US3820384A - Soil testing apparatus and method - Google Patents

Abstract

The method and apparatus of this invention relates to the measuring of the in-place static friction of soils. It consists of driving a flat or planar test plate into the soil; extracting the test plate and recording the maximum force required to effect extraction. The test plate is removably connected to a driving rod, which embeds it down in the soil. The driving rod is removed, and the test plate is then extracted by a cable secured thereto. The maximum extraction force is a measure of the inplace static friction of the soil. The test plate is temporarily connected to the driving rod by a line which breaks readily upon separation of the driving rod from the test plate.

Description

United States Patent [191 Brill [4 June 28, 1974 SOIL TESTING APPARATUS AND METHOD [76] Inventor: Murray I. Brill, 383 Ocean Ave.,

Massapcqua Park, N.Y. H762 [22] Filed: July 17, 1972 [21] Appl. No: 272,592

[52] US. Cl. 73/84, 73/101 [51] Int. Cl. G0ln 33/24 [58] Field of Search 73/84, 101

[56] References Cited UNITED STATES PATENTS 2,826,065 3/1958 Grimes 73/84 X 3.6l0,035 10/1971 Handy 73/84 X Primary Examiner-Jerry W. Myracle 7 Attorney, Agent, or Firm-Jessup and Beecher 57 1 ABSTRACT and the test plate is then extracted by a cable secured thereto. The maximum extraction force is a measure of the in-place static friction of the soil. The test plate is temporarily connected to the driving rod by a line which breaks readily upon separation of the driving rod from the test plate.

7 Claims, 9 Drawing Figures SOIL TESTING APPARATUS AND METHOD BACKGROUND OF THE INVENTION This invention relates generally to the field of determining friction pile capacities and more particularly to the determination of friction pile capacities by static analysis of the soil into which the pile is to be driven.

In the building of any structures upon the soil it is normal for foundation studies to be performed upon the soil. The reason for these foundation studies is to predict the load carrying capacity of a friction pile that is to be installed within the soil strata. The normal procedure is to advance a hole, either cased or uncased, in the soil strata. It is common to make certain tests of the soil as the hole is advanced through the soil. It is the ob jective of these tests to obtain knowledge of the soil conditions at various depths of the hole. In order to extract soil samples from the hole a standard drill rod is normally employed of a diameter of 1% inches or larger. This drill rod is made up of a series of segments which are to be formed into a string and progressively lowered to greater and greater depths. Various types of soil sampling devices are attached to the lower end of the standard drill rod to take the soil sample at the bottom of the hole.

One way to avoid the driving of test piles is to employ some means to determine the capacity of the soil by measuring the frictional resistance of the soil. There have been known for a substantial period of time apparatuses which measure the frictional resistance of soil. One form of such previously known apparatuses relates to the driving of a rod into the soil, then extracting the rod and then measuring the force required to effect such extraction. However, rods exhibit a rather small area in contact with the soil and also the displacement volume and efi'ect is great in proportion to the surface area. Therefore, a series of tests are performed in a given area with a rod type of measuring indicator with the test results averaged. It has been found that the results of such tests will vary widely, and there is no guarantee that even an average figure represents a true value of the frictional resistance of the soil.

Previously known forms of apparatus to measure the frictional resistance of the soil have not been designed to measure directly the static frictional resistance between the soil layer and a non-displacement smooth steel surface. The apparatuses of the prior art have been more concerned with measuring the internal friction or the shear strength of the soil instead of correctly measuring the in-place static friction. Surface friction is a main factor in predicting pile load capacity.

SUMMARY OF THE INVENTION The method of this invention involves the embedding of a substantially flat or planar test plate about 16 inches below the bottom of a drill hole, by a driving rod which forces it down. Force from the driving rod is transmitted to the test plate by an adaptor shaft threaded onto the rod which presses the test plate down. Extraction of the test plate is accomplished by means of a hydraulic jack which is connected to a cable secured to the plate. During the inserting of the test plate down the drill hole, it is temporarily held to the adapter shaft by a rubber band, string, thin wire, or the like. After the test plate has been embedded into the soil, the driving rod is removed, fracturing the securing band. The test plate is then removed by pulling up the extraction cable. The maximum removal force is measured and recorded by an appropriate measuring apparatus; it represents the in-place static friction between the soil and a non-displacement smooth steel surface.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view of the apparatus of this invention showing the driving rod which embeds the test plate within the soil;

FIG. 2 is a side view of the apparatus of this invention taken along line 2-2 of FIG. 1;

FIG. 3 is a diagrammatic view showing a means to effect extraction of the test plate and the structure to measure the force required to effect such extraction;

FIG. 4 is an enlarged view of the test plate showing in more detail the connection between the test plate and the driving rod;

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4;

FIG. 6 is an edge view of the test plate during removal, taken along the same line as FIG. 2;

FIG. 7 is an enlarged view of one form of hydraulic jack which may be used to effect extraction of the test plate;

FIG. 8 is a side view of the hydraulic jack taken along line 8-8 of FIG. 7; and

FIG. 9 is a cross-sectional view of the hydraulic jack taken along line 99 of FIG. 8.

