WO2022025756A1

WO2022025756A1 - Testing system

Info

Publication number: WO2022025756A1
Application number: PCT/NL2021/050405
Authority: WO
Inventors: Jasper Stefan Winkes
Original assignee: Ihc Holland Ie B.V.
Priority date: 2020-07-30
Filing date: 2021-06-29
Publication date: 2022-02-03
Also published as: EP4189171B1; EP4189171A1; NL2026169B1; TW202215024A

Abstract

A test element (100) for determining ground characteristics is disclosed. The test element comprises a longitudinal body (110) configured to receive a driving force from a driving means and a penetration end; and at least two lateral stiffness sensors (130, 140) interspaced along the length of the longitudinal body. Each of the at least two lateral stiffness sensors are configured to determine the lateral stiffness of the ground at a corresponding elevation level once the test element is driven to a predetermined depth.

Description

TESTING SYSTEM

The present invention relates to a testing system and a method of testing. In particular, but not exclusively, the present invention relates to a testing system for determining ground characteristics and a method of determining said ground characteristics for piling.

Background

Driving a pile into the ground offshore typically involves dropping a ram or hammer on to the top of the pile from a height. It is known that the characteristics of the soil into which a pile is intended to be driven can affect the driveability of the pile, and the overall design of the pile chosen. Testing systems are used as a way of predicting soil characteristics, from which suitable parameters for driving the pile can be chosen (for example, the energy level of the hammer and/or the number of blows from the ram or hammer required to drive the pile to a final position).

These known tests include a cone penetration test (CPT), which measures: tip resistance; shaft friction; and/or pore water pressure. For a CPT all measurements are made at the tip of the test element as it is driven downwardly in the soil. Thus, the soil characteristics at each elevation are measured only once as the test element is driven into the ground. However, soil characteristics such as the soil friction can change as a pile is driven into the ground (caused by a mechanism typically referred to as soil friction fatigue). There can therefore be large deviations between predicted characteristics from such the testing and the final characteristics.

In use monopiles can be subject to a large overturning moments as a result of waves acting on the foundations and the wind acting on the rotor of the wind turbine. These moments can be large - for example up to 1GNm. Current testing methods lack an effective way of assessing the suitability of the soil for supporting a pile subject to such moments.

It would be useful to provide an improved testing system/method for better determining the various soil characteristics, such that more accurate predictions for piling and in-situ behaviour can be made.

Summary of the Invention

Certain embodiments of the invention provide the advantage that more accurate determinations of soil characteristics can be made, which can inform and subsequently improve piling operations.

According to a first aspect of the present invention there is provided a testing system for determining ground characteristics, the testing system comprising; a driving means; and a test element comprising: a longitudinal body configured to receive a driving force from the driving means and a penetration end; and a set of two or more sensors interspaced along the length of the longitudinal body, each of the two or more sensors being configured to provide information about a ground characteristic, wherein the set of two or more sensors comprises a first sensor spaced a first distance from the penetration end and a second sensor spaced a second, larger, distance from the penetration end; wherein, in use, the driving means is configured to: provide a driving force to the test element to drive the penetration end of the test element into the ground to a first ground depth, wherein the first sensor of the two or more sensors provides information about the ground characteristic at or across an elevation level as the test element is driven into the ground to the first ground depth; and provide a driving force to the test element to further drive the penetration end of the test element into the ground to a second ground depth, wherein the second sensor of the two or more sensors provides information about the ground characteristic at or across the elevation level as the test element is further driven into the ground to the second ground depth.

The provision of an elongate test element with a set of two or more (or a plurality of) sensors interspaced along the body thereof allows a ground characteristic to be repeatedly measured at a given depth or elevation level as the test element is driven into the ground (i.e. measured by each sensor as it passes the given depth). As such, the effect of the driving process on the ground characteristic can be analysed to provide a more accurate ground characterisation that can be used to perform corresponding (i.e. scaled-up) piling operations. Moreover, the system provides in-situ measurements, allowing optimization of the foundation resulting in a more efficient foundation through optimized design.

Suitably the system further comprises a controller, the controller being configured to receive and compare the information provided by the first and second sensors about the ground characteristic at the elevation level. Direct comparison of information provided about a particular elevation level or depth by different sensors (i.e. provided when the test element has reached a different depth) allows better ground characterisation particularly an improved dynamic characterisation.

Suitably wherein the two or more sensors of the set of sensors are friction sensors. This allows the driving resistance experienced by the test element to be measured.

The friction can be determined through local measurements on the test element or it can be determined via a measurement of the stress in the test element, between two positions in the test element, whereas the difference in stress can be contributed to the shaft friction (and potentially inertia component) of the test element in between the two positions.

