EP3626890B1 - Method for testing the load bearing capabilities of a foundation - Google Patents

Description

Technical field of the invention

The present invention relates to a method for testing the load-bearing capacity of a foundation. In particular, the invention relates to a method in which the values of the various loads with which the foundation is successively loaded during the process, and the loading times of the various loads, are determined on the basis of the reaction of the foundation with the previous load.

State of the art

Foundations form the structural and static transition between the structure and the ground. The most important task of the foundations is therefore to absorb loads from the structure and to pass them on to the subsoil without the resulting compression of the soil leading to disadvantages for the structure or the environment. The load-bearing capacity of the installed foundations is accordingly an important safety parameter and must be checked as precisely as possible. Depending on their design, foundations can be rammed into the ground, screwed in or inserted, for example in the case of pile foundations, screw foundations or prefabricated foundations or in-situ concrete foundations.

Ground screws, also known as ground screws, usually made of steel, are an interesting alternative to concrete foundations. Their length can vary from a few tens of centimeters to several meters. Generally considered, screw foundations have a shape comparable to a normal screw, ie they consist of an elongated body in the form of a cylinder with a part which includes an external thread. Screw foundations are often designed as a hollow body, which is closed with a flange.

The great advantage of screw foundations is that they can be loaded immediately, can be completely dismantled and reused. In addition, there is no need to wait for curing times. Screw foundations are increasingly being used in a wide variety of situations, for example as foundations for noise barriers, solar panels, or for small or medium-sized houses.

Like all foundations, ground screws must be checked for their load-bearing capacity after they have been placed in the ground. Nowadays, the load-bearing capacity test of foundations is mostly carried out using static, static or dynamic test methods. The reaction of the foundation, such as the displacement path, the displacement speed, the acceleration or the occurrence of vibrations when a test load is applied, is recorded. Unfortunately, these procedures are long and complex. Faster methods, especially dynamic methods, are often too imprecise.

Methods for testing the load-bearing capacity of foundations, in which foundations are loaded with a load sequence defined before the start of the test, until either a certain load transfer or a so-called soil break is achieved, are known from the prior art, see e.g. FR 3021678A1 . However, these methods have the disadvantage that in most cases they take a very long time, since neither the first load nor the load increments are determined on the basis of the values measured during the laying process of the foundation. Usually, the first load is chosen to be very small compared to the "hoped for" load-bearing capacity in order to ensure that it cannot cause a ground failure. The increments are also chosen to be small so that the load-bearing capacity of the foundation to be tested can be precisely determined. Since the load must be maintained for a predetermined time for each load, the methods known from the prior art take a very long time. Long test times cause high costs when testing foundations and delay the completion of the construction project due to the required test times.

Proceeding from the prior art, the present invention is therefore based on the object of overcoming the aforementioned disadvantages and introducing a To provide a method for the load-bearing capacity test of foundations, which enables more precise and faster tests.

Summary of the invention

According to the present invention, these objectives are achieved primarily through the elements of the independent claim. Further advantageous embodiments also emerge from the dependent claims.

1. a. Einbringen des Fundaments in den Boden und Ermittlung von Einbringparametern,
2. b. Ermittlung einer ersten Last und einer ersten Belastungszeit,
3. c. Belastung des Fundaments mit der ersten Last,
4. d. Kontinuierliche Aufzeichnung der Reaktion, welche das Fundament auf Grund der ersten Last erfährt,
5. e. Aufrechterhaltung der Belastung mit der ersten Last während der ersten Belastungszeit oder bis eine vorbestimmte Reaktion erreicht ist,
6. f. Belastung des Fundaments mit einer zweiten Last, welche um ein Inkrement grösser als die erste Last ist,
7. g. Kontinuierliche Aufzeichnung der Reaktion, welche das Fundament auf Grund der zweiten Last erfährt,
8. h. Aufrechterhaltung der Belastung mit der zweiten Last während einer zweiten Belastungszeit oder bis eine vorbestimmte Reaktion erreicht ist, und
9. i. Wiederholung der Schritte f bis h bis die aufgezeichnete Reaktion gleich wie oder grösser als ein Reaktionsgrenzwert ist,

