Deep Cement Mixing Piles Research Articles

Analytical approach for vertical dynamic responses of stiffened deep cement mixing pile in unsaturated ground

Stiffened deep cement mixing (SDCM) piles present excellent engineering performance compared with conventional pipe piles and thus are often applied to the structure foundation in coastal soft-soil area. This study intends to explore the vertical dynamic behavior of a SDCM pile in unsaturated soil by developing an analytical approach. In the proposed approach, the SDCM pile divides into two parts. The first part is considered as a composite pile formed by a prestressed high-strength concrete (PHC) pipe pile and a cement mixing pile through high-strength bonding, and the second part formed by the PHC pipe pile and an unsaturated soil column. The closed-form solution for the dynamic impedance of the SDCM pile has been determined and then verified by contrasting with the existing solutions, where the dynamic impedance is mainly characterized by dynamic stiffness and dynamic damping at SDCM pile head in the vertical direction. Numerical discussions are finally implemented to analysis the dependence of physical parameters of cement mixing pile, PHC pipe pile, and unsaturated soil on the vertical dynamic impedance of SDCM pile. It can be concluded that increasing the depth, radius and elastic modulus of the cement mixing pile at relatively low load excitation frequencies is beneficial for enhancing the vertical vibration resistance of the SDCM pile, while the reverse is true at higher load excitation frequencies. Quantitatively, under relatively low load excitation frequencies, the reinforcement depth of the cement mixing pile should not exceed 2/3 of the length of the PHC pipe pile, while its elastic modulus should be 5 ‰ to 2 % of the elastic modulus of the PHC pipe pile.

Consolidation of unsaturated composite foundation reinforced by T-shaped deep cement mixing piles

T-shaped deep cement mixing piles are variable section piles designed to reinforce unsaturated composite foundation under the embankment loading, which can effectively reduce regional settlement and construction costs. However, how to calculate the consolidation settlement of the reinforced ground is unclear when considering the T-shaped deep cement mixing piles. To investigate the consolidation process, the governing equations for unsaturated composite foundation with T-shaped deep cement mixing piles are firstly derived under the equal strain assumption. Then, semi-analytical solutions for settlement and excess pore pressures are obtained using Laplace transform and transfer matrix methods, and Crump’s method is employed to get analytical solutions in the time domain. The accuracy of the proposed solutions is verified by comparing them with existing ones. Finally, the analysis of the parameters is conducted to explore the consolidation characteristics of unsaturated composite foundation with T-shaped deep cement mixing and deep cement mixing piles. The findings indicate that accounting for the enlarged pile cap leads to a quicker dissipation of excess pore pressures, resulting in a notable reduction in foundation settlement. As the height of the enlarged pile cap and the area replacement ratio increase, the settlement decreases markedly because the enlarged pile cap carries more load.

Integrated Assessment of Bearing Capacity and GHG Emissions for Foundation Treatment Piles Considering Stratum Variability

Foundation treatment piles are crucial for enhancing the bearing capacity and stability of weak foundations and are widely utilized in construction projects. However, owing to the complexity of geological conditions, traditional construction methods fail to meet the demand for low-carbon development. To address these challenges, this study introduced a comprehensive decision-making approach that considers the impact of stratum variability on greenhouse gas (GHG) emissions and pile bearing capacity from the design phase. During the design process, the GHG emissions and bearing capacities of deep cement mixing (DCM) and high-pressure jet grouting (HPJG) piles were quantitatively assessed by analyzing the environmental and performance impacts of foundation treatment piles related to materials, transportation, and equipment usage. The results suggest that the bearing capacity of piles in shallow strata is highly susceptible to stratum variability. Using piles with a diameter of 800 mm and a length of 20 m as an example, compared with DCM piles, HPJG piles demonstrated a superior bearing capacity; however, their total GHG emissions were 6.58% higher, primarily because of the extensive use of machinery during HPJG pile construction. The GHG emissions of foundation treatment piles in shallow strata were influenced more by geological variability than those in deep strata. Sensitivity analysis revealed that the pile diameter is a critical determinant of GHG emissions and bearing capacity. Based on the bearing capacity–GHG emission optimization framework, a foundation treatment strategy that integrates overlapping and spaced pile arrangements was introduced. This innovative construction method reduced the total GHG emissions by 22.7% compared with conventional methods. These research findings contribute to low-carbon design in the construction industry.

