Marine Soft Soil Research Articles

Physical model study on the clay–sand interface without and with geotextile separator

In most marine reclamation projects, sand fill is placed directly on soft marine seabed soils. The sand particles can easily penetrate into the soft marine soils, and the soft soil can also move into the pore spaces inside the sand at the initial contact interface between the sand and the soft marine soil. In this case, the permeability and the volume of the sand above the initial surface are reduced. To avoid this problem, a geotextile separator is often placed on the surface of the soft marine soils before placing the sand. In this study, a two-dimensional physical model is utilized to study the geotextile separator effects. The initial conditions of a clayey soil, sand fill, and surcharge loading were kept the same in the physical model test with the only difference being that a geotextile separator was either placed on the clay surface or omitted. The settlements of the initial interface were recorded and compared for the two cases without or with the geotextile separator. The particle size distribution of the soils taken across the interface zone for different time durations was then measured, analyzed, and compared. Based on an analysis of the results, the sand percolation depth was 40 mm and fine particle suffusion was apparent when the sand was placed directly on the marine slurry surface without a geotextile separator. However, when a geotextile separator was used sand percolation was avoided, and the fine particle suffusion was effectively diminished. A relative fine particle fraction is defined to illustrate the migration of fine particles from the clay to the sand soils. The fine particle percentages of the Hong Kong Marine Deposits–sand mixtures were calculated for the cases with and without a geotextile separator using an empirical formula and micromechanical modeling to obtain a better understanding of the effects of geotextile separators in practice.

Deformation Characteristics Analysis of Supporting Structure Caused by Deep Excavation of Large-Span Subway Parking Lot in Deep Silt Stratum

With the rapid development of China’s economy and the continuous improvements in urban modernization, the high-rise buildings, subways, civil defense fortifications, underground substations, underground storage, and other projects have increased, and the subsequent foundation pit projects, especially deep foundation pit engineering, have grown as well. Concurrently, the technical challenges and construction risks faced by deep foundation pit engineering have increased, especially in the coastal soft soil areas along rivers, due to the extremely fragile and sensitive geological environment. For this purpose, the ABAQUS finite element simulation software was used for numerical simulation analysis to study the influencing factors and the deformation rate of the diaphragm wall and aimed at different failure mechanisms of instability of deep foundation pit projects in the Yitian Parking Lot of Shenzhen Metro Line 10. Moreover, preventive measures for the deformation of supporting structures were proposed. The results showed that: (1) In the engineering mechanical properties of marine soft soil, deformation of the diaphragm wall is sensitive to the changes in the e-lnp rebound curve slope $$ \upkappa $$ and Poisson’s ratio v; moreover, the maximum surface settlement behind the wall is sensitive to changes in the critical state parameter M and Poisson’s ratio v. (2) A mechanical analysis model for diaphragm wall was established. All the external conditions are regarded as generalized loads or foundations. Furthermore, the interaction between the diaphragm wall and the soil is considered, which is closer to the actual situation. (3) The elasto-viscoplastic model of soft soil by Borja was established, and the deformation rate formula of the diaphragm wall was proposed.

Performance Improvement in Pile Anchor System for Deep Foundation Excavation Using Electroosmotic Chemical Treatment

Anchoring force is vital to ensure the acceptable performance of a pile anchor system when supporting deep foundation excavation. The soft soil has several physical properties, such as low shear strength, high water content, large void ratio, and high flowability. Traditional grouting and anchoring techniques have demonstrated technical limits to deal with these soil properties in engineering projects, and accordingly, the anchoring force in the pile anchor system is difficult to meet design requirements. This paper conducted an experimental investigation on the performance improvement in a pile anchor system using the electroosmotic chemical treatment method, with an emphasis on the deep foundation application. Experimental tests and field studies were designed to enhance anchor capacity of a pile anchor system using self‐designed devices. The laboratory experiments utilized a simplified anchor system in which anchors were designed as the electrodes to conduct the electroosmotic chemical treatment and consolidate the soft marine soil collected from the project site. In addition, static load tests were conducted on the tested soil to measure the anchoring force. Finally, parametric analyses were performed to investigate effects of several parameters on anchoring force in terms of the ultimate pull‐out capacity of the anchor, identifying critical parameters for the field study. Based on laboratory test results, field studies were carried out in the Yingkou city. The results from field studies were compared with laboratory test results to validate feasibility of electroosmotic chemical treatment for a pile anchor system.

