AASHTO T 306-2011 Standard Method of Test for Progressing Auger Borings for Geotechnical Explorations.pdf

1、Standard Method of Test for Progressing Auger Borings for Geotechnical Explorations AASHTO Designation: T 306-11 (2015) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1b T 306-1 AASHTO Standard Method of Test for

2、Progressing Auger Borings for Geotechnical Explorations AASHTO Designation: T 306-11 (2015) 1. SCOPE 1.1. This practice covers equipment and procedures for the use of earth augers in geotechnical subsurface explorations. 1.2. This procedure is applicable in soils that permit auger drilling to obtain

3、 representative or in situ samples and when information concerning resistance to driving casing or drive pipe is not necessary. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 13, Conducting Geotechnical Subsurface Investigations T 206, Penetration Test and Split-Barrel Sampling of Soils T 207, Thi

4、n-Walled Tube Sampling of Soils Manual on Subsurface Investigations (1988) 3. SIGNIFICANCE AND USE 3.1. Auger borings provide a simple method of soil investigations and sampling. They are used for collecting representative, split-spoon, or undisturbed tube samples, determining groundwater levels, ob

5、serving changes in earth strata, and setting of slope inclinometers. Depths of auger investigations are, however, limited by groundwater conditions, soil characteristics, and the equipment used. Location, depths, and number of auger borings should be established in accordance with R 13 and the 1988

6、AASHTO Manual on Subsurface Investigations. 4. APPARATUS AND TERMINOLOGY 4.1. Hand-Operated Augers for Obtaining Soil Samples: 4.1.1. helical augerssmall lightweight augers generally available in sizes from 25.4 through 76.2 mm (1 through 3 in.) in diameter. 4.1.1.1. spiral typea flat, thin metal st

7、rip, machine twisted to a spiral configuration of uniform pitch having, at one end, a sharpened or hardened point, with a means of attaching a shaft or extension at the opposite end. 4.1.1.2. ship typesimilar to a carpenters wood bit. It is generally forged from steel and machined to the desired siz

8、e and configuration. It is normally provided with sharpened and hardened nibs at the 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 306-2 AASHTO point end and with an integral shaft extending th

9、rough its length for attachment of a handle or extension at the opposite end. 4.1.2. open tubular augersranging in size from 38 through 200 mm (1.5 through 8 in.) in diameter and having the common characteristic of appearing tubular when viewed from the digging end. 4.1.2.1. orchard-barrel typea tub

10、e having cutting lips or nibs hardened and sharpened on one end to penetrate the formation and an adaptor fitting for an extension or handle on the opposite end. 4.1.2.2. open-spiral typea flat, thin metal strip that has been helically wound around a circular shank to form a spiral in which the flat

11、 faces of the strip are parallel to the axis of the augered hole. The lower helix edges are hardfaced to improve wear characteristics. The drive end is fitted with an adaptor for extension. 4.1.2.3. closed-spiral typenearly identical to the open-spiral type, except the pitch of the helically wound s

12、piral is much less than that of the open-spiral type. 4.1.3. post-hole augersgenerally 50 through 200 mm (2 through 8 in.) in diameter, and having a means of blocking the escape of soil from the auger. 4.1.3.1. clam-shell typeconsisting of two halves, hinged to allow opening and closing for alternat

13、ively digging and retrieving. Generally, it is not used deeper than about 1.5 m (5 ft). 4.1.3.2. Iwan typeconsisting of two tubular steel segments, connected at the top to a common member to form a nearly complete tube, but with diametrically opposed openings. It is connected at the bottom by two ra

14、dial blades pitched to serve as cutters, which also block the escape of contained soil. Attachment of the handle or extension is at the top connector. 4.2. Machine-Operated Augers for Obtaining Disturbed Soil Samples: 4.2.1. continuous-flight augersa boring device that has a solid center shank with

15、a flat, metal strip helically wound around itself to form a continuous spiral or flight to bore into and convey or store cut soil. The drive end is fitted with a socket for applying power. The cutting head is affixed with replaceable carbide teeth of various styles to penetrate hard soil formations.