For example, suitably, at least one of the friction sensors includes or is positioned on a sleeve element surrounding a section of the longitudinal body and/or, suitably, at least one of the friction sensors is configured to determine the difference between the axial stress or strain in the longitudinal body at different longitudinal positions on the longitudinal body. Suitably the controller is configured to determine the change in driving resistance to the test element as the test element is driven into the ground. This allows the friction fatigue of the surrounding ground to be characterised.

Suitably the test element comprises at least one further set of two or more sensors interspaced along the length of the longitudinal body, each of the two or more sensors being configured to provide information about a further ground characteristic. As such, a single test element is provided that can produce a more complete ground characterisation, including information about multiple ground characteristics (for example at least one of friction, pore water pressure, acceleration) and how this characteristic varies as the test element is driven into the ground.

Suitably the two or more sensors of the further set of sensors are water pressure sensors. Suitably the driving means is a pile-driver assembly. Aptly the pile-driver assembly is a continuous or discontinuous pile driver assembly.

Suitably the system further comprises a clamping assembly and/or an abutment removably attached to the test element, wherein the driving force is transferred to the test element via the clamping assembly or abutment.

Suitably the system further comprises a set of at least one acceleration sensor.

Suitably, the pile driver assembly comprises: a casing defining a chamber, the chamber being configured to house a fluid; and actuating means coupled to the chamber, wherein actuation of the actuating means displaces the chamber relative to the test element, such that the chamber moves away from the test element, and wherein the actuating means is configured to release the chamber for displacement towards the test element such that a force is exerted by the chamber on the test element, to controllably drive the pile into the ground. According to a second aspect of the present invention there is provided a method of determining ground characteristics, wherein the method comprises: providing a driving means; providing a test element comprising: a longitudinal body configured to receive a driving force from the driving means and a penetration end; and a set of two or more sensors interspaced along the length of the longitudinal body, each of the two or more sensors being configured to provide information about a ground characteristic, wherein the set of two or more sensors comprises a first sensor spaced a first distance from the penetration end and a second sensor spaced a second, larger, distance from the penetration end; providing a driving force to the test element with the driving means, to drive the penetration end of the test element into the ground to a first ground depth; determining, using the first sensor of the two or more sensors, information about the ground characteristic at or across an elevation level as the test element is driven into the ground to the first ground depth; and providing a driving force to the test element with the driving means, to further drive the penetration end of the test element into the ground to a second ground depth, determining, using the second sensor of the two or more sensors, information about the ground characteristic at or across the elevation level as the test element is further driven into the ground to the second ground depth.

Suitably the method further comprises: determining the change in driving resistance to the test element as the test element is driven into the ground from the information provided by the first and second sensor. Suitably the method further comprises determining, using at least one further set of two or more sensors interspaced along the length of the longitudinal body, information about a further ground characteristic.

Suitably the method further comprises the step of removing the test element from the ground.

Suitably the longitudinal body comprises a plurality of segments, wherein the test element is driven into the ground by at least partially driving a first segment of the longitudinal body into the ground; attaching a further segment of the longitudinal body to an end of the first segment; and at least partially driving the further segment of the longitudinal body into the ground.

Suitably, the driving means comprises: a casing defining a chamber, the chamber being configured to house a fluid; and actuating means coupled to the chamber, wherein the method further comprises the steps of: providing the pile-driver assembly with the chamber in a coaxial arrangement with the test element; actuating the actuating means such that the chamber is moved away from the test element; and further actuating the actuating means to release the chamber such that the chamber displaces towards the test element and exerts a force on the test element, to controllably drive the test element into the ground.

According to a third aspect of the present invention there is provided a test element for determining ground characteristics, the test element comprising: the test element comprising: a longitudinal body configured to receive a driving force from a driving means and a penetration end; and at least two lateral stiffness sensors interspaced along the length of the longitudinal body; wherein each of the at least two lateral stiffness sensors are configured to determine the lateral stiffness of the ground at a corresponding elevation level once the test element is driven to a predetermined depth.

The provision of an elongate test element with at least two, or a plurality of, lateral stiffness sensors allows a profile of lateral stiffness of the ground surrounding the test element with increasing depth to be characterised. This provides information to enable the preparations in determining the suitability of the ground for expected moments applied to the pile. Suitably the at least two lateral stiffness sensors comprises a first sensor spaced a first distance from the penetration end and a second sensor spaced a second, larger, distance from the penetration end.

Suitably at least one of the lateral stiffness sensors comprises a probe element having: an extended position in which the probe element protrudes from the longitudinal body; and a retracted position in which the probe element is housed within the longitudinal body.

Suitably the at least one lateral stiffness sensor comprises an actuating element configured to actuate the probe element from its retracted position to its extended position. Suitably, the actuating element comprises an inflatable sleeve or a hydraulic cylinder. Suitably the at least one lateral stiffness sensor comprises measuring means configured to measure the force required to move the probe element from its retracted position to its extended position and/or to measure the distance by which the probe element protrudes from the test element in its extended position.