wobei die erste Last aufgrund der gemessenen Einbringparametern und/oder eines vorbestimmten Lastabtrags bestimmt wird, und wobei die Inkremente und die Belastungszeiten aufgrund der aufgezeichneten Reaktion, welche das Fundament aufgrund der vorherigen Last erfahren hat, bestimmt werden.In particular, the objectives of the present invention are achieved by a method for testing the load-bearing capacity of a foundation, which comprises the following steps:

1. a. Placing the foundation in the ground and determining placement parameters,
2. b. Determination of a first load and a first load time,
3. c. Loading the foundation with the first load,
4. d. Continuous recording of the reaction that the foundation experiences due to the first load,
5. e. Maintaining the load with the first load during the first load time or until a predetermined response is achieved,
6. f. loading the foundation with a second load which is one increment greater than the first load,
7. G. Continuous recording of the reaction that the foundation experiences due to the second load,
8. H. Maintaining the exposure to the second load for a second exposure time or until a predetermined response is achieved, and
9. i. Repeat steps f to h until the recorded reaction is equal to or greater than a reaction limit value,

wherein the first load is determined on the basis of the measured introduction parameters and / or a predetermined load transfer, and wherein the increments and the loading times are determined on the basis of the recorded reaction which the foundation has experienced due to the previous load.

Thanks to the method according to the invention, the load-bearing capacity test of a foundation can be carried out quickly and precisely. In contrast to the methods known from the prior art, in which predetermined increments and / or loading times are required, the increment and loading time for the next load level are determined based on the recorded reaction of the foundation at the previous load. In other words, the method according to the invention represents a feedback method in which the information obtained in the previous stage contributes to the determination of the level of exposure in the next stage. In this way, for example, large increments and short loading times can be selected if the reaction to the previous load indicates a high load-bearing capacity. In addition, the first load is determined on the basis of the measured introduction parameters and / or the predetermined load transfer. As a result, a large first load can be determined without the risk that this first load is already above the breaking load. This results in a reduction in the number of load levels and the load times and consequently in the entire test procedure. For the customer there are consequently no costs due to the acceleration of the test procedure.

In addition, the method is continued until the recorded reaction of the foundation due to the load is equal to or greater than a reaction limit value. The response limit, so when the process should / can be stopped can either be predetermined, i.e. before the process begins, or determined on the basis of, for example, the recorded installation parameters or reactions of the foundation at the respective load levels in the course of the process. Accordingly, the method according to the invention also represents a feedback method in this respect. Of course, several reaction limit values can also be predetermined or determined in the course of the method. For example, a lower and an upper limit value can be determined. The process is continued until one of these limit values is reached.

In a first preferred embodiment of the method according to the invention, before a method step in which the load is increased by an increment, an additional method step is carried out in which the load on the foundation is reduced. In this way, increments and load times can be better determined. In particular, the reaction of the foundation during these so-called relief stages can be included in the determination of these parameters.

In another preferred embodiment of the method according to the invention, the foundation is a screw foundation. This means that the foundation can be simply screwed into the ground. Compared to ramming, turning has the advantage that the introduction process can be carried out more precisely and steadily. In addition, additional relevant introduction parameters can be determined during the screwing in, which can be included for the determination of the first load and the first loading time.

In another preferred embodiment of the method according to the invention, the introduction parameters include the screwing-in torque and the screwing-in path. This enables a torque-displacement curve to be created for the foundation to be tested. It could be shown that there is a close connection between the torque-displacement curve of a foundation and its load-bearing capacity exists. Therefore, based on this scientifically proven relationship, a well-founded and optimal choice can be made for the first load and the first load time. This leads to a reduction in the number of load levels and thus to a reduction in the overall duration of the procedure.