16、 Auger sections generally come in 0.6- and 1.5-m (2- and 5-ft) lengths with other lengths available on special request. When coupled together, the sections provide a continuous flight to convey the soil throughout the full length of the borehole. 4.2.1.1. available sizesgenerally, these augers come

17、in nominal sizes ranging from 100- through 300-mm (4- through 12-in.) outside diameter. 4.3. Machine-Operated Augers for Obtaining Split-Barrel and Tube Samples: 4.3.1. continuous hollow-stem augersbasically the same as continuous flight augers, except the center shank is a hollow tube whose inside

18、diameter is large enough to allow the passage of split-barrel and tube samplers. 4.3.1.1. available sizesinside diameters shall be 57, 82, and 95 mm (2.25, 3.25, and 3.75 in.). Additional and larger sizes are acceptable, provided the sampler clearance requirement of Section 4.3.1.2 is met. 4.3.1.2.

19、Sampler clearance shall be such that no sampler or core barrel will be operated in or through a hollow-stem auger whose bore diameter is less than 108 percent of the sampler outside diameter. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplicat

20、ion is a violation of applicable law.TS-1b T 306-3 AASHTO 4.3.1.3. The hollow-stem auger may be advanced and sampling or coring conducted by any power-operated drilling machine having sufficient torque and ram range to rotate and force the auger to the desired depth, provided the machine is equipped

21、 with the accessory equipment needed to take the required sample or core. 4.4. Casing (when needed)Pipe of slightly larger diameter than the auger used. 4.5. Accessory EquipmentLabels, field log sheets, sample jars, sealing wax, sample bags, and other necessary tools and supplies. 5. DRILLING PROCED

22、URES 5.1. Progressing Hand- and Machine-Operated Solid Shaft Auger Borings: 5.1.1. Progress the boring by rotating and advancing the auger the desired distance into the soil. If continuous flight augers are not used, withdraw the auger from the hole and remove the soil for examination and tests. Ret

23、urn the empty auger into the hole and repeat the procedure. Continue the sequence until the required depth is reached. 5.1.2. Casing is required in unstable soil in which the borehole fails to stay open, and especially when the boring is extended below the groundwater level. The inside diameter of t

24、he casing must be slightly larger than the diameter of the auger used. The casing shall be driven to a depth not greater than the top of the next sampling location and shall be cleaned out by means of the auger. The auger can then be inserted into the borehole and turned below the bottom of the casi

25、ng to obtain a sample. 5.1.3. The continuous flight auger can be used both for boring the hole and for bringing up disturbed samples of the soil encountered. The structure of a cohesive soil is completely destroyed and the moisture content may be changed by the auger. The samples may be contaminated

26、 with soils from the overlying strata, especially when the cohesive soil is overlain by sand and the casing has not been placed through the sandy strata. Seal all samples in a jar or other airtight container and label appropriately. If more than one type of soil is picked up in the sample, prepare a

27、 separate container for each type of soil. 5.1.4. Field ObservationsRecord complete groundwater information in the field logs. Where casing is used, measure groundwater levels before and after the casing is pulled. In sands, determine the water level at least 30 min after boring completion; in silts

28、, after at least 24 h. In clays, no accurate water level determination is possible unless pervious seams are present. As a precaution, however, water levels in clays should be checked after at least 24 h. 5.2. Progressing Machine-Operated, Hollow-Stem Auger Borings: 5.2.1. Method A: 5.2.1.1. Advance

29、 the hollow-stem auger with the plug or pilot bit in place to the desired sampling depth. 5.2.1.2. Retract the plug or pilot bit by withdrawing the center drill rods. Remove the plug or pilot bit from the drill rods and replace with the desired sampling or coring tool. Lower and seat the sampling to

30、ol through the hollow-stem auger into the exposed undisturbed material at the bottom of the hole. 5.2.1.3. Proceed with the sampling operation by rotating, pressing, or driving, in accordance with the standard or approved method governing use of the particular sampling tool. Retract the loaded sampl

31、er by withdrawing the center rods. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 306-4 AASHTO 5.2.1.4. Replace the sampler with the plug or pilot bit and return to the bottom of the hole. Add a

32、n additional auger and lock the plug or pilot bit in place and advance the hollow-stem auger to the next desired sample depth. 5.2.1.5. Repeat the sequence for each sample desired. 5.2.2. Method B: 5.2.2.1. Advance the hollow-stem auger with plug or pilot bit in place to the desired sampling depth.