Suitably at least one of the lateral stiffness sensors further comprises a water pressure sensor for determining the pore water pressure. According to a fourth aspect of the present invention there is provided a testing system for determining ground characteristics, the testing system comprising; a driving means; and a test element, wherein the pile-drive assembly is configured to deliver a driving force to the driving surface of the test element to drive the test element into the ground.

Suitably, the driving means is a pile-driver assembly.

Suitably, the pile-driver assembly comprises: a casing defining a chamber, the chamber being configured to house a fluid; and actuating means coupled to the chamber, wherein actuation of the actuating means displaces the chamber relative to the test element, such that the chamber moves away from the test element, and wherein the actuating means is configured to release the chamber for displacement towards the test element such that a force is exerted by the chamber on the test element, to controllably drive the pile into the ground. Suitably the system further comprises a clamping assembly and/or an abutment removably attached to the test element, wherein the driving force is transferred to the test element via the clamping assembly or abutment.

According to a fifth aspect of the present invention there is provided a method of determining ground characteristics, wherein the method comprises: providing a test element comprising: a longitudinal body configured to receive a driving force from a driving means and a penetration end; and at least two lateral stiffness sensors wherein each of the at least two lateral stiffness sensors are configured to determine the lateral stiffness of the ground; driving the test element into the ground to a predetermined depth; and determining the lateral stiffness of the ground at elevation levels corresponding to each of the lateral stiffness sensors using the at least two lateral stiffness sensors..

Suitably the step of determining the lateral stiffness of the ground using a lateral stiffness sensor comprises actuating the lateral stiffness sensor to move a probe element from a retracted position in which the probe element is housed within the longitudinal body to an extended position in which the probe element protrudes from the longitudinal body.

According to a sixth aspect of the present invention there is provided a method of modelling the lateral pile capacity of the ground, wherein the method comprises: providing a test element comprising: a longitudinal body configured to receive a driving force from a driving means and a penetration end; and at least two lateral stiffness sensors wherein each of the at least two lateral stiffness sensor are configured to determine the lateral stiffness of the ground; driving the test element into the ground to a predetermined depth; determining the lateral stiffness of the ground at elevation levels corresponding to each of the lateral stiffness sensor using the lateral stiffness sensor; and using the lateral stiffness to predict lateral pile capacity in the ground.

Throughout the description reference is made to “ground characteristics”. As used herein this term is intended to indicate a property(s) of the ground, for example the ground into which a pile may be driven (for example soil or sand). Ground characteristics include, but are not limited to ground friction (that is, the friction experienced by an object, such as a pile as it moves through/into the ground), ground stiffness (that is, the resistance to deformation of the ground when subject to an applied load, for example the lateral, or radial, stiffness of the soil), pore water pressure (that is, the pressure of water within pores defined within the ground) and axial (tip) resistance of the pile. Specifically, ground characteristics described herein are those related to, or that have an effect on, piling operations.

As used herein the term “ground depth” shall be understood as a depth below the ground surface. For example in the context of driving a pile or test element into the ground, the ground depth of the pile or test element shall be understood as the depth reached by a penetration end thereof.

As used herein the term “elevation level” shall be understood to be, in general, interchangeable with “ground depth”. That is, an “elevation level” is a depth below a ground surface. However, in the context of driving a pile or test element into the ground, to avoid confusion with the “ground depth” of the pile/test element as a whole, an “elevation level” may refer to another depth below a ground surface that is not the depth reached by a penetration end thereof. For example, the “elevation level” may be a distance from the surface of the ground reached by a section of the pile/test element once the penetration end thereof has been driven to a specified ground depth (for example the ground position corresponding to a sensor positioned on a test element). It would be understood that the “elevation level” may refer to a discrete depth (for example 10m) or a depth level (for example 10-12m), which may, for example, correspond to a strata or layer of soil/material within the ground.

As used herein the term “driving force” shall be understood as a force or pressure applied to drive or push an object in a particular direction. For example, a driving force exerted by a driving means on a test element is a force used to propel or drive the test element into the ground.

Brief Description of the Drawings

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Fig. 1 illustrates a perspective view of an example of a test element;

Fig. 2 illustrates an enlarged view of a segment of the test element of Fig. 1 ;

Fig. 3 illustrates a perspective view of a testing system including the test element; Fig. 4 illustrates an enlarged view of a region within the testing system of Fig. 3;

Fig. 5 illustrates a perspective internal view of a sensor in a test element;

Fig. 6a illustrates a perspective view of a test element with a sensor in a retracted position; and

Fig. 6b illustrates the perspective view of the test element of Fig. 6a with the sensor in an extended position.

In the drawings like reference numerals refer to like parts.

Detailed Description

The present disclosure relates to systems and methods for determining ground characteristics to aid in the placement of monopiles or the like. The systems and method disclosed herein are aptly but not exclusively intended for use on offshore applications for example undersea piling although aspects of the disclosure may also be also be used for onshore applications.

