WO1995021302A1

WO1995021302A1 - Soil probing apparatus

Info

Publication number: WO1995021302A1
Application number: PCT/GB1995/000226
Authority: WO
Inventors: Peter Dunn
Original assignee: Mini Soil Surveys Limited
Priority date: 1994-02-03
Filing date: 1995-02-03
Publication date: 1995-08-10
Also published as: GB9402036D0; AU1543995A; GB9502196D0; GB2286249A

Abstract

A soil probing apparatus (10) includes a weight (18) which can be repeatedly dropped from a fixed height to drive a probe end member (42) into the ground using one or more driving rods (26). The probe end member (42) includes a ratchet (40) enabling the torque resistance of the apparatus to be determined with the probe member engaged and disengaged.

Description

Soil Probing Apparatus

This invention relates to soil probing apparatus and has particular reference to apparatus for probing and penetration testing of soils.

Penetration testing is commonly carried out in order to determine the load bearing capability of the soil, the nature of the soil for example sand, clay, or other types of soil, and the depth of hard and soft strata.

Various types of apparatus have been developed and used to conduct this type of soil survey. There are two main types of surveying method and these are commonly known as the DIN 5094 (in Germany) or SRS 15 method and the Dutch cone method. The SRS 15 method employs a cone which is driven into the soil by means of rods which are of a smaller diameter than the maximum diameter of the cone. A standard weight is dropped a fixed distance and the number of blows are recorded to achieve a fixed depth of penetration. The apparatus is therefore percussively driven and is known as "dynamic" probing. The rods are withdrawn relatively easily because the cone makes a hole which is larger than the diameter of the rods. This method only provides a reliable measure of the load bearing capacity of the soil in non-cohesive soils, eg. sand and gravels. It does not give an indication as to whether the soil is cohesive or non-cohesive and the soil type has therefore to be determined by bored holes or other means.

The Dutch cone method forces a cone and sleeve into the soil so that the point resistance and sleeve resistance (or skin friction) can be measured. This apparatus provides an indication as to whether the soil at any level is cohesive or non-cohesive and the strength of the soil without having to withdraw the probe. The cone and sleeve are forced into the ground at a slow pace and it is commonly known as the static cone method.

Both methods and their associated apparatus have their benefits and limitations according to the nature of the soil being surveyed, the type of site being surveyed and the type of information required, and the information available from other sources such as bore holes.

The SRS 15 method uses relatively simple apparatus but has limitations particularly the scope of information which can be obtained, whilst the apparatus relating the Dutch cone method is relatively complex as it uses hydraulic power to force the cone and the sleeve into the soil and can only be used on large sites where the cost and complexity of the apparatus can be justified even though the apparatus does provide a wide range of valuable and relatively accurate information. The above types of apparatus and other soil surveying apparatus are described in some detail in British Standard 5930/1981, page 43 to 47, the contents of which are hereby included by way of reference.

The present invention seeks to provide an apparatus which can measure both point resistance and skin friction in a wide range of soil types and on a wide range of sites. The point resistance would be related to dynamic/percussion probing. The skin friction would be related to the static method.

Accordingly, the present invention provides a soil probing apparatus comprising a retrievable ground penetrating probe end member; a leading rod engageable with the ground penetrating probe end member; extending rods engageable with the leading rod; driving means engageable with the extending rods, and the leading rod and retrievable ground penetrating probe end member, the driving means being .arranged to force the assembled ground penetrating probe end member and rods into the ground by percussive means and means for measuring the torsional frictional resistance of the apparatus both including and excluding the presence of the ground penetrating probe end member when the ground penetrating end member is at rest between periods of being driven into the ground.

The ground penetrating probe end member can have a cone shaped end with a cone angle of approximately 60°. The ground penetrating probe end member can have an extension secured to the leading rod. The probe end member may further comprise a ratchet which includes an extension engageable with the leading rod.

The driving means may comprise a plurality of rods which can be releasably secured together in a vertical sequential manner.

