Effective Reinforcement Depth Research Articles

A Study on the Influence of Hydraulic Compactor Reinforcement on the Force Law of an Independent Foundation Under a Column and Its Safety Standard

Due to the complexity of the actual geotechnical environment, the backfill compaction design theory and calculation method are not reflected in the current specification. Therefore, in order to investigate the effect of the hydraulic compactor on the foundation structure during the treatment of the backfill of an independent foundation under a column, the Menard formula was modified. At the same time, relying on an independent foundation project under a column in Jinan, the dynamic model of compactor tamping backfilling soil was established. The applicability of the calculation formula is verified by simulating the single-point multiple tamping on the backfill directly above the foundation tie beam, and the influence law of two factors, the thickness of the backfill and the tamping energy, on the force of the foundation tie beam is elucidated. The results show that after reaching the optimum number of tamping, the cumulative soil settlement and the effective reinforcement depth of tamping show a stable trend, and their simulation results are in good agreement with the analytical solution, which provides a supplement to the relevant safety standards. At this critical point, the force on the tie beams peaked and showed up and down fluctuations under the subsequent ramming action. The tamping action of the compactor has a significant effect on the structural forces within the effective reinforcement range, and there is a negative correlation between the magnitude of the structural forces and the thickness of the backfill. According to the numerical calculation results to choose the best construction programme, the on-site monitoring shows that under 42 KJ tamping energy and 1.5 m single backfilling thickness, the tie beam reinforcement stress reaches 18.5~55.5% of the specification warning value, which meets the safety standard. The research results of this paper can provide important guidance for the hydraulic tamping treatment of an independent foundation backfill project.

Response of a Coral Reef Sand Foundation Densified through the Dynamic Compaction Method

Dynamic compaction is a method of ground reinforcement that uses the huge impact energy of a free-falling hammer to compact the soil. This study presents a DC method for strengthening coral reef foundations in the reclamation area of remote sea islands. Pilot tests were performed to obtain the design parameters before official DC operation. The standard penetration test (SPT), shallow plate-load test (PLT), and deformation investigation were conducted in two improvement regions (A1 and A2) with varying tamping energies. During the deformation test, the depth of the tamping crater for the first two points’ tamping and the third full tamping was observed at two distinct sites. The allowable ground bearing capacity at two disparate field sites was at least 360 kPa. The reinforcement depths were 3.5 and 3.2 m in the A1 and A2 zones, respectively. The DC process was numerically analyzed by the two-dimensional particle flow code, PFC2D. It indicated that the reinforcement effect and effective reinforcement depth were consistent with the field data. The coral sand particles at the bottom of the crater were primarily broken down in the initial stage, and the particle-crushing zone gradually developed toward both sides of the crater. The force chain developed similarly at the three tamping energies (800, 1500, and 2000 kJ), and the impact stress wave propagated along the sand particles primarily in the vertical direction.

Reinforcement of Different Sands by Low-pH Bio-Mineralization.

Different sands have significant influences on MICP reinforcement effects. Using calcium carbonate production and bioflocculation lag period as evaluation criteria, this study investigates the optimal theoretical pH values of bacterial solutions with different concentrations. We reinforced four different sands using MICP at the optimal theoretical pH, and based on permeability, moisture retention, raindrop erosion, wind erosion, penetration, and SEM tests, the influence of sand properties on low-pH MICP reinforcement was analyzed and the low-pH MICP mechanism was revealed. The results indicate the following: (1) The optimal theoretical pH values for bacterial solutions with concentrations of 0.67 × 108 cells/mL, 3 × 108 cells/mL, and 10 × 108 cells/mL are 4.5, 3, and 4, respectively. (2) With 0.67 × 108, 3 × 108, and 10 × 108 cells/mL bacterial solutions, the strength of tailings sand containing calcium salt was 21.15%, 44.42%, and 13.61% higher than that of quartz sand, respectively. The effective reinforcement depth of alkaline reclaimed sand was 10, 8, and 6 mm lower than that of neutral calcareous sand, respectively. The strength of fine tailings sand was 70.41%, 58.04%, and 22.6% higher than that of coarse reclaimed sand. The effective reinforcement depth of fine quartz sand was 6, 4, and 4 mm lower than that of coarse calcareous sand. (3) Low pH temporarily suppresses urease activity, delaying calcium carbonate flocculation and enhancing reinforcement uniformity. To achieve optimal reinforcement effects, adjusting the actual optimal pH values of bacterial solution based on sand properties is essential in engineering applications.

