CN112964577A - Series probe for measuring non-drainage shear strength of soft clay and test method - Google Patents
Series probe for measuring non-drainage shear strength of soft clay and test method Download PDFInfo
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- CN112964577A CN112964577A CN202110193664.4A CN202110193664A CN112964577A CN 112964577 A CN112964577 A CN 112964577A CN 202110193664 A CN202110193664 A CN 202110193664A CN 112964577 A CN112964577 A CN 112964577A
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- 239000000523 sample Substances 0.000 title claims abstract description 43
- 239000004927 clay Substances 0.000 title claims abstract description 41
- 238000010998 test method Methods 0.000 title claims abstract description 11
- 238000012360 testing method Methods 0.000 claims abstract description 63
- 239000007787 solid Substances 0.000 claims abstract description 19
- 238000000034 method Methods 0.000 claims abstract description 14
- 239000002689 soil Substances 0.000 claims description 23
- 230000035515 penetration Effects 0.000 claims description 18
- 230000005484 gravity Effects 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 238000003756 stirring Methods 0.000 claims description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 2
- 229920006395 saturated elastomer Polymers 0.000 description 13
- 238000010586 diagram Methods 0.000 description 3
- 238000011065 in-situ storage Methods 0.000 description 3
- 241001149930 Protura <class> Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000012669 compression test Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000009533 lab test Methods 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000007790 scraping Methods 0.000 description 1
- 239000013049 sediment Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/24—Investigating strength properties of solid materials by application of mechanical stress by applying steady shearing forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0025—Shearing
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- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
The invention provides a series of probes for measuring the non-drainage shear strength of soft clay, wherein each probe comprises a traction part and a conical head main body part. Specifically, the total weight of the conical head is 60g, the cone angle is 60 degrees, and the height of the conical head is 25 mm; the total weight of the spherical conical head is 60g, and the radius of the sphere is 22 mm; the total weight of the solid cylindrical cone head is 60g, and the radius of the solid cylinder is 22 mm. The invention also provides a test method for measuring the non-drainage shear strength of the soft clay by using the series of probes, which is called as a falling cone method. The invention has the advantages of convenient test, high efficiency and higher accuracy.
Description
Technical Field
The invention belongs to the field of foundation investigation of ocean engineering, and particularly relates to a computing system capable of rapidly measuring the non-drainage strength of extremely soft saturated clay.
Background
Unlike inland geotechnical engineering, the unique deposition characteristics of the ocean lead to the fact that most of sediments in shallow sea bed layers are soft clay. Because the strength of the surface saturated soft clay is very small, the strength of the surface saturated soft clay is difficult to accurately determine by adopting a conventional testing method. As an important parameter in ocean engineering, the accurate determination of the non-drainage strength of soil is a precondition for ensuring the stability and safety of ocean engineering structures.
The non-drainage shear strength of clay is affected by various factors, such as test method, loading rate, initial stress state, stress path, etc. The traditional clay non-drainage shear strength test method has many kinds, and can be divided into an indoor test and an in-situ test. The laboratory tests are as follows: single shear test, direct shear test, unconfined compression test, torsional shear test, triaxial test and the like; the in situ test comprises the following steps: cross plate test, pocket penetration test, CPT test, side pressure test, full flow penetrometer test, and the like.
However, the saturated soft clay on the surface layer of deep sea has very low shear strength and high sensitivity, and most of the clay is in a solid state or a fluid state. Therefore, indoor tests such as a triaxial test, a direct shear test and the like cannot be normally carried out, which increases the difficulty in determining the non-drainage shear strength of the saturated soft clay; in the in-situ test, accurate parameters of the surface soil body are difficult to obtain due to various reasons, and the determined shear strength is calculated by selecting parameters according to engineering experience.
Disclosure of Invention
In view of the above, the present invention provides a series of probes and a test method for reliably, simply and accurately measuring the non-drainage shear strength of soft clay, especially saturated soft clay, wherein the non-drainage shear strength of soft clay is determined by the penetration depth of the cone head measured after the cone falls into the soil body. In order to solve the technical problems, the invention is realized by the following technical scheme:
a series of probes for measuring the non-drainage shear strength of soft clay is composed of a traction part and a conic head, and is characterized by that it is divided into conic one, spherical one and solid cylindrical one according to their shapes, and the depth scales are arranged on the side walls of three conic heads.
