Evaluation of Static Pile Load Test Results of Ultimate Bearing Capacity by Interpreting Methods

in geotechnical engineering, foundation piles are ideal for deep foundations that cannot bear higher loads. This architectural expansion places a great deal of responsibility on the engineer to anticipate the appropriate load for the constructor. Unfortunately, calculations of the pile’s bearing capacity are not accessible. It has always been a source of concern for geotechnical engineers, as the structure’s safety depends on the pile’s bearing capacity and gives it a safe value. These research tests are previously known pile load test data from several locations in Nasiriyah to determine the ultimate load-carrying capacity using various interpreting methodologies. A database that was used to test the pile load for three different areas in Nasiriyah, southern Iraq: The Main Drain River Bridge Project, the Al-Eskan Interchange Project, and the Al-Hawra Hospital, as determined by analytical methods, as well as evaluating the final loading values resulting from the methods used, by ASTM D-1143, American and British Standard Code of Practice BS 800. The final capacity for the pile bearing is estimated using these approaches, which are depicted in the form of a graph-based on field data. Chin-Kondner and Brinch Hansen algorithms anticipate the highest failure load for all piles based on the comparison. On average, Chin–Kondner’s ultimate load is 22% higher than Hansen’s maximum load for the 22 pile load tests. Decourt and DeBeer, and Mazurkiewicz’s techniques yielded the closest average failure load. Buttler-Hoy approach yielded the smallest failure load.


Introduction
Static load tests are used to verify the pile's final ultimate load capacity for ultimate theoretical capacity. The ultimate capacity can be defined as the rapid settlement when the pile collapses or when the load is too heavy. However, often the ultimate load is not established during the test [1]. Therefore, the ultimate capacity of the pile can be obtained with some criteria using load-settlement data. A type of pile loading test is the static pile loading test. Static loading experiments include axial compression and axial tensile testing [2]. Therefore, it is necessary to decide the ultimate load as clearly as practicable. Determining  The purpose of this research is to determine he applicability of various pile load test procedures. Fifteen methods were used to predict the capacity of bearing and choose the suitable technique of the pile for the southern Iraq region. In addition, this study interpreted the results using pile load test data from 12 piles built in different localities.

Database for pile load test
Data were collected from three different areas in the city of Nasiriyah. The general shape of the site is shown in Google Earth for the city of Nasiriyah. The studied projects' locations are Al-Iskan Interchange (1), Power Plant (2), (Figure 1, Figure 2), show the static test load for Al-Iskan Interchange project.
Test piles of different lengths and dimensions were used, as shown in Table 1. Then, the 15 methods mentioned above were applied to each pile. Finally, the final bearing capacity was obtained with the specific settlement of each pile, where both load and settlement are done according to ASTM D 1143 [11].

Geology of region
The study area is the city of Nasiriyah, the center of Dhi Qar Governorate, located in southern Iraq within a flat plane (the Mesopotamian Plain). Holocene deposits, comprising floodplain sediments, river sediments, swamp sediments, and Aeolian deposits, all of the Mesopotamian sediments, cover the city's floor [3]. Three selected sites in Nasiriyah constitute the field of study. IOP Conf.

The procedure of static loading test
Static load testing is a commonly dependent method for determining the pile's bearing capacity [16]. A hydraulic jack applies the load to the pile.
Step loads are applied to the pile, and enough time is left between each load to allow for a small degree of settlement. Dial gauges are used to measure the pile's settlement [17]. As a result, a load-settlement curve is produced. Static pile loading tests are a form of pile loading test; static loading investigations include axial pressure and axial tensile testing. These experiments were carried out using the following standards: ASTM D 1143-81 (1994) [17], ASTM D 3689 (1995), and ASTM D 3966-90 (1990) (1995) [19], ASTM D-1143/D1143M [18], ASTM D 3966-07 (2013) (2013) [20].

2.4.
Graphical approaches to determine pile capacity The final load capacity of the test pile from several recommendations and methods to understand pile loading test data can be found in the literature and several different standards. These methods can be described as analyzing the distribution of load settlement data using various principles such as total settlement/load ratios, settlement, or plastic settlement. It is a summary of the methods of obtaining ultimate bearing capacity as the methods were applied to a pile of boring type for the North Nasiriyah bridge project with a design load of 325 (ton) and a testing load of 650 (ton) of the pile (length 25 m and diameter 1.5 m). First, for each pile, load-settlement graphs are created in Figure 3. Then, in Figure 19, the final capacities of the same pile are calculated using the same procedures.

