discussion of calculation method on ultimate bearing ... · discussion of calculation method on...

The Indian Concrete Journal December 2016 67

POINT OF VIEW

Discussion of calculation method on ultimate bearing capacity of composite piles

Yue Jain-Wei, Xu An-quan, Song Da and Zheng Kai

A composite pile is a new-style pile which is formed by a reinforced concrete pile inserting into a soil cement mixing pile. The research results show that the frictional resistance of the soil around the pile not only plays a critical role in the pile’s ultimate bearing capacity , but also directly affect the construction quality of composite piles, the diffusion range of cement-soil and the soil’s compaction effect around pile. The ultimate bearing capacity calculation methods of the composite pile are different under the influence of many factors. In order to unify the vertical bearing capacity calculation method of the composite pile, based on the experimental results and related design rules, the relationship between the average of the frictional resistance

η η and η and ~ 4 Q ~ s

ηη += ∑

=, the formula of Yunnan regulation ∑

=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η

∑ η and η ∑∑

of each set of test ,collates

η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~

and and , η η Qs ~ ~ η η .

of Qs

η t

. of the end resistance takes 500kPa, it can be calculated that η takes1.70 and takes 43.20 according to the formula 1.

The results as shown in Tab.6 and Fig.6 can be obtained after collating η and got in the experiments.

.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa

According to the formula 2 and the experience of engineering construction, η increases with

the increase of η . Checking the geological data, we found that is too small that the whole soil compactness is low and soft, and even there is some silty soil. The actual diameter of piles may be magnified during the process of composite pile construction , but the amplification effect of η is not obvious because of the soil.

within the scope of pile length and the ultimate bearing capacity pile is analyzed. Based on the average of the frictional resistance, pile side resistance adjustment factor η η and η and

~ 4 Q ~ s

ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is proposed and the calculating formula of vertical bearing capacity of composite piles is presented. Though analyzing the relationship between η η and η and

~ 4 Q ~ s

ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and η η and η and ~ 4 Q ~ s

ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



in each experimental group, the relationship curve between


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and η η and η and ~ 4 Q ~ s

ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is fitted out. By comparing each scatter diagram of theoretical and experimental bearing capacity, results show that the calculating formula of vertical bearing capacity of the composite pile proposed in this paper is not only practical, simple in calculation, but also helpful for engineers to master.

1. IntroDuctIonDeep mixing method for soft foundation reinforcement technology has been exploited successfully at the same time in of Japan [1] and Sweden [2] since the 1970s and has been widely applied [3]. Construction site and laboratory measurement results show that the bearing capacity of mixing pile measured is much larger than that calculated according to the nominal diameter of agitating vane when the soil around pile is destroyed [4,5]. Along with more and more high-rise buildings in China, the bearing capacity of mixing piles is so low that can’t satisfy the need of foundation treatment, while the static pressure pile and bored concrete pile construction technology is complex and high-cost, therefore it gets the attention of engineering field to explore a economic and safety foundation treatment method.

Since 1998, Tianjin University, Hebei University of Technology and other units have carried out the researches and development about composite pile and have successively promulgated the “Technical specification for composite pile “ and “Technical specification for concrete core cement-soil pile composite foundation”. Quande Sun [6] conducted pullout test on steel threaded on both sides, and the results showed that there is approximate relationship between the bond strength and the unconfined compressive strength of cement soil. A study about the composite pile conducted by

The Indian Concrete Journal December 201668

POINT OF VIEW POINT OF VIEW

Guangrong Ling, Jinjun Li, Jianwei Yue [7,8,9] shows that the bearing capacity of single composite pile is 1.36 ~ 4 times higher than the filling pile’s. A high core pile can improve the bearing capacity of single pile, and the ultimate side friction resistance value between the core pile and soil can reach 0.194 times above the compressive strength of cement-soil. Studies of Ping Dong etc.[10] have shown that the load transmitted to the end of composite pile less than 7% of the total load and its working principle is purely friction pile. Experimental researches of Jinli Liu and Jinbo Liu[11] show that side resistance of composite pile is 50% ~ 70% higher than ordinary bored concrete pile’s, the bonding performance between cement-soil pile and soil is far better than the ordinary pile’s; the Q ~ s curve of concrete core cement-soil pile belongs to the gradient type, and there are no obvious steep fall and damage feature points.