The relevant information for determining the first load and the first loading time can be extracted from the torque-displacement curve in various ways. For example, the first and second derivatives of the torque-displacement curve can provide highly relevant information. It is particularly important to note that depending on the situation in which the foundation is used, the interpretation of the torque-displacement curve may not be the same. For example, a torque-displacement curve of a foundation that is to be used in a situation where it has to withstand a compressive load should not be the same as that of a foundation that has to carry a tensile load. This must be taken into account when determining the first load and the first loading time based on the torque-displacement curve.

To measure the torque, force sensors can be used directly, which are attached to the machine that is used to screw in the foundations. In addition, a direct measurement by force sensors that are installed on the foundation itself is also possible. However, it is also possible to use an indirect measurement of the torque, which is based on the measurement of the current (electrical built-in devices) or the pressure (liquid-based rotating devices), taking into account drive-specific multipliers. The turning path can also be measured very easily by means known to a person skilled in the art.

It should also be noted that the method according to the invention enables traceability. Each foundation can be assigned a torque-displacement curve. This can be beneficial in the event of future problems, as it enables an even better understanding of the complex relationship between insertion torque and load capacity.

In another preferred embodiment of the method according to the invention, the introduction parameters include the angular speed of rotation. Using the angular speed and the winding gradient of the foundation, a turning path can be determined and compared with the actually measured turning path. This enables a so-called slip analysis to be carried out. This ensures that if the foundation slips during the turning process, this is taken into account when determining the values of the first load and the first loading time.

In another preferred embodiment of the method according to the invention, the introduction parameters include the maximum value of the insertion torque. It could be shown that a high correlation also exists between the maximum insertion torque value and the load-bearing capacity of a foundation. This allows the first load and the first load time to be determined even better.

In another preferred embodiment of the method according to the invention, the introduction parameters include the final torque value. This is particularly advantageous for determining the first load and the first loading time for a foundation that has to absorb a compressive load. A low final torque value means nothing other than that the top of the foundation is in a less stable soil. This therefore indicates a lower load-bearing capacity in the event of a pressure load.

In another preferred embodiment of the method according to the invention, the introduction parameters include the amount of the torque-displacement-curve integral. It could be shown that there is a particularly high correlation between the amount of the torque-displacement-curve integral and the load-bearing capacity of a foundation. With the amount of the torque-displacement-curve integral, the determination of the first load and the first loading time can therefore be carried out even more precisely and on a more well-founded basis.

The amount of the torque-displacement curve integral is usually determined over the entire screw-in displacement and taken into account for the determination of the first load and the first loading time. However, it is also conceivable to determine and use an absolute value of the integral only over a partial range of the screwing-in path. This can be particularly advantageous if the foundation was placed in a very heterogeneous soil. In addition, for a foundation that has to absorb a pressure load, it is advantageous to determine the value of the integral over the range of the screwing-in path that corresponds to the end of the installation. On the contrary, it is advantageous for a foundation that has to withstand a tensile load to determine the value of the integral over the entire screw-in path.

In another preferred embodiment of the method according to the invention, the loads are dynamic and / or static. With dynamic loading or unloading, the test time can be massively shortened again by eliminating holding times. In addition, statements about expansions and accelerations in the case of the dynamic forces acting are possible. Statnamic loads represent a combination of static and dynamic loads. As a result, the static and dynamic behavior can be recorded in a single loading process.

In another preferred embodiment of the method according to the invention, the first load, the loading times, the increments and the reaction limit value are additionally determined on the basis of the shape of the foundation. This allows these parameters to be determined better.

In another preferred embodiment of the method according to the invention, the first load, the loading times, the increments and the reaction limit value are additionally determined on the basis of the load to be carried. This allows these parameters to be determined better. The direction and / or the type of load to be carried are advantageously taken into account. The type of load to be borne is used for For example, understood what permanent load the foundation has to bear or whether and to what extent the foundation is additionally loaded with gusts of wind, i.e. with temporary loads.

In a further preferred embodiment of the method according to the invention, the first load, the loading times, the increments and the reaction limit value are additionally determined on the basis of previous soil assessments. This enables these parameters to be determined even better.

