1、Standard Method of Test for Deep Foundation Elements under Bidirectional Static Axial Compressive Load AASHTO Designation: TP 100-12 (2015)1American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1b TP 100-1 AASHTO Standar
2、d Method of Test for Deep Foundation Elements under Bidirectional Static Axial Compressive Load AASHTO Designation: TP 100-12 (2015)11. SCOPE 1.1. This test method describes procedures for testing vertical or inclined deep foundation elements to determine their behavior characteristics in response t
3、o an internally applied axial static load. This method is applicable to all deep foundations that function in the same manner as bored piles, regardless of their method of construction and installation. Note 1Bidirectional load testing has been successfully performed on driven piles. However, the in
4、stallation and procedural differences associated with bidirectional load testing of driven piles are not covered in this standard. 1.2. This standard provides minimum requirements for bidirectional testing for deep foundation elements under controlled application of static axial compressive load. 1.
5、2.1. The engineer responsible for the foundation design, referred to herein as the engineer, shall approve any deviations, deletions, or additions to the requirements of this standard. Note 2Plans, specifications, or provisions, or some combination thereof, prepared by a qualified engineer, may prov
6、ide additional requirements and procedures as needed to satisfy the objectives of a particular test program. Note 3To determine the long-term performance of the foundation, the duration of each load step application may be extended and the test results may need additional interpretation. 1.3. A qual
7、ified engineer shall design and approve all loading apparatus, loaded members, and test procedures. 1.4. The values stated in SI units shall be regarded as the standard. The inch-pound equivalents of the SI units may be approximate. 1.5. All observed and calculated values shall conform to the guidel
8、ines for significant digits and rounding established in ASTM D6026. 1.6. The method used to specify how data are collected, calculated, or recorded in this standard is not directly related to the accuracy to which the data can be applied in design or other uses, or both. How the results obtained usi
9、ng this standard are applied is beyond the scope of this test standard. 1.7. This standard may involve hazardous materials, operations, or equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this st
10、andard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 100-2 AASHT
11、O 2. REFERENCED DOCUMENTS 2.1. AASHTO Standard: R 13, Conducting Geotechnical Subsurface Investigations 2.2. ASTM Standards: D653, Standard Terminology Relating to Soil, Rock, and Contained Fluids D1143/D1143M, Standard Test Methods for Deep Foundations Under Static Axial Compressive Load D3740, Sta
12、ndard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction D6026, Standard Practice for Using Significant Digits in Geotechnical Data 3. TERMINOLOGY 3.1. In this document, the term “pile” is used to repres
13、ent any type of deep foundation element that functions in the same manner as drilled shafts or bored piles, regardless of their method of construction and installation. 3.2. Except as defined in Section 3.2, the terminology used in this test method conforms to terminology in ASTM D653. 3.2.1. bidire
14、ctional loading device (or jack)A fabricated assembly of one or more symmetrically positioned hydraulic load cells capable of producing an accurately measured axial force (or load) sufficient to mobilize the resistive forces of the foundation element, both above and below the device. Multiple jacks
15、may be used on a single level to increase load capacity, or jacks may be installed on different levels. Generally herein, “jack” may refer to one or more jacks. 3.2.2. fracture planeThe horizontal planar fracture zone created in the pile when the load applied by the hydraulic load jack assembly exce
16、eds the tensile capacity of the pile concrete. 3.2.3. side shear (skin friction)The force resistance that develops on the perimeter surface of the pile at the interface of the pile and the surrounding soil or rock strata when applying loads with the bidirectional loading device. 3.2.4. end bearingTh
17、e force resistance that develops at the base or toe of the pile when applying loads with the bidirectional loading device. 3.2.5. telltale casing, rodA telltale casing is typically half-inch National Pipe Thread (NPT) steel pipe. A telltale or telltale rod is typically a solid steel rod 6 mm to 8 mm
