spt期刊投稿系统si

One of the most common in-situ tests is the standard penetration test，or SPT. This test was originally developed in the late 1920s and has been used most extensively in North and South America，the United Kingdom，and Japan. Because of this long record of experience， the test is well established in engineering practice. Unfortunately，it is also plagued by many problems that affect its accuracy and reproducibility and is slowly being replaced by other test methods，especially on larger and more critical projects.

The test procedure was not standardized until 1958 when ASTM standard D1586 first appeared. It is essentially as follows:

1) Drill a 60 to 200 mm ( 2. 5 － 8 in) diameter exploratory boring to the depth of the first test.

2) Insert the SPT sampler ( also known as a split-spoon sampler ) into the boring. The shape and dimensions of this sampler are shown in Figure 6. 1. It is connected via steel rods to a 63. 5 kg ( 140 lb) hammer，as shown in Figure 6. 1.

3) Using either a rope and cathead arrangement or an automatic tripping mechanism，raise the hammer a distance of 760 mm ( 30 in) and allowit to fall. This energy drives the sampler into the bottom of the boring. Repeat this process until the sampler has penetrated a distance of 450 mm ( 18 in) ，recording the number of hammer blows required for each 150 mm ( 6 in) interval. Stop the test if more than fifty blows are required for any of the intervals，or if more than one hundred total blows are required. Either of these events is known as refusal and is so noted on the boring log.

4) Compute the N value by summing the blowcounts for the last 300 mm ( 12 in) of penetration. The blowcount for the first 150 mm ( 6 in) is retained for reference purposes，but not used to compute N because the bottom of the boring is likely to be disturbed by the drilling process and may be covered with loose soil that fell from the sides of the boring. Note that the N value is the same regardless of whether the engineer is using English or SI units.

5) Remove the SPT sampler; remove and save the soil sample.

6) Drill the boring to the depth of the next test and repeat steps 2) through 6) as required.

Figure 6. 1 The SPT sampler in place in the boring

Thus，N values may be obtained at intervals no closer than 450 mm ( 18 in) .

Unfortunately，the procedure used in the field varies，partially due to changes in the standard，but primarily as a result of variations in the test procedure and poor workmanship. The test results are sensitive to these variations，so the N value is not as repeatable as we would like. The principal variants are as follows:

1) Method of drilling.

2) Howwell the bottom of the hole is cleaned before the test.

3) Presence or lack of drilling mud.

4) Diameter of the drill hole.

5) Location of the hammer ( surface type or down-hole type) .

6) Type of hammer，especially whether it has a manual or automatic tripping mechanism.

7) Number of turns of the rope around the cathead.

8) Actual hammer drop height ( manual types are often as much as 25 percent in error) .

9) Mass of the anvil that the hammer strikes.

10) Friction in rope guides and pulleys.

11) Wear in the sampler drive shoe.

12) Straightness of the drill rods.

13) Presence or absence of liners inside the sampler ( this seemingly small detail can alter the test results by 10 to 30 percent) .

14) Rate at which the blows are applied.

As a result of these variables，the test results will vary depending on the crewand equipment.

Fortunately，automatic hammers are becoming more popular. They are much more consistent than hand-operated hammers，and thus improve the reliability of the test.

Although much has been said about the disadvantages of the SPT ，it does have at least three important advantages over other in-situ test methods. First，it obtains a sample of the soil being tested. This permits direct soil classification. Most of the other methods do not include sample recovery ，so soil classification must be based on conventional sampling from nearby borings and on correlations between the test results and soil type. Second，it is very fast and inexpensive because it is performed in borings that would have been drilled anyway. Finally ，nearly all drill rigs used for soil exploration are equipped to perform this test，whereas other in-situ tests require specialized equipment that may not be readily available.