Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Figure 12-1: Example of a two-way lateral load test setup fora drilled shaft
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| Figure 12-1: Example of a two-way lateral load test setup fora drilled shaft. If a strut is used between the test pile and the reaction pile (e.g., in a pushing type test, it is good practice to install a pinned connection using a swivel joint (clevis) atone end of the strut to allow rotation without eccentricity of load application, as shown in Figure 12-3. Use of this type of connection also reduces the risk of the bearing plate or reaction frame components from becoming dislodged during the test, or worse popping out of the system, presenting a safety hazard as well as compromising the test data. The jacks used to apply the load must function when oriented horizontally, without leaking of hydraulic fluid, and without piston malfunction. Although the load applied in lateral load testing of piles and drilled shafts is usually much less than axial tests, the displacements (and hence the amount of jack travel) will likely be greater. The amount of travel of the ram in the jack must be able to accommodate the anticipated magnitude of displacement. It is therefore important that during the planning of a lateral load test, a preliminary analysis is made so that the load capacity and lateral displacement are estimated so the capacity of the jack and load cell and the available travel of the ram and associated external instrumentation (see Section 12.6) can be selected appropriately. Jacks can also be controlled by compressed air. Some jacks are reciprocating, or double acting, so that reversals in load direction can be performed. An alternative to jacks are electric winches, pulley blocks and turnbuckle devices. 182 Figure 12-2: Example of a one-way lateral load test setup on a deep foundation. To reduce thermal effects on the reference beam (the reference point for measuring horizontal displacements, it is good practice to shield the test site from direct sunlight with a canopy and to protect the site from wind and frost action. Depending on location and season, a temporary enclosure around the test setup maybe required, with temporary heating to keep the ambient air temperature above 50 o F. The temporary enclosure maybe constructed using framing, wood panels, canvas, tarpaulins and other materials. Ambient air temperature should be monitored during the test. The reference beam, which is typically steel, should be robust so as not to deflect between its supports. Painting the beam white can help to reduce thermal induced movements in the beam. The load measurement device should be independent of the jack, although the pressure gauge on the jack itself is a useful backup device in the event that the load cell malfunctions during a test. Although rarely done, if combined axial and lateral load tests are performed (ASTM D Procedure H, then an anti-friction bearing plate assembly is required between the axial load and the head of the pile or drilled shaft. Steel plates with roller bearings, or a PTFE polymer slide bearing on a stainless-steel plate can be used. The purpose of the plate is to enable lateral movement of the head of the pile or shaft without being restrained by the axial load above. 183 Given the expense and time associated with planning, mobilizing, pile/shaft installation and testing, it is advisable to require the testing contractor to be equipped with spare parts for the key electrical and hydraulic components in the jacking systems used, and to have onsite a backup system for the pumps, ram jacks, and load cell. Some economy can be achieved in a lateral load test program if the reaction piles or shafts from a conventional axial compression load test are used for lateral load testing after the axial test has been performed. If this approach is adopted, the locations and types of reaction pile/shaft need to be considered in the planning so that an appropriate lateral load test setup can be constructed. It is also possible to test two adjacent piles/shafts simultaneously by pulling the piles together or pushing them apart (Figure 12-3). By adopting this approach, two independent data sets are obtained that may provide insights into the repeatability of the construction means and methods. Download 6.03 Mb. Share with your friends:
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