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Geotechnical Laminar Box

Geometry

The UB Full-scale prototype 1-g soil and soil-structure interaction testing facility consists of a 2-D modular laminar box (Module A1: 2.75x5x6.2m, internal dimensions). The 2-D laminar box is made of 24 laminates, separated and supported by ball bearings, facilitating 2-D motions, including ability to simulate sloping ground subjected to large deformations. The box can simulate boundary stresses closely to that of a free ground. The laminar box can also be reconfigured into two other configurations or modules (module B1: two boxes 2.75x2.5x3.1m each or module B2: 2.75x2.5x6.2m) or at a reduced height. The box can allow up to 15% shear strain in general, larger deformations for selected cases of loadings, and large permanent deformations on a case-by-case basis, subject to safety and other limitations. Figures 3 present schematic diagrams of the laminar box modules. Figure 4 shows a picture of the laminar box.

(a) Module B1: 2.75x 2.5x3.1 m       (b) Module B2: 2.75x 2.5x6.2 m        (c) Module A1: 2.75x5x6.2m           (d) 2-D Bearing

(e) Module A2: 2.75x5x3.2 m (not shown)

Figure 1:  2D Laminar Box Modules at SEESL

Figure 2: Laminar Box (1-g Full scale Tests) on the Strong Floor

Figure 3: A typical pile test configuration

Figure4: Laminar Box in Test Area 2

Features

Table 1: Laminar Box Module Dimensions & Details

Table 1 presents the dimensions and details of the various modules. The load capacity characteristics are to be considered preliminary, subject to verification and update. In its largest configuration (Module A1: 2.75x5x6.2m), the laminar box is supported on the strong floor, on a steel shaking base frame supported on rubber/sliding bearings. It can be actuated in 1-D using one or more of the UB-NEES 100 ton fast dynamic actuators (MTS), or in 2-D by using two or more 100 tons fast actuators mounted at 45 degrees on the new UB-NEES reaction wall (30ft high, 41ft wide). The total weight of the box filled with sand is about 150-170 tons, whereas the maximum horizontal dynamic actuator capacity is 90 tons in each horizontal direction simultaneously or 180 tons in any one direction. Thus very large shaking g levels are possible. The actuators can be fed with any recorded motion and the controllers can be set to compensate for any compliance effects to accurately shake the base of the soil to meet any desired recorded earthquake motion. Data acquisition systems are available to monitor up to 256 channels at high frequencies. High resolution imaging tools can be positioned to capture deformation patterns at any selected zone in the soil box.

In its smaller configurations (modules A2, B1 and B2), the laminar box may be mounted on a shake table with a maximum payload capacity of 50 tons weight including the box weight. Where higher weights are expected the box may be assembled over a steel base frame supported by two identical shake tables allowing up to 100 tons maximum weight, including the weight of the box and the steel base frame. The shake table payload-acceleration characteristics are presented elsewhere. Typically each shake table can operate at up to 1.15g at a nominal payload weight of 20 tons, and the acceleration decreases with an increase in payload weight. The shake tables have 6 degrees of freedom, but the 1-g soil tests are limited to 1-D or 2-D at this time.

Sand may placed inside the box by air pluviation, wet pluviation, or hydraulic filling. Due to dust control considerations the hydraulic filling method is preferred. A close-loop system has been developed to pump sand-slurry using sand-slurry pump from sand containers located just outside the Test Area 2 building. In the case of dry pluviation, soil saturation may be achieved by percolating by CO₂ through the soil and seeping water with the aid of vacuum suction.

The facility also has capability to simulate the inertial effects of the building/bridge pier etc. on the foundation/pile cap via mass-spring system and/or hybrid system where the loads/moments from the building/bridge pier can be applied via fast actuators mounted on the reaction wall. The soil experiments also can be coupled with other physical experiments at UB or elsewhere and/or computational models that simulate the response of the system or structure supported on the soil.