Dry Jet Mixing Research Articles

In-situ solidification/stabilization of heavy metals contaminated site soil using a dry jet mixing method and new hydroxyapatite based binder.

In this study, in-situ treatment using dry jet mixing construction method and SPC (single superphosphate and calcium oxide) new binder are used to solidify/stabilize a heavy metal contaminated site soil with relatively high content of organic matters. Time-dependent field performance of the soils at 41 and 326 days after treatment is evaluated, which includes electrical conductivity (EC), leachability of heavy metals and chemical oxygen demand (COD), soil penetration resistance, acid neutralization capacity (ANC), and chemical speciation of heavy metals. The results indicate that the stabilized soils exhibit satisfactory performance which is comparable with the laboratory study. In-situ SPC treatment significantly decreases EC values and increases penetration resistance values of the soils. Leachability of lead, zinc, cadmium and COD decreases with increasing SPC content or curing time. Large percentages of heave metals in the soils are transformed from exchangeable fractions to residual fractions after treatment. These, coupled with the improved ANC, result in low heavy metal leachability in stabilized soils.

Numerical analysis for widening embankments over soft soils treated by PVD and DJM columns

The appropriate selection of treatment methods for a soft soil subgrade is critical to highway widening projects. In this paper, plane strain conditions are considered in the analysis of prefabricated vertical drains (PVD) and dry jet mixing (DJM) columns. PLAXIS is used to develop the finite element models for the simulation of PVD and DJM treated embankments over soft soils for highway widening projects. The model results include the settlements during and after embankment construction and the lateral displacements of the subgrade. This paper also investigates the working mechanisms when the two subgrade treatment methods are adopted for the widening of embankments over soft soils by analysing the excess pore water pressure distribution in the soft soils. In-situ embankment tests are used to validate the proposed numerical model. The results show that the conventional PVD method causes a soil arching effect in the old embankment and excessive ground disturbance during construction despite the fact that this method can reduce the post-construction soil settlement and the lateral displacement during construction. In comparison, the DJM treatment can greatly reduce the settlement during construction, the settlement and differential settlement after construction, and the lateral displacements. Finally, several techniques are summarised to improve the conventional PVD method, providing practical value for widening highway embankments over soft soils.

A Combined Dry Jet Mixing-Prefabricated Vertical Drain Method for Soft Ground Improvement: A Case Study

A remarkable combined dry jet mixing (DJM) and prefabricated vertical drains (PVDs) method was used to enhance the performance for soft ground improvement. In the combined method, PVDs are first installed and then DJM columns are installed between the PVDs at larger spacing. This combined method improves the effectiveness of the ground improvement and creates a more economical solution. This paper presents a case study of the combined method for marine clay improvement in Lianyugang of China. The excess pore water pressure in soils created by the installation of DJM columns with and without PVDs was monitored and compared. In situ standard penetration tests were conducted in the DJM columns and before-and-after piezocone penetration tests were performed in soils surrounding the columns. Long-term settlement monitoring under embankment loading was carried out for the ground improved by combined method and DJM method alone. The field tests, settlement monitoring and economic benefit analysis results demonstrated that the DJM-PVD method is technologically sound and cost-effective as compared with the conventional DJM method.

Analysis for Engineering Example of Dry Jet Mixing Pile Consolidating Foundation

Dry jet mixing pile is the general technique of composite ground consolidation , which is used in foundation treatment of soft soil under highway. It has a widespread applying due to so many advantages. This passage adopts an example of dry jet mixing pile combined with Longkou Shugang expressway engineering, it aims to state that dry jet mixing pile consolidating foundation along intertidal zone would obviously improve bearing capacity, strength and compressive modulus of foundation soil, reduce settlement and make a difference of consolidating foundation in according to data analysis of field or laboratory experiment. This technique is an effective way to solve the Jump Car problem and economic and quick.

Testing Study on DJM Pile Composite Foundation under Flexible Load

Dry jet mixing (DJM) piles are widely used in silt foundation treatment to improve foundation stability and control post-construction deformation. As the work mechanism of DJM composite foundation is very complex, though many useful calculation theories have achieved, the theoretical study of DJM pile composite foundation is still far behind engineering practice, the settlement and stress calculation precision is unsatisfied. Then it is still necessary to reveal the work mechanism of DJM pile comprehensively. A field test of DJM pile composite road foundation is carried out and many measurement methods are adopt to collect the test information, such as soil pressure sensors, pore pressure sensors, settlement plates, inclinometer tubes, stratified settlement pipes, multi-point displacement meters in piles and so on. Then the surface settlement, internal deformation and stress developing of soils and piles are monitored Real-time. Through in-site test, the settlement and internal deformation of piles and soils, the stress ratio between pile and soil, and the negative friction around pile are studied.