2.4.1.
‫݊ݏݏ݅ݒܽܦ‬ ‫ݐ݁ݏ݂݂‬ ‫ݐ݈݅݉݅‬ (1972) According to Davisson (1972), the ultimate load exceeds the pile's elastic compression by 0.15-inch (ca. 4 mm) plus a factor equal to the pile diameter divided by 120 as indicated in equation 1, plus the soil fast as shown in Figure 4. This method is likely the most well-known and widely utilized since it provides the least estimate of axial compression potential from the natural load-settlement curve without extrapolation criteria [1]. The methodology is based on the assumption that at a specific small toe movement. The capability is then attained, an attempt is made to estimate the movement by accounting for the rigidity of the pile (length and diameter) [18]. Finally, set the plot scales to a slope of roughly 20 degrees for the pile elastic compression line [19] [20].

ܶℎ݁ ‫݊݁ݏ݊ܽܪ‬ ‫݁ݐܽ݉݅ݐ݈ݑ‬ ‫݈݀ܽ‬ (1963)
In 1963, Brinch Hansen suggested a description of pile capacity as the load that for 80 percent of the load, it produces four times the pile head movement that was previously obtained. As a result, the 80 per centcriterion can be predicted immediately from the load movement curve, as shown in Figure 5. Still, it can be calculated more precisely by plotting the square root of each meaning of movement divided by the load value and plotted against the movement as an equation 3 [21]. As a result, relationships for capacity calculation or ultimate resistance Qu, 80% according to the Hansen -criterion for the ultimate load, can be developed:

Decourt Extrapolation (1999)
Decourt (1999) proposed an approach comparable in structure to Chin-and Kondner's Hansen's methods. To use the procedure, divide each load by its associated movement and plot the resulting value vs. the applied load, as shown in Figure 6. The ratio of the y-intercept to the slope of the line is equivalent to Decourt's extrapolation load limit [5], as the following equation: Where Qu = final pile load, C1= The Line's Straight Slope, C2 = the straight line's y-intercept.

‫ܥ‬ℎ݅݊ − ‫ݎ݁݊݀݊݇‬ ‫݊݅ݐ݈ܽܽݎݐݔܧ‬ (1971)
Chin referred to determining the pile's final weight by dividing each movement by its applied load and graphing the results against the movement. Based on the application of general kondner's work of the piles, Chin assumed that the outputs of this connection were hyperbolic [23]. As demonstrated in equation 5, the inverse of a straight line (c1) slope is retrieved from Figure 7.

‫ݏ'ݖܿ݅ݓ݁݅݇ݎݑݖܽܯ‬ ‫݀‪ℎ‬ݐ݁݉‬ (1973)
Mazurkiewicz provides us with a hypothesis that the resulting drawing is a curve of load-settlement approaching parabolicity. These operations are carried out by selecting a set of settling lines for the pile head separated at equal intervals and differentiated on the load axis by the respective loads ( Figure 8). Then, at a 45-degree angle to the loads defined, a line is drawn. The ultimate load is the intersection of this line with the load axis [14].

‫‪′s‬ݎ݁݁ܤ݁ܦ‬ ‫݀‪ℎ‬ݐ݁݉‬ (1968)
DeBeer (1968) and Deeper and Walays (1972) proposed drawing the linear, logarithmic curve of loads. For the data before and after reached the ultimate load, this curve gives diffrent slopes of the intersection axis. When the ultimate load is reached, the calculation of the tow line will become visible, one occurring before and the other after the final load, as Figure 9. Except for De Beer's, all of the previously described methods evaluate a failure load, and these lines will intersect [22], [14].

ܸܽ݊ ‫ݎ݁݀‬ ‫ݏ′ܸ݊݁݁‬ ‫݀‪ℎ‬ݐ݁݉‬ (1953)
For different assumed ultimate load values (P)equivalent load and all of Ln and Pu assumed ultimate load, natural logarithm indicates) the settlement graph versus Ln (1-P / Pu). The assumed ultimate load number at which the curve becomes straight, similar to a straight line, is known as the ultimate capacity. [23] as Figure 11.