Study on Reinforcement Mechanism and Reinforcement Effect of Saturated Soil with a Weak Layer by DC

This paper presents a numerical investigation on the improvement mechanism of dynamic compaction (DC) in saturated soil of a weak layer with high levels of groundwater, using an improved fluid–solid coupling method with a Drucker–Prager–Cap soil model. The numerical model is verified by comparing with published test data at first, which show that the dual-phase coupling method can approximately reflect the development law of excess pore water pressure and the improvement effect of layered saturated soil foundation under DC. Then, based on the numerical model, the influences of the thickness and depth of the weak layer as well as tamping energy on the development and dissipation of excess pore water pressure, effective stress, and the relative degree of reinforcement during DC were investigated. The results showed that the embedment depth and thickness of the weak interlayer may greatly affect the effective reinforcement depth of DC. Meanwhile, the tamping energy and the groundwater table also play a great role in the improvement of the layered saturated soil under DC. The groundwater table should be lowered by dewatering or adding a drainage layer to achieve a better compaction effect during DC.

Numerical investigation on epi-off crosslinking effects on porcine corneas

Experimental inflation tests, conducted on 90 pig corneas before and after corneal collagen crosslinking (CXL) treatment, are simulated with the finite element method. The experimental sample consists of five groups of corneas treated with different UV-A irradiation times (2.5, 5, 10, 15, and 20 min) at constant irradiance 9 mW/cm2. The linear elastic shell theory is used to estimate the equivalent material stiffness of the corneas, revealing that it increases with the exposure time in CXL corneas. In the view of numerical simulations, a simple mechanical model assuming piecewise constant elastic modulus across the corneal thickness is introduced, to estimate the effective increment of the material stiffness in the anterior stroma and the effective depth of the stiffness increment. The two effective quantities are used in the finite element models to simulate the post-CXL tests. Numerical models are able to describe the mechanical effects of CXL in the cornea. The increment of equivalent material stiffness has to be ascribed to a localized increment of the material stiffness in the anterior layers of the cornea, while the posterior layers preserve the original material stiffness. According to the simplified model, the increment of the material stiffness of the anterior cornea increases with the irradiation dose, while the effective reinforcement depth decreases with the irradiation dose. This trend, predicted by a simple mechanical model by imposing equilibrium and compatibility, has been verified by the numerical calculations that captured the global mechanical response of the corneas in untreated and post-CXL conditions.

Real-Time Monitoring Method for Layered Compaction Quality of Loess Subgrade Based on Hydraulic Compactor Reinforcement.

Hydraulic compactor is an efficient reinforcement machine for loess subgrade. However, it is difficult to control the layered compaction quality of the subgrade. This research presents a real-time layered compactness monitoring method for hydraulic compactor reinforcement of subgrade in loess areas. The hydraulic force coefficient is first introduced, and the dynamic response model of the hydraulic rammer and soil is established. The relationship between the acceleration of the hydraulic rammer and the compactness of subgrade is then obtained based on the collision theory in elastic half space. A full-scale test using a hydraulic compactor to reinforce loess subgrade was also carried out. Results show that the hydraulic compactor obtains the effective influence depth for the reinforcement of loess subgrade. Within the effective reinforcement depth, the relationship between the peak acceleration of the rammer and the layered compactness of subgrade can be well fitted by a quadratic function model. The layered compactness of the subgrade and the working state of the hydraulic compactor can then be remotely monitored at a mobile terminal in real time. Furthermore, the monitoring technology was applied to Huangling-Yan’an Expressway in China, significantly improving the accuracy and efficiency of real-time monitoring of the layered compactness of subgrade in the loess area.

Load-bearing characteristics of square footing on geogrid-reinforced sand subjected to repeated loading

A series of dynamic model tests that were performed on a geogrid-reinforced square footing are presented. The dynamic (sinusoidal) loading was applied using a mechanical testing and simulation (MTS) electro-hydraulic servo loading system. In all the tests, the amplitude of loading was ±160 kPa; the frequency of loading was 2 Hz. To better ascertain the effect of reinforcement, an unreinforced square footing was first tested. This was followed by a series of tests, each with a single layer of reinforcement. The reinforcement was placed at depths of 0.3B, 0.6B and 0.9B, where B is the width of footing. The optimal depth of reinforcement was found to be 0.6B. The effect of adopting this value versus the other two depths was quantified. The single layer of geogrid had an effective reinforcement depth of 1.7B below the footing base. The increase of the depth between the topmost geogrid layer and the bottom of the footing (within the range of 0.9B) did not change the failure mode of the foundation.