In another preferred embodiment of the method according to the invention, the recorded reaction comprises the speed of displacement of the foundation. In this way, the increments and the next loading times can be determined on the basis of the recorded displacement speed of the foundation.

In another preferred embodiment of the method according to the invention, the recorded reaction comprises the displacement path of the foundation. In this way, the increments and the next loading times can be determined on the basis of the recorded displacement path of the foundation.

In another preferred embodiment of the method according to the invention, the recorded reaction comprises the direction of displacement of the foundation. In this way, the increments and the next loading times can be determined based on the recorded direction of movement of the foundation. In addition, on the basis of the recorded direction of displacement, it can also be determined whether, for example, a relief step needs to be inserted and whether the next load should be purely vertical or with a horizontal component.

In another preferred embodiment of the method according to the invention, the recorded reaction comprises the creep factor. This allows the increments and the next Load times can be determined based on the recorded creep factor of the foundation.

In another preferred embodiment of the method according to the invention, the reaction limit value corresponds to a displacement direction, a displacement speed, a displacement path, a creep factor, a load or a combination thereof. This will carry out the procedure until the most relevant response limit for the foundation to be tested is reached.

In another preferred embodiment of the method according to the invention, the reaction limit value is determined on the basis of the introduction parameters. As a result, the reaction limit value can be optimally determined and the process can only be carried out for as long as necessary. Thanks, for example, to the high correlation between the amount of the torque-displacement integral and the load-bearing capacity of the foundation, it is not necessary to carry out the process until the foundation is loaded with the actual load to be carried. It is sufficient to measure the reaction of the foundation with several smaller loads and to extrapolate the load-bearing capacity of the foundation from this. The duration of the entire procedure can thus be reduced considerably.

In another preferred embodiment of the method according to the invention, the method is implemented by a computer. This means that the entire process can be fully automated and carried out more quickly. In particular, the reactions of the foundation to the various loads can be analyzed using suitable algorithms, and the increment and the load time for the next load level can be determined quickly, well-founded and precisely.

Further details of the invention will become apparent from the following description of the preferred embodiment of the invention, which are shown in the accompanying drawings. The description also reveals the further advantages of the present invention as well Suggestions and suggestions as to how the subject matter of the invention could be modified or further developed within the scope of what is claimed.

Brief description of the drawings

• Figure 1 shows different models of ground screws;
• Figure 2 illustrates the screwing in of a screw foundation;
• Figure 3 shows a preferred embodiment of the method according to the invention for testing the load-bearing capacity of foundations;
• Figure 4 shows a schematic representation of a torque-displacement curve;
• Figure 5 shows real measured torque-displacement curves;
• Figure 6 illustrates the course of a method known from the prior art for testing the load-bearing capacity of a foundation;
• Figure 7 shows a schematic representation of the course of a preferred embodiment of the method according to the invention for testing the load-bearing capacity of a foundation;
• Figure 8 illustrates a real course of a preferred embodiment of the method according to the invention for testing the load-bearing capacity of a foundation; and
• Figure 9 shows real creep curves that were recorded during the implementation of a preferred embodiment of the method according to the invention for testing the load-bearing capacity of a foundation.

Preferred embodiments of the invention

While the preferred embodiment of the method according to the invention described below specifically illustrates the load-bearing capacity test of a screw foundation, the method according to the invention can just as well be used for the load-bearing capacity test of other types of foundations.

Figure 1 shows different models of screw foundations, the length of which can vary from a few tens of centimeters to several meters. Generally considered, screw foundations have a shape comparable to a normal screw, ie they consist of an elongated body in the form of a cylinder with a part which includes an external thread. Screw foundations are often designed as a hollow body, which is closed with a flange.

In Figure 2 a typical driving process of a screw foundation into the ground B is illustrated schematically. During the screwing in, various penetration parameters such as the screwing-in path W and the screwing-in torque D are continuously determined by means known to a person skilled in the art. In the case of foundations that are rammed into the ground, the penetration parameters can also include the penetration force, frequency, impulse, expansions and accelerations in addition to the penetration path.