Fig. 1 shows a test element 100 for determining ground characteristics. For example the test element 100 may be used for determining ground characteristics in preparation for piling operations - that is, the driving of piles or similar structures into the ground.

The test element 100 includes a longitudinal body 110. That is, the test element 100 includes an elongate or slender body that extends longitudinally. In this example, the longitudinal body 110 comprises a rod or tubular element. In this example, the longitudinal body includes a plurality of segments 120, that can be bolted together in an ‘end to end’ arrangement. However, in other examples the longitudinal body may be a single piece.

In this example the longitudinal body 110 has a penetration end 114. The penetration end 114 is configured to be the first part of the test element 100 to enter the ground during driving. In some examples the penetration end 114 may be tapered to allow easier entry into the ground.

In general the test element 100 is sized so as to be smaller than the ‘end product’ structures to be driven into the ground - for example, a monopile or the like. More specifically, the test element 100 may be sized so as to be a generally scaled-down version of the monopile. It is to be understood that the test element 100 may not be hollow like a monopile. As such, the test element 100 can be driven into the ground to provide test data that helps inform the installation of the full-scale ‘end product’ structures.

For example, the test element 100 may have dimensions scaled down from a full-size monopile by a ratio of about 1:50 to about 1:200, aptly 1:100. For example, the test element may have a dimeter of from about 5cm to about 30cm, aptly about 12cm to 25cm. In a particular example, for a monopile with a 10m diameter and about 8 cm wall thickness (for example a hollow tube pile) a test element 100 having a diameter of 18cm may be used (for a massive rod).

The test element 100 may be between about 15m to about 50m in length, aptly between about 20m and 35m in length.

The test element 100 includes at least one set of sensors 130, 140. In this example, the test element includes a first set of sensors 130 and a second set of sensors 140.

Referring only to set 130 for simplicity (but equally applicable to set 140), the first set of sensors 130 includes at least two sensors. Any suitable number of sensors 130 may be used in the first set. For example, there may be 5, 10, 15, 20 or more sensors spaced along the length of the test element 100. In the section illustrated in Figure 2, three sensors 130a-c are illustrated. For simplicity these sensors 130a-c will be referred to when describing the set of sensors 130.

The sensors 130a-c are configured to provide information about a ground characteristic. That is, each of the sensors 130a-c is configured to provide information about the same ground characteristic. In other words, in general, the sensors 130a-c within the set 130 are identical, or identical in function. The second set of sensors 140 are configured to provide information about a different ground characteristic. In other words each sensor 140a-c within the second set of sensors 140 is configured to provide information about the same ground characteristic, different from the ground characteristic of sensors 130a-c. Each of the sensors 130a-c in set 130 are spaced apart along the length of the longitudinal body 110. For example, the set of sensors 130 includes a first sensor 130a spaced a first distance from the penetration end 114 and a second sensor 130b spaced a second, larger, distance from the penetration end 114 (and further sensors spaced an increasing distance from the penetration end 114). In other words the sensors 130a-c,140a-c in each set 130, 140 are spaced apart from the other sensors in that set 130, 140 such that the length of the longitudinal body 110 has sensors spaced or distributed along it. This allows for a high volume of measurements to be taken and compared, improving the accuracy of data collected. In this example the set of sensors 130 are spread over the length of the longitudinal body 110. Alternatively, the set of sensors 130 may be spread over only a portion of the longitudinal body 110, for example on a single segment 120 or alternate segments.

In general the sensors 130a-c may be spaced apart by any suitable distance depending on the resolution of required measurements along the length of the longitudinal body 110. For example the sensors 130a-c may be spaced apart by between about 0.5m and about 3m along the length of the longitudinal body 110, aptly between 1m and 2m.

Each sensor 130a-c within set 130 is configured to provide information about the corresponding ground characteristic as the test element 100 is driven into the ground. In general, each sensor 130a-c is configured to provide information about the ground characteristic at a number of elevation levels as the test element as the test element 100 is driven into the ground. That is, each sensor 130a-c may provide information continuously or intermittently about the surrounding ground as the test element 100 is driven into the ground.

The information provided by each sensor 130a-c may correspond to a specific elevation level (that is, a specific depth from the ground surface) or across an elevation level (that is, across a layer or band of ground depth, for example between 10 and 11m from the ground surface).

The provision of information by a sensor 130a-c may be associated with actuation of the sensor 130a-c at a given time (for example at intervals as the test element 100 is driven into the ground).

In this example, the first set of sensors 130 are friction sensors 130a-c. The friction sensors may be sensors that measure the friction locally or indirectly through the measurement and comparison of information at more than one location in the test element. For example, the fiction sensors 130a-c may be sleeves which measure the friction locally, the sleeves extending circumferentially around a portion of the outer surface of the longitudinal body. In other examples the friction sensors 130a-c may measure the increase in axial or compressive load across a length interval of the longitudinal body (for example across 1m intervals or less) allowing the wall friction to be estimated (including inertial components). For example each friction sensor may be at least one strain gauge configured to measure the increase in compressive stress/strain due to shaft friction.