Existing researches show that the composite pile as a new type of piles not only can use the large specific surface area to provide friction resistance, but also can use core concrete with high strength to bear the load. Thus there are high bearing capacity and small settlement with little investments, which abstractly is an economic and effective method of disposing soft soil foundation [9,10]. However, the load transfer mechanism of composite pile is complex, and there are many factors on its bearing capacity, such as the section size and the length of core pile, the diameter of the cement mixing pile, the strength of cement-soil, the size of the grouting pressure, etc, and the study on the bearing mechanism of composite pile is relatively lag, compared with other types.

As the large grouting pressure of the mixing pile construction, the obvious blade mixing effect and high saturated soft soil water content, excess pore water pressure of pile soil comes into being in the course of mixing construction and the soil stress state changes. Maharjan M [12], Songyu Liu [13] etc. studied the growth dissipation law of pore water pressure during the construction of powder spraying pile and after that; Yunfei Guan etc.[14] analyzed the stress field distribution of the elastic zone and plastic zone during construction of the cement mixing pile; Shuilong Shen etc.[15] analyzed stress change of pile soil caused by the deep mixing pile construction using the cylindrical cavity expansion theory; Shidong Tang etc.[16] insisted that the size, distribution and influence scope of excess pore water pressure caused by pile construction is different from single pile, and soil between piles has been fully into the plastic zone during the construction of pile group. In recent years, Shuilong Shen [15], Cheng Dong and Wuming Leng [17], Jun Wang and Guangya Ding [18], Songyu Liu [19], etc. studied

to improve the liquefaction resistance of foundation using cement-soil mixing pile, and found that the cement particles is beneficial to increase the clay content in sandy soil and then the sand liquefaction resistance is improved. There are two kinds of force acting on the surrounding soil of mixing pile which is an important component of the composite pile: one is the expansive force caused by the injection of chemical curing agent; the second is shear action caused by blade rotation [20]. These two kinds of force and excess pore water pressure caused by precast pile insertion are beneficial to increase the effective diameter of composite piles, increase the cement diffusion range and improve the strength of pile soil.

Recent years, although the composite pile has been applied in practical engineering, but the theory of the characteristics of vertical bearing capacity of the pile is still not perfect and the technology regulations [21-23] is not the same everywhere, such as the formula of Tianjin procedures η η and η and ~ 4 Q ~ s

ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



, the formula of Yunnan regulation η η and η and ~ 4 Q ~ s

ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa




ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



. It is difficult to determine the parameter values because of the large range of values, which makes it hard to keep economic and reasonable in the preliminary design. Maximizing its bearing performance is still the major subject in the engineering circle.

2. Put forWArD the formulAIn process of preliminary design, according to the soil parameters provided by geological report, especially lateral friction and end resistance of the pile, designers calculated the bearing capacity of the pile, while many scholars studied the calculation method of bearing capacity of composite piles though there are more influence factors, but it is relatively complex. In this paper, a calculation formula of composite piles’ vertical ultimate bearing capacity based on geological report was put forward according to relevant test data in our country:


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



...(1)


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



— the characteristic value of side resistance in the i-th soil layer around the composite piles with pile core section (kpa);


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



— the characteristic value of side resistance in the i-th soil layer around the composite piles without pile core section (kpa);


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



— the circumference of the composite pile;


POINT OF VIEW


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



— the thickness of the i-th layer within the scope of pile length for calculating the lateral resistance;

l — the length of core pile ;

h — the length of mixing piles;


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



— the cross section area of composite piles;


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



—the lateral resistance characteristic value of composite piles (kPa) ;


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



—the lateral resistance adjustment coefficient around the composite pile.

