US2824445A

US2824445A - Soil testing apparatus

Info

Publication number: US2824445A
Application number: US603361A
Authority: US
Inventors: Lymon C Reese
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1956-08-10
Filing date: 1956-08-10
Publication date: 1958-02-25
Anticipated expiration: 1975-02-25

Description

L. c. REESE son. TESTING APPARATUS Filed Aug, 10,1956

Feb. 25, 1958 POWER SOURCE .74 7 HYSEEQIPLIC RECORDER 2 l 48 g 72 54 I! I v 22 ll l0 ;6 l2 i v FIG 2 24 69 1s 44 FIG I so as 2 34 2 L 30 I 30 32- 32 i l I 34 5o 22 36 42 68- lNVENTOR 78 LYMON .c. .REESE l so B T 3 ms ATTORNEY 4 Uni ed States 2,824,445 Patented Feb. 19,58

SOIL TESTING APPARATUS Lymon C. Reese, Austin, Tex assignor to Shell Development Company, New York, N. Y., a corporation of Delaware Application August 10, 1956, Serial No. 603,361

7 Claims. (Cl. 73-89) This invention pertainsto soil testing and relates more particularly to an apparatus for determining S011 behavior characteristics preparatory to the designing of pile sup-.1

ported structures which must resist lateral loads such, for

example, as oil well drilling platforms used in marsh areas.

or at off-shore drilling sites.

One of the factors considered in the designing of pile supported structures is the lateral reaction characteristics of the soil at the construction site. It has been found that the use of estimated lateral soil reaction data frequently results in costly design errors.

Although, in many cases, it has been the practice .to Db-1 tain data by running laboratory tests on...core samples. taken from the construction site, the cost of obtaining such data is also high. Moreover, while this method somewhat.

facilitates the task of the designer, it does not provide a basis from which truly reliable figures can be obtained as to the lateral reaction characteristicsof the soil or earth formations when under actual load conditions at the construction site.

Accordingly, while it is a general object of the present invention to provide an apparatus for determining su b surface soil behavior characteristics, it is a more particu:

lar object to provide an apparatus whereby more truly reliable and representative data can be obtained relating to the lateral reaction characteristics of soil when under stresses simulating actual load conditions at the construction site.

gin-accordance with one embodiment of the present invention, a pile is constructed including a testing section which is shiftable transversely "with respect to the axis of the pile. The pile is driven into the earth at the construction site, and the testing section is shifted transversej ly of the pile for applying a lateral stress to the soil-or earth formation which resists the movement-of the testing section, while measurements relating to the lateralreaction characteristics of the soil or earth formation in connection with the accompanying drawings wherein:

Fig. 1 isa diagrammatic view of the pile or soil testing apparatus of the present invention, showing the pileafter it has been driven into the earth and after the testing section has been shifted transversely of the pile;

Fig. 2 is a diagrammatic sectional view taken, along the 1 line2-2 of Fig. 3; and, I p

Fig. 3 is a diagrammatic sectional view taken along the line 3-3 of Fig. 2.

Referring now to the drawings, the apparatus of the present invention comprises an elongated cylindrical pile 19 which is adapted to be driven or lowered into the earth. As shown in Figs. 1 and 2, the pile carries a test, ing section 12 preferably arranged nearerto or-adjacent to the lower end of the pile and disposed between the adjacent ends of two cylindrical pile members 14. 'While,

since most piliugs are cylindrical" in form, and'thus the pile and testing section of the present invention are referred to as cylindrical, it is understood that they may be constructed in other forms as circumstances'may require; and that, in addition, a single pile may include 5 morethan one testing section. The members 14 are rigidlyconnected in a spaced relation by an axially extend- 7 ing rectangular column or mandrel 16. The lower end fthe mandrel is welded or otherwise rigidly attached to an end, plate 18 of the lower pile member 14. The upper end is preferably threaded whereby a threaded coupling is-made with an end plate 20 of the upper pile member 14 to facilitate the assembling or dismantling of the lie.

p The testing section 12 comprises a hollow cylindrical metal casing 22 having an outer diameter equal to that of .:the pile. The ends of the casing 22 include a pair of similarly constructed plates 24 having a pair of axially; aligned rectangular openings 26 through which the mandrel 16 extends As shown in Fig. 3, the openings 26 have a width slightly greater than the cross sectional width of the mandrel and a length which is substantially greater than thecross sectional length of the mandrel.

