Calculation of Pile Side Friction by Multiparameter Statistical Analysis

There are many factors influencing the ultimate bearing capacity of pile foundation in karst development area. The current design method usually adopts a large safety factor, which inevitably leads to an increase in engineering cost and a prolonged period. Grey theory is a kind of mathematical theory based on known information. It can describe the change law of unknown information by generating and developing some known information. Based on the above characteristics, combined with numerical simulation results, the effects of aspect ratio and karst scale on the ultimate bearing capacity of bridge piles are studied by using grey theory. The results show that the ultimate bearing capacity of piles increases with the increase of aspect ratio, and decreases with the increase of karst scale. The degree of influence of karst scale is larger than that of aspect ratio. Grey theory can better reflect the variation of ultimate bearing capacity of pile foundation under aspect ratio and karst scale, and the error between calculation result and numerical simulation result is about 9%. The grey theory can be applied to the estimation of the ultimate bearing capacity of bridge piles.

Analysis on the synergistic variation of soil freezing and pile foundation bearing capacity in permafrost regions

Vertical ultimate bearing capacity of static pressure pipe pile is influenced by comprehensive factors, such as pile body, soil around pile and construction conditions., and the relationship between the impact factors and ultimate bearing capacity of a single pile is highly complexity and non-linear. This paper is based on collecting the data from static load tests in typical geological conditions of Liao-shen area, construction records, and test pile sites. And then combine analysis of principal component with SVM to analysis the prediction of the single pile’s vertical ultimate bearing capacity. This model can reduce the number of SVM input variable dimension to improve speed of training support vector effectively. At the same time it can eliminate the influence factors of multiple correlation. The results show that the proposed principal component analysis SVM model has good predictive accuracy and generalization ability, and opens up new avenue of research for analysis of static pressure pipe pile vertical bearing properties.

In view of the weak vertical bearing capacity and low safety performance of the traditional soft rock pile foundation for human settlements, this paper proposes to monitor the vertical bearing capacity of the soft rock pile foundation for human settlements in Lhasa. The vertical mechanism of soft rock is analyzed, including the uniaxial compressive strength of rock around the pile, the relative displacement of pile rock and the interface condition of pile rock. The vertical bearing capacity of the pile foundation in soft rock is calculated by load transfer method. The side friction model and the pile end of the pile are established to determine the pile foundation. The calculation formula of the load settlement curve is obtained by using the side friction model and the pile end resistance model. The vertical bearing capacity of the pile foundation in soft rock is analyzed when the pile side rock is in the elastic stage and the surrounding rock is in the plastic stage. The test results show that friction pile plays an important role in the test pile under the working load. This method can effectively monitor the vertical bearing capacity of pile in the soft rock geological environment of human settlements, and can be applied to practical projects.

Though the wide applications of jacked pile in engineering in Shenyang district, the problem is also exist in engineering for the capacity of the jacked pile is hard to account. The relationship between the standard penetration test and the ultimate vertical bearing capacity of jacked pile is established in this paper; also an empirical formula is put forward for calculating the ultimate vertical bearing capacity of the jacked pile in this district with blow count of standard penetration test (SPT). The engineering examples indicated that the empirical formula is feasible because the calculating bearing capacity of the silent pipe pile is coincided with the static load tests. The calculated results satisfy the engineering requirement andt can be concluded that the method is also convenient to choose the diameter and length of the pile during the initial stage of design.

There are 5∼8 m thick non self weight collapsible loess in the project site of a power plant. In order to study the bearing relationship between compressive and uplift piles in loess site, static load tests were carried out on PHC pipe piles with diameter of 400 mm and 500 mm and pile length of 12 m. Under the same pile top load, the displacement of uplift pile top is greater than that of compression pile top. Based on the measured load displacement curve, the uplift bearing capacity of PHC pipe pile with pile diameter of 500 mm is 32.5% higher than that of pile diameter of 400 mm. When the pile diameter is 400 mm and 500 mm respectively, the ultimate bearing capacity of PHC uplift pile is 26.24% and 27.70% of compression pile respectively. GM (1,1) model of grey system can fit and predict the load displacement curve of PHC pipe pile under compression and pull-out. Compared with the measured results,the relative error of GM (1,1) model of grey system is larger in the previous stages of load, and decreases gradually with the increase of load.

