Soft Soil Subgrade Research Articles

Enhancing soft subgrade soil with a sewage sludge ash/cement mixture and nano-silicon dioxide

In this study, a mixture of sewage sludge ash (SSA) and cement was applied to improve the properties of soft cohesive soil. In addition, nano-SiO2 was applied as an additive to the SSA/cement-treated soil. Four different mix ratios of SSA/cement (1:1, 2:1, 3:1, and 4:1) were used as stabilizers to improve the strength of the soft cohesive subgrade soil, and the total amount of SSA/cement added was fixed at 15 % of the soil weight. The effect of 2 % nano-SiO2 was also investigated. Experiments, including Atterberg limit measurements, compaction tests, unconfined compressive strength (UCS) tests, and scanning electron microscopy, were performed. The test results indicated that a mixture of SSA and cement improved the engineering properties of soft subgrade soil, generating a UCS that was 6.5–8.4 times better over 28 days and a CBR value that was 61–97 higher. Furthermore, the addition of nano-SiO2 enhanced the engineering properties after adding various SSA/cement ratios, increasing the UCSs that were 30–47 kPa higher over 28 days and generating CBR values that were 3–9 higher. This study suggests that to best develop the additive efficiency, nano-SiO2 should be added to soil treated with an SSA/cement ratio of 3:1.

Field evaluation of soft highway subgrade soil stabilized with calcium carbide residue

Calcium carbide residue (CCR) is a by-product of acetylene gas production. Stockpiles of CCR continue to accumulate worldwide, in both developed and developing countries. Sustainable reuse options for CCR in civil infrastructures, such as road embankments, have been recently evaluated in the laboratory. However, to date there are limited studies on the actual field performance of CCR in stabilizing clayey soils in highway subgrades. In this study, a field trial was conducted to ascertain the viability of using CCR stabilized clayey soil as a highway subgrade course material. Quicklime was selected as a control binder in the field trial for comparison purposes. The construction procedures of the CCR and quicklime stabilizations in two field sections are presented. A series of field tests, including California Bearing Ratio (CBR) test, plate loading test, Benkelman beam deflection test, and dynamic cone penetrometer (DCP) test were undertaken after the embankment construction. The results indicated that in the top zone of the filled soil layers with 94% degree of compaction, the CCR stabilized subgrade soil exhibited higher values of CBR and resilient modulus, and lower values of resilient deflection and DCP Index relative to the quicklime stabilized soil. The field trial results indicated that CCR had negligible environmental effects and furthermore resulted in low construction costs. Based on the field test results, CCR was found to be a viable alternative binder for stabilizing soft subgrade soils. The outcomes of this research are significant from engineering, economic and environmental perspectives.

Degradation of soft subgrade soil from slow, large, cyclic heavy-haul road loads: a review

Extraction of resources in remote locations can require temporary haul roads to transport extremely large, slow-moving, indivisible loads (e.g., plant, oil–gas production modules, and reactors, weighing in excess of 1000 t) without interruptions. Poor subgrade soils may experience larger cyclic strains and greater cyclic degradation under these conditions than under conventional roads, yet the short engineering life precludes many foundation-strengthening options due to cost. As there is little research into this unique situation, this paper synthesizes research from a broad range of applications to discuss implications on expected soil response. Reference is made to critical state theory and discrete element method (DEM) modelling to develop fundamental concepts considering particle-scale interactions. Cyclic failure is proposed to be a kinematically unstable process, triggered by shear banding on the Hvorslev surface, tensile liquefaction or fabric-governed meta-stable liquefaction; the latter is particularly influenced by stress history and anisotropy. This paper finds pore-water pressure accumulation under load and dissipation between loads are key to cyclic degradation and furthermore to be dependent upon load duration, principal stress rotation, and repetition frequency. For meta-stable, liquefiable soils in particular, inclination of principal stresses is at least as important in assessing failure risk as magnitude of stresses.

Dynamic Response Characteristic of Layer Interface of Soft Soil Subgrade with Dry Crust Covering and Its Engineering Application

AbstractConsidering the obvious wave impedance difference between dry crust and soft, the phenomenon of dynamical stress mutation at the hard-soft soil interface, which is a specific performance of shell effect of dry crust in dynamic scope, is revealed by the transmission coefficient based on stress-wave theory. The attenuation law of vertical dynamic stress peak in subgrade soil under vehicle load is obtained by numerical simulation. Based on the negative exponential function characteristic of an attenuation curve, a transfer coefficient at soil layer interface is derived. This coefficient can synthetically represent the law of dynamical stress mutation. The corresponding calculation method and application range of the transfer coefficient are offered. This calculation method has simpler processing and higher precision than existing methods based on monitoring data verification. By practice validation of expressway engineering, the mechanical state of subgrade soil can be correctly evaluated, and its re...