There are two kinds of force acting on the surrounding soil of mixing pile during construction: the first is the expansive force caused by the injection pressure of chemical curing agent; the second is shear action caused by blade rotation [20] And two kinds of force on the surrounding cement soil and soil will be produced during insertion process of precast concrete core pile: the first is the compaction effect caused by down force and vibratory action of precast concrete core pile; the second is extruding and filling effect of the precast concrete core pile. These effects squeeze and disturb the surrounding soil constantly, and increase the pore water pressure in soil, eventually form a plastic zone around the pile, thus the actual diameter of pile is larger than the theoretical value and it’s more obvious in the part with core pile. To consider that the construction of mixing pile and precast pile is beneficial for the bearing capacity of composite pile, the formula 1 focuses on considering the amplification effect of the composite pile with core section. As for the amplification effect of non-core segment, it’s not considered as a safety reserve. So it is more concise than formulas in other literature which consider separately various influence

coefficients of core and non core segments and also avoids a lot of troubles to choose parameter values.

When it comes to the large range of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



value, it is difficult to get from theoretical analysis because of the complex soil condition. Make reference to each test condition of our country each area in recent years [7,8,10], this paper uses every available data of piles in each test group to determine the value ranges of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



, and takes characteristic values of ultimate bearing capacity and side resistance of each layer of soil


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



into the formula 1 to calculate the weighted average


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



, namely


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



( h is the thickness of the core section of the soil). It takes the average of the survey results as the thickness of each layer of soil during calculation, and then calculates


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa




ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa





ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of each test and draws a scatter of soil, and finally fits a curve to determine the value of amplification coefficient, as shown below.

3. recentlY teStS In our countrY

1 Shanghai Wanli district [10]

The


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of filling soil stratum takes 25 kpa and its layer thickness is 0.6 ~ 1.3 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of brown yellow silty clay takes 30 kpa and its layer thickness is 1.3 ~ 2.4 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of gray sandy silty clay takes 40 kpa and its layer thickness is 1.8 ~ 3.0 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of gray silty clay takes 25 kpa and its layer thickness is 8.9 ~ 10.3 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of gray clay takes 45 kpa and its layer thickness is 2.5 ~ 3.5 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of gray silty clay takes 50 kpa and its layer thickness is 2.0 ~ 4.0 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of dark green silty clay takes 55 kpa and its layer thickness is 2.5 ~ 4.1 m, and the pile top is located at 0.3 m below the natural ground. The Q-s curve of test pile as shown in Figure 1, the list of test pile as shown in Table 1.

Table 1. The list of test pileTest pile number

Parameters of cement mixing pile

Parameters of precast concrete core pile

Ultimate load/KN

Settlement Failure mode


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



psqkPaPile

diameterPile

lengthCement

parameterCore pile

lengthCore pile

top/bottom section

Concrete strength

1 700 18 20% 17 200×200/150×150 C30 ≥1300 24.76 No destruct 1.0159 30.24

2 700 18 20% 17 200×200/150×150 C30 1440 24.00 Pricking

destruction 1.060 30.24

3 700 18 20% 17 200×200/150×150 C30 1200 21.82 Pricking


4 700 24 20% 23 250×250/150×150 C30 ≥2000 21.92 No destruct 1.001 35.70

5 700 24 20% 23 250×250/150×150 C30 2070 27.38 Pile head


6 700 24 20% 23 250×250/150×150 C30 2070 26.25 Pile head




It can be seen from Figure 1 and Table 1 that the No.1 pile does not destroyed and the ultimate load is taken as 1400 kN according to the destruction form and Q-s curve of No. 1 pile and referencing to the failure load of No. 2 and No. 3 pile; Although the destruction form of No. 2 and No. 3 Pile are pricking destruction, but the curve has tended to drop before the destruction, and by inference the sum of composite pile side friction resistance and end resistance is slightly larger than the limit load, so their limit loads are respectively taken as 1450 KN and 1400 KN; though the No. 4 pile is not destroyed, while the pile head of No. 5 and No. 6 are destroyed, it is found through observation that their respective settlement curve is close to steep fall, which shows that the sum of composite pile side friction and end resistance is slightly larger than the limit load value 2000 KN, the ultimate load and the tip resistance


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of the 3 piles

are respectively taken as 2100 KN and 300 kPa according to the failure load of No. 5 and No. 6 pile, then we can obtain


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of each test pile by putting each parameter into the formula 1 , considering the length of the pile and using the weighted average method to calculate


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



= 1.02,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



=33.38.