Monitoring of early curing stage of cemented soil using polymer optical fiber sensors and microscopic observation

Deep cement mixing (DCM) piles are widely utilized for reinforcing soft clay foundations, particularly in coastal regions where soil stability is critical. Monitoring the quality and early-stage behavior of cemented soil is essential to ensure the effectiveness of DCM pile projects in meeting design requirements. Innovative methods for on-site monitoring are necessary to enhance the reliability and efficiency of these reinforcement techniques. In this study, a novel approach is proposed utilizing polymer optical fiber (POF) sensors based on physical optical sensing principles to monitor the initial hydration degree and overall quality of cemented soil during the early curing stage. The proposed method relies on the principle of physical optical sensing, where POF sensors are employed to measure changes in reflected light intensity (LI) and temperature in cemented soil. Two crucial variables, namely the initial water content and the amount of cement, are considered in analyzing their impact on the LI and temperature changes over time. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) analysis are conducted on cemented soil samples with varying water-cement ratios to investigate their mechanical properties and microstructure evolution. The results of the UCS tests indicate that higher initial water content prolongs the initial hydration reaction time required for cemented soil with different cement contents. Analysis of LI curves reveals a rapidly rising trend as the hydration reaction progresses, particularly evident in samples with higher initial water content. SEM analysis further demonstrates that a stable POF LI corresponds to the completion of the hydration process, with hydrated gel formation resulting in a more compact microstructure and smaller voids. The findings highlight the significant influence of cement quantity and initial water content on the mechanical strength and microstructure of cemented soil. By analyzing changes in reflected LI and temperature, the proposed monitoring method provides valuable insights into the early-stage behavior and quality of cemented soil during the curing process. This innovative use of POF sensors for on-site monitoring offers a novel approach to evaluating cemented soil in DCM pile projects.

Load-bearing response of deep content mixing soft soil composite foundation based on the geotechnical centrifugal model test

Deep cement mixing (DCM) is an effective method of treating soft underwater soil foundations. Currently, the real-time failure development of a composite foundation cannot be obtained by most model tests of DCM pile foundation reinforcement. In this study, a circuit device for identifying pile failure and that can reflect the real-time working state of piles arranged at different positions in a soft soil composite foundation was developed. By applying this device to a geotechnical centrifugal model test, the load-bearing response process of a bank slope reinforced with a soft-soil composite foundation and DCM piles was studied. The failure development law of the DCM piles, ultimate surcharge of the bank slope, failure mode of the foundation, and the pile-soil stress ratio were determined from the test results. The law obtained in this study provides a reference for the application of DCM piles in underwater soft soil foundation engineering.

Numerical analysis of failure mechanism and stability of reinforced embankment with DCM soft soil composite foundation

The deep cement mixing (DCM) method has been widely used in offshore geotechnical engineering. At present, the reinforcement form of pile has been researched widely, but there is a lack of understanding of the failure mode of DCM pile composite foundation reinforcement for bank slopes. In this paper, a series of unconfined compression tests was conducted to obtain necessary numerical analysis parameters. A series of study on the failure mechanism and stability control of DCM pile composite foundation reinforcement bank slope has been conducted through numerical analysis. The results of numerical analysis indicate that under different reinforcement conditions, there exists an optimal reinforcement depth, and the safety coefficient will gradually stabilize at 1.45; The bending moment of the piles under the bank slope the bending moment of the pile body under the road surface Under different overloads. The maximum bending moment of the pile body is located near one-third of the pile body, and the maximum bending moment of the pile body is located between the shoulder and foot of the slope.

Pore Water Pressure and Stress Changes During the Construction of Stiffened Deep Cement Mixing Piles

Pore Water Pressure and Stress Changes During the Construction of Stiffened Deep Cement Mixing Piles

Nonlinear Analysis of Bearing Characteristics of Stiffened Deep Cement Mixing Piles under Vertical Loading