33、5.2.2.2. Retract the plug by reeling in the wire line and attached in-hole hammer and auger plug. Remove the auger plug from the in-hole hammer and replace it with the desired drive sampler. Lower the wire line and attached in-hole hammer and sampler through the hollow-stem auger to seat the sampler

34、 into the exposed undisturbed material at the bottom of the hole. 5.2.2.3. Proceed with the sampling operation in accordance with the standard or approved method governing use of the sampler and hammer. Free the loaded sampler by overaugering until the auger mouth is at the sampler shoe depth, or by

35、 bumping back. Retrieve the sampler by reeling in the wire line and attached in-hole hammer and sampler. 5.2.2.4. Remove the sampler from the hammer and replace with the auger plug or pilot bit or, in the case of continuous sampling, with another sampler. Lower the in-hole hammer with plug or sample

36、r attached and again advance the auger or begin sampling, as appropriate, to the incremental or continuous sampling being conducted. 5.2.2.5. Repeat or continue the sequence to the desired completion. 5.2.3. Method C: 5.2.3.1. The small hollow-stem auger, approximately 57 mm (2.25 in.) or less, may

37、be used without the plug or pilot bit. When so used, a plug of soil may be expected to form at the mouth of the auger. This plug will seldom exceed 100 to 150 mm (4 to 6 in.) in thickness. Samplers can normally be pressed or driven through this plug. However, the plug of soil then becomes the upper

38、part of the sample. Accordingly, samplers for use in the hollow-stem auger should be fitted with spoil reservoirs or spoil barrels, if the auger is to be used without a plug or pilot bit. 5.2.3.2. The hollow-stem auger may be utilized with a constantly positive liquid head within the center tube of

39、the auger when working without the center plug. Liquid may be water or drilling mud weighted as necessary to preclude entry of saturated free-flowing formation into the auger. Care shall be taken to avoid blowout of the formation by excessive pressure or weight of liquid in the center tube. Normally

40、 weighted liquid shall be introduced into the auger only by gravity flow and only as necessary to maintain the level within the auger center tube above the formation water level. Sampling within the liquid-filled auger shall be conducted in the normal manner prescribed for use of the particular samp

41、ler in a liquid-filled borehole. 5.2.3.3. In the event of inflow of the formation into the auger from loss of positive internal head or other cause, the center tube is to be washed out in the same manner as prescribed for casing cleanout. Sampling may then be conducted as prescribed for use of the p

42、articular sampler in the liquid-filled borehole; however, the boring report should always indicate that loss of formation occurred before sampling was conducted. Note 1The inflow of cohesionless materials into the bottom of any type of borehole normally results in the loosening of natural material a

43、t or below the bottom, and thus a sample or N value taken may not be truly representative of the undisturbed condition of the material. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 306-5 AASHT

44、O 6. REPORTING 6.1. The data obtained in Section 5 shall be recorded in the field logs and shall include the following: 6.1.1. Date of start and completion of boring. 6.1.2. Identifying number of boring. 6.1.3. Reference datum including direction and distance of boring relative to reference line of

45、project or other suitable reference points. 6.1.4. Type and size of auger used in boring. 6.1.5. Depth of changes in strata. 6.1.6. Description and classification of soil in each major stratum. 6.1.7. Groundwater elevation and location of seepage zones, when found. 6.1.8. Condition of augered hole u

46、pon removal of auger; that is, whether the hole remains open or the sides cave in, when such can be observed. 6.2. In addition, the data obtained in Section 6.2 shall be reported as required in accordance with T 206 or T 207, or both. 7. PRECISION AND BIAS 7.1. This standard provides qualitative data only; hence, precision and bias are not applicable. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.