Thus, the casing 22 is shiftable transversely of the pile from an axially aligned or intermediate position (Fig. 2) wherein its outer surface is flush with the outer surface of 3 the pile, and into diametrically opposite laterally displaced positions (Fig. 1) whereby the opposite faces of the section serve to apply pressure to a surrounding earth forma-: tion. I a 4 ..-Any suitable means may be provided for sealing the in- ".terior of. the testing section from fluid in the formation. being tested such, for example, as a number of 0 rings 28 carried by the

end plates

18 and 20. The O ringsextend circumferentially around the opposite ends of the mandrel 16 in fluid tight engagement with the respective adjacent-surfaces of the end plates 24 of the casing 22. l n orderto obtain data relating to lateral soil reaction characteristics, it is preferable to measure at any instant. the pressure exerted on the testing section 12 by an earth formation and to measure the lateral displacement of the testing-section from a fixed reference point. To this-end,-:. the testing section is provided with a plurality, for example, a pair of pressure responsive devices carried in the opposite faces of the casing, and a plurality, for example; four lateral displacement measuring devices which are .arranged in pairs on opposite sides of the mandrel. "[hese devices may beof any suitable construction and, as illustrated, embody two types of transducers employing atype of strain gauge.

The pressure responsive devices each include a diaphragm 30 which is preferably formed of metal and is "rigidly attached to the casing- 22 with its outer surface substantially flush with the outer surface of the casing.

The inner surface of each diaphragm 30 is provided with integrally attached strain gauge elements 32.-

The displacement measuring devices each comprise a Ll shaped spring steel clip 34, the ends of which are attach'ed to the inner wall of the casing 22 and the mandrel 1 16. The opposite sides of the intermediate portion of 60 each clip are provided with integrally attached strain 3 gauge elements 36. Strain gauge devices operate on the well-known theory that the electrical resistance of a conductor changes in proportion to its strain. Since the strain gauge elements 66 32 and 36 form an integral part of each diaphragm 30 v. or clip 34, respectively, the strain of each element is a measure of the stress applied to the clipor diaphragm to which itis attached.

i As shown in Figs. 1 and 2, the strain gauge elements 70 32 and 36 are connected to the insulated conductors 38 of an -.e. ec trieal cable 40, the conductors extending through a transverse passage 42 in the mandrel. The cable 411" extends through an axial passage 44 in the mandrel and up the interior of the pile to the surface where .it is connected to a recorder 48 and an energizing power source 46. The recorder 48 may be'of any suitable type adapted for measuring the change in resistance of each strain.

gauge

32 and 36 forrecording acontinuous graphical Suitable :filter the spring clips 34 due to the transverse motion of the testing section 12, and any flexure in thediaphragms 30 caused by a pressure on the testing section operates to change the resistances of the

strain gauge elements

32 and 36. Thus, readings can be taken from the continuous recordof the signals from the gauges fordeter-mining the pressure exerted on'the testing section 12-by an earth formation-at any laterally displaced position of .the testing section with regard to any selected referencepoint. For example, therecorder may indicate and record the lateral displacement of the testing section from the intermediatepos'ition shown in Fig. 2.

It is understood that any suitable number of pressure responsive -or displacement'measuring' devices may be used. These devices may be arranged in any suitable manner with respect to "the testing section to meet various operating conditions. For example, with the instrumentation shown (using two 'pressure responsive devices arranged at two difl'erent points on the'testing section) it is necessary to approximate-the pressure distribution on the entire testing section, based on the measurements 'at the two "points, and to integrate this area to determine the soil reaction -orthe resultant force per unit length of the 'pile which would be developed "against the pile by the 'soil due to the lateral movement of the pile against the soil. Under some conditions better accuracy might be obtained by using additional pressure responsive devices distributed around the circumference of the testing section. Also under some conditions better results might be obtained by replacing the pressure responsive devices with a force transducer which would make a direct determination of the soil reaction or force against the pile. A plurality of lateral displacement measuring devices are preferred since their signals can be checked against each other, and in case of a failure of one or more of the devices, the use of the pile could be continued without delay so long as one device'remained operative.

More particularly, in the embodimentshown, the 'diaphragms 30 are disposed intermediate the ends of the casing 22 and lie along the diameter of the pile which defines the direction of the lateral path moved through by the testing section during its transverse movements. The spring clips 34 are symmetrically arranged with respect to the diaphragms 30, and lie in a plane defined by this diameter and the axis of the casing. Thus,the spring clips flex along the path moved through by the diaphragms, and the change in resistance of any spring clip strain gauge 36 is a true indication of the lateral 'displacement of the diaphragms 30.