18、 (1/4in. to 5/16in.) in diameter that extends from some point in a pile to the top of the pile or above. 3.2.6. encased compression telltales (ECT)Similar to a telltale casing and rod except that the transducer measuring the telltale movement is attached directly to the rod and the outside is attach
19、ed to the casing. The entire apparatus is then embedded (encased) in concrete with only the data cable extending to ground surface. 3.2.7. carrying frameA rigid steel structure made of channel, angle, or beams that may be used instead of a rebar cage when specified as part of the load test program a
20、nd as approved by the engineer. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 100-3 AASHTO 4. SIGNIFICANCE AND USE 4.1. This test method is used to measure displacement response and internal s
21、train of an individual pile when subjected to a known internal axial force. The objective of the test is to obtain response data used to estimate or measure directly nominal values of end bearing and side shear for a specific test pile. These data may be used to evaluate the load-displacement respon
22、se relating to pile construction methods and to estimate settlement characteristics and nominal axial geotechnical resistance of the tested foundation element. The results from test piles may be used to optimize pile diameters, tip elevations, and other improved design criteria for other similar fou
23、ndation elements and conditions. Note 4The quality of the results produced by this test method is dependent on the competence of the personnel performing the test and the suitability of the equipment and facilities used. Agencies that meet the criteria of ASTM D3740 are generally considered capable
24、of competent and objective testing and inspection. Users of this test method are cautioned that compliance with ASTM D3740 does not in itself assure reliable results. Reliable results depend on many factors; ASTM D3740 provides a means of evaluating some of those factors. Note 5In order to evaluate
25、nominal axial geotechnical resistance, it is necessary to cause sufficient movement in all pile elements so that ultimate side shear curves can be obtained for multiple elements (or shear zones) and so that an ultimate end bearing curve can be obtained. Note 6The engineer may interpret from the bidi
26、rectional load test data an estimated equivalent top-load deflection response comparable to the results provided by ASTM D1143/D1143M. 5. APPARATUS 5.1. General: 5.1.1. This method uses a sacrificial hydraulic load jack assembly in conjunction with instrumentation to measure hydraulic pressure (load
27、 force), concrete strain, and the displacements of various sections of the test pile. A schematic section showing a typical instrumentation layout for a single-level bidirectional test is illustrated in Figure 1. 2015 by the American Association of State Highway and Transportation Officials.All righ
28、ts reserved. Duplication is a violation of applicable law.TS-1b TP 100-4 AASHTO Figure 1Bidirectional Loading Device (Jack) Configuration 5.1.2. The jack shall be embedded at the location as designed for the objectives of the testing program and as approved by the engineer. The resultant force appli
29、ed by the jack shall coincide with the central axis of the pile. Jacks shall be placed a minimum distance of one-half pile diameter above the pile bottom, unless otherwise directed by the engineer. Note 7The construction of the test pile should resemble, as closely as practicable, the construction m
30、ethods and requirements of the proposed production piles considering the inherent differences created by the embedded jack. The use of a lighter rebar cage or carrying frame made of angle, channel, or beam may be used, provided the load test program objectives are satisfied, as approved by the engin
31、eer. 5.1.3. Post-test grouting techniques and materials must be approved by the engineer if the test pile is to be used as a production pile for integration into the structure. 5.2. Apparatus for Applying Load Using a Bidirectional Loading Device: 5.2.1. This testing method uses an appropriately siz
32、ed sacrificial calibrated hydraulic jack assembly. Special attention to the design of these embedded jacks is required to ensure that they have negligible internal friction during operation. The jack will be internally pressurized, creating an upward force on the pile in upper side shear and an equa
33、l but downward force in combined lower side shear or end bearing, or both. Two or more hydraulic lines shall be used to provide redundancy. The jacks load is determined by relating the applied hydraulic pressure to the linear load calibration curves. Calibrated, high-pressure gauges will be used to
34、read the pressure on the 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 100-5 AASHTO pump line and on the return line. A defined ultimate condition may occur either in end bearing or side shear