Studies on Engineering Performance of Geogrid Reinforced Soft Subgrade

One of the preferred materials for construction of road embankments on soft subgrade soils being coarse grained soils. During the recent past utilization of geosynthetics has been increased to improve bearing resistance of weaker subgrades. Previous researches addressed the problems due to soft subgrade in several ways and provided solutions namely geosynthetics & coarse fill for construction on these soils insitu. However considering scarcity of fill material and cost of project a viable alternative can be bulk utilization of locally available weak soils. Neglecting construction difficulties etc., effective utilization is possible in small scale projects if engineering performance is enhanced. These improved soils can be used as fill over soft subgrades and adds benefit in the form of cost reduction.In the present study an attempt has been made to study the engineering performance (CBR) for different types of soil subgrades reinforced with geogrids. Tests are conducted on soil in lab and field and CBR value is determined. Studies are carried out and influence of parameters soil plasticity, geogrid tensile capacity, soaking and unsoaking on CBR property is examined. Enforced with geogrids and the performance of geogrids in soaked condition both lab & field are studied and the performance is quantified. The results obtained have shown the influence of plasticity & fines (%) and possible usage of geogrid in improving soaked CBR performance which in the absence of grid is very poor.

EFFECT OF REINFORCEMENT ON IMPROVE SURFACE PAVEMENT FOR WEAK SUBGRADE CONDITIONS

A pavement structure consists of several layers for the primary purpose of transmitting and distributing traffic loads to the subgrade. Rutting is one form of pavement distresses that may influence the performance of road pavements. Soft subgrade soils are distinguished by their low undrianed shear strength and high compressibility. The effect of geogrid and steel mesh to improve the performance pavement is experimentally investigated and evaluated. To compare the experimental and analytical outputs, three dimensions finite element throughout models using ABAQUS ver.6.12.3 software are developed to simulate and analyze the relations between the cycling load and deformation of the suggested pavement modes. Based on the results and the limitation of this study it is concluded that, using geogrid and steel mesh in pavement layers leads to increases in load carrying capacity and decrease the permanent deformation in surface pavement for (1000) cycles load by (27.3%) and (18.3%) respectively, as compared with unreinforced model. The results of ABAQUS program are very close to results of laboratory tests.

Laboratory Investigation in the Improvement of Subgrade Characteristics of Expansive Soil Stabilised with Coir Waste

Soft soils form problematic subgrade for pavements due to its low bearing capacity and strength. Pavement loads coming on the soft subgrade soil may cause detrimental pumping actions when they are located in areas with high water table which causes both construction and in-service performance problems. The common solutions on encountering such problems include excavation and replacement of soil, lime treatment or chemical stabilization. Excavation and replacement of soil becomes very expensive especially when usable soils have to be hauled to significant distance. Stabilization using various additives can improve the properties of soft soils. A recent trend in stabilization is to utilize locally available industrial wastes to improve the properties of soft soils. This method has the dual advantage of increasing the strength of soil and a solution for the problematic disposal of such wastes. Coir waste consisting of coir pith and coir fibre is a by-product of coir manufacturing industry obtained from coconut husk during the extraction of coir fibre. The pollution caused due to the polyphenol leaching and the resistance to degradation due to the stable lignin structure makes the coir waste a potential threat to the land resources. This paper presents an investigation on the behavior of soft soil stabilized with varying percentages of coir pith (0-3%) and coir fibre (0-1%) by carrying out Standard Proctor, Static Triaxial test and California Bearing Ratio(CBR) tests. The test results showed that stabilization with coir waste had a significant effect on the compaction, Elastic modulus as well as CBR characteristics.