The second set of sensors 140 may include one of water pressure sensors configured to determine the pore water pressure and/or acceleration sensors configured to determine the acceleration of the test element into the ground. In other examples, the test element may include a single set of one of friction sensors / water pressure sensors / acceleration sensor or a number of sets featuring any combination of said sensors. In some examples the penetration end 114 may include a tip sensor configured to measure the tip resistance of the penetration end 114.

The test element 100 may include a memory for collecting and storing the information generated by the sensors of one or more sets of sensors until the test element 100 is removed. Alternatively or additionally the sensors may be configured to send the information about the ground characteristic to a controller, for example through a communication line located within the test element. In this way the test element 100 can be monitored during the driving process.

Fig. 3 illustrates an example of a testing system 360 including a test element 100 and a driving means 370. Fig. 4 illustrates an enlarged view of Fig. 3. The driving means 370 is configured to provide a driving force to the test element 100 to drive the penetration end 114 of the test element 100 into the ground 380. In this example, the driving means 370 is a pile-driver assembly (described further below).

In examples where the longitudinal body 110 is a single piece component, the test element 100 may extend into the pile-driving assembly (for example partially into the hammer of the assembly). As such, the test element 100 is supported laterally by the hammer during driving. In examples where the longitudinal body 110 is formed from a plurality of segments 120, the longitudinal body 110 may be assembled below the pile-driver assembly during driving. For example a first segment 120 may be driven partially into the ground. Once this segment 120 has penetrated far enough into the ground an additional segment is attached to an end of the first segment to be subsequently driven into the ground. As such, the force is always exerted on the test element 100 close to ground level to prevent buckling of the test element 100.

During a testing operation the driving means 370 of the testing system 360 provides a driving force to the test element 100. The penetration end 114 of the test element 100 is driven to a first ground depth as a result of the driving force. As the test element 100 is driven into the ground 380 to the first ground depth, the longitudinal body 110 is also partially present in the ground 380. To arrive the first ground depth at least one of the sensors 130 is driven to below the ground surface. During driving to the first ground depth, the first sensor can provide information about the ground characteristic at any number of elevation levels (at or across at least one elevation level).

The driving means 370 then provides a driving force to the test element 100 to further drive the penetration end 114 of the test element 100 into the ground 380 to a second ground depth (the second ground depth being further from the surface than the first ground depth). As the test element 100 is further driven into the ground 380 to the second ground depth a second/further sensor (located further from the penetration end 114 relative to the first sensor) can provide information about, or determine, the ground characteristic at or across the same elevation level(s) as the first sensor.

Put another way, as the test element 100 is driven into the ground, successive sensors within a set of sensors (in terms of their longitudinal position along the longitudinal body) can provide information about, or determine, the ground characteristic at or across an elevation level. In this way, multiple readings of a ground characteristic at a particular elevation level can be achieved using one test element 100 (i.e. the multiple readings corresponding to multiple sensors), while taking into account the effect that the test element might have in the ground.

It follows that multiple readings can be achieved at multiple elevation levels as the test element is driven into the ground. That is, a sensor can determine the ground characteristic at multiple elevation levels, with subsequent sensors determining the ground characteristic at said elevation levels. As such a profile of the ground characteristic with depth can be determined and the changes in this profile associated with the driving of the test element into the ground can be monitored.

In some examples, the driving forces applied by the driving means in driving the test element 100 to first and second grounds depths may be part of a single continuous drive or blow from the driving means 370. Alternatively, the driving forces applied by the driving means in driving the test element 100 to first and second ground depths may result from separate, distinct, blows, for example a plurality of impacts. Specifically, a first driving force may be applied to drive the test element 100 to a first ground depth and a second driving force may be applied to further drive the test element 100 to a second ground depth.

The (or a) controller may be configured to receive and compare the information provided by the sensors 130 about the ground characteristic. That is, the relationship between the ground characteristic and depth determined from the information provided by a first sensor may be compared with the same relationship determined from the information provided by one or more subsequent sensor. As such, the ground can be properly characterised taking into account the effects of test element/pile interaction during driving.

For example, when the sensors are friction sensors, the controller may be configured to determine the change in driving resistance to the test element 100 as the test element 100 is driven into the ground. The change in driving resistance (or another characteristic) may be used to inform pile operations. For example, the change in driving resistance may be used to predict the required energy/force levels required to drive a pile to a predetermined depth and/or the number of blows required.

For example a method of determining a pile response during driving may include: providing or selecting a test element, scaled down from a pile; performing a testing operation (as described above) in which a profile of a ground characteristic with increasing ground depth is calculated and the change in said profile during driving of said test element is determined; predicting a pile response during a driving operation from the information provided by the testing operation. The predictions may, for example, result from informing a id model of the pile with the information provided by the test operation (optionally the information may be first normalised and parameterised) and computing or determining the pile response from the model.