Prediction Method for Overconsolidation Ratio of Marine SoftSoil Based on the Piezocone Penetration Tests

Because of the strong structural and sensitive behavior, the properties of marine soft soil change greatly when subjected to external disturbances, which leads to great difficulty in reflecting its real mechanical properties in the laboratory soil tests. The piezocone penetration test (CPTU) is one of the main technologies for in situ testing of geotechnical engineering. CPTU has the advantages of being fast and convenient, no sampling, low disturbance to soil, large amount of data, and reliable testing. The determination of the overconsolidation ratio (OCR) based on the CPTU results can solve the problems of soil disturbance and stress release, which occur during the consolidation test in the laboratory. However, there are still some problems such as lack of strict theoretical analysis of penetration mechanism and incomplete interpretation theory of in situ test parameters of CPTU. In this paper, the CPTU cone head is assumed to be hemispherical considering the penetration mechanism of CPTU. Moreover, the compaction modes of the CPTU probe penetrating into soil are adopted as spherical and cylindrical cavity expansion modes, respectively. The ultimate expansion pressures of the probe penetrating into soil under the spherical and cylindrical cavity expansion modes are first obtained by virtue of the theory of cavity expansion. Then, two prediction methods for OCR considering the roughness and penetration rate of the cone are proposed by combining the ultimate expansion pressures of the probe penetrating the approximate closed solution of cavity expansion in the modified Cambridge model, which is suitable for predicting the OCR of marine soft clay. Finally, to verify the reliability of the two proposed prediction methods, comparisons with the in situ CPTU tests of marine soft clay in two coastal areas and two existing prediction methods are made. The comparison results show that predictions of OCR of marine soft clay in this paper are close to Wayne’s method and more accurate than Chanmee’s method since the factors such as cone roughness and penetration rate are considered in the new proposed prediction methods. In order to improve the applicability in different cases of the OCR predictions, the average values of the two proposed methods are recommended as the reference value for the OCR of marine soft soil.

Experimental Study on Improvement of Marine Soft Soil with Alkali Residue

Industrial alkali slag is the discharge waste in the process of alkali production. About one million tons of alkali slag is discharged in China in one year. It is a burden on the environment, whether it is directly stacked or discharged into the sea. If we can realize the use of resources, it is a multi-pronged move, so alkali slag is used to improve solidified marine soft soil in this paper. The test results show that the alkali residue can effectively improve the engineering properties of marine soft soil. Among them, the unconfined compressive strength and compressive modulus are increased by about 10 times, and the void ratio and plasticity index can all reach the level of general clay. It shows that alkali slag has the potential to improve marine soft soil and can be popularized in engineering.

不同固结程度海洋软土动强度试验研究

为研究循环应力比和频率对不同超固结比的海洋软土动强度的影响，本文对珠江海洋软土进行室内动三轴试验，并对试验结果进行拟合分析。试验结果表明：总应变随着频率和超固结比的增大而减小，随着循环应力比的增大而增大；软化指数随着振次、循环荷载的增大而减小，随着频率的增大而增大；对软化曲线和动强度曲线进行回归分析，分别得到关于超固结比的软化系数和动强度经验公式。 In order to clarify the effects of cyclic stress ratio and frequency on dynamic strength of soft ma-rine soil, a series of dynamic triaxial tests are performed. The test results show that: 1) the total strain decreases along with the increase of the frequency and over-consolidation ratio, but in-creases along with the increase of the cyclic stress ratio; 2) the softening index decreases along with the increase of vibration times and cyclic loading, but increases along with the increase of the frequency; 3) by conducting regression analysis on the softening curve and dynamic strength curve, we have obtained the softening coefficient on over-consolidation ratio and the empirical equation of dynamic strength.