Permanent deformation behaviour of reinforced flexible pavements built on soft soil subgrade

This study focuses on evaluating the effectiveness of using various geogrid products to improve permanent deformation resistance in soft subgrade soils commonly encountered during roadway construction in Pennsylvania. Permanent deformation behaviours of the soft soils both with and without the inclusion of geogrids were investigated. Cyclic moving wheel loads were applied through a reduced-scale accelerated pavement testing (APT) device, a one-third-scale model mobile load simulator (MMLS3). Tests were conducted on two soil types, each modified with three different biaxial geogrids placed at the base–subgrade interface. The total permanent deformation/surface rutting of the pavement and the permanent deformation of the subgrade were measured at selected intervals of the wheel loading applications. The pavement sections were trenched upon completion of the accelerated testing to measure the deformed profiles of the cross sections from which the permanent deformations in the asphalt layer and the base layer were determined. Sections modified with geogrids were found to have similar performance with the control section in terms of the total permanent deformation. While the geogrids did not show significant effects on the asphalt layer permanent deformation, sections with geogrids consistently showed a significantly higher base layer permanent deformation as compared to the control sections. Measurements of the subgrade permanent deformation showed that two of the geogrids consistently reduced the permanent deformation of subgrade built with the two types of soft soil. The relative layer contribution to the total permanent deformation suggested a base layer failure in both sets of the accelerated tests, most likely due to the inadequate compaction of the base layer during construction. Sections modified with geogrids exhibited a significantly higher base layer contribution, along with a significantly lower subgrade contribution, to the total permanent deformation, whereas the control section showed the opposite of the layer contributions.

Mechanistic-empirical approach to characterizing permanent deformation of reinforced soft soil subgrade

This study focuses on characterizing the permanent deformation of geogrid-reinforced soft soil subgrade by using the mechanistic-empirical (ME) approach based on both experimental measurements and results of numerical modeling. Two sets of small-scale pavement sections were built over two types of soft soil subgrade and subjected to cyclic moving loads by means of a reduced-scale accelerated pavement testing (APT) device. Each set of pavement sections included one control section and three sections reinforced by different geogrids placed at the base–subgrade interface. The pavement sections were instrumented to measure vertical deformation and vertical stresses at the top of the subgrade. Strains developed in the geogrids were also measured by strain gauges throughout the construction and accelerated testing. Simplified finite element (FE) models were created to simulate both the control and geogrid-reinforced pavement sections and to compute the pavement mechanistic responses. With the experimental measurements from the first set of tests and results of FE analysis, the permanent deformation model in NCHRP 1-37A for unbound layers was adapted and calibrated to model the permanent deformation of the geogrid-modified subgrade. The effects of geogrids on the subgrade permanent deformation were integrated into the ME performance model through both the mechanistic response modeling and the empirical calibration. Predictions from the permanent deformation model were then compared with the second set of measurements and found to underestimate the permanent deformation of the geogrid-modified subgrade. However, the model was able to distinguish the difference in performance among the sections, i.e. the predicted rank of the performance was consistent with the measurements.

Soft Soil Subgrade Vacuum Preloading Consolidation Deformation Analysis of Large Rigid Foundation

The large rigid foundation has a high requirement on subgrade consolidation deformation, especially the soft soil subgrade, of which the design and construction is very difficult. Through the analysis on subgrade treatment process of a sewage treatment plant in Zhejiang Province, this paper introduces the mathematical calculation model and the specific calculation method for treating the soft soil subgrade with the vacuum preloading method. The calculation results obtained has basically reflected the actual deformation process of the subgrade; it is a rational referential calculation method to guide the design and construction.

Performance of geosynthetic reinforcement on the ballasted railway track

Geosynthetics provide an important option to improve track support stabilization and thereby reduce the track maintenance costs and operation costs due to train delays. In railroad construction, geosynthetics may be installed within or beneath the ballast or subballast layers. In this present study, model tests were performed on model tracks laid at 1:3 scale to the prototype with adequate thickness of subballast layer and placed on soft subgrade soils. Model tracks were adequately instrumented to record induced stresses and displacements in the track. Model tracks were reinforced with geogrid or geotextile or both at suitable interfaces. Track condition after a heavy rainfall was simulated. In this present study, three dimensional finite element analyses of geosynthetic reinforced railway track sections have been carried out using MIDAS/GTS 2013 and compared with unreinforced sections. The result shows that the reinforcement can be used to improve the performance of railway tracks on clayey subgrade.