Dynamic stress properties of dynamic compaction (DC) in a red-sandstone soil–rock mixture embankment

The characteristics of dynamic stress and displacement are investigated in this study with laboratory and field tests of dynamic compaction (DC) in a red-sandstone soil–rock mixture embankment. Under four different DC energies (i.e., 1200, 1080, 960, and 840 kN m), the properties of the vertical and horizontal displacement and the dynamic stress contours at different depths induced by DC are obtained in an on-site test. The test results indicate that the effective reinforcement depth and range are approximately 4.0–6.0 and 3.0–4.0 m, respectively. When the dynamic stress in the contours is greater than 10 kPa, the dynamic stress attenuates dramatically. The regression analysis method is adopted to obtain the control equations and the parameters of settlement and dynamic stress attenuation. Based on settlement and dynamic stress data fitting method, the fitting parameters are obtained. The dimensionless analysis method is used for obtaining the design approach of the effective reinforcement depth and range for the red-sandstone soil–rock mixture embankment. The proposed design approaches are applied to the construction program of the Changji Expressway in Hunan, China. By means of long-term settlement observation of DC section K212 + 475 and ordinary section K180 + 655, the effectiveness of the red-sandstone soil–rock mixture embankment in the DC section K212 + 475 is 534.78% greater than that of the ordinary section K180 + 655, which demonstrates that the designed calculation equation and formulae are practicable.

Research of Dynamic Compaction: A Review of Recent Academic Literature

Dynamic compaction is one of the densification techniques of ground improvement and extensive theoretical, experimental and in-situ tests have been used to clarify its mechanism. In this paper, a literature review about the dynamic compaction is carried out and the emphasis is put on the reinforcement mechanism, effective reinforcement depth and influence range of vibration to give a reference for the ongoing researches of dynamic compaction method.

The Bearing Characteristics and its Influencing Factors of Reinforced Soil Foundation

The reinforced soil foundations have been widely used in various geotechnical engineering applications, such as bridge approach slab, bridge abutment and so on. However, many problems of reinforced foundation still need to be solved and the behavior of the reinforced foundation requires further study. Therefore, finite element analyses were conducted on unreinforced and reinforced clay subgrade soil to evaluate the influence of various factors affecting the performance of strip footing on studied soils. Conclusions are drawn: the effective reinforcement depth is about 1.5B for the reinforced soil and it is independent of the geogrid type; At a given settlement, the bearing capacity of the footing decreases with the increase in reinforcement spacing, with larger decrease rates at small spacings; A geogrid with a tensile modulus ranging from 5MPa to 25MPa will maximize the benefits of the reinforced soil footing, etc.

Research of the Dynamic Compaction Effective Reinforcement Depth of Cohesionless Soil

The effective reinforcement depth is one of the most important parameters of dynamic compaction method design and construction, so far it is still lack of in-depth theoretical study. In this paper, combined with the field test, FLAC3D was used to do the numerical simulation of dynamic compaction reinforcement to cohesionless soil. By the simulation, this paper analyzed the factors which may influence the effective reinforcement depth, such as the hammers weight, drop distance, base area, and the soil parameters. The orthogonal design method was used to analyze the soil parameters sensitivity to the effective reinforcement depth. Combined with the results of numerical analysis and the traditional empirical formulae, the effective reinforcement depth calculation formula was established for cohesionless soil. Engineering verification shows that, the results estimated by the formula is reliable, and can provide certain reference for the future engineering.

Experimental Research on Deep Collapsible Loess Foundation Treatment by Dynamic Compaction under Super High Fill

Taking one foundation project as an example, a series of tests are carried out to study the dynamic compaction parameters and its effects on the deep collapsible loess foundation under super high fill in Lvliang region. Analyses are made on the average settlement of each test area before and after dynamic compaction and on the regularity of the main physical and mechanical indexes of soil. At the energy levels of 2000 kN•m, 3000kN•m and 6000kN•m, the main parameters are gained, such as the effective reinforcement depth, the centre distance of tamping points , the standard of stopping ramming, and the optimal ramming number; hence, the empirical formula of the effective reinforcement depth of dynamic compaction. The results of the tests show that the deep collapsible loess foundation in Lvliang region can be effectively reinforced by dynamic compaction, that the stability of foundation is good, and that the loess collapse in the reinforced range is eliminated basically. Moreover, after dynamic compaction above the energy levels of 2000 kN•m, the eigenvalue of the bearing capacity of collapsible loess foundation in Lvliang can reach over 300kPa; the deformation modulus of foundation soil is more than 25MPa. Therefore, the results of the tests can provide a reference for the design and construction of projects of the same kind; it can also provide a reliable basis for relevant norms and standards.