Prestressed high-strength concrete (PHC) pipe piles have been widely used in engineering fields in recent years; however, the influencing factors of their ultimate bearing capacity (UBC) in multilayer soil need to be further studied. In this paper, a static load test (SLT) and numerical analysis are performed to obtain the load transfer and key UBC factors of pipe piles. The results show that the UBC of the test pile is mainly provided by the pile shaft resistance (PSR), but the pile tip resistance (PTR) cannot be ignored. Many factors can change the UBC of pipe piles, but their effects are different. The UBC of the pipe pile is linearly related to the friction coefficient and the outer-to-inner diameter ratio. Changes in the pile length make the UBC increase sharply. Low temperatures can produce freezing stress at the pile–soil interface. The effect of changing the Young modulus of pile tip soil is relatively small.

The Chin's plot method is the most widely used method in Singapore to assess the ultimate skin friction and ending bearing separately based on static pile load test results. In this study, a large number of pile load tests for driven piles were back analyzed using the Chin's plot method. The obtained data were examined in order to evaluate the appropriate design ranges for skin friction coefficient, Ks and end bearing coefficient Kb, which are the two key parameters for pile capacity estimation in design. It was revealed that, generally, the currently adopted design ranges were over-conservative for displacement piles. New design ranges and limits for Ks, Kb and unit end bearing, qb, were suggested, and their typical values for conventional designs were recommended. Further, the importance of pile load test in the design of piling foundation was emphasized. Whenever practicable the ultimate pile bearing capacity should be obtained from pile load tests, and all indirect estimations of pile capacity should be evaluated against the static load test results.

Assessment of direct CPT and CPTU methods for predicting the ultimate bearing capacity of single piles

According to optimized fitting analysis for measured data in static load test of 22 different types of single piles, a new modified exponential model was proposed by authors in this paper. In comparison between the hyperbolic model and the integrated exponential curve model, the correlativity coefficients R of the modified exponential model were over 0.996. The fitting effect of the model of proposed in this paper is better than that of other models above-mentioned. The deviations between fitting and measured data in static load test for single pile was small, especially, in the tail pasts of fitting curves, the mean deviations of 2 test pile given in the paper are 1.61% and 1.99% respectively. The modified exponential model can be better described Q-S curves of single piles. It can be used to better evaluate the ultimate bearing capacity of single piles.

The ultimate bearing capacity of rigid vertical and batter piles and pile groups in clay has been determined under various inclinations of the load, varying from the vertical to horizontal directions. The results of load tests on single model piles of different lengths and inclinations and on free-standing groups and piled foundations are compared with theoretical estimates. The influence of load inclination on the bearing capacity can be represented by simple interaction relationships between the axial and normal components of the ultimate load. The effect of eccentricity of the load on the ultimate bearing capacity of pile groups is discussed on the basis of previous theory and model test results.

The differences in development and situation of karst caves lead to two kinds of karst caves, and the karst cave may be on the pile side or at the pile bottom, which has a different influence on the bearing capacity of pile foundation. The paper presents a numerical analysis of the influence of karst caves at pile side on the bearing capacity of super-long pile foundation in karst areas. According to the size of pile foundation of a real bridge project, this paper modelized karst caves and investigated the karst cave from the effect of length, height, and thickness of roof on horizontal and vertical bearing capacity of pile foundation. The main conclusions can be drawn as: when the horizontal displacement at the top of pile foundation is greater than 0.05 m, the horizontal load is correlated positively with the length of karst cave; when the vertical displacement is greater than 0.07 m, the vertical load is correlated negatively with the thickness of the roof of karst cave. However, the height of karst cave has little effect on the bearing capacity; also the existence of karst cave has little influence on the dynamic response of pile foundation. The results of this study can be important with reference to the design and construction of pile foundations in karst areas.