Performance of Reinforced–Stabilized Unpaved Test Sections Built over Native Soft Soil under Full-Scale Moving Wheel Loads

This paper presents the findings from an ongoing research study that evaluated two recently developed geosynthetic products: a triaxial geogrid and a high-strength woven geotextile for reinforcing or stabilizing roads constructed over native soft soil in the state of Louisiana. Six full-scale test lane sections were constructed: two were reinforced by one and two layers of triaxial geogrids, respectively, while high-strength geotextile was used to reinforce two of the other sections with aggregate layers of different thicknesses. The remaining two sections were left as controls: one was constructed over a sand embankment 30 cm thick representing the common practice in southern Louisiana. The unpaved test sections were subjected to a full-scale moving wheel load applied by the accelerated loading facility. A variety of instrumentation was used to measure the load-associated and the environment-associated pavement responses and performance. Results of the full-scale testing on the unpaved test sections demonstrated the benefits of geosynthetic reinforcement–stabilization in reducing the permanent deformation in the pavement structure. The test sections’ resilient behavior did not seem to be influenced by the presence of geosynthetics. In addition, instead of the soft soil subgrade, the aggregate layer was the primary contributor to the total permanent deformation–surface rutting of the unpaved sections under the testing conditions in this study. Geosynthetics were mobilized and generally exhibited a strain around 0.2%.

The Long History of Geosynthetics Use on Forest Roads

Geosynthetics have been used in a wide range of applications on forest roads over the past 40 years. Some of the earliest uses involved reinforcement in simple walls, drainage or filtration in geocomposite underdrains, and subgrade stabilization. These early efforts were typically experimental. Geosynthetic application over time became better defined by function, and use was specified for drainage, filtration, separation, or reinforcement. Road uses were typically in underdrains to keep a granular filter material clean, for separation over soft subgrade soils to keep aggregate from becoming contaminated, as reinforcement layers within a mechanically stabilized earth retaining wall or reinforced fill, and as interlayers within a pavement. Today geosynthetic use is more sophisticated and better defined: materials for each function have specific strength and durability properties appropriate for their use. New combinations of materials have resulted in drainage geocomposites, multilayer filters, geogrids with geotextiles, geofoam, and geocells. Many applications in erosion control, as well as other creative uses, have also been developed. Today, more attention is given to quality control and properties testing to better characterize the materials. Although use of geosynthetics has gained wide acceptance in many sectors of civil engineering and highway construction, it is still limited on forest roads. This paper documents the evolution of geosynthetics' use on forest roads, highlights current creative and cost-effective applications of geosynthetics, and promotes geosynthetics in the construction of low-volume roads.

The Dynamic Analysis of Soft Soil Subgrade in High-Speed Railway Strengthened by PHC Pile

The combination of PHC pile (prestressed concrete pile) with geogrid to reinforce the foundation has been widely used in high-speed railway, and the response of dynamic stress under the high-speed train is worth studying. By using Midas/GTS NX software to establish a 3-D model of pile-net composite foundation in one section of Hangzhou - Shenzhen line, the influence of pile-net composite foundation generated by high-speed train is studied. Moreover, this paper also studies the distribution and propagation of dynamic stress generated by train load in soft soil area. The results show that the dynamic stress reducing quickly in the embankment structure and the time –history curve of the dynamic stress behaves differently along the depth. With the depth increasing, there is phenomenon of peak superposition in the time-history curve of the vertical dynamic stress. In the meanwhile, the PHC pile is the main structure to propagate and sustain the dynamic stress in soft soil area, and with the tendency of ‘large in the middle, small on both ends’.

Using the Finite Element Method Analysis of Tianjin 112 State Line Road Soft Soil Subgrade

By using the finite element method we had studied the Tianjin Expressway Subgrade Settlement.Through the comparison of the reinforcement and the unreinforced two case we studied the principles of strengthening soft soil subgrade and results show that the mixing pile to improve the bearing capacity of the embankment foundation, reduce the settlement of foundation has played a very good role.The finite element method can reflect the nonlinear characteristics of the coupling effect between composite foundation pile, soil and the soil around the pile, the soil using elastoplastic model, and considering the different medium, different distribution,which has great advantages in the analysis of various factors.The finite element method can better reflect the reinforcement of soft soil subgrade.So ,it also can optimize the engineering design.

The Plate Body Stabilization Technology of Soft Soil Subgrade in Caofeidian Area

The applicability of the plate body stabilization technology was determined basing on the different treatment methods on soft foundation in Caofeidian areas. It discussed the construction technology and the main points of construction furtherly on the plate body stabilization technology. The soft foundation bearing capacity reached 200kpa and the settlement amount was less than 16mm through static load test after dealing with the soft foundation. The results meet the specifications and project requirements.