35、 when sufficient load is applied. Should ultimate capacity of the jack system be reached, no further increase in load is possible. 5.2.2. An apparatus capable of applying a total load greater than or equal to the desired test load shall be considered acceptable, noting that in a bidirectional test,
36、the total load applied is the sum of the load applied above and below the loading assembly plus the mass of the pile above the jack. However, it is preferred to have load capabilities well beyond the test load to allow full mobilization of the pile and to provide data for possible foundation redesig
37、n. The jack shall be able to maintain a constant load for appropriate durations of time (according to specified loading schedules) to within 2 percent. The typical method of measuring this force includes the use of calibrated jacks. 5.2.3. The hydraulic jacks shall be confined in a symmetrical arran
38、gement (centered if a single jack) between the upper and lower reinforcing cages or carrying frames to facilitate construction of the pile and to locate the loading device at the designed level. Steel bearing plates having cutouts of sufficient size shall be provided to accommodate the nominal diame
39、ter of the tremie pipe and to allow for adequate flow of concrete around the apparatus. These bearing plates shall be symmetrical and centered about the longitudinal axis of the reinforcing cage or carrying frame. Appropriate spacers shall be used to centrally locate the reinforcing cage or carrying
40、 frame pile within the borehole. 5.2.4. The loading assembly shall be accurately placed at a distance above the pile toe level as specified for the test and shall be a minimum distance of one-half pile diameter above the pile bottom, unless otherwise directed by the engineer. This assembly shall be
41、welded or otherwise securely attached to the reinforcing cage or carrying frame. The spiral reinforcement and vertical steel bars shall be terminated immediately above and below the expected fracture plane. 5.2.5. All pumps, hydraulic jacks, hoses, and fittings shall be designed and rated to safely
42、confine the internal operating pressures. 5.2.6. Vent tubes shall be installed at the fracture plane to minimize any vacuum resulting from expansion of the load jack, unless otherwise directed by the engineer. The vent tubes shall be secured along the length of the pile. Vent tubes shall be clean an
43、d filled with clear water for testing. 5.3. Data Acquisition Instrumentation: 5.3.1. General: To determine the behavior characteristics of the foundation element, the test instrumentation must be capable of accurately measuring values of applied force (load), jack expansion, top-of-pile displacement
44、, linear pile compression, and concrete strain as required by the engineer. Using these data, the engineer can determine reasonable values for unit side shear, unit end bearing, and settlement. These measurements must be recorded at specified time intervals not greater than 1 min unless otherwise di
45、rected by the engineer. The measured displacements provide for the following: Top-of-pile movement (measured by displacement transducers attached to the reference beam set over the pile or by remote optical electronic levels); Pile compression (measured by encased compression telltales ECTs and trad
46、itional telltale rods set from the top of hydraulic jack and referenced to top of pile or reference frame); Upward top of jack movement (calculated as measured pile compression above the jack plus measured top-of-pile movement); 2015 by the American Association of State Highway and Transportation Of
47、ficials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 100-6 AASHTO Hydraulic jack expansion (measured directly by displacement transducers attached between top and bottom bearing plates or by the difference in displacement between top and bottom bearing plates measured w
48、ith using telltales from ground level); Downward bottom of hydraulic jack movement (calculated as measured hydraulic jack expansion minus upward top of jack movement); and Downward pile toe movement (measured by telltale rods attached near the pile toe less top-of-pile movement or by calculation of
49、compression measured with an embedded compression telltale plus bottom plate movement). 5.3.2. Apparatus for Obtaining Applied Force (Load) Measurements: When using a calibrated jack as the sacrificial loading device, the hydraulic pressure of the system directly corresponds to the force applied equally in the upward and downward directions. A pressure transducer or Bourdon gauge, or both, is used to measure the internal pressure of the system which, along with calibration data from the jack, is used to determine the force applied. The pressure