Stiffened deep cement mixing (SDCM) piles are composite piles that combine the advantages of single large-diameter deep cement mixing (DCM) and precast concrete piles. They comprise precast concrete piles as the core and cast-in-place DCM piles as the outer layer. This study evaluates the bearing characteristics of SDCM piles under vertical loading. The composite modulus of elasticity of SDCM piles is first introduced and determined using the area-weighted average method. Then, the reliability of the proposed method is described by comparing the calculated results with the findings of the existing literature. Furthermore, a nonlinear simplified analysis method based on the load transfer method is proposed for vertical bearing characteristics of equal- and short-core SDCM piles under vertical loading. This method is developed by the finite difference method. The accuracy of the simplified method is validated by comparing its results with those from existing tests, theoretical analysis, and finite element simulations. The results of their study indicated that the area-weighted average method calculates the composite modulus of elasticity of the composite pile section of the SDCM piles with an error below 0.5% compared to the analytical method. This finding represents sufficient accuracy. The simplified calculation method established in this study is computationally stable. When the iteration factor is set to 10−6, as the number of discrete nodes n on the pile increases, the calculation results are stable with a good convergence when n > 30. The vertical bearing capacity and pile top stiffness of SDCM piles increased with the length of the core piles. There was a reasonable core-to-length ratio for SDCM piles in specific scenarios. An excessively long DCM pile section made its lower part force-free for a given length of core piles. The appropriate length of core piles should be determined in actual projects to avoid unnecessary material waste. An optimum ratio of core piles for SDCM piles was determined. Beyond this optimal value, an increase in the ratio of core piles controlled the pile settlement in a limited manner.

Experimental study on the bearing property of the composite foundation with stiffened deep cement mixing pile based on the PHC pile

Inserting a prestressed high-intensity concrete pipe pile into a cement–soil mixing pile can form a new composite pile named the composite foundation with stiffened deep cement mixing (SDCM) pile. The Huanghuai alluvial stratum in China is selected to carry out the in situ test for the SDCM pile, and the bearing capacity of the SDCM pile is tested by the slow-speed maintenance load method. The results show that for an SDCM pile with dense silt and fine sand as the bearing layer, the characteristic value of bearing capacity can reach 2,300 kN, which means an SDCM pile with a length of 8.0 m meets the load requirement of a general high-rise building. Further analysis shows that the SDCM pile saves more than 40% of the cost compared with the traditional CFG pile and has better quality control advantages at the same time. This research can provide basic data and design references for similar site foundation projects.

Numerical analysis of load-transfer mechanism of stiffened deep cement mixing pile foundation

ABSTRACT To reveal the load-transfer mechanism of stiffened deep cement mixing (SDCM) piles, the three-dimensional numerical analysis of a pilot pile was first conducted using the finite element software Diana, which can simulate the Mohr-Coulomb friction interface. Comparisons show that the computed load-settlement curve and distribution law of the skin frictions agreed well with the measurements. Then, the numerical method was employed to model the group pile foundations with four SDCM piles. It shows that the bearing capacity increased with increasing pile spacing and core lengths. And most loading was shared by the stiffened cores. It indicates that negative skin frictions may arise at the bottom of a reinforced concrete pile cap or the end of a stiffened core. And there is a hysteresis effect for the peak frictions on the two interfaces to mobilize. Meanwhile, plastic shear zones in soil and DCM pile may sequentially arise with increasing load.

Quality evaluation of ground improvement by deep cement mixing piles via ground-penetrating radar

Deep cement mixing piles are a key technology for treating settlement distress of soft soil subgrade. However, it is very challenging to accurately evaluate the quality of pile construction due to the limitations of pile material, large number of piles and small pile spacing. Here, we propose the idea of transforming defect detection of piles into quality evaluation of ground improvement. Geological models of pile group reinforced subgrade are constructed and their ground-penetrating radar response characteristics are revealed. We have also developed ground-penetrating radar attribute analysis technology and established ground-penetrating radar technical system for evaluating the quality of ground improvement. We further prove that the ground-penetrating radar results integrating single-channel waveform, multi-channel section and attributes can effectively detect the defects and stratum structure after ground improvement. Our research results provide a rapid, efficient and economic technical solution for the quality evaluation of ground improvement in soft soil subgrade reinforcement engineering.

