The Model Test And Analysis Of The Modified Stiffening Core Soil-cement Composite Pile In Yellow River Flooded Area

In recent years, with the development of urbanization, small high-level buildings and high-risebuildings have formed a large amount. Cement-soil mixing pile has been adopted in foundation treatmentand foundation pit bracing in Kaifeng, which represents the Yellow River flood area. However, mostscholars keep their eyes on the use of cement-soil mixing pile in the coastal soft soil, and the study ofcement-soil mixing pile in Yellow River flooded area hasn’t been taken seriously. As a result, thetheoretical research lags far behind the actual engineering application. According to this, doing research oncomment-soil mixing pile in Yellow River flooded area is of great significance in civil engineering.In addition, static pressure pile is widely used in the Yellow River flood area. However, becauseof thick sandy soil layer below, it’s common to meet that the static pressure pile can’t get into the designeddepth during the construction. Besides, the necking down defect and the ground subsidence defect go alongwith the construction of the CFG pile. So a reasonable foundation treatment method hasn’t been found sofar. As a new type of composite pile, stiffening core soil-cement composite pile offers a new method forfoundation treatment in the soft soil layer. It’s not unified on its bearing capacity as researchers havedifferent understanding because of its insufficient research during a short time. The bearing capacitycalculation method in two local standards which has issued for construction is different. So doing researchon stiffening core soil-cement composite pile in Yellow River flood area is of great practical significance.As the cement-soil plays an essential role during the load transfer of stiffening core soil-cement compositepile, the research on the quality of cement-soil should be an important part of stiffening core soil-cementcomposite pile in the article.In this article, we take the most common silt soil in Kaifeng as the samples. Under the conditionof no admixtures, we try to study the mechanical properties which are related to the different dosage ofcement, different age and different ways of curing conditions. According to the study, we found that thedosage of cement is not more than20%, cement-soil strength increases faster with the increase dosage ofcement, and the dosage of cement is more than20%, strength increase slower. So it would be better thatcement dosage shouldn’t be greater than20%in the practical engineering.With the cement dosage of16%, we take calcium fly ash, sand and ash calcium as admixture todo the mixing experiment respectively. Experiments show that cement-soil with fly ash can improve the cement-soil strength and the ash calcium also has a certain strength increase. Compared with the single24%cement block, the lateral compressive strength of the cement block with16%dosage of cement andcement ratio reached60%is higher. Fly ash price is about1/3of the cement, so it will reduce theengineering cost in the practical engineering if we replace the part of cement with the right amount of flyash cement to meet the bearing capacity of the cases.By doing static load test on the stiffening core soil-cement composite pile model which areproduced in the laboratory, used the counterforce frame to provide counterforce, loaded in a similar way tothe quick load method and buried with strain gage in the core pile and the soil, we obtained the loadsettlement curve of pile, axial force change curves of core pile and cement-soil under vertical load indifferent dosage of cement, different pile length and under the condition of different ratio of fly ash.Researches show that the increasing cement content can improve stiffening core soil-cement composite pileultimate bearing capacity, however, when the cement content is more than16%, the improvement ofultimate bearing capacity of pile will no longer obvious. The ultimate bearing capacity of cement-soil pilecan be improved a lot when fly ash is mixed in the cement-soil and the dosage should better vary from60%to80%. When the strength of the cement-soil and the core pile are well matched, suitable growth of thecore pile length will be helpful to improve the bearing capacity of the pile. The core pile bears the mainvertical force among a stiffening core soil-cement composite pile and the axial force of a core pile tends tobe high in the top and low in the downside. However, cement-soil bears tiny vertical force and only havethe effect on transmitting side friction.The indoor model are simulated and analyzed by the finite element software ABAQUS. Theresult are basically similar with the actual results and the related parameters can be used in similar model.