The driving means may further comprise a weight which can be raised and dropped to force the probe end member into the ground.

The present invention further provides a method of determining soil characteristics using a ground penetrating probe end member, the torque resistance is measured using a torque measuring means both with the ground penetrating probe end member engaged, by rotating the leading rod via the extending rods in a first rotational direction, and disengaged by rotating the leading rod and extending rods the opposite direction of rotation and subtracting the two torque measurements from one another to provide the friction resistance of the probe end member.

The present invention will now be described in more detail with reference to the accompanying drawings in which: Figure 1 shows diagra matically a general arrangement of one form of soil probing apparatus according to the present invention;

Figure 2 shows a detail of the apparatus shown in Figure 1 illustrating part of the driving means;

Figure 3 shows a detail of the driving rods of the apparatus as assembled in a vertical sequential manner;

Figure 4 shows a detail of the leading driving rod and the probe end member of the apparatus shown in Figure 1.

Figure 5 shows a detail of the spring pins used throughout the apparatus to secure components together.

Figure 6 shows the engaging of the torque spanner to the top driving rod in order to measure the torque resistance of the apparatus.

With reference to Figure 1 of the drawings, the present invention provides a soil probing apparatus (10) comprising a base (12) , an upright frame (14) including two columns (16) and two guide rods (16a) upon which a weight (18) is slidably secured. The weight (18) is attached to a rope (20) which passes over a pulley (22) attached to the frame (14) and then to an electric motor (24) and a slip winch. The weight (18) is engaged within a slidable frame (15) attached to the deiving dolly (32) so that the drop height (X) may be fixed to a predetermined height.

A number of driving rods (26) are sequentially secured together in a vertical manner by spring pins (44) and a ground penetrating probe end member (42) which is attached to the leading driving rod (34) is driven into the soil by the weight (18) striking the uppermost one of the pinned rods (26) via a dolly (32) , the weight being raised by the electric motor (24) . The ground penetrating probe end member (42) terminates with a point of angle approximating 60°.

The upper end of each rod (26a) is engageable with a cavity (26b) located at the lower end of each rod. The rods (26) are secured through the upper (26a) and lower (26b) ends by a spring pin (44) passing through holes (28) of the upper rods (26a) and lower end (26b) of the adjacent rod (26) .

Referring to Figure 3 in particular, it may be seen that the upper end (26a) of one rod contacts the lower end (26b) of an adjacent rod and provides the bearing surface when the rods are driven into the soil.

Referring to Figure 4 of the drawings, the lowermost rod is a leading rod (34) which comprises an upper end (34a) which is engageable with the lower end (26b) of an adjacent rod (26) . The ground penetrating probe end member (42) is secured to the leading rod (34) by means of a rod (38) of the ground penetrating probe end member (42) engaging in the cavity (34b) of the leading rod (34) . A spring pin (44) is inserted through holes (36) of the lower end (34b) of the leading rod (34) and the upper end (38) of the probe end member (42) to attach the probe end member (42) to the leading rod (34) . The rod (38) of the ground penetrating probe end member (42) is attached to a ratchet (40) which engages when the leading rod (34) is rotated clockwise, hence rotating the ground penetrating probe end member (42) in the same direction. When the leading rod (34) is rotated anti clockwise, the ratchet (40) disengages and the ground penetrating probe end member (42) does not rotate.

In operation the probing apparatus (12) is positioned at the site where penetration is to take place. The ground penetrating probe end member (42) is pinned to the leading rod (34) using a spring pin (44) . This assembly is placed in the frame (14) with the dolly (32) engaging with the upper end (34a) of the leading rod (34) . The ground penetrating probe end member (42) is driven into the ground by means of standard blows provided by the weight (18) being dropped repeatedly from a set height on the dolly (32) . The weight can be 63.5Kg and the set height can be 760mm. The number of standard blows required to penetrate the preset depth, for example 300mm, is recorded.