Figure 3 illustrates a preferred embodiment of the method according to the invention for testing the load-bearing capacity of a foundation, in which the foundation is a screw foundation. In this embodiment, the method according to the invention begins with the introduction, here the turning, of the foundation into the ground. While the foundation is being screwed in, the screw-in path and screw-in torque are continuously determined. It is of course also possible to determine other relevant introduction parameters such as, for example, the angular speed of rotation. In addition, the driving of the foundation can include breaks, interruptions or reverse rotation phases, during which the reaction of the foundation is recorded. During a break, for example, the inertia behavior and, when turning backwards, information about static and sliding friction of the foundation shell or the tip can be determined. These recorded parameters can also represent part of the introduction parameters.

In the next method step, the value of the first load L1 and the first loading time t1 are determined on the basis of the determined introduction parameters. The foundation is then loaded with the load L1. During the loading with the first load L1, the reaction of the foundation is continuously recorded. For example, the displacement path and displacement speed of the foundation are measured. The reaction of the foundation can also include the creep factor of the foundation under load L1, or the displacement direction (horizontal / vertical).

The loading with the load L1 is maintained until a predetermined response is reached or during the first loading time t1. The predetermined reaction can correspond, for example, to a specific displacement speed or a specific displacement path. For example, the load with the load L1 is maintained until the displacement speed has reached the value zero, i.e. when the foundation no longer moves. If the foundation has never moved due to the load L1, this load stage is of course canceled after the load time t1, since it is obvious that the load can be increased. The predetermined reaction can, however, also correspond to a certain value of the creep factor. It is generally known that if the creep factor is below one and develops from the straight line k = 1 in the direction of 0, the acting load is below the breaking load, so that the test load can be increased. The predetermined reaction limit value can, however, also be a combination of different and any number of values, such as, for example, creep factor and displacement path.

In the next step, the increment I1 and the load time t2 are determined for the next load level. In the method according to the invention the determination of these values is based on the recorded reaction of the foundation due to the previous load. As indicated in the figure, there is therefore a feedback between two subsequent load levels. For example, if the load L1 has caused no or only a small displacement path of the foundation and / or the creep curve is close to 0, the increment I1 can be selected to be large and the loading time t2 to be small. On the other hand, if the reaction in the first load stage was large, the increment I1 should be selected to be rather small.

After determining the increment I1 and the loading time t2, the foundation is loaded with the load L2 = L1 + I1. During the loading with L2, as during the previous load level, the reaction of the foundation is continuously recorded. The loading with the load L2 is maintained until a predetermined response is reached or during the loading time t2. As with the previous load stage, the predetermined response of the foundation can correspond to different parameters or a combination of any number of different parameters.

A new increment and a new loading time are then determined based on the reaction of the foundation at load L2. As in Figure 3 shown, the process is continued until a reaction limit is reached. The reaction limit value can be both a specific load and a displacement speed, a displacement path, a displacement direction, a loading time, a creep factor, an elasticity / restoring force after unloading, or a combination thereof. The reaction limit values can be dependent on the acting load, the application parameters or the previously determined soil properties. Or the reaction limit value is determined based on the reaction behavior in the previous stress levels. Any combination of these factors can also define the response limit.

The method according to the invention can be used both in the case of a load test, for example a pull-out test according to the Swiss standard SIA 267, in which no predefined load is to be removed, but rather the load-transfer behavior is to be checked, and a quality test, for Example of a tensile test according to the Swiss standard SIA 267, in which a predefined load transfer, for example during an acceptance test, is to be checked. In the case of an acceptance test, an engineer usually determines which load transfer device the foundation must be able to carry. The method according to the invention is thus carried out until the load with which the foundation is loaded is equal to or greater than the load transfer, or until a ground break has been caused with a smaller load. In the case of an acceptance test, the response limit value can thus correspond, for example, to a combination of the load transfer and the creep factor. It is known that a creep factor greater than two corresponds to a ground failure. It should be noted that it is not always necessary to wait until the creep factor is actually above two in order to be able to determine that the breaking load has been reached. In many cases, an analysis of the behavior of the creep factor over time is much more meaningful than the value of the factor (see below for a discussion of the creep factor). In addition, as is generally known, the displacement can already adequately describe a fracture behavior.