Study on the Settlement of Soft Soil Subgrade with a Crust Layer

By using the finite element method, the settlement of soft soil subgrade with a crust layer has been investigated. To find the influence of thickness of the crust layer on the settlement, four different thicknesses, which are 0.0m, 1.5m, 3.5m and 5.5m, are selected. Besides, the settlement during the construction and post construction are also analyzed. It is found that the crust layer can reduce the settlement and uneven settlement of subgrade effectively. Besides, the settlement of the subgrade decreases with the increase of the thickness of crust layer. Moreover, with the increase of time, the uneven settlement of the pavement increases gradually. And when the time is up to a certain degree, the uneven settlement tends to be stable.

Utilization of a New by-Product Material for Soft Subgrade Soil Stabilization

Silt soil cannot satisfy the requirements of highway construction because of its low strength. A new stabilizer from waste aluminum industry is developed (aluminum chops (AC) and wires (AW)) to evaluate the effect of reinforcing the subgrade with low-cost by-product materials on its mechanical and durability characteristics. Laboratory tests, including modified proctor compaction, compressive strength, splitting tensile strength, and CBR are developed to evaluate the mechanical properties. The durability properties are investigated by studying the influence of environmental conditions such as water immersion effect on compressive strength, mass loss after freezing and thawing cycles, water absorption by capillarity and wetting-drying durability. Moreover, a practical application about the base course thickness saving and its economically viable as well as correlations between mechanical properties are investigated. The results indicated that the aluminium fiber can effectively improve the mechanical and durability characteristics of silt subgrade where the increase in aluminum chops grade leads to improve the majority properties. While aluminum wires of 2.0 cm length produces reduction in CBR and compressive strength compared to smaller length. Stabilization with aluminium fiber has a remarkable influence in reducing the base course thickness (especially at using 4% of AW1.0) and increasing the construction cost saving (especially at using 1% of AW1.0).

EFFICACY OF OVERLYING COARSE AGGREGATE AND GEOSYNTHETIC SEPARATOR ON CBR VALUE FOR SOFT SUBGRADE OF VARYING PLASTICITY - A LAB STUDY

Soft subgrade soil poses challenge for construction of pavements. These soft subgrade soils have a ten dency to absorb high moisture content and exhibit high compressibility. Under loa ds. Because of which the life of pavement construct ed over these is highly suffered. Among notable properties plasticity index is a reli able property as listed in literature for identifying these soft soil and nature of compressibility. Soil stabilization is one of the techniques listed in literature for improving these soft soils. Often the stabilization suffers due to high cost particularly improving dee p deposits of soft soil and time consuming. . Provi ding stiff layer with gravelly soil can solve the problem to majority extent. These gra velly layer of soils bear the load and distribute tarch action, to, minimize the stresses to soft soil. .However the efficiency of these gravely layer depends on their relative thickness and prevention from mixing with soft subsoil. This paper discusses the efficacy of overlying aggregate to improve CBR val ues of soft subgrade in the presence of separator geotextile. The thickness of aggregate is varied and expressed by H r (a fraction to soil thickness given as Ha/Hs.). Laboratory CBR tests are conducted on four subgrade types with varying in plasticity & fines content overlying with gravelly aggregate with H r varied from 0, to 0.5 in increments of 0.1.It is observed that PI, H r and fines content effect CBR. The influence is more pronounced with Plasticity and percent fines. Also the increase (%) is marginal for samples with high H r. The problem of mixing of aggregate with soft soil tested without separato r is more with H r.

Effect of the Length of Geogrid Layers in the Bearing Capacity Ratio of Geogrid Reinforced Granular Fill-soft Subgrade Soil System

In the present study, blast furnace slag in granulated form has been used as a granular fill overlay on soft subgrade soil. The effectiveness of geogrid-reinforced granular fill overlay on soft subgrade soil has been assessed by small scale model tests in the laboratory by evaluating two parameters bearing capacity ratio (BCR) and reduction factor. The effect on BCR of strip footing for various lengths of geogird layers in the best performing thickness has been observed. Best performing thickness of the granular fill layer has been found by the parametric study which is not included in this paper. Parametric study has been performed to observe the effect of length of geogrid layers in granular fill overlay on soft subgrade soil. The test results indicate substantial improvement in terms of increase in bearing capacity and reduction in the footing settlement due to provision of geogrid in the granular fill overlay on soft subgrade soil. It has been found that b/B ratio of 4 gives substantial improvement in BCR and beyond b/B ratio of 4, there is no significant improvement in BCR.