ܵℎ݁݊′‫ݏ‬ ‫݀‪ℎ‬ݐ݁ܯ‬ (1980)
This method assumes that it is possible to obtain the ultimate load from drawing the relationship between settlement and applied load, where the settlement is plotted against the log load. This relationship results in a curve with a linear tail where the final load is determined at the starting point of the linear tail [23], as

Fuller and Hoy method (1970)
According to Fuller's technique, the ultimate load corresponds to the point when the slope of the load settlement curve is 1.27 mm/ton. As a result, the ultimate load is computed by locating the point on the graph where the curve is Tangent to the 1.27 mm/ton slope curve [24], as shown in Figure13.

‫ݐ݊݁݃݊ܽܶ‬ ‫݀‪ℎ‬ݐ݁݉‬
The curve in the load-settlement graph is Tangent to the end parts indicating the commencing, and plastic states reflecting the elastic state. The ultimate responsibility is the value of the load corresponds to the point at which these two lines intersect [23] as Figure 15.

‫ݏݎܥ‬ ‫݂‬ ‫ݏݎ݁݁݊݅݃݊ܧ‬ ‫݀‪ℎ‬ݐ݁݉‬ (1991)
Most engineering corps employ this approach. First, we draw a load-settlement curve from which it defines three loads of failure. The first load (Q1) is the load that versus the settlement level of 6.4 mm, the second load (Q2) is the load, which corresponds to the point of the tangential method obtained. Finally, the third (Q3) is the load, versus the point at which a 0.025 mm / kN angle intersects with the line curve for load settlement [2], as Figure 16.

‫ݕ݊ܽݎ݅ܪ‬ ܽ݊݀ ‫ݕݓܽ‪݈ℎ‬ݑܭ‬ ‫݀‪ℎ‬ݐ݁݉‬ (1989)
This approach states that the ultimate load is calculated from the load-settlement curve, representing the start of the final straight line of the load-movement curve [25], as Figure 17.

Estimating the value of the pile bearing capacity by different codes
The bearing resistance of the pile was calculated based on three different codes: Standard Test Method for Piles under Static Axial Compressive Load ASTM D-1143 [27], American, British Standard Code of Practice BS 8004 [28] and IS 2911 (1995) / Indian Code [29] (Table 2). On the other hand, in Table 3, three codes giving different loading results are shown for the pile whose results were previously shown with a length of 25m, a diameter of 150 cm, and a design load of 325 tons. IOP Conf.