In the case of a load test of the installed foundation, the method according to the invention is carried out until the ground break is caused or until a certain load is reached, which enables the load-bearing capacity of the foundation to be determined by extrapolation. It was shown that there is a high correlation between the behavior of a foundation with small loads and the actual load-bearing capacity of the same foundation under defined boundary conditions. In such cases it is not always necessary to actually achieve the breaking load in order to determine the load-bearing capacity of the foundation. It has been scientifically shown that it is then sufficient to record the reaction of the foundation due to several small loads in order to be able to extrapolate the load-bearing capacity of the foundation. The extrapolation of the load-bearing capacity can, for example, be made on the basis of the measured application parameters or the comparison of the reaction behavior and the application parameters with comparable data sets. Specifically, it could be shown, for example, that there is a close relationship between the amount of the torque-displacement-curve integral and the Breaking load of a foundation. Therefore, mathematical models have been developed which allow the extrapolation of the load-bearing capacity of a foundation based on the reaction of the foundation under one or more small loads and with the aid of the amount of the torque-displacement-curve integral. Extensive experimental tests of these models have shown that it is actually possible to sufficiently "predict" the load-bearing capacity of a foundation in this way.

Figure 7 shows schematically how the time sequence of the method according to the invention (upper part of FIG Figure 7 ) and the reaction of the foundation (lower part of the Figure 7 ) due to the different loads. As seen in this figure, and as in Figure 2 indicated, so-called relief stages, ie stages in which the load is reduced compared to the previous stage, can be introduced between two load levels. The reaction of the foundation during these relief stages can provide important information for determining the next increment and the next loading time.

Figure 8 shows real curves of a load-bearing capacity test of a screw foundation according to the present inventive method. The upper curve shows the recorded displacement that the foundation experiences due to the various loads. The lower curve shows the development of the load during the test procedure. As can be seen, both the increments and the loading times are different for the various loading levels. During this procedure, relief stages were performed between two stress levels.

For comparison shows Figure 6 an example of a course of a load-bearing capacity test according to a method known from the prior art. In such a method, the loading times and the increments are constant throughout the test. Since the breaking load must not be "missed", small increments and long loading times are usually chosen, which significantly increases the duration of the test.

As explained above, in the method according to the invention the first load L1 and the first loading time t1 are determined on the basis of the measured application parameters and / or the load transfer. Particularly meaningful parameters are the screw-in torque and the screw-in path of the foundation. As in Figure 4 shown, a so-called screw-in torque-path curve can be created with the determined screw-in torque and screw-in path. As could be shown, there is a close relationship between the torque-displacement curve and the load-bearing capacity of a foundation. The information that can be extracted from this curve is therefore particularly suitable for determining the first load L1 and the first loading time t1. If the torque-displacement curve indicates a high load-bearing capacity, the first load L1 of the method according to the invention can already be selected to be high without the risk of "missing" the breaking load. Specifically, the determination of the first load L1 can be based, for example, on the amount of the insertion torque-displacement curve integral, the insertion torque maximum value, the insertion torque end value, or a combination of these values. Other parameters that can contribute to the determination of the first load L1 and the first loading time t1 include the screwing-in time and the screwing-in angular speed. In addition, subsoil information, such as soil parameters determined in advance by subsoil characterizations, can contribute to the determination of the first load L1 and the first loading time t1.