A successive rod (26) may be added to the leading rod (34) by matching the upper end (34a) of the leading rod (34) and the lower end (26b) of the adjacent rod (26) and securing with a spring pin (44) . After each new rod (26) has been added and driven to the preset depth, a torque measuring means such as a torque spanner (48) may be used to measure the torque resistance of the probe end member (42) and the rods, or the rods alone as described below.

Figure 6 shows an adapter (46) which may be fitted to the upper end (26a) of the uppermost rod (26) as the cavity (46a) of the adapter is matched to the upper end (26a) of the uppermost rod (26), and a spring pin (44) is inserted through holes (28) of the uppermost rod (26) and the adapter (46) respectively of the inner rod (26a) and outer sleeve (46b) respectively. The torque spanner (48) is fitted into the adapter (46) and a measurement of torque resistance is taken both with the ground penetrating end member (42) engaged by rotating the rod clockwise, and disengaged by rotating the rod anti clockwise.

A further rod (26) may then be added by matching the upper end (26a) of the uppermost rod (26) and the lower end (26b) of an additional rod (26) and securing with a spring pin (44) . The then uppermost rod (26) is driven further into the ground by the driving means, and the number of standard blows required to achieve the preset depth is recorded. The torque resistance is then measured, and the process is repeated until an optimum number of results have been recorded. Upon the completion of the soil test, the whole apparatus may be withdrawn, relatively easily, from the soil.

It will be appreciated that it is not known whether the torque resistance is due solely to the skin friction on the ground penetrating probe end member (42) , or whether it is partially due to the friction in the rods (26) . By disengaging the probe end member (42) , that is by rotating the rod anti-clockwise, the friction in the rods (26) alone is determined, and the friction due to the probe end member (42) may be calculated as the difference between the two measurements as the probe end member (42) is both engaged and disengaged.

It will also be appreciated that in relative terms the size and cost of equipment is small and the equipment can be used on a wide range of sites and in a wide range of soil types in order to produce accurate measurements of both soil strength and soil cohesiveness.

The means for driving the rods and thus the pin (44) and the probe end member (42) can take a variety of forms, and is not restricted to the means shown in the drawings. Also, the rods (26) can be coupled together by means other than that shown, for example by a threaded coupling, a bayonet fixing, or other types of releasable couplings.

Claims

1. A soil probing apparatus comprising a retrievable ground penetrating probe end member, a leading rod engageable with the ground penetrating probe end member, extending rods engageable with the leading rod, driving means engageable with the extending rods and the leading rod and retrievable ground penetrating probe end member, the driving means being arranged to force the assembled ground penetrating end member and rods into the ground by percussive means, and means for measuring the torsional frictional resistance of the apparatus both including and excluding the presence of the ground penetrating probe end member, when the ground penetrating probe end member is at rest between periods of being driven into the ground.

2. An apparatus as claimed in claim 1 in which the ground penetrating probe end member has a cone shaped end.

3. An apparatus as claimed in claim 2 in which the cone angle of the cone shaped end is approximately 60°.

4. An apparatus according to any one of the preceding claims in which the ground penetrating probe end member has an extension secured to the leading rod.

5. An apparatus as claimed in any one of the preceding claims in which the ground penetrating probe end member comprises a ratchet which includes an extension engageable with the leading rod.

6. An apparatus as claimed in any one of the preceding claims in which the driving means includes a plurality of rods which can be releasably secured together in a vertically sequential manner.

7. An apparatus as claimed in any one of the preceding claims in which the driving means comprises a weight which can be raised and dropped successively to force the probe end member into the ground.

8. A method of determining soil characteristics using a ground penetrating probe end member as claimed in any one of the preceding claims in which the torque resistance is measured using a torque measuring means both with the ground penetrating probe end member engaged, by rotating the leading rod via the extending rods in a first direction of rotation and disengaged by rotating the leading rod and extending rods in the opposite rotational direction and subtracting the two torque measurements obtained one from the other to provide the frictional resistance of the probe end member.