Results and discussion
It is not easy to determine the best method among the methods of interpretation used in this study. Although varied numbers for the piles' bearing capacity were obtained using the 15 approaches, the results showed an apparent variation in the load values from one method to another, making determining the most appropriate value difficult. Since ancient times, the geotechnical engineer has been concerned about determining the most appropriate value with bearing capacity. The structure's safety depends on choosing the appropriate value, which makes a great responsibility on the shoulders of engineers. As a result of the importance of this engineering component, several methods for estimating that value and making an evaluation and comparison to reach the best prediction have been developed. The tolerance value of the substrate was interpreted in this study using 15 techniques based on field data load-settlement:  Table 3. The Davisson offset of 0.15 inches plus a value equal to the diameter divided by 120 from the elastic line represents the settlement required to mobilize toe resistance. Davison and the Brazilian standard method rely on the same principle for calculating capacity by specifying the displacement value. However, the bearing capacity value is not determined.
As a result, the displacement calculated from the equations for each method exceeds the value generated from the test. Therefore, Davisson's Offset Capacity is exceptionally susceptible to inaccuracies in load and weight readings; it necessitates well-maintained equipment and precise measurements. The Brinch-Hansen 80 percent criterion typically yields a Qu-value close to what one subjectively accepts as the ultimate natural resistance based on the static loading test results. However, the value is less than that of Chin-Kondner, as shown in Table 3. Therefore, extrapolation is always used to obtain these two methods. Decourt's approach has the advantage of allowing the user to notice the rated capacity right after the straight-line chart starts appearing while performing a static load test. However, the calculated results showed that the resulting capacity of the extrapolation method is less than the expected load calculated from the Chin-Kondner method in most of the piles adopted in the study. Abdelrahman [15] studied DeBeer's method and other methods, agreeing with this study's result. Although agreed, the study showed that the results. The loading limit influences Chin's approach on average, Chin-Kondner extrapolation ultimate load is 22% higher than Hansen's ultimate load for the 12 pile load tests.
The values acquired using the Mazurkiewicz and Hansen ultimate load methods are more conservative than those obtained using the Chin and Decourt methods. As a result, it is easier to construct and more reliable, particularly for piles loaded close to failure. The ultimate load values of Mazurkiewicz are on average 27% lower than those of Chin. Several previous studies reinforced the results of the study. Kedar [14], the study agreed with the results. Van der method gave very high and exaggerated values compared with the methods adopted in this study. Therefore, this method is considered unsuitable as it gives a safety factor value greater than 3.
The De Beer method demands that the pile be loaded close to failure; otherwise, the plotted load settlement values will fall on a single straight line, and the limit load will not be specified. The standard Brazilian approach has also failed to provide the ultimate load ( Table 3). As a result, the displacement calculated from the equation exceeds the value generated by the static load test. Shen gave results 14% lower than the bearing capacity value generated by the static test load for all piles approved in the study. Therefore, the values are considered close to the field. The values of the BC obtained by Shen and the product from the DeBeer and Fuller technique show a strong convergence in Table 3 16 Tangent method and Hirany (1989) gave a low and convergent estimate of the bearing capacity of the piles compared to the methods with high values. It is difficult to determine the best method for evaluating the load among the different methods that give different values for the loads. This discrepancy in values is difficult to choose the appropriate bearing capacity value. Moreover, the difference between the values obtained from the methods between the largest and the smallest value leads to different points of view in determining the logical load value, increasing the level of unreliability.
According to ASTM Table 4, the pile is loaded up to 200 percent of the intended design load. Apply the load in increments of 25% of the design load for the tests on the individual pile. The load is increased until the axial rate is reached; movement is limited to 0.25 mm (0.01 in) hourly. According to ASTM, the results are close to those calculated by the field. For example, the first and second projects piles in Table 4 had equal load values calculated from the field, which was calculated according to the ASTM. British standard code unless the value of the bearing capacity is determined explicitly by some observable characteristic of the load/settlement curve, the bearing capacity may be regarded as that load applied to the head of the pile that causes the head of the pile to settle 10% of the pile diameter [28]. The British code specified the maximum load at this ratio to consider when the pile begins to fail. Thus, override the settlement at which failure occurs for the landing produced from the field. The friction resistance ends by continuing the settlement of the pile without adding a load or adding loads by a small amount, the end bearing resistance of the pile begins. Therefore, the load at failure has defined the load which the rate of settlements continues to decrease without further loading [30].
In IS 2911 (1995) / Indian, the maximum load of one-half of the working load. Table 4 shows that the loads calculated by the code are less than the load obtained from the field static load test except for the first project, which gave according to the code IS 2911 (1995) / Indian a load equal to the calculated BC the field.

Acknowledgments
The study is based on this participatory research, and the first author expresses his gratitude to the Department of Roads and Bridges for providing the necessary information to the study.

Conclusion
There are many different methods for obtaining the bearing value of the pile. This paper has been based on 15 methods to interpret the results obtained and a laboratory comparison based on data from the static load test field for three projects in Nasiriyah. According to the ultimate load values acquired through various methods within the study's aims: The greatest values were obtained from the methods of Chen Kondner and Hansen for all piles. Decourt, Mazurkiewicz and Shen methods produced values that averaged the different methods used in the study. The values obtained from the Davison and Corps of Engineers method have been neglected. The load-bearing capacity of the pile based on the van der method was not acceptable. Fuller and Hoy (1970), Buttler and Hoy (1977), Tangent method, Hirany and Kulhawy (1989), and Slope tangent these methods estimated a low bearing capacity of the piles. The ASTM code gave the results of the highest expectation of the value from the field. The British Code does not specify the bearing capacity of the pile. The settlement at which the code determines the failure load exceeded the upper limit of the field.