2 The in-situ test in Jiangyin oriental pearl district [10]

The soil layers of experimental plots in sequence from top to bottom are miscellaneous fill soil, silt, muddy silt and silt. Concretely, the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of miscellaneous fill soil takes 20 kpa and its layer thickness is 1.3 ~ 1.7 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silt takes 30 kpa and its layer thickness is 0 ~ 1.5 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of muddy silt takes 20 kpa and its layer thickness is 0 ~ 1.9 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silt


POINT OF VIEW

Table 2. The list of test pileTest pile

number


Parameters of precast concrete core pile Ultimate load/KN



ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



psqkPaPile

diameterPile

lengthCement

parameterCore pile

length

Core pile top/bottom section

Concrete strength

1 600 10.7 18% 10.0 200×200/150×150 C30 ≥720 9.11 No

destruct 1.156 36.20

2 600 10.5 18% 9.5 200×200/150×150 C30 800 53.96 settlement


3 600 11 18% 10.0 200×200/150×150 C30 720 63.12 Pricking


4 600 7.8 18% 7.0 250×250/150×150 C30 720 Sharp drop Pricking


takes 50 kpa and its layer thickness is greater than 6.5 m, and the pile top is located at 0.3 m below the natural ground.

The Q-s curve of test pile is shown in Figure 2. The list of test pile is shown in Table 2.



According to the corresponding geological profile of No. 1-4 pile given in the references [10], it’s not hard to find via calculating that the result is still bigger than the limit bearing capacity even if the amplification effect of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and the pile tip resistance are not considered and the pile side friction resistance is only considered , such as the No. 3 pile, the side friction resistance is (25×1.7+30×1.5+20×1.9+50×5.9) ×3.14×0.6 = 790 KN, which is bigger than the ultimate bearing capacity 720 KN. It shows that the pile diameter given in the literature is too big. The stiffness core adopts C30 concrete, the end bearing capacity of 970 KN is higher than the ultimate load of each pile, ruling out the possibility of pile head destruction. It can be inferred that the No. 3 and No. 4 composite piles in the experiment should have been happened to pricking destruction, and the side friction did not fully play out when the destruction of the pile occurred according to the test pile settlement curve and the S-lgt curve of each test. Referring to the settlement curve of the test pile, 800 KN is more reasonable to be the ultimate bearing capacity of each pile.


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



take 450 kpa,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 300 kPa. Referring to the settlement curve of the test pile, the pile ultimate bearing capacity by 800 KN values is

more reasonable.


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



take 450 KPa, and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 37.59. According to the formula 1,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of each test composite pile can be calculated while pile diameter is 500 mm. Thus


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 1.21,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 37.59. The result accords well with the actual situation.

3 Test in Tianjin university Liulitai play-ground [6]

The soil layers of experimental plots in sequence from top to bottom are miscellaneous fill soil, clay layer , silty soil, mixture of silty clay and clay, and silty clay. Concretely, the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of miscellaneous fill soil takes 25 kpa and its layer thickness is 1.4 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of clay layer which is plastic takes 55 kpa and its layer thickness is 1.8 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silty soil whose compression is Moderate takes 48 kpa and its layer thickness is 2.2m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of the mixture consisted of silty clay and clay takes 30 kpa and its layer thickness is 5.8 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silty clay which is plastic takes 52 kpa and its layer thickness is 3.2 m; and the pile top is located at 0.3 m below the natural ground. The Q-s curve of test pile as shown in Figure 3, the list of test pile as shown in Table 3.