As mentioned above, the determination of the first load L1 can additionally or alternatively be made on the basis of the load transfer, ie the load to be carried. This is particularly relevant in the case of an acceptance test in which an engineer defines the minimum load to be borne. The method according to the invention can thus start with a load L1 which corresponds to a certain fraction, for example half or three quarters, of the load transfer. It is even conceivable that the method begins with a first load L1 which is equal to or greater than the load transfer. In such a case, two response limits, an "upper" and a "lower", can be predetermined. A first limit value could, for example, consist of a combination of a creep behavior to be fulfilled (creep factor must always remain below 1 and the first derivative must be positive, i.e. approach 0) and a maximum Shift (the shift must not exceed 1.0mm) can be defined. The fulfillment of this “upper reaction limit value” would fulfill the engineering acceptance test with regard to the required load-bearing capacity at the maximum permitted deformation. On the contrary, a “lower response limit” could be used to define non-compliance with the acceptance test. If, for example, the combination of the creep factor is greater than 1 and the first derivative of the creep curve is negative (the creep factor is "increasing") or exceeds a maximum displacement of the foundation of 4mm, this means nothing other than that the engineering acceptance test has not been met.

In the process according to the invention, and as in Figure 2 illustrated, the increments and the loading times are determined based on the reaction of the foundation at the previous load level. As already explained above, the reaction of the foundation can correspond to the displacement path and the displacement speed, for example. But other parameters such as the direction of displacement (vertical / horizontal) can be included in the reaction. In the case of the displacement speed, i.e. the displacement path per unit of time, a so-called creep analysis can be carried out. Such an analysis is exemplified in Figure 9 in which the displacement of thirteen (1 to 13) subsequent load levels of a load test are shown logarithmically as a function of the load time. Usually, two reference lines are also drawn in such a creep behavior graph, which correspond to a creep factor equal to 1 or a creep factor equal to 2. As is known, the creep factor k is a measure of the time-dependent increase in the displacement of the foundation under a constant load. It is normally defined with the creep law as follows: k = (v2-v1) / log (t2 / t1), where v2 - v1 means the increase in displacement of the foundation in the period t1 to t2. In the construction industry, it is common to define the breaking load based on the creep behavior. Specifically, the breaking load of a foundation can be defined as the load at which the displacement of the foundation increases noticeably in the load-displacement diagram or the creep factor in the time-displacement diagram reaches the value k = 2. The analysis of the creep behavior of the foundation at the The respective load levels of the method according to the invention can therefore represent the basis for determining the increment and the loading time for the next load level. A creep curve above the reference straight line k = 1 means that the increment can be selected rather large and the next loading time rather small. In addition, the continuous recording of the creep factor during the load can be used to determine how long the load should be sustained. For example, the first and / or second derivatives of the creep curves can be used for this. If you look at the creep diagrams in Figure 9 viewed, it can be seen that the creep curves 1-13 in the diagram tend noticeably with increasing load. The first curves, i.e. with a low load, are all above the straight line k = 1. While at load level 7 the curve is still close to 0, i.e. the foundation is not yet shifting, curves 8 and 9 are between 0 and k = 1 but move towards 0, i.e. have a slope smaller than k = 1. This means that the foundation will come to a standstill. Load level 10 indicates that a load that is critical in terms of creep behavior is acting on the foundation. The curve 11 shows that the creep criterion has been exceeded, since the slope is greater than k = 2. The acting load therefore leads to continuous creep and thus foundation failure under permanent load. Curve 12 shows the creep behavior of the relief, ie load = 0 kN. The subsequent application of the last load level 13 causes a creep behavior with a slope k> 2 and thus an actual indentation of the foundation due to a broken ground, which means nothing other than that the foundation fails. This "visual" observation described here can be made better by a continuous creep curve analysis by looking at the first and second derivatives thereof. Based on this analysis, it is possible to recognize early on that the loads 1-9 are not critical for the foundation and can therefore be loaded with the next load level. It can also be seen at load level 11 that the creep criterion was exceeded by exceeding the slope of the straight line k = 2; without waiting until the curve intersects the straight line k = 2 itself. The examination time can thus be reduced or, as in the borderline case of stress level 10, increased. This ensures that the test time is generally reduced without loss of information and that the In particular, however, sufficient test time in the area of the load limit is effective. If one now compares the curves 1-13, one can understand how the creep behavior at a certain load can be taken into account for the choice of the increment. Since the creep factor of the foundation at load level 9 already indicates that the load has approached a critical value, the next load level, i.e. load level 10, should be defined by a smaller increment. This means that the method ensures that the load levels approach the load limit through the result-based, step-by-step reduction of the increments. If the load is critical, i.e. smaller but parallel to k = 1, a further slightly increased load level 11 can make a clear statement on an only slightly increased load level. Thanks to this gradual approach to the load limit, which is integrated in the process, and the subsequent slight overload, the statements of the load tests are not only faster, but also more accurate.

