Soil Modulus Values Research Articles

Laboratory characterization of fine-grained soils for Pavement ME Design implementation in Idaho

The subgrade layer often represents the weakest component of a pavement system, and can significantly affect pavement response and performance under loading. Adequate characterization of subgrade properties is critical to the design and construction of long-lasting, economical pavement systems. The Mechanistic-Empirical (M-E) pavement design protocol implemented through AASHTOWare Pavement ME Design requires resilient modulus of the subgrade soil as one of the primary input parameters. However, performing repeated load triaxial tests to establish the resilient modulus properties of soils is a cumbersome task, and is rarely undertaken by state transportation agencies on a regular basis. The Idaho Transportation Department (ITD) has recently invested significant amount of time and resources to facilitate state-wide implementation of M-E pavement design practices. This study was recently undertaken to characterize typical subgrade soils in Idaho. Extensive laboratory characterization of the soils was carried out including repeated load triaxial testing for determining the resilient modulus values. Several different pavement sections were analyzed by using currently used default values and laboratory-established soil properties as subgrade layer inputs during M-E design. Default soil modulus values that are currently used, were found to be significantly higher than laboratory-established values, and therefore, resulted in the design of pavement sections that would fail considerably early into their service lives. The effect of moisture content on subgrade soil properties was also studied, and the importance of restricting soil moisture contents to the dry side of optimum was highlighted.

Seismic behavior of pile-supported systems in unsaturated sand

The seismic behavior of pile-supported systems has been an active area of research over the past decades. However, focus has mostly been on evaluating the seismic response of structures embedded in either dry or fully saturated soil conditions. In this study, series of dynamic centrifuge tests were conducted to investigate the effects of soil's degree of saturation on the seismic behavior of pile-supported superstructures. The scaled physical model tests were carried out on two distinct pile-mass systems embedded in uniform sand layers. A steady state infiltration technique was used to control matric suction profiles in the sand layer prior to shaking. The obtained results from these experiments were illustrated in terms of peak accelerations, peak lateral displacements, and frequency content of the structural motion. The observed response showed higher acceleration amplification and lower lateral deformation for the pile-supported systems with foundations embedded in unsaturated sand comparing with those in dry sand. An inverse simple pseudo-static analysis was performed to back-calculate soil modulus values from the pile lateral deformations. The calculated values of soil modulus were higher for unsaturated sands showing consistency with the effect of matric suction on increasing the soil stiffness.

A Three Dimensional Comparative Study of Seismic Behaviour of Vertical and Batter Pile Groups

To a practicing foundation engineer, the performance of batter pile under seismic conditions still remains a questionable prospect. The contradictory findings reported by various investigators with regard to the performance of batter piles add to this dilemma. This calls for a rigorous three-dimensional investigation to evaluate seismic behavior of batter pile groups. In this study, a comparative assessment of three-dimensional seismic behavior of a 2 × 2 vertical and batter pile groups having batter angle of 15° was carried out using a full three-dimensional finite element code developed in MATLAB (Sarkar 2009). The effects of centre to centre spacing of piles and soil modulus values were investigated. Idealized soil profiles having constant and triangular variation of soil modulus were adopted for the study. Results of analyses for both the vertical and batter pile groups are presented in terms of dynamic stiffness and kinematic interaction factors. Results indicate better seismic performance of batter pile groups in comparison