DETAILED DESCRIPTION OF THE SHOWN EMBODIMENT The method and apparatus of this invention is found to be particularly adapted to the testing of the soil located at the bottom of a deep drill hole 10. A casing 12 may be included within the hole but is not requisite to this invention.

The apparatus of this invention employs a substantially flat or planar test plate 14 having an integral upstanding connecting end 16. Around the periphery of the plate 14 is a sharpened edge 18. The edge 18 facilitates the embedding of the test plate 14 within the soil and enhances the non-displacement character of the test. The plate 14 is of steel about one-fourth of an inch in thickness. Approximately 50 square inches has been found to be a good effective surface area.

The connecting end 16 is ensmalled to an upstanding stud 20, which mates in a sliding fit with a socket 22 formed in a short adaptor shaft or member 24. In use, shaft 24 is a part of the driving rod assembly which also includes the conventional driving rod 26, which forms no specific part of this invention. The driving rod 26 is threaded at 28 onto the connecting member 24.

In order to extract the plate 24 after it is embedded, a cable 30 is attached to the plate 14 by being passed through aperture 32 located through the connecting end 16. The end of the cable 30, after being passed through the aperture 32, is looped back onto itself and secured by a clamp 34. The cable 30 is fed from a source such as a reel 36 which is located at the top of the hole 10.

In lowering the test plate 14 to the bottom of the hole 10, some means is desirable to secure the plate 14 to the driving rod assembly, because the stud 20 is free to slide from the socket 22. Thus a band 38 is wrapped around the shaft 24 and the cable 30, sufficiently tight to prevent the test plate 14 from dropping off the shaft 24 during the lowering operation. The band 38 can take any of numerous forms such as a rubber band, a string, a thin wire, a band of material, fabric, thin cable, or any other similar devices. After the test plate 14 is embedded within the soil, the band 38 readily fails or slips off to permit free release of the driving rod assembly from the test plate 14.

The embedding procedure is accomplished in a conventional manner, by simply pushing or driving by any means the test plate 14 into the soil by means of the rod 26 and shaft 24. The test plate 14 is preferably embedded into the soil about 16 inches. Up to this particular moment, the cable 30 remains loose, being merely paid out from the reel 36.

After the plate 14 is embedded, the driving rod 26 and its connected shaft member 24 are lifted and removed from the hole. It slips off the connecting end 16 with very little resistance, as the band 38 fails or slips off. As a result the plate 14 is left embedded within the soil in an undisturbed manner with the attached cable 30 hanging loosely from the reel 36.

The test is then performed by measuring the maximum force developed in the cable 30 during the extraction of the plate 14 from the soil. This extracting force is preferably supplied by a simple pull type hydraulic system assembly, the'maximum hydraulic pressure developed within the assembly during the extracting operation being in turn a measure of a maximum force required. The maximum pressure is determined in conventional fashion by a maximum reading needle on a hydraulic gauge which measures the pressure in the hydraulic apparatus.

In case a pull type or tension jack is not available the more widely used push or compression type jack may be readily adapted to this function by the technique il-v lustrated in FIGS. 3, 7,8 and 9.

This hydraulic ram assembly 40 includes a tripod 42 mounted over the hole 10, a hydraulic jack 44, a source of hydraulic fluid (not shown) and a pumping apparatus 46. A pressure gauge 48 is connected to the pumping apparatus and is adapted to register the pressure required to effect withdraw] of the test plate 14. The pressure gauge reading may be empirically converted to a force reading and divided by the surface area of the plate to obtain the unit value of frictional resistance. However, time will be saved and errors avoided if the face of the dial on the pressure gauge 48 reads directly in tons per square foot.

The pumping apparatus 46 is shown as a conventional hand operated pump. However, any other conventional type of pumping apparatus may be employed. The hydraulic fluid from the pumping apparatus 46 is conducted through conduit 50 to the jack 44. As noted, the jack 44 may comprise either a pull type or the more common push type (which exerts a compression force) as shown specifically in the drawings, FIGS. 3, 7, 8 and 9. This push type has here been converted to apply a pulling force on the cable 30.

Although, as noted, a hydraulic jack of the pull type is preferred, the push type is more readily available, and is here depicted. It is to be understood that the structure depicted in the FIGS. 3, 7, 8 and 9 is to be considered an alternate to the preferred pull type.

It is believed to not be necessary to go into explicit detail of the construction of the compression jack 44 (push type) as such jacks are extremely common. The cylinder 76 of the jack 44 is screwed in to a sleeve 52, which includes a pair of diametrically located longitudinal slots 54 and 56.