Once the test element has been driven to a suitable depth (for example between about 20m to about 50m, aptly between about 20m to about 40m, aptly about 30m) the test element 100 may be removed from the ground 380, such that a monopile may be driven into the ground 380. The test element 100 may be removed from the ground 380 using hydraulic cylinders that push or pull the test element 100 upwards, for example.

Fig. 5 to Fig. 6b illustrates another example of a test element 500 for determining ground characteristics.

In the manner as described for test element 100, the test element 100 includes a longitudinal body 510 having a penetration end (not shown). The test element 500 may have corresponding dimensions to that described above for test element 100.

In this example, the test element 500 includes at least two lateral stiffness sensors 540 interspaced along the length of the longitudinal body 510 (with only one shown). Each of the lateral stiffness sensors 540 can measure the lateral stiffness of the surrounding ground such that the lateral stiffness can be measured at a plurality of points along the length of the test element 500.

Any suitable number of sensors 540 may be used. For example, there may be 5, 10, 15, 20 or more sensors spaced along the length of the test element 500. In general the sensors 540 may be spaced apart by any suitable distance depending on the resolution of required measurements along the length of the longitudinal body 510. For example the sensors may be spaced apart by between about 0.5m and about 3m along the length of the longitudinal body 110, aptly between 1m and 2m.

In this example, each lateral stiffness sensor 540 is positioned within the longitudinal body 510, and includes a probe element 542. The probe element 542 has a retracted position (shown in Fig. 6a) in which the probe element 542 is housed or contained within the longitudinal body 510. In the retracted position the lateral stiffness sensor 540 does not protrude from the periphery of the longitudinal body 510. This allows for a smooth insertion of the test element 500 into the ground.

In addition, the probe element 542 is extendable in a direction radially outward from the longitudinal body 510 to an extended position (shown in Fig. 6b). Each lateral stiffness sensor 540 includes an actuating element 544 which is configured to actuate the probe element 542 between the extended and retracted position. Any suitable actuating element 544 may be used. For example the actuating element may be an inflatable sleeve within the test element 500 which pushes the probe element 542 outward upon inflation. Alternatively the actuating element 544 may be a hydraulic cylinder.

Each lateral stiffness sensor 540 includes measuring means configured to measure the force required to move the probe element 542 from its retracted position to its extended position (i.e. measure the force required to move the probe a predetermined amount) and/or measure the distance by which the probe element protrudes from the test element 500 in its extended position (i.e. measure the displacement resulting from a specified applied force). As such, the measuring means can calculate or determine the lateral stiffness from the measured/predetermined force/displacement values.

In use, the test element 500 is driven by a driving means to a predetermined depth, for example (for example between about 20m to about 50m, aptly between about 20m to about 40m, aptly about 30m).

Once at the predetermined depth, the lateral stiffness sensors 540 can be actuated to determine the lateral stiffness of the ground at elevation levels corresponding to each of the lateral stiffness sensors 540. In some examples, the lateral stiffness sensor 540 may also include an integral water pressure sensor (not shown) for determining the pore water pressure at said elevation levels.

The multiple measurements of lateral stiffness along the length of the test element 500 allows a profile of the lateral stiffness of the soil with increasing depth to be calculated. Such a profile can be used to model or predict lateral pile capacity in the ground (i.e. the distributed lateral load that a pile may apply to the surrounding ground without comprising the orientation of the pile or the integrity of the pile within the ground). For example the lateral stiffness profile may be used to determine the stiffness of the pile in the ground. This stiffness is important in determining the frequency of the support structure, which needs to be within a bandwidth.

For example a method of determining a pile response during driving may include: providing or selecting a test element, scaled down from a pile; performing a testing operation (as described above) in which a profile of lateral stiffness with increasing ground depth is calculated; predicting the pile response from the information provided by the test operation. The predictions may result from informing a 1d model of the pile with the information provided by the test operation (optionally the information may be first normalised and parameterised) and computing or determining the pile response from the model.

The method may include a further processing step of the information provided by the testing operation. For example, the maximum capacity/tip resistance and the lateral stiffness profile may be used to calculate the “quake” (that is, the amount of deformation before plastic deformation occurs).

In general for the test elements 100, 500 described above it is advantageous to use a high-mass / low acceleration pile-driver system. That is, in this example, a high-mass hammer is used to apply a large force to the test element at low accelerations (in comparison, for example, to a conventional low mass / high acceleration hammer). The lower accelerations reduce the stresses on the test element to help ensure that the (potentially fragile) sensors in the testing element are not damaged during driving. For example it is expected that the lateral stiffness sensors 540 of test element 500 would not survive the accelerations of conventional impact hammers. Put another way, the use of such pile-drivers allows a test element with increased sensing capabilities to be used with a lower risk of damage to said sensors during driving.