number



Ultimate load/KN



ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



psqkPa

Pile diameter

Pile length

Cement parameterUp/down

Core pile

length

Core pile top/bottom

section

Concrete strength

1 500 8.5 12/18% 3.5 200-100 C30 300 11.52 accelerated destruction — —

2 500 8.5 12/18% 5 180-180 C30 400 13.35 accelerated destruction — —

3 500 8.5 12/18% 5 180-180 C30 500 13.25 accelerated destruction — —

4 500 8.5 12/18% 5 250-100 C30 700 24.21 settlement destruction 1.417 42.68



7 500 10 12/18% 5 400-100 C30 700 27.16 settlement destruction 1.206 42.68







POINT OF VIEW

It can be inferred from Figure 3 and Table 3 that the failure form of No. 1~3 piles belong to brittle fracture. As the tip resistance is not considered , the end resistance


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



take 250 kPa while


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



take 300 kPa. According to the formula 1,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of each test composite pile can be calculated, and then it can be calculated


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



that takes 1.37 and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 41.10.

4 The in-situ test of a community in Kaifeng

The experiment is a test of piles which has been done by the research team. The soil layers of experimental plots in sequence from top to bottom are silt layer, silty clay layer, silt layer, powder clip silty clay, silt layer and silty clay layer. Concretely, the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silt layer takes 35 kpa and its layer thickness is 3.08 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silty clay layer takes 41 kpa and its layer thickness is 2.53 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa





ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of powder clip silty clay takes 43 kpa and its layer thickness is 5.72 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silt layer which is slightly dense and compact takes 46 kpa and its layer thickness is 2.79 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silt layer which is slightly dense takes 42 kpa and its layer thickness is 1.14 m; the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa





ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of silty clay layer takes 40 kpa and its layer thickness is 3.05 m. The pile top is located at 0.3 m below the natural ground. The Q-s curve of test pile is shown in Figure 4 and the list of test pile is shown in Table 4.

As shown in Figure 4 and Table 4, the top of the pile core is crushed when the load of the No. 1 and No. 2 pile respectively reach 2350 KN, and at this time the settlement curve is close to a steep drop. It shows that the sum of side friction resistance and end resistance of composite pile is slightly larger than the ultimate load, so the load takes 2450 KN. When the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of the end resistance takes 500 kPa, it can be calculated that


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 1.49 and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 42.30 according to the formula 1.




number

Parameters of cement mixing pile Parameters of precast concrete core pile

Ultimate load/KN



ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



psqkPaPile

diameterPile

lengthCement

parameterCore pile

length


section

Concrete strength

1 600 22 18% 14 300×300/300×300 C30 2350 -19.04 The pile

core crush 1.486 42.30

2 600 22 18% 14 300×300/300×300 C30 2350 -18.51 The pile

core crush 1.486 42.30

5 Guo village Xiqing district Tianjin [8]

The soil layers of experimental plots in sequence from top to bottom are the artificial filling soil layer, clay layer, silty clay and silty clay. Concretely, the layer thickness of the artificial filling soil layer is 0.9 m and it would be dug up artificially when conducting the test. The top of pile is 0.5 m higher than the undersurface of the artificial filling soil layer, and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 0. The layer thickness of clay layer which is tawny plastic and well-proportioned is 2.20 m, and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 55 kpa; The layer thickness of silty clay which is sallow

soft plastic and well-proportioned is 1.4 m, and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 50 kpa. The layer thickness of silty clay which is gray soft plastic and well-proportioned is 4 m, and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 40 kpa. The layer thickness of silty clay which Contains high levels of silt and is gray soft plastic and well-proportioned is 5.9 m, and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 44 kpa.

The Q-s curve of test pile is shown in Figure 5, the list of test pile is shown in Table 5. When the


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



of the end resistance takes 500 kPa, it can be calculated that


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 1.70 and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



takes 43.20 according to the formula 1.

Table 5. The list of test pileTest pile number



Ultimate load/KN



ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



psqkPaPile

diameterPile

lengthCement

parameterCore pile

length


section

Concrete strength

1 600 14 18% 13.5 270×270270×270 C30 2070 -23.55 settlement


2 600 14 18% 13.5 270×270270×270 C30 2070 -21.53 settlement



POINT OF VIEW

6 Summary of the test results

The results as shown in Table 6 and Figure 6 can be obtained after collating


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



got in the experiments.