As can be understood from the description of the preferred embodiment and various actual measurements of the driving parameters and the response of the foundations to loads, there are many complex relationships between a large number of parameters. As already mentioned, these relationships also allow predictions to be made about the load transfer behavior of the foundations. It is therefore of course advantageous if the method according to the invention is implemented by means of a computer. The complex relationships between the input parameters, foundation reaction, loading times, subsoil characterization, etc. can thus be written in clever algorithms. With a computer implementation, preferably with the use of artificial intelligence methods, the test method can be carried out more quickly and more precisely.

Claims (15)

1. Method for testing the load bearing capabilities of a foundation comprising the following steps:

   a. Placement of the foundation in the ground and determination of placement parameters,

   b. Determination of a first load and a first load period,

   c. Loading the foundation with the first load,

   d. Continuous recording of the reaction which the foundation experiences due to the first load,

   e. Maintaining the loading with the first load during the first load period or until a predetermined reaction is reached,

   f. Loading the foundation with a second load, which is greater than the first load by one increment,

   g. Continuous recording of the reaction which the foundation experiences due to the second load,

   h. Maintaining the loading with the second load during a second load period or until a predetermined reaction is reached, and

   i. Repetition of steps f to h until the recorded reaction is the same as, or greater than, a reaction limit value,

   characterized,
   in that the first load is determined on the basis of the measured placement parameters and/or a predetermined load transfer, and
   in that the increments and the load periods are determined on the basis of the recorded reaction which the foundation experiences due to the previous load.
2. Method according to claim 1, characterized in that before a method step in which the load is increased by one increment, an additional method step is carried out in which the load on the foundation is reduced.
3. Method according to one of the claims 1 or 2, characterized in that the foundation is a screw foundation.
4. Method according to one of the preceding claims, characterized in that the placement parameters comprise the insertion torque and the insertion path.
5. Method according to one of the preceding claims, characterized in that the placement parameters comprise the insertion speed.
6. Method according to one of the preceding claims, characterized in that the placement parameters comprise the insertion torque maximal value and/or the insertion torque final value.
7. Method according to one of the preceding claims, characterized in that the placement parameters comprise the amount of the insertion torque-path-curve-integral.
8. Method according to one of the preceding claims, characterized in that the loads are dynamic and/or statnamic.
9. Method according to one of the preceding claims, characterized in that the first load, the load periods, the increments and the reaction limit value are determined in addition on the basis of the foundation design.
10. Method according to one of the preceding claims, characterized in that the first load, the load periods, the increments and the reaction limit value are determined in addition on the basis of the load to be carried.
11. Method according to one of the preceding claims, characterized in that the first load, the load periods, the increments and the reaction limit value are determined in addition on the basis of previous soil assessments.
12. Method according to one of the preceding claims, characterized in that the recorded reaction comprises the shift speed of the foundation, the shift path of the foundation, the direction of displacement of the foundation and/or the creep factor.
13. Method according to one of the preceding claims, characterized in that the reaction limit value corresponds to a displacement direction, a shift speed, a shift path, a creep factor, a load or a combination thereof.
14. Method according to one of the preceding claims, characterized in that the reaction limit value is determined on the basis of the placement parameters.
15. Method according to one of the preceding claims, characterized in that the method is computer-implemented.

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