For example a pile-driver assembly using BLUE Piling™ technology may be used.

In this example (as illustrated in Figures 3 and 4), the pile driver assembly 370 includes a casing 372 defining a chamber, the chamber being configured to house a fluid, for example water. In other words, the chamber provides a generally sealed space configured to house and maintain a volume of fluid therein. The casing 372 may include a valve in a wall thereof, coupled to a fluid source/reservoir (for example via a pipe or conduit) to allow the chamber to be filled before or during use. In this manner the assembly may be transported to the operation site with an empty chamber. The chamber may then be filled up to a desired level in situ (either prior to lifting the chamber or when lifted and when waiting for release). It would be understood that the ‘desired level’ may be predetermined to produce a predetermined impact energy for driving a pile into the ground. The water used to fill the chamber may be water pumped from the offshore location, for example sea water.

In this example the pile driver assembly 370 further includes actuating means 374. In this example, the actuating means 374 includes at least one actuator, for example hydraulic or pneumatic actuator.

In this example the actuators 374 are coupled to both a support structure 376 (for example a crane) and the casing 372.

In this example the actuators are located at an end of the casing 372 that is distal from the test element 100. In particular, the actuators extend downwardly from a portion of the support structure 376 towards the casing 372 and are coupled to an upper end of the casing 372.

In use, the chamber is positioned in a coaxial arrangement with the test element 100. Actuation of the actuating means 374 displaces the casing/chamber 372 relative to the test element 100, such that the chamber moves away from the test element 100. In this example, actuation of the actuators causes the active length of the actuators to decrease pulling the casing 372 upwardly towards an upper end of the support structure 376.

Further actuation of the actuating means 374 causes the actuating means 374 to release the chamber such that the chamber displaces towards the test element 100. As a result the chamber exerts a force on the test element 100, to controllably drive the test element into the ground.

In general, it is advantageous if the pile-driver assembly used to drive the test element into the ground is of the same configuration/type as that used to perform the subsequent piling operations (i.e. the subsequent piling operations that utilise the ground characterisation obtained using the test element). This ensures that the soil conditions /the change in soil conditions during driving are replicated as best as possible between the testing operations and the piling operations.

For example, the pile-driver assembly used for the testing operations may be a generally scaled-down version of the pile-driver assembly used for the piling operations. For example a ‘full-scale’ pile-driver assembly used for the piling operations may include a chamber with a volume capable of holding from about 1000 to 5000 tons of water (suitable for driving monopiles of a diameter of from about 6 to 15 meters into the ground). When the chamber is filled with water, the total mass of the casing (including the water therein) may be at least 8 times later than the mass of a typical driven hammer used for piling operations (aptly around 8 to 12 times larger). For example, the mass of a large hydraulic impact hammer may be from about 200 to about 270 tons, whereas the total mass of a casing with water may be approximately 2700tons.

A ‘scaled-down’ assembly used for the testing operations may have dimensions scaled down by a ratio of about 1:50 to about 1:200, aptly 1:100.

It is advantageous if the pile-driver assembly used for the piling operations (and therefore also for driving the test element into the ground) produces a low level of vibrations in use (for example relative to a vibratory hammer). For example, use of a vibratory hammer in the piling operations would alter the ground characteristics during the driving process reducing the applicability of the measurements obtained by the test element.

Modifications

The driving force may be transferred to the test element 100, 500 in any suitable manner (put another way the longitudinal body of the test element may be configured to receive a driving force from the driving means in any suitable manner). For example, the test element may include a driving end, or driving portion, configured to receive a driving force from the driving means (i.e. a blow from a hammer).

Advantageously the driving force is transferred to the test element 100, 500 in a manner so as to minimise the risk of the test element buckling during driving. For example, the test element may include a removable abutment, protrusion or pin that extends laterally from the test element. The pile-driver assembly may apply a force to the abutment which drives the test element downwardly. The abutment may be initially located a pre-determined distance above the ground. Specifically, the pre-determined distance may be large enough so as to allow the test element to be driven downwardly (without the abutment contacting the ground) but also small enough so as to minimise the unsupported length of test element between the abutment and the ground to reduce the likelihood of buckling. That is, the load introduction is done as close to the ground as possible. As the abutment approaches the ground, the abutment may be removed and re-inserted at a different position for further impacts.

Alternatively (or additionally) the testing system may further include a clamping assembly (for example as part of the pile-driver assembly) configured to engage with the testing element in a position proximate the ground. The clamping assembly may provide lateral support to the unsupported portion of the test element during driving or the driving force may be transferred to the test element via the clamping assembly.

The test elements 100, 500 may be made from any suitable material, for example a high grade stainless steel.

In some examples the test element may include soil sampling devices, to collect test portions of the ground for further analysis. The test element may include equipment configured to detect Unexploded Ordnances. The test element may include detection equipment configured to detect boulders within the ground.