Plunger 60, which is connected to the piston (not shown) of the jack 44, is screwed into a short connecting sleeve 62 which operates within the chamber 58 forming the interior of sleeve 52. The connecting sleeve 62 has a pair of aligned openings therein which receive a diametric pin 64. The length of the slots 54 and 56 matches the full length of travel of plunger 60.

The pin 64 spans a ring 66, which encircles the sleeve 52. Ring 66 has a pair of trunnions 68 located diametrically opposite each other and transverse of the pin 64. The trunnions 66 are pivotally mounted, through posts 70, to a base ring 72. The base ring 74 is pivotally connected to the upper ends of the legs of the tripod 42.

Thus, a universal connection is established between plunger 60 and the tripod 42, which permits the jack 44 to self align itself with cable 30 as force is applied to extract the test plate 14.

A hook 74 is fixedly secured to the free lower end of the sleeve 52, and receives a loop formed at the upper end of the cable 30.

When a pull type of hydraulic jack is employed, it is simply suspended by universal joint from the head of the tripod 52, and the operating pull member is connected to the cable 30.

As the hydraulic fluid is pumped by the pumping apparatus 46 through conduit 50 into the jack 44, the plunger 60 moves downward with respect to the cylinder 76.

However, since the plunger 60 is supported by the fixed tripod 42, the net result is that the cylinder 76 and sleeve 52 move upward, tensioning the cable 30 and extracting the plate 14. The force developed is indicated on the pressure gauge 58. A maximum reading needle on gauge 58 records the maximum pressure and hence the maximum extraction force. The invention thus obtains the in-place static friction between a smooth steel plate and each soil layer. The plate 14 is designed to be installed in each soil layer and tested in a similar manner to that commonly done through soil sampling in other known penetration tests. One distinction of the method of this invention is that the drill rod 26 is removed prior to extraction of the test plate 14.

The apparatus and method of this invention provides for the obtaining of most accurate results to predict the load carrying capacity of a friction pile to be installed within the soil strata. The apparatus and method of this invention eliminates virtually all variables and sources of error by measuring directly only the static frictional resistance of each soil layer acting on the surface of a steel plate when the plate is subject to the static load. The method and apparatus of this invention may be easily and accurately accomplished even at the great depth to which soil borings may be carried out. The plate 14 of this invention, being relatively thin with sharp edges, measures practically pure friction on its flat surfaces with the displacement effect and disturbance to the natural soil density being so small as to be negligible. The results are therefore directly applicable to any non-displacement pile of any size or shape having a smooth surface in contact with the soil. Therefore, all variables inherent in the pile type (size, shape,

method of installation and material composition) are eliminated, and only the actual soil conditions at a given depth and location are measured.

There are pile type coefficients or correction factors available to convert the values obtained by this invention to other types of piles, materials, effects when displacement driven, and other variables. Given the soil static friction values which are obtained by the method and apparatus of this invention and the available pile type correction factor or factors, the static load carrying capacity of any pile installed in the investigated soil strata may be calculated with a high probability of certainty. This invention decreases the full scale load testing of piles, by reducing the number of tests necessary or completely eliminating the need for them in certain instances. Therefore, more accurate and reliable prediction of pile load capacity or required pile length to develop a given pile load is accomplished.

A further advantage of the present invention is that because of its simplicity, accurate readings can be rapidly obtained. After the plate 14 is embedded into the soil and the drill rod 26 has been removed, the placement for the hydraulic jack on the tripod 42 over the hole, the looping of the cable 30 and the manual pumping of the pumping apparatus 46 are all done easily and quickly with no disturbance to other equipment located around the hole. The maximum load resistance will be automatically determined by a maximum reading indicator pointer on the face of pressure gauge 48. The measured load will be a pure static force with no eccentricity or other secondary sources of error regardless of depth.

The load capacity of the apparatus of this invention need not be more than about one-quarter ton, since the highest value of unit friction encountered in various soils is not likely to exceed 7% tons per square meter.

What is claimed is: 1. The method of measuring the frictional resistance of soil at the bottom of a hole comprising:

providing a substantially flat test plate;

attaching an extraction cable to the test plate;

providing a driving rod;

temporarily securing together the test plate and the driving rod to thereby prevent disassociation by gravity of the test plate from the driving rod while being lowered into the hole;

applying a compressive force to the driving rod to embed the test plate in the soil at the bottom of the hole;

extracting the driving rod and causing release of the test plate from the driving rod;

extracting the test plate from the soil, and

measuring the maximum extraction force required to extract the test plate from the soil.

