Analysis of bearing capacity of composite foundati

Analysis of bearing capacity of deep mixing pile and jet grouting pile composite foundation

with the development of foundation treatment technology and the promotion and use of various treatment methods, composite foundation has been more and more applied. Engineering practice has accumulated a lot of data. This paper takes the composite foundation of deep mixing piles and jet grouting piles commonly used in foundation treatment in Tianjin as an example, combined with engineering tests (the test in this paper adopts the surcharge method, and the load plate adopts 1 m × 1 m) based on the measured data, the bearing capacity of composite foundation is analyzed from three aspects. 1 factors affecting the bearing capacity of composite foundation the bearing capacity of composite foundation is jointly borne by soil and piles, so the factors affecting the bearing capacity of composite foundation can be divided into two categories: (1) the influence of stratum. This includes the composition, saturation and unit weight of the foundation soil. Understanding these characteristics is essential for designers to choose the appropriate treatment method and estimate the treatment effect. (2) Impact of piles. Whether the selected construction technology is suitable for the stratum, the size of lime soil ratio, and the quality of construction personnel all have a great impact on the pile quality

according to the characteristics of Tianjin strata, deep mixing piles and cement powder spraying piles are often used for treatment. The pile diameter is generally 500 mm, the pile length is 5 ~ 15 m, the lime soil ratio is 15% ~ 18%, and the replacement rate is 17% ~ 20%. The bearing capacity of composite foundation provides integrated solutions for industry customers, with a range of 120 ~ 180 kPa

through load tests on more than 20 sites, more than 60 cores were found that due to the construction quality (or improper selection of Technology), the bearing capacity of the foundation could not be improved, but would be reduced. For example, two engineering strata are similar. One has a bearing capacity of 1. The latest materials and technology make selle Royal have a new breakthrough of 70 kPa in the task of creating the world's most environmentally friendly cushion series, and the other is only 120 kPa, which is lower than the bearing capacity of 130 kPa. It is also found that the quality of the upper part of the pile (more than 5 m) has a great impact on the bearing capacity of the pile. 2. The degree of foundation treatment improving bearing capacity and economic pile length 2.1 evaluation of the degree of foundation treatment improving bearing capacity in order to reflect the effect and economy of foundation treatment and make the data comparable, a parameter is introduced to increase the multiple σ= The sum of the measured value/the bearing capacity of the inner layer within the pile length range. The measured value is determined by the load test, because the Q-S curve of composite foundation is generally slow deformation, there is no obvious inflection point, and it is generally determined by the relative deformation value. For deep mixing pile or jet grouting pile composite foundation, take the load corresponding to s/b (load plate width) or s/d (load plate diameter). For 1 m plate pile diameter of 500 mm, the value range of Settlement s is 4 ~ 10 mm. In the test, it is found that the settlement is within 4 ~ 10 mm, and the dispersion of the bearing capacity of the composite foundation is very large. For convenience and comparability, take the load corresponding to s=7 mm and select 20% replacement rate to determine the standard value of the site foundation bearing capacity for research. The sum of the bearing capacity within the pile length is calculated by multiplying the standard value of the bearing capacity within the pile length by the layer thickness. The statistical results are shown in Table 1. Table 1 statistical results of bearing capacity site number test

number of piles bearing capacity standard

standard value/kpa sum of bearing capacity in the range of pile length/(kPa. M) σ Value 20

it can be seen from table 1 σ The variation range of the value is small and σ The value contains information such as stratum, pile length, treatment effect, etc., so it can be used for pile length design and foundation treatment effect prediction. When the proposed method of unknowingly expanding 3D printing to carbon neutral materials has opened up a new direction in the field of sustainable development, it can be used for estimation. 2.2 economic pile length economic pile length can be calculated by the design value of pile length and σ Ratio, and then calculated according to the actual stratum bearing capacity, this pile length can be used as a design reference value. 3. The value of bearing capacity of composite foundation. The Q-S curve of composite foundation is generally slow deformation, which is generally determined by the relative deformation value. For deep mixing pile or jet grouting pile composite foundation, when the pile diameter is 500 mm, the value of 1 m plate is 4 ~ 10 mm, and the statistics of bearing capacity of the corresponding foundation representing 3 points of 4 mm, 7 mm and 10 mm are shown in Table 2. Table 2 foundation bearing capacity under corresponding settlement and λ Bearing capacity under the settlement corresponding to the number of piles in the site/kpa λ 4 mm7 mm10 mm..... 09

from table 2, it can be seen that the value range of foundation bearing capacity is very discrete, but it is reasonable from the perspective of specifications, which makes it difficult to evaluate the bearing capacity of composite foundation, and also leads to disputes. In our study, we found that only taking a little value from the curve can not reflect the change characteristics and trends of the curve. If the relative deformation value and the change of deformation value are taken, it can not only reflect the size of the bearing capacity of the composite foundation statically, but also the development trend of the dynamic response curve, which makes the selection of the bearing capacity of the composite foundation more reasonable. In this paper, when s=7 mm, the change rate of settlement corresponding to the corresponding level of load is taken λ See Table 2

it can be seen from table 2 that the variation rate of settlement is 0.05 ~ 0.16. After more than 10 comparisons, it is believed that λ It is better to retrieve 0.05 ~ 0.09. introduction λ The value aims at superior quality. There is a quantitative reference value when using the relative deformation value to determine the bearing capacity of composite foundation. When λ When the value is large, s is taken as a small value, and the purpose is always λ Keep the value within a certain range, as set λ The value is 0.05 ~ 0.09. 4 conclusion in view of the fact that deep mixing pile or jet grouting pile composite foundation is often used for foundation treatment in Tianjin (generally, the pile diameter is 500 mm, the lime soil rate is 15% ~ 18%, and the replacement rate is 17% ~ 20%), through the test data research, the conclusions are as follows:

(1) under the same stratum, the quality of construction is very important, which is related to the success or failure of foundation treatment, and through the test, it is found that the quality of 5 m above the pile has the greatest impact on the bearing capacity of the foundation

(2) Introduction σ The value can be used as a reference for the estimation and design of pile length and bearing capacity of composite foundation

(3) using the relative deformation value and the change rate of deformation value can more reasonably determine the bearing capacity of composite foundation and better reflect the change of curve, so that the value of bearing capacity of composite foundation is more in line with the stratum