It will be clear to a person skilled in the art that features described in relation to any of the embodiments described above can be applicable interchangeably between the different embodiments. The embodiments described above are examples to illustrate various features of the invention. For example, from this disclosure a test element is envisaged, which combines aspects of the test element 100 (for example at least one set of friction sensors or other sensors for determining information during driving) and the test element 500 (for example at least two lateral stiffness sensors for determining lateral stiffness in situ). That is, a plurality of lateral stiffness sensors as described in Figure 5 may be used as a second or third set of sensors in the test element 100. In this manner a test element, which can measure both the changing soil characteristics during driving and the lateral stiffness profile in situ can be provided. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A test element for determining ground characteristics, the test element comprising: a longitudinal body configured to receive a driving force from a driving means and a penetration end; and at least two lateral stiffness sensors interspaced along the length of the longitudinal body; wherein each of the at least two lateral stiffness sensors are configured to determine the lateral stiffness of the ground at a corresponding elevation level once the test element is driven to a predetermined depth.

2. A test element as claimed in claim 1, wherein the at least two lateral stiffness sensors comprises a first sensor spaced a first distance from the penetration end and a second sensor spaced a second, larger, distance from the penetration end.

3. A test element as claimed in claim 1 or 2, wherein at least one of the lateral stiffness sensors comprises a probe element having: an extended position in which the probe element protrudes from the longitudinal body; and a retracted position in which the probe element is housed within the longitudinal body.

4. A test element as claimed in claim 3, wherein the at least one lateral stiffness sensor comprises an actuating element configured to actuate the probe element from its retracted position to its extended position.

5. A test element as claimed in claim 4, wherein the actuating element comprises an inflatable sleeve or a hydraulic cylinder.

6. A test element as claimed in any of claims 3 to 5, wherein the at least one lateral stiffness sensor comprises measuring means configured to measure the force required to move the probe element from its retracted position to its extended position and/or to measure the distance by which the probe element protrudes from the test element in its extended position.

7. A test element as claimed in any preceding claim, wherein at least one of the lateral stiffness sensors further comprises a water pressure sensor for determining the pore water pressure.

8. A testing system for determining ground characteristics, the testing system comprising; a driving means; and a test element as claimed in any preceding claim, wherein the pile-drive assembly is configured to deliver a driving force to the driving surface of the test element to drive the test element into the ground.

9. A testing system as claimed in claim 8, wherein the driving means is a pile-driver assembly.

10. A testing system as claimed in claim 9, wherein the pile-driver assembly comprises: a casing defining a chamber, the chamber being configured to house a fluid; and actuating means coupled to the chamber, wherein actuation of the actuating means displaces the chamber relative to the test element, such that the chamber moves away from the test element, and wherein the actuating means is configured to release the chamber for displacement towards the test element such that a force is exerted by the chamber on the test element, to controllably drive the pile into the ground.

11. A testing system as claimed in any of claims 7 to 10, wherein the system further comprises a clamping assembly and/or an abutment removably attached to the test element, wherein the driving force is transferred to the test element via the clamping assembly or abutment.

12. A method of determining ground characteristics, wherein the method comprises: providing a test element comprising: a longitudinal body configured to receive a driving force from a driving means and a penetration end; and at least two lateral stiffness sensors wherein each of the at least two lateral stiffness sensors are configured to determine the lateral stiffness of the ground; driving the test element into the ground to a predetermined depth; and determining the lateral stiffness of the ground at elevation levels corresponding to each of the lateral stiffness sensors using the at least two lateral stiffness sensors.

13. A method as claimed in claim 12, wherein the step of determining the lateral stiffness of the ground using a lateral stiffness sensor comprises actuating the lateral stiffness sensor to move a probe element from a retracted position in which the probe element is housed within the longitudinal body to an extended position in which the probe element protrudes from the longitudinal body.

14. A method as claimed in any one of claims 12 to 13, wherein the driving means comprises: a casing defining a chamber, the chamber being configured to house a fluid; and actuating means coupled to the chamber, wherein the method further comprises the steps of: providing the pile-driver assembly with the chamber in a coaxial arrangement with the test element; actuating the actuating means such that the chamber is moved away from the test element; and further actuating the actuating means to release the chamber such that the chamber displaces towards the test element and exerts a force on the test element, to controllably drive the test element into the ground.

15. A method of modelling the lateral pile capacity of the ground, wherein the method comprises: providing a test element comprising: a longitudinal body configured to receive a driving force from a driving means and a penetration end; and at least two lateral stiffness sensors wherein each of the at least two lateral stiffness sensor are configured to determine the lateral stiffness of the ground; driving the test element into the ground to a predetermined depth; determining the lateral stiffness of the ground at elevation levels corresponding to each of the lateral stiffness sensor using the lateral stiffness sensor; and using the lateral stiffness to predict lateral pile capacity in the ground.