2. The process of determining the in-place static friction of a soil stratum comprising:

drilling a hole into the soil stratum;

passing a substantially flat test plate down the hole into the soil stratum;

providing a driving rod;

embedding the plate into the stratum by means of the driving rod;

removing the driving rod;

extracting the test plate from the soil stratum; and

measuring the maximum extraction force required during the extraction of the test plate from the soil stratum.

3. Apparatus for measuring in-place static friction of soil strata comprising:

a substantially flat test plate adapted to be injected into the soil strata;

a drive rod releasably connected to said test plate for driving said test plate into the soil strata;

means for removing the drive rod from the test plate while leaving the test plate embedded in the strata;

a cable secured to said test plate;

tensioning means connected to the cable for exerting tension on said cable to extract said test plate from the strata; and

means coupled to the tensioning means for measuring the maximum tension developed in said cable during the extraction of said test plate, thereby to measure the maximum extraction force required to extract said test plate from the strata.

4. Apparatus in accordance with claim 3 wherein said tensioning means comprises a hydraulic jack; and said tension measuring means comprising means for measuring the maximum hydraulic pressure developed in said jack during the extraction of said test plate.

5. Apparatus for predicting the load carrying capacity of a friction pile in a soil strata, said apparatus comprising:

a flat test plate having an integral upstanding connecting end; a driving rod; an adapter shaft connected to one end of said driving rod in coaxial relationship therewith and slidably receiving said connecting end of said flat test plate to position said test plate in axial alignment with said driving rod and said adapter shaft; means for introducing an embedding force through said driving rod to said test plate to embed said plate a predetermined distance within the soil strata;

releasable securing means attaching said connecting end of said test plate to said adapter shaft to permit said drive rod and said adapter shaft to be lifted and removed from the test plate without affecting the position of said test plate;

a cable attached to said test plate for extracting said test plate from the soil strata;

extraction means connected to said cable to extract the test plate from the soil strata; and

means coupled to said extraction means to measure the maximum force deveoped by the cable during the extraction of the test plate.

6. The apparatus defined in claim 5, in which said test plate is composed of steel.

7. The apparatus defined in claim 6, in which said test plate has a sharpened peripheral edge to facilitate the embedding of the test plate in the soil strata.

Claims (7)

1. The method of measuring the frictional resistance of soil at the bottom of a hole comprising: providing a substantially flat test plate; attaching an extraction cable to the test plate; providing a driving rod; temporarily securing together the test plate and the driving rod to thereby prevent disassociation by gravity of the test plate from the driving rod while being lowered into the hole; applying a compressive force to the driving rod to embed the test plate in the soil at the bottom of the hole; extracting the driving rod and causing release of the test plate from the driving rod; extracting the test plate from the soil, and measuring the maximum extraction force required to extract the test plate from the soil.

2. The process of determining the in-place static friction of a soil stratum comprising: drilling a hole into the soil stratum; passing a substantially flat test plate down the hole into the soil stratum; providing a driving rod; embedding the plate into the stratum by means of the driving rod; removing the driving rod; extracting the test plate from the soil stratum; and measuring the maximum extraction force required during the extraction of the test plate from the soil stratum.

3. Apparatus for measuring in-place static friction of soil strata comprising: a substantially flat test plate adapted to be injected into the soil strata; a drive rod releasably connected to said test plate for driving said test plate into the soil strata; means for removing the drive rod from the test plate while leaving the test plate embedded in the strata; a cable secured to said test plate; tensioning means connected to the cable for exerting tension on said cable to extract said test plate from the strata; and means coupled to the tensioning means for measuring the maximum tension developed in said cable during the extraction of said test plate, thereby to measure the maximum extraction force required to extract said test plate from the strata.

4. Apparatus in accordance with claim 3 wherein said tensioning means comprises a hydraulic jack; and said tension measuring means comprising means for measuring the maximum hydraulic pressure developed in said jack during the extraction of said test plate.

5. Apparatus for predicting the load carrying capacity of a friction pile in a soil strata, said apparatus comprising: a flat test plate having an integral upstanding connecting end; a driving rod; an adapter shaft connected to one end of said driving rod in coaxial relationship therewith and slidably receiving said connecting end of said flat test plate to position said test plate in axial alignment with said driving rod and said adapter shaft; means for introducing an embedding force through said driving rod to said test plate to embed said plate a predetermined distance within the soil strata; releasable securing means attaching said connecting end of said test plate to said adapter shaft to permit said drive rod and said adapter shaft to be lifted and removed from the test plate without affecting the position of said test plate; a cable attached to said test plate for extracting said test plate from the soil strata; extraction means connected to said cable to extract the test plate from the soil strata; and means coupled to said extraction means to measure the maximum force deveoped by the cable during the extraction of the test plate.

6. The apparatus defined in claim 5, in which said test plate is composed of steel.

7. The apparatus defined in claim 6, in which said test plate has a sharpened peripheral edge to facilitate the embedding of the test plate in the soil strata.

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