As shown in Fig. 2; the testing'section 12 is shifted transversely of the pile by'the operation of four hydraulic jacks or motors 50 which arearranged in opposed pair's near or adjacent to the opposite ends of the'mandrel lti. and testing section. In the embodiment shown, this arrangement of the motors is'preferred as it minimizes any effect on the centrally arranged diaphragms of stress concentrations set up in the opposite ends of the casing by the motors. The arrangement and number of hydraulic motors can be varied according to thearrangement and number of diaphragms used.

The motors may be of any suitable construction and,

as shown, are of the telescoping or cylinder and piston type, the motors on one side of the mandrel being diagrammatically shown in section vfor illustrative purposes. Each motor comprises a cylinder 52 which is mounted on the mandrel 16, and a hollow piston embodying two telescoping cylindrical members 54 and 56. The outer end of the inner member 54 is closed by an end plate which is mounted to the casing. The stroke of the intermediate member 56 is determined by contact between a seal 58 carried by the member .56.and:a.fiange 60:0f the cylinder 52. The stroke of the inner member 54 with respect to the intermediate member 56 .is determined by contact between a seal 62 carried by the inner member with a pair of flanges 64 carried by the intermediate member.

. It may be seen from Fig. 2', that the combined stroke of each piston is suflicient toshift the testing section 12 transversely of the pile betweenth'e limits determined by the lengths of the openings 26 in the end plates 24 of the casing through which the mandrel 16 extends.

The motors .on each :side of the mandrel are supplied with hydraulic fluid through

branch channels

66 and 67 leadingfrom a pair of hydraulic :

fluid channels

68 and 69 in the

mandrelr Channels

68 and 69 are connected to hydraulic lines 70 and. 72, respectively, which arepassed up through the pile and are connected, at the surface, to .any suitable hydraulic unit 74 embodying a control valve 173', a .pump, :anda hydraulic reservoir (not shown). The pump of the hydraulic unitmay be oper* ated from the power source 46.

From the foregoing it .is apparent-that in order to shift the testing section 12 to the right of the intermediate posi' tion, as shown-in Fig. 2, the control valve 73 of the hydraulic unit 'is operated to connect the line 70 to the discharge side of the pump and to connect the line 72 to the intake side-of the pump. When the pump is energized the motors ,on the sight hand side of the mandrel are expanded whi-le' the others are contracted. By reversing the hydraulic connections through operation of the control valve, the testing section can be shifted in the opposite direction.

Preferably, the pile 10 -is-co'nstructed from .a number of threadably connected pipe sections whereby its length may be varied to meet different operating conditions. This construction enables the pile to be conveniently transported in-sections-and assembled at a test site, although, under mostconditions, the pile may be readily transported in an assembled condition. A

'If conditions at a testsite besuch that pre-assembly of the pile into the length required is impractical, the pipe sections can be provided with suitable hydraulic and electrical connections, and the pile can be made up ash is lowered or driven into the earth by adding pipe sections as required.

As shown in Fig. 3, the casing '22 may be provided with an access hole 78 having a removable cover plate 80 whereby the instruments and hydraulic motors in the testing section may be adjusted or replaced without disassemblying the pile.

In operation, the pile'is driven or lowered a predeterminal depth into the earth with the testing section "hydraulically locked into the intermediate position. The recorder is energized and the hydraulic motors on one sided the mandrel are operated to shift the testing section12 transversely of the 'pile in one direction. This action applies a'lateralload over an area of the earthformation which resists the movement of the testing section, and from readings recorded at the surface relating to the pressure required to permitmovement of the testing section, the initial lateral reaction'or resisting force of the earth formation can be determined. By operating the hydraulic system, the lateral load may be applied in various manners inthis same direction while the signals from the testing section are "recorded for determining the lateral reaction characteristics of the formation under different simulated actual load conditions. For example,

load conditions may be simulated by continuously apply V ing the lateral load by shifting the testing section from the intermediate position and into the extreme laterally displaced position in the one direction. ample, data is being obtained for use in designing piles for an offshore platform which may be subjected to hurricane loads, the testing section can be shifted into the extreme position at a faster predetermined rate than in the case where such loads need not be considered. Alternatively, the testing section can be shifted for alternately applying and relieving the load in this one direction to permit observation of the changes in the lateral reaction characteristics of the resisting formation. This type of loading may be used, for example, to simulate the wave loads which are anticipated at the construction site. After sufiicient data has been recorded by selectively shifting the testing section in the one direction from the intermediate position, corresponding data can be recorded by operating the hydraulic system and selectively shifting the testing section in a similar manner in the opposite direction from the intermediate position.