Assessment of Unconfined Compressive Strength of Cement Stabilized Marine Clay

Two aspects of deep mixing method, the difference relating strength gain in dry jet mixing (DJM, reagent powder introduced into the ground) and cement deep mixing (CDM, reagent slurry introduced into the ground), and prediction of unconfined compressive strength of cement stabilized marine clay, are discussed in this paper. The first part of this paper concentrates on the difference between DJM and CDM on strength gain, and suggests a guideline for DJM and CDM selection. An indicator in terms of water content ratio, which is defined as the ratio of water content to the liquid limit of the soil, is presented by statistical analysis from the laboratory and field test data as a guideline for the selection of DJM or CDM. Based on the laboratory test data, a mathematical model relating strength gain of cement stabilized marine clay to related variables is developed. A new simple index designated as total water-cement ratio, which is defined as the ratio of water weight in the soil-cement to the weight of cement in dry state, is proposed for interpretation of test data of soil-cement. The proposed method is then verified with available test data published by other different researchers.

A combined DJM-PVD method for soft ground improvement

Dry jet mixing (DJM) and prefabricated vertical drains (PVDs) have been successfully used for soft ground improvement worldwide. They both have advantages and limitations, and have been used independently so far. In this study, DJM and PVDs were used in combination to enhance the performance of soft ground improvement. In the combined method, PVDs are first installed and then DJM columns are installed between the PVDs at larger spacing. This combined method improves the effectiveness of ground improvement and creates a more economical solution. This paper presents the concept, mechanisms, construction procedures, and field validation of this new method. In situ standard penetration tests were performed in dry mixed columns and cone penetration tests and field vane shear tests were performed in soils between the columns. Plate load tests were subsequently conducted on the treated ground. Excess porewater pressures were monitored during and after the installation of DJM columns with and without PVDs. Field validation was conducted through a pilot highway embankment on very soft clay in Jiangsu, China. Long-term settlement monitoring was carried out for the construction of this highway embankment. Field tests and monitoring clearly showed that the DJM-PVD method performed well in enlarged spacing as compared with the conventional DJM method with close spacing.

Ground Improvement by Dry Jet Mixing Method to Stabilize Embankment of an Irrigation Tank

Ground Improvement by Dry Jet Mixing Method to Stabilize Embankment of an Irrigation Tank

Lateral Displacement of Ground Caused by Soil–Cement Column Installation

Closed form equations for calculating the lateral displacement caused by the installation of soil–cement columns are derived based on cylindrical cavity expansion theory. The radius of the cavity needs to be predetermined empirically, mainly with reference to the amount of admixture injected and injection pressure as well as the stiffness of the surrounding soil. Also, an empirical equation is proposed for considering the partial “plane strain” effect of installing a row of columns. The proposed method has been applied to four reported field tests conducted in Saga, Japan, using the slurry double mixing (SDM) method, the dry jet mixing (DJM) method, and the wet jet mixing (WJM) method. The radius of influence, i.e., where the lateral displacement in the soil is less than 5 mm during the installation of soil–cement columns, is found from the field data to be approximately 30, 40, and 50 m for the SDM, DJM, and WJM, respectively. It is shown that the proposed method yielded a reasonable prediction of these field measurements. The field data also indicate that the installation sequence has a considerable influence on the observed lateral displacement; but the proposed method can only consider two extreme conditions of this influence. It is suggested that the method is a useful tool for the design of soft subsoil improvement resulting from the installation of soil-cement columns.

Evaluation and Quality Control of Dry-Jet-Mixed Clay Soil-Cement Columns by Standard Penetration Test

Dry jet mixing has been widely used since the 1980s for stabilization of soft soil. The quality and strength of the dry-jet-mixed columns must be evaluated to confirm the success of the stabilization. The standard penetration test (SPT) is shown to be a simple and effective method for this task. The strength characteristics along the length of the column were determined, and correlations between the SPT blow count and the unconfined compressive strength were developed.

Decentralized tracking for a class of interconnected nonlinear systems using fuzzy variable structure control with application to a drill and dry jet mixing machine

In this paper we have presented a novel decentralized fuzzy variable structure controller (DFVSC) for the tracking problem of a class of uncertain interconnected nonlinear systems. The decentralized variable structure control principle is utilized to deal with model uncertainties, nonlinear interactions between subsystems, control input gain uncertainties and external disturbances. A fuzzy logic function is applied to eliminate the chattering problem and improve the tracking performance. The proposed DFVSC is applied to a drill and dry jet mixing machine. The performances of the proposed DFVSC are compared with the conventional decentralized variable structure control (DVSC) and suboptimal PID control (SPIDC) by computer simulation. Simulation results show that the proposed DFVSC can achieve excellent transient performance, faster response, better precision and good robustness against system parameter uncertainties, various airflow conditions and uncertain time-varying external disturbance.

Decentralized tracking for a class of interconnected nonlinear systems using fuzzy variable structure control with application to a drill and dry jet mixing machine

Decentralized tracking for a class of interconnected nonlinear systems using fuzzy variable structure control with application to a drill and dry jet mixing machine