Dynamic Analysis of a Concrete-Cored Deep Cement Mixing Pile under Horizontal Dynamic Loads

Concrete-cored deep cement mixing (DCM) pile is a novel type of pile foundation, and its lateral dynamic response analysis has great practical significance. Based on the elastic dynamic theory, this study investigated the lateral dynamic response of a concrete-cored DCM pile in the single-phase viscoelastic soil using theoretical deduction and parametric analysis. Considering the special structure of the concrete-cored DCM pile, the lateral vibration equation of the concrete-cored DCM pile is first established with mechanical equilibrium, and then the dynamic behavior of the soil around the pile is described using the existing governing equations of single-phase soils. Subsequently, the solutions for the dynamic impedances at the pile top are deduced after a series of rigorous theoretical derivations. Finally, the influence of the pile and soil parameters on the dynamic impedances at the pile top is studied using calculation examples and parameter analysis. The results reveal that the radius of the concrete-cored DCM pile obviously affects the dynamic impedances at the pile top. Enhancing the elastic modulus of the concrete-cored DCM pile is beneficial for augmenting the dynamic impedances at the pile top. An improvement in the soil density will increase the stiffness factors of the dynamic impedances at the pile top but will reduce their damping factors.

Three-Dimensional Analysis of Load Transfer Mechanism for Deep Cement Mixing Piled Embankment under Static and Cyclic Load

Piles have been widely used to improve the bearing capacity of the soft foundation. The existing research obtains significant findings on the load transfer mechanism for rigid piled embankments. However, limited studies have been focused on the deep cement mixing (DCM) piled embankment. To grasp the load transfer characteristics of DCM piled embankments, a three-dimensional numerical simulation was conducted in this study, which was validated by the measurements from the field case. It was found that the effect of soil arching was reduced compared with the rigid piled embankment. This induced approximately 61.5% larger vertical stress transferred to the subsoil surface and approximately 83–150% larger settlement of the embankment in DCM piled foundation system. To further understand the working mechanism of this system, the factors which influence the load transfer mechanism were investigated. It is found that the area replacement ratio is the most influential factor affecting the settlement at the top of the embankment, whereas the elastic modulus of the DCM pile influences most the vertical stress and the earth pressure coefficient. The cyclic load with vehicle speeds of 90 km/h will lead to approximately 34% growth of embankment settlement and about 11% reduction in the maximum earth pressure coefficient. Based on the numerical simulation results, the analytical equation of the normalized vertical stress acting on the subsoil surface for the DCM piled foundation was proposed and validated by two field cases, with the difference in the range of 13.8~16.7%.

Study of Construction Technology of Large Diameter and Ultradeep Cement Mixing Pile in Road Engineering

As the soft soil in the Pearl River Delta area is deep, 50 cm-diameter cement mixing pile composite foundation is often used for road engineering. A municipal road in the Hongwan District of Zhuhai adopted a mixing pile with a diameter of 80 cm and a length of 27 m, which brought great difficulty to the construction of the project. To ensure the engineering quality, the bit optimization scheme was adopted to improve the blades from the conventional two layer and four groups of blades to three layer and six groups of blades. The projection direction of each layer of blades was vertical, which could increase the mixing times and improve the mixing uniformity. At the same time, double-channel teeth were added to effectively increase the smoothness of slurry flow. The optimized nozzle is improved from a nozzle located at the bottom of the drill bit to the left and right sides of the bottom of the drill pipe to effectively relieve the blockage of the nozzle, silt backflow, and other problems. The grouting pressure is generally 0.4–0.6 MPa. After the optimization of the grout pressure, the upper limit of 0.6 MPa was used in the first stirring and spraying process, and 0.4 MPa was used in the second stirring and spraying process. The advantage is that in the first mixing, excess cement grout is ejected for mixing, and in the second mixing, the total grout dosage can be controlled by reducing the grouting pressure, which effectively improves the quality of pile body and controls the cost. To ensure uniform soil mixing, measures were taken to improve the drilling speed of the drill pipe, accelerate the speed when sinking, slow down the speed when lifting. Through the above measures, the strength of the mixing pile body was improved, and the integrity of the pile body was guaranteed. Pile integrity, effective pile diameter, pile length, and pile strength uniform accord with the design. The difficult problem of large diameter and deep cement mixing pile is solved, which provides a good reference value for similar engineering.

Performance of T-Shaped and conventional Cement-Soil deep mixing piles to stabilize soft base of High-Speed trains

ABSTRACT The dramatic increase in train speeds has made settlement control in the train bed a critical issue. High differential settlements on railway tracks, especially high-speed trains, can derail trains and cause irreparable financial and human losses. Deep Cement Mixing (DCM) piles are among the efficient methods to control the train path’s settlement, especially paths on soft clay soils . Recently, T-shaped cement soil mixing (TDM) piles became more popular than a single DCM pile. In this study, total and differential settlements along the path of a high-speed train on a loose bed reinforced with DCM and TDM piles were studied using PLAXIS 3D software. . Three different configuration patterns of the pile were investigated to determine the performance of DCM and TDM piles. Unlike the DCM piles, no differential settlements were captured in the TDM piles with a distance of 60, 120, and 180 cm between the piles.