Preferably, the conical head has the total weight of 60g, the cone angle of 60 degrees and the head height of 25 mm; the total weight of the spherical conical head is 60g, and the radius of the sphere is 22 mm; the total weight of the solid cylindrical cone head is 60g, and the radius of the solid cylinder is 22 mm.
The invention also provides a test method for measuring the non-drainage shear strength of the soft clay by the series of probes, which is called as a falling cone method. The method comprises the following steps:
(1) uniformly stirring the soil sample, filling the soil sample into a sample cup according to known density, and manufacturing a plurality of groups of soft clay samples;
(2) determining a first test demarcation point, a second test demarcation point and a third test demarcation point in a sequence from low to high;
(3) selecting a conical probe for testing;
(4) placing the sample on a horizontal plane, and adjusting the conical head to a height that the conical tip just contacts the surface of the soil sample;
(5) setting timing time, and releasing the conical head to enable the conical head to freely fall under the action of gravity; after timing is finished, acquiring the penetration depth h of the conical head, and taking the penetration depth h as a test result;
(6) if the test result is smaller than the first test demarcation point, judging that the soil body is not suitable for testing the non-drainage strength by adopting a cone falling method;
(7) if the test result is larger than the third demarcation point, judging that the test of the non-drainage strength is not suitable to be carried out by adopting the conical probe;
(8) selecting a spherical probe to repeat the steps (4) and (5), and if the test result is greater than the second demarcation point, selecting a solid cylindrical cone head to test the non-drainage strength;
(9) repeating the steps (4) and (5), and recording the test result;
(10) and selecting corresponding test results for different intervals determined by the three demarcation points, and substituting the penetration depth h of the conical head into the following formula to calculate the non-drainage shear strength Su of the clay:
lnSu＝alnh+b
in the formula: su is the non-drainage shear strength, the unit is kPa, h is the penetration depth of the conical head, the unit is mm,
a. b is the shape coefficient of the conical head, wherein the conical head a is-1.97, and b is 5.08; the spherical conical head a is-0.96, and b is 1.29; the solid cylindrical cone head a is-1.02, and b is 0.45.
Further, the first, second and third test demarcation points are respectively: 6mm, 10mm, 15 mm.
The invention has the following beneficial effects:
1. the method determines the non-drainage strength of the saturated soft clay by using the penetration depth of the cone head obtained by cone falling into the soil sample, and has the advantages of simplicity and high reliability. The method has important significance for determining the non-drainage strength of the soft clay.
2. The utility model provides three kinds of different grade type conical heads and correspond the not drainage intensity's of penetration depth and soft clay mathematical equation, can select suitable conical head type according to the consistency state of actual measurement soil sample, solved because the soil body consistency is less leads to the problem that can't carry out the strength test.
Drawings
Fig. 1 is a flowchart of a test method for measuring the undrained shear strength of saturated soft clay according to the present invention.
FIG. 2 is a schematic structural diagram of a conical head provided by the present invention;
FIG. 3 is a top view of a conical head provided by the present invention;
FIG. 4 is a schematic structural diagram of a ball-type conical head provided by the present invention;
FIG. 5 is a top view of the ball-type bit provided by the present invention;
FIG. 6 is a schematic structural diagram of a solid cylindrical cone head provided by the present invention;
FIG. 7 is a top view of the solid cylindrical cone head provided by the present invention;
in the above figures: 1. a depth scale;
FIG. 8 is a graph comparing the results of the non-drainage shear strength calculated by the conical cone head of the present invention with the shear strength of the cross plate.
FIG. 9 is a graph comparing the calculated non-drainage shear strength of the ball-type cone head of the present invention with the cross plate shear strength.
FIG. 10 is a graph comparing the calculated undrained shear strength with the cross plate shear strength for a solid cylindrical cone head of the present invention.
Detailed Description
To further explain the contents and features of the present invention, the following calculation examples are given and illustrated with the following figures:
fig. 2 to 7 show three different types of conical heads, namely a conical head, a spherical head and a solid cylindrical head, provided by the present embodiment. The proper cone head type can be selected according to the consistency state of the tested soil sample.
The three conical heads are all made of stainless steel materials, and the total weight is 60 g. The cone angle of the conical head is 60 degrees, the height of the conical head is 25mm, the traction part is a cylinder with the height of 10mm, and the total height is 35 mm. The sphere radius of the spherical conical head is 11mm, the height of the spherical conical head is 22mm, the height of the traction part is 10mm, and the total height of the traction part is 32 mm. The radius of the solid cylindrical conical head is 11mm, the height is 25mm, and the traction part is 10mm in height and 35mm in total height.
The method for calculating the non-drainage strength of the saturated soft clay by using the cone head comprises the following steps:
1. the soil sample is stirred uniformly by a soil adjusting knife and filled into a sample cup according to the known density. And scraping the soil sample higher than the sample cup by using a scraper.
2. A cone type probe was first selected for testing.
3. The sample cup is placed on a horizontal surface. The cone head is adjusted to a height where the cone tip/cone surface just touches the sample surface.
4. Releasing the conical head to enable the conical head to freely fall under the action of gravity; and (5 +/-1) s of timing, and reading the reading of the scale corresponding to the side surface of the cone to obtain the penetration depth h of the cone head.
5. If the test result is less than 6mm, the soil body is not suitable for testing the non-drainage strength by adopting a cone falling method;
6. if the test result is more than 15mm, the test is not suitable for the cone type probe.
7. Preparing 3 groups of soil samples according to the method in the step 1;
8. and 4, selecting a spherical probe to repeat the steps 4-5, and selecting a cylindrical probe to test if the test result is greater than 10 mm.
9. And recording the penetration depth h of the conical head, and substituting the penetration depth into a formula to calculate the non-drainage shear strength Su of the clay.
The penetration depth of the conical head, the spherical conical head and the solid cylindrical conical head is respectively substituted into the shear strength of the soft clay without water drainage calculated by the formulas (1), (2) and (3).
ln Su＝-1.97ln h+5.08 (1)
ln Su＝-0.96ln h+1.29 (2)
ln Su＝-1.02ln h+0.45 (3)
In the formula: su is the non-drainage shear strength of the soil body, and h is the penetration depth of the conical head.
The calculation system of the invention is used for calculating the non-drainage strength of the soft clay at a certain position, and the test method is as described above. The non-drainage strength of the soil body is calculated according to the test data, and the comparison result of the non-drainage strength of the soil body and the shear strength of the actually measured cross plate is shown in fig. 8-10. As can be seen from fig. 8 to 10, the calculated non-drainage shear strength test result of the saturated soft clay body is very close to the actually measured non-drainage shear strength of the soft clay in the cross shear test, which proves the effectiveness and accuracy of calculating the non-drainage shear strength of the saturated soft clay body by using the falling cone.
In the embodiment of the invention, after three probes are manufactured, through a large number of tests, the penetration depths h of different cone heads obtained by the falling cone method test provided by the invention are compared with the actual measured shear strength without drainage of the soft clay in the cross plate shear test, a formula for calculating the shear strength Su without drainage of the clay is fitted, and specific numerical values of three dividing points are determined. In engineering practice, a proper probe type and a calculation formula of the non-drainage shear strength Su of the clay can be selected according to the consistency of the saturated soft clay, and the testing of the non-drainage shear strength of the saturated soft clay by a cone falling method is realized.
Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and those skilled in the art can make various changes and modifications within the spirit and scope of the present invention without departing from the spirit and scope of the appended claims.
Claims (4)
1. A series of probes for measuring the non-drainage shear strength of soft clay is composed of a traction part and a conic head, and is characterized by that it is divided into conic one, spherical one and solid cylindrical one according to their shapes, and the depth scales are arranged on the side walls of three conic heads.
2. The series of probes according to claim 1, wherein said conical head has a total weight of 60g, a cone angle of 60 ° and a head height of 25 mm; the total weight of the spherical conical head is 60g, and the radius of the sphere is 22 mm; the total weight of the solid cylindrical cone head is 60g, and the radius of the solid cylinder is 22 mm.
3. The test method for measuring the shear strength of soft clay without water drainage, which is realized by the series of probes of claim 2, is called as a falling cone method. The method is characterized by comprising the following steps:
(1) uniformly stirring the soil sample, filling the soil sample into a sample cup according to known density, and manufacturing a plurality of groups of soft clay samples;
(2) determining a first test demarcation point, a second test demarcation point and a third test demarcation point in a sequence from low to high;
(3) selecting a conical probe for testing;
(4) placing the sample on a horizontal plane, and adjusting the conical head to a height that the conical tip just contacts the surface of the soil sample;
(5) setting timing time, and releasing the conical head to enable the conical head to freely fall under the action of gravity; after timing is finished, acquiring the penetration depth h of the conical head, and taking the penetration depth h as a test result;
(6) if the test result is smaller than the first test demarcation point, judging that the soil body is not suitable for testing the non-drainage strength by adopting a cone falling method;
(7) if the test result is larger than the third demarcation point, judging that the test of the non-drainage strength is not suitable to be carried out by adopting the conical probe;
(8) selecting a spherical probe to repeat the steps (4) and (5), and if the test result is greater than the second demarcation point, selecting a solid cylindrical cone head to test the non-drainage strength;
(9) repeating the steps (4) and (5), and recording the test result;
(10) and selecting corresponding test results for different intervals determined by the three demarcation points, and substituting the penetration depth h of the conical head into the following formula to calculate the non-drainage shear strength Su of the clay:
ln Su＝a ln h+b
in the formula: su is the non-drainage shear strength, the unit is kPa, h is the penetration depth of the conical head, the unit is mm,
a. b is the shape coefficient of the conical head, wherein the conical head a is-1.97, and b is 5.08; the spherical conical head a is-0.96, and b is 1.29; the solid cylindrical cone head a is-1.02, and b is 0.45.
4. The test method for measuring the non-drainage shear strength of soft clay realized by the series of probes according to claim 3, wherein the first, second and third test demarcation points are respectively: 6mm, 10mm, 15 mm.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11435272B1 (en) | 2022-01-19 | 2022-09-06 | King Abdulaziz University | Method of determining shear strength of soil using fall cone apparatus |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN204461908U (en) * | 2015-04-09 | 2015-07-08 | 中国电力工程顾问集团华北电力设计院有限公司 | A kind of soft clay undrained shear strength proving installation |
| CN106546480A (en) * | 2015-09-22 | 2017-03-29 | 中国电力工程顾问集团华北电力设计院有限公司 | The test device of soft clay undrained shear strength |
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| CN215677921U (en) * | 2021-02-20 | 2022-01-28 | 天津大学 | Series probe for measuring non-drainage shear strength of soft clay |
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- 2021-02-20 CN CN202110193664.4A patent/CN112964577A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN204461908U (en) * | 2015-04-09 | 2015-07-08 | 中国电力工程顾问集团华北电力设计院有限公司 | A kind of soft clay undrained shear strength proving installation |
| CN106546480A (en) * | 2015-09-22 | 2017-03-29 | 中国电力工程顾问集团华北电力设计院有限公司 | The test device of soft clay undrained shear strength |
| US10823880B1 (en) * | 2020-03-10 | 2020-11-03 | Ramesh Chandra Gupta | Subsurface exploration using load tests on short model piles at various depths of a soil deposit for determining load-settlement relationship and engineering properties of soils and intermediate geomaterials |
| CN215677921U (en) * | 2021-02-20 | 2022-01-28 | 天津大学 | Series probe for measuring non-drainage shear strength of soft clay |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11435272B1 (en) | 2022-01-19 | 2022-09-06 | King Abdulaziz University | Method of determining shear strength of soil using fall cone apparatus |
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