Combined with the technical regulations of Tianjin and Yunnan, the formula 2 for calculating amplification coefficient


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



can be deduced with the method of mathematical statistics.


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



=1.00


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



≤ 33 kpa


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



=0.85+0.15×e


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



33 kpa <


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



< 43.2 kpa ... ( 2 )


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



=1.70


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



≥ 43.2 kpa

According to the formula 2 and the experience of engineering construction,


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



increases with the increase of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



. Checking the geological data, we found that


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is too small that the whole soil compactness is low and soft, and even there is some silty soil. The actual diameter of piles may be magnified during the process of composite pile construction , but the amplification effect of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is not obvious because of the soil.

The same calculated results are represented by a point when the values of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



calculated by the formula 2 are substituted into formula 1. Then a scatter diagram about composite pile comes into being, as shown in Figure 7. The comparison between the theory values of bearing capacity and the experimental values shows that the proposed calculation formula about the vertical bearing capacity of the composite piles is closer to the engineering practice. Compared with existed computing methods, the formula 1 in this paper is not only practical, simple to calculate, but also beneficial to engineering designers to master .

4. concluSIonSAccording to the analysis on the relationship between the average side friction and ultimate bearing capacity within the scope of pile length, a formula is put forward to calculate the vertical bearing capacity of composite piles.


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



increases with the increase of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



. Checking the geological data, we found that


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is too small that the whole soil compactness is low and soft, and even there is some silty soil. The actual diameter of piles may be magnified during the process of composite pile construction , but the amplification effect of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is not obvious because of the soil.

The comparison between the scatter diagram of theory and experimental bearing capacity of each test pile shows that the proposed calculation formula of vertical bearing capacity of the composite pile is not only practical, easy to calculate, but also is conducive to engineering designers to master .

According to the study of the test data of Shanghai Wanli village, it’s found that


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



tends to 1 when the pile diameter is 700 mm; according to a similar experiment to Jinbo Liu’s [11], it’s found that the calculation of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is 1.16 when the pile diameter is 900 mm. Thus, the amplification coefficient of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



is not obvious when the pile diameter is more than 700 mm. When the pile diameter becomes bigger, the lateral swelling force caused by cement grout injection during construction becomes smaller, the pore water pressure of mixing pile becomes smaller at the same time; in addition, the increasing diameter of soil-cement mixing pile doesn’t obviously cause driving effects. Eventually the amplification effect is limited because of the above reasons.

References

Terashi,M., Tanaka, H., Okumura, T. Engineering properties of line treated marine soils and DMM[A]. Proc 6th Asian Regional Conference on Soil Mechanics and Foundation Engineering [C1 Bangk-ok, 1979 191-194Bergado, D.T., Anderson,L.R., Miura. N., et al Soft ground improvement in low land and other environments [M]. ASCE Press, New York.1996.427LI Xiang-jun, Cement mixing pile complex base technique research and practice, Tianjin University, 2003

1.

2.

3.

4.

1.

2.

3.

Table 6. Summary table of


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



and


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



Shanghai Jiang

yinTianjin 1

Kaifeng

Tianjin 2


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



1.02 1.21 1.37 1.49 1.70


ηη += ∑


=

=

η

++ ∑η .It is

++= ∑∑η (1)

η

η η , , η



η and η ~ 1.3 ~ ~ ~ ~ ~ η η η . ~ ~ ~


of Qs

η t



.