Practice Research on Wet-Collapsible Loess Foundation Treatment by High Energy Dynamic Compaction

A systematic and comprehensive study on the design, construction and testing of large scale of Ⅲ～Ⅳ grade wet-collapsible loess foundation treatment by 8000 kN•m high energy dynamic compaction is done in this paper. Effect on the treatment for collapsible loess foundation by dynamic compaction is analyzed through Rayleigh wave velocity test, standard penetration test, lab soil test and static cone penetration test. By comparison with physical and mechanical properties index of the foundation soil without dynamic compaction treatment, the effective reinforcement depth, the elimination of collapsibility and the bearing capacity of foundation are found to meet the design requirements. The results of this paper could supply some reference for the design, construction and testing of other collapsible loess foundations by dynamic compaction treatment.

Experimental Study on Dynamic Consolidation Method to Improve Saturated Soft Soil Foundation

A new technology of dynamic compaction method is successfully used to reinforce the saturated soft soil foundation. The field monitoring laws of lateral displacement of the foundation after dynamic compaction, the increasing and dissipation regularity of the excess pore water pressure are analyzed and discussed. The improvement effect is verified by static cone penetration test and loading test. The determination methods of effective reinforcement depth after dynamic compaction are put forward. The practice shows that, by field-testing methods, such as static cone penetration test and pore water piezometer test, to determine the effective reinforcement depth after dynamic compaction and other design parameters is reliable.

Test Study on Effective Reinforcement Depth of Dynamic Compaction and Filling Replacement

Filling replacement combined with dynamic compaction is a very effective method to preprocess the soft soil to obtain larger bearing capacity. That not only has remarkable effect to improve soil bearing capacity, but also has some advantages, such as quick construction, simple equipment, low cost and so on. And that is appropriate for large area ground treatment engineering. The purpose of ensuring the reinforcement effect and saving the project cost, and providing references for the similar projects can be achieved through the test study on effective reinforcement depth of dynamic compaction and filling replacement.

Study on the Effective Reinforcement Depth of Dynamic Consolidation

The effective reinforcement depth was the main design basis of dynamic consolidation. The concept and affecting factors of the effective reinforcement depth were analyzed in the paper. The evaluating standards and determining methods were also summarized. The effective reinforcement depth could be determined from the field test and the in-situ test index. Three kinds of methods could be used to determine the effective reinforcement depth: field testing method, numerical simulation method and formula method.

Study on the Changing Rule of Excess Pore Water Pressure during Dynamic Compaction

The changing rule of excess pore water pressure during dynamic compaction is important for construction. The following conclusions could be drawn by observing and analyzing the excess pore water pressure in test area. Under ramming strike energy of 2000kN•m, the best hit number during the 1~2 times is 8~9, the best hit number during the third time is 6~8. After compaction, the shallow excess pore water pressure is basically larger than the deep. The shallow excess pore water pressure needs more time to dissipate. The horizontal distance of the shallow excess pore water pressure is larger than that of the deep. During the dissipating process of the pore water pressure, we should pay attention to avoid vibration interference of load in the surface and prevent liquefaction of the powder soil. Under ramming strike energy of 2000kN•m, the biggest influence depth of dynamic compaction is 8～9m, the effective reinforcement depth is 6～8m. The conclusions can provide the theoretical basis for dynamic compaction construction.

Testing Study and Numerical Analysis of Dynamic Compaction on the Red Sandstone Rubble Soil

The drop distance, times of dynamic compaction and other parameters are studied by on-site testing in order to analyse quantitatively the impact on effective reinforcement depth and radius of the red sandstone rubble soil. Large amounts of on-site test data shows that compactness standard is 93%, strong encryption range is 1.0～4.0m, the effective impact depth is 4～6m and the effective impact radius is 2.5～3.5m. At the same time, through comparison and verification the on-site testing data and numerical analysis, the relationship between times of dynamic compacting and sandstones subside is . Further more, it is revealed that dynamic compaction can restrain effectively the deformation of high fill embankment of the red sandstone rubble soil.

Numerical Parametric Study of Strip Footing on Reinforced Embankment Soils

Finite element analyses were conducted to assess the benefits of reinforcing embankment soil of low to medium plasticity with geogrids beneath a strip footing from the perspective of the ultimate bearing capacity and footing settlement. The embankment soil was modeled with the Drucker-Prager constitutive model, and the soil-geogrid interaction was modeled by the Coulomb friction model. The finite element model was verified first by laboratory model tests; it was then used to analyze the strip footing sitting on the reinforced soil to seek an optimum reinforcement design. To this end, several geogrid-reinforcement design parameters–including effective reinforcing depth, vertical spacing between reinforcement layers, geogrid stiffness, soil-geogrid interaction coefficient, depth (top spacing) of first geogrid layer, footing embedment, and footing width–were investigated. The results of this study showed that the effective reinforcement depth was approximately 1.5 times the footing width, and an optimum depth of first reinforcement layer existed where the highest bearing capacity could be achieved. The influence of other design parameters on footing's bearing capacity and settlement was also analyzed.