Experimental Study on the Vertical Bearing Capacity of Stiffened Deep Cement Mixing Piles

Experimental Study on the Vertical Bearing Capacity of Stiffened Deep Cement Mixing Piles

Reliability-based settlement analysis of embankments over soft soils reinforced with T-shaped deep cement mixing piles

Reliability-based settlement analysis of embankments over soft soils reinforced with T-shaped deep cement mixing piles

Analytical modeling for the load-transfer behavior of stiffened deep cement mixing (SDCM) pile with rigid cap in layer soils

A new composite structure named stiffened deep cement mixing (SDCM) piles has recently been considered and applied in many geotechnical engineering projects. The SDCM pile was formed by inserting a stiffened core into the deep cement mixing (DCM) pile that has just finished construction, thereby combining the advantages of DCM piles and concrete piles. This study developed a load-transfer analytical approach for SDCM pile with rigid cap in layer soils from the theoretical solution view. Herein, the nonlinear mechanical behaviors of the DCM pile–soil and DCM pile–stiffened core interfaces were characterized by a tri-linear bond-slip model, and the action of soil on the pile end was simulated by an elastic-perfectly plastic model. Three-dimensional finite element simulations were conducted for SDCM piles embedded in homogeneous soil and double-layer soils. The reasonable matches between the predictions and the results from FE simulations and physical model tests confirmed the applicability of the theoretical approach. The full-range load-transfer behavior and the bearing performance of SDCM piles were further discussed. Parametric studies were finally conducted, providing insights into the design practice of SDCM piles.

Investigation on load-carrying capacity of geogrid-encased deep cement mixing piles

This article discusses the feasibility of a geogrid-encased deep cement mixing (EDCM) pile for enhancing the load-carrying capacity (Qult) of a conventional deep cement mixing (DCM) pile, based on the results of experimental and numerical investigations. Firstly, physical model tests were conducted to observe the load–settlement response and load-transfer mechanism. Subsequently, a series of three-dimensional (3D) finite-element analyses was performed to investigate the effect of the stiffness and length of the geogrid encasement. The results indicated that the geogrid encasement effectively improves the Qult of the DCM piles by a factor of two. With the additional confinement provided by the geogrid encasement, the geogrid can also provide a greater contribution to the loading transfer. The increase in Qult became more significant with a lower strength of the DCM. For a particular amount of geogrid, the EDCM pile with a thicker geogrid provided a higher Qult than that with a longer geogrid. The optimum length of the geogrid-EDCM pile was found to be approximately twice that of the pile diameter. Finally, a chart for estimating the efficient effect of geogrid encasements on the Qult of EDCM piles was proposed.

Numerical study of the deformation performance and failure mechanisms of TDM pile-supported embankments

The T-shaped deep cement mixing (TDM) pile is a technique newly used to support embankments built on soft clays. However, comprehensive studies considering the cost effectiveness have not yet been performed, and the TDM pile bending moment behavior under embankment loading is not fully understood. Hence, this paper aims to evaluate the performance of a TDM pile-supported embankment (TPSE) over soft foundation subsoils using 3D numerical modeling based on a case history of a conventional deep cement mixing (DCM) pile-supported embankment (DPSE). The performances of pile-embankment systems are investigated and discussed through several parameters, including the embankment center settlement, lateral movement at embankment toe, deflection and bending moment of the pile at the embankment shoulder, and embankment stability. First, to capture the thickness effect of the uppermost fill material layer, numerical analyses with different fill material thicknesses are examined. Subsequently, extensive parametric studies of TPSE are carried out to assess the TDM pile cap size and length influences. The results of the parametric studies are analyzed and compared to those obtained from DPSE systems with equivalent embankment loading and volume between the TDM and DCM piles. Finally, a preliminary guideline for evaluating the overall improvement performance of TPSE is proposed to determine the best TDM pile cap size for each pile length in comparison with the DPSE case. Some guidelines are also defined, and small TDM piles with thicker caps are suggested to improve pile-embankment systems.