η =1.00 ≤33kpa η =0.85+0.15×e −

33kpa 43.2kpa (2)

η =1.70 ≥43.2kpa



33.38 37.59 41.10 42.30 43.20


POINT OF VIEW

XIANG Qi-lin, Application and study on deep mixing pile method in treatment of bearing capacity of composite Central South University, 2007 ZHOU Hao, Study of the bearing capacity and the settlement of deep mixing composite foundation, Wuhan University of Technology 2002SUN De-quan. A new method of ground treatment in Japan-Cement soil and steel pipe pile construction method[ J ]. The Proceedings of the fourth national academic conference on foundation treatment. 1995: 441- 445 .LING Guang-rong, AN Hai-yu, XIE Dai-zong etc. Experimental study on concrete core mixing pile[J], Journal of building structures, 2001 , 22 ( 02 ) : 92-96 .LI Jin-jun, Experimental study on load transfer mechanism of reinforced mixing pile, Tianjin University, 2006YUE Jian-wei, BAO Peng. Characteristics of the vertical bearing capacity of composite piles [J]. China civil engineering journal. 2008 , 41 ( 05 ) : 59-64 . Dong Ping, Load Transfer Mechanism of Concrete-cored DCM Pile. Chinese Academy of Sciences, 2004LIU Jin-li, LIU Jin-bo. Experimental study on dry-bored composite pile under groundwater[J]. Chinese journal of geotechnical engineering, 2001 , 23 ( 05 ) : 536- 539 . MaharjanM , Takahashi A . Centrifuge model tests on liquefaction-induced settlement and pore water migration in non - homogeneous 5011 deposits[ J ]. 5011 Dynamics and Earthquake Engineering . 2013 : 161-169 . ZHANG Qing-song, LI Shu-cai, LIU Song-yu etc. Study on test and numerical simulation of soil disturbed around pile by dry jet mixing pile construction[J], Rock and soil mechanics, 2006 ,27(2):127-130 . GUAN Yun-fei, ZHAO Wei-bing. Excess pore water pressure around deep mixing column in soft clay[J]. Chinese journal of solid mechanics. 2008,29 (2) : 122- 126

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SHEN Shui-long, XU Ye-shuang. Analysis research on soil fracturing around deep mixing column[J], Rock and soil mechanics, 2006,27 ( 03 ) : 378-381 . TANG Shi-dong,WANG Yong-xing. Excess pore water pressure caused by installing pile group in saturated soft soil[J]. Journal of Tongji University.Natural Sciences. 2003 ,31(11) : 1290-1294 .DONG Cheng, LENG Wu-ming, LI Zhi-yong. Experimental study of dynamic resilient modulus of cement-improved high liquid limit clay[J], Rock and soil mechanics, 2013 ,34(l) : 133-136 .WANG Jun, DING Guang-ya, PAN Lin-you. Study of mechanics behavior and constitutive model of cemented soil under static triaxial tests[J]. Rock and soil Mechanics, 2010,31(5) .LI Chen, ZHANG Zheng-fu, LIU Song-yu. Ettringite formation in lime and cement-stabilized clay[J]. Chinese journal of geotechnical engineering. 2013 ,35(2) : 662-665 .SHEN Shui-long,PANG Xiao-ming, On the Diameter of Deep Mixed Column[J]. Journal of Disaster Prevent ion and M it iga tion Engineering, 2005,25(03) : 235-238.DB 29-102-2004 Technical Specifications for mixing piles with stiffness core of Tianjin, Tianjin Construction Management Committee, 2004.YB-2007 Technical specification for concrete core mixing pile, Yunnan, The Construction Department of Yunnan Province, 2007DB-2010 Technical specification for Strength composite piles, Jiangsu, Department of Housing and Urban-rural Development of Jiangsu province, 2007JGJ 94-2008, Technical code for building pile foundations[S],Beijing, China Architecture and Building Press,2008

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

Song Da is pursuing her Masters degree at the College of Civil Engineering, Henan University. She is mainly engaged in the research of foundation treatment and soil constitutive model.

Zheng Kai is pursuing his Masters degree at the College of Civil Engineering, Henan University. He is mainly engaged in the research of foundation treatment and soil constitutive model.

Professor Yue Jian-wei holds a doctorate from Tianjin university. He is an Assistant Dean at the College of Civil Engineering in Henan University, Kaifeng, China. He has been working on soil dynamics and foundation treatment for two decades.

Xu An-quan is pursuing his Masters degree at the College of Civil Engineering, Henan University. He is mainly engaged in the research of foundation treatment and soil constitutive model.

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