In their paper the authors present an interesting study on the application of the wave equation analysis to instrumented and production piles. The results are especially interesting to the discusser because, charged by the German Pile Committee, he is investigating the applicability of loading tests by impact instead of static loading. In addition to the wave equation analysis (in its most recent form developed by Goble et al. 1975), the discusser has also studied a similar method developed by the Di~tcll Institute TNO for Building Materials and Building Structures at Delft. For the prediction of the ultimate bearing capacity of piles these methods require the measurement of force and motion at the pile top. Simple test equipment has been developed for in situ tests. The discusser considers these measurements to be a prerequisite for a precise prediction of the bearing capacity. The authors present calculations of the ultimate bearing capacity of precast piles driven in a homogeneous sand deposit at the Saint-Charles River site (see Table 2 of their paper). In these calculations the wave equation was applied, based on blow counts only. They show that there is only a poor correlation between the computed and measured ultimate bearing capacity Q,, and Qfl,, (regression coefficient r = 0.3). This is due to a nonlinear relation between Qf,,. and Q,,,,. A much better correlation can be achieved by a regression of Qflll on 7 = Qfn/Qc1,, (correlation coefficient Y = 0.78, Fig. I ) . It can be seen in Fig. 1 that the prediction of the ultimate bearing capacity tends to be on the safe side with increasing pile bearing capacity. In addition to the regression lines the confidence interval on the 95% level for the prediction of Qc,,, from 7 is shown in Fig. 1. Of course this relationship is restricted to the piles driven into the sandy layers of the Saint-Charles River,

The influence of foundation pit excavation on the bearing behavior of concrete tubular piles at the pit bottom remains unclear. Based on the Vesic cavity expansion theory, this paper proposes a method for calculating pile driving resistance, which takes into account the residual effect of vertical pressure changes on earth pressure during excavation. Furthermore, relying on the statistical regularity between Qu/Pu (ratio of ultimate bearing capacity to ultimate cavity expansion pressure) and L/d (length-to-diameter ratio), theoretical formulas for calculating the ultimate bearing capacity of tubular piles before and after foundation pit excavation are established, with their reliability and influencing factors analyzed. This method only requires determining the L/d of the tubular piles and the theoretical value of pile driving resistance. With its simple parameter requirements, it is suitable for estimating the ultimate bearing capacity of tubular piles affected by excavation. By comparing the computed penetration resistance, earth pressure, and driving resistance of tubular piles with field measurements, the computed results show good agreement with field measurements, and the accuracy of the proposed method meets the requirements of engineering design, verifying its feasibility as an empirical method. The fitting results of the Qu/Pu ratios indicate that the deviations between the measured and computed values are 4.17% and 5.64% before and after excavation, respectively. Additionally, L/d and L/H (ratio of pile length to excavation depth) significantly affect the earth pressure, driving resistance, and vertical bearing capacity of monopoles. Smaller L/d and L/H ratios lead to greater earth pressure on the pile and more pronounced effects on driving resistance and vertical bearing capacity. The development of this method offers an approach for estimating the ultimate bearing capacity of tubular piles before and after foundation pit excavation during preliminary design, thereby holding substantial engineering significance.

This paper examines shaft and base grouted concrete piles by conducting vertical static load tests (SLTs) and dynamic load tests. Three concrete piles with shaft and base grouting, with base grouting only, and without grouting techniques were selected, and compressive SLTs were conducted. Two piles with grouting were also assessed with dynamic load tests. Another two uplift SLTs were conducted to one shaft and base grouted pile and one pile without grouting. Traditional presentations were provided to check whether the bored piles reached the design requirement. Interpretations of test results were also provided to determine the ultimate pile capacity. Results from these 5 SLT programs indicated that double-tangent and DeBeer's methods are close to each other, and Chin's method overestimates the pile capacity. Comparison of the results from the SLTs and dynamic load tests shows that the results from Chin's method are close to dynamic results, and Mazurkiewicz's method overestimates for friction resistance. The results also demonstrate that base and shaft grouted pile and base grouted pile increase by 9.82% and 2.89% in compressive capacity, respectively, and compared to the uplift SLTs; there is a 15.7% increment in pile capacity after using base and shaft grouting technology.