. The depth of the constructed sample was 30 cm and the soil used was Firoozkoh sand No. 161 with a relative density of 50% and a water content of 6%. The nails were sand-coated brass pipes and the facing was made of cement grout with a steel mesh. The process of applying surcharge and subsequent excavation was carried out at the target acceleration -40g acceleration. Surcharge application was simulated by filling the loading tank with water at the target acceleration and then by draining the water from the membrane that was in front of the excavation and was filled with water at 1g acceleration, the excavation process was simulated. The first four tests at 40g acceleration simulated a 12meter excavation and the next six tests simulated 12- and 18-meter excavations at 40g and 60g accelerations, respectively. Two categories of surcharge (the first category includes 40, 70 and 100 kPa) in 40g acceleration such as a 12-meter deep excavation and (the second category includes 60, 105 and 150 kPa) in 60g acceleration such as s 18-meter deep excavation), three nail density patterns, three different nail lengths and three types of sand, sand with low clay (20% clay) and sand with high clay (40% clay) were used to investigate the effect of different factors on the behavior of the nailed excavations. Using miniature pressuremeter, the lateral pressure distribution of the soil behind the facing was recorded for six tests. Using image processing analysis, failure surfaces and profile of excavation deformations were also investigated. The results showed that it is not recommended to use nailing with low or medium nail density in order to stabilize the excavation next to the neighboring building. However, nailing with a high density of nails can be investigated for excavations with a depth of less than 12 meters in the vicinity of buildings with 3 floors or less according to the characteristics of the soil. Also, the failure surface is bilinear, and the mechanism of failure is pulling out the nails, and bending is not seen in the nails. The deformation of the facing at the moment of failure includes translational, rotational, and buckling movements. For the high-density nail pattern with sand, the lateral pressure distribution applied to the facing has a significant difference with the pressure recommended by Terzaghi-Peck and also the pressure recommended by FHWA. The denser the arrangement of nails is, the lower the lateral pressure applied to the facing. For sand and both clayey sands, two distributions of lateral soil pressure were seen behind the facing for nailed excavations under surcharge. An increase in the surcharge causes an increase in the lateral deformation and settlement of the nailed excavations. The amount of surcharge affects the deformation mode. It was also seen that the lateral deformation profile occurs in two ways. For an excavation with a low or medium nail density pattern, the lateral deformation is the highest at the top of the excavation and the lowest at the bottom of the excavation (cantilever type), in this case, the settlement profile will be multi-linear, so that the amount of settlement increases as it gets closer to the edge of the excavation. For an excavation with a high nail density pattern, the maximum lateral deformation occurs in the middle of the excavation (bulging type) and the corresponding settlement profile is such that the maximum amount of settlement affected by the surcharge occurs with the distance from the edge of the excavation. The presence of 20% clay in sandy soil significantly reduces the settlement and lateral deformation of the soil, although the presence of 40% clay has the opposite effect and leads to a significant increase in the settlement and lateral deformation of the soil behind the facing.