Effect of strain rate on pore pressure evolution and effective stress path of soft soil under different stress history conditions

Soft marine soils are highly plastic fine-grained soils and known for their high compressibility, large water content and low shear strength behaviour. The previous research on soft soils is restricted to stress–strain response under conventional loading conditions with and without its treatment. The effect of strain rate on pore pressure evolution and effective stress path of soft soil under different stress history conditions has not been explored. In the current research, an extensive experimental research has been performed on Kanjurmarg soft marine soil to evaluate its pore pressure evolution, effective stress path, obliquity and effective stress ratio at different strain rates and varying stress history conditions. A wide range of strain rate, 0.005% per min to 5% per min, was used to perform the CU triaxial tests on soft soil. Such large strain rates are used to analyse the behaviour of soil under various field conditions such as rapid excavation, rapid application of surcharge, aircraft wheel loading on runways, fast installation process of pile and projectile penetration. The effect of stress history on soft soil was also explored for OCR values of 1, 2, 5, 10 at different strain rates. The soil was also tested at different confining pressures at varying strain rates to evaluate the combined effect of strain rate and confining pressure.

Seismic Parameter Research of Marine Soil

In East China Sea, especially in Zhejiang and Fujian Provinces, classic marine deposit soft soil with characteristics of high compressibility, high sensitivity and low strength is widely distributed. Seismic subsidence occurs under earthquake causing substantial losses. Though a number of effective studies are carried out on the causes, mechanisms and methods on seismic subsidence, there are more other aspects to be studied due to marine soil’s complexity. In this paper, the classic marine soft soil in southern sea area of Taizhou Bay is studied on its seismic parameter based on the tri-axial seismic experiment. The seismic parameters and residual strain formula are obtained, and compared with normal continental deposit soft soil.

The Application for Reinforced Concrete Piles of Marine Sedimentary Soft Soil Foundation Treatment

Marine sedimentary soft soil is larger water content, higher compressibility, and lower strength and buried deep. The sluice project in the marine soft soil foundation construction is beneficial to the people's livelihood needs to conduct foundation treatment. Through the scheme comparison, the sluice wing wall is located in the Yellow River estuary uses reinforced concrete pile to treat foundation. The pile diameter is 0.5m, the pile length is 19m, and the pile end is located in the sand to meet the requirements of various conditions.

Primary Physical-Mechanical Characteristics on Marine Sediments from Zhoushan Seas in Sino Mainland

Marine sediment laboratory test model was developed by excavation on site and application of GDS triaxial loading system. The grading characteristics on representative soft marine soil from Wushitang (MS1) and Dongsha Seas (MS2) were studied and the key evaluating indicators, i.e., curvature coefficient CC and non-uniform coefficient Cu were analyzed. Based on the systematically physical-mechanical test data, the constitutive model on step deviatonic-stress and strain development was researched. The result shows the exponential mapping relationship is applicable for stress-strain constitution. The fluid-solid coupling non-linear function was established by spatial pore pressure surface fitting. The key consolidation treatment for soft marine sediments was discovered.

Study on Deformation Behavior of Bucket Foundation with Marine Soft Soil Materials under Horizontal Loading

The 21st century is the new era which mankind develop and utilize the ocean，In order to exploit and utilize of marine resources，the bucket foundation is emerged under this condition. In the process, a lot of marine soft soil materials is inevitably encountered with in engineering practice. Traditionally, the bucket foundation is only a upside-down bucket and no compartment is set inside. Using the finite element method, this paper makes a systematical expatiation on the research on the horizontal bearing capacity of bucket foundation with marine soft soil materials under cyclic loading conditions.

Analysis of Subsidence and Bearing Capacity of Consolidated Ground

There is high requirement to the foundation of the raceway of container gantry crane. However, the marine soft soil is distributed extensively at Dalian ports. In the paper, the settlement and bearing capacity of natural and composite foundation of raceway of container gantry crane under design load is analyzed by finite element method on the basis of geological data, foundation treatment. The relationship of different deformation modulus and foundation bearing capacity is obtained by considering the strength of foundation and the requirement of settlement. The settlement and the inclination value of two sides of container gantry crane which is less than the permitting value of laws under consolidated ground and corresponding load condition is obtained. The corresponding deformation modulus of consolidated ground is obtained under different load condition. The boundary of basis is easy to failure, the treatment range extension of foundation should be considered.