Preferably, however, data is recorded by operating the hydraulic system to shift the testing section from the intermediate position into the extreme'laterally displaced position in one direction, the rate of travel etc., being determined by the load conditions being simulated; shifting the testing section in a similar manner in the opposite direction into the other extreme laterally displaced position; and subsequently repeating the operation a number of times and, if desired, varying the load conditions as circumstances may require. Upon completion of these tests, the testing section is returned to the intermediate position and the pile is driven or lowered into a deeper position. The depth of the testing section is again recorded, and another series of tests is completed. Following the completion of tests at the final depth at which data is desired, the testing section is returned to the intermediate position and the pile is withdrawn and driven or lowered into the earth at other predetermined positions at the construction site. The tests are repeated until suflicient data have been obtained.

From the test data obtained to date, it appears that the nature of the top thirty feet of soil is the most important factor affecting the behavior of a laterally loaded pile. Thus, under most conditions it is not necessary to employ the testing section at great depths below the mud line. This fact, of course, greatly enhances the value of the testing pile and permits soil-behavior data to be obtained at a construction site more quickly and economically than was heretofore possible.

I claim as my invention:

1. An apparatus for determining the lateral soil rcaction characteristics of sub-surface earth formations comprising: a pile adapted to be driven into the earth, said pile including an interposed transversely movable testing section of substantially the same outer diameter as said pile, means in said pile for shifting said testing section transversely of the pile and against the pressure of an earth formation, and means carried by the testing section for sensing the pressure exerted on said section by an earth formation and the lateral displacement of said movable testing section with reference to a fixed element of said pile.

2. An apparatus for determining the'lateral soil reaction characteristics of sub-surface earth formations comprising: a cylindrical pile adapted to be driven into Where, for ex the earth, said pile including an interposed coaxial testing section, said section having the same outer diameter as said pile and being arranged for movement transversely of the pile between an axially aligned position wherein the outer surface of said section is flush with the outer surface of the pile and a laterally displaced position into which said section is adapted to move against the pressure of an earth formation, means in said pile for shifting said section between said aligned position and said displaced position, pressure responsive means carried by the testing section for sensing the pressure exerted on said section by an earth formation, and means in said test section for sensing the lateral displacement of the testing section against said pressure.

3. The apparatus as set forth in claim 2 wherein said pressure responsive means comprises a strain gauge including a diaphragm having an outer surface disposed substantially flush with the outer surface of said testing section, and wherein the means for measuring the lateral displacement of the testing section comprises a strain gauge including a flexible member attached to the testing section and a fixed member of the pile.

4. An apparatus for determining the lateral soil reaction characteristics of sub-surface earth formations comprising: a pile adapted to be driven into the earth, said pile including an interposed transversely shiftable hollow testing section which is normally axially aligned with said pile, an axially extending mandrel forming a fixed part of the pile and extending longitudinally through said testing section, means mechanically connected between said mandrel and said testing section for shifting the testing section along a diameter of the pile from the axially aligned position into oppositely disposed laterally displaced positions, pressure responsive means carried by the testing section for sensing a pressure exerted on said section by an earth formation, and means in said test section for sensing the lateral displacement of said test ing section from the axially aligned position.

5. The apparatus as set forth in claim 4 wherein said means for shifting the testing section includes an opposed pair of hydraulic motors mechanically connected between said mandrel and the testing section.

6. The apparatus as set forth in claim 4 wherein said pressure responsive means includes at least a pair of strain gauges arranged to move along a path in a direction defined by said diameter of the pile, said strain gauges being disposed in opposite face portions of the testing section, and wherein the means for measuring the lateral displacement of the testing section comprises at least one strain gauge including a flexible member attached to the testing section and said mandrel and arranged to flex along the path moved through by said pair of strain gauges.

7. The apparatus as set forth in claim 6 wherein said means for shifting the testing section include four hydraulic motors arranged in opposed pairs adjacent to the opposite ends of the testing section, and wherein said pair of strain gauges are disposed intermediate the opposite ends of said testing section.

References Cited in the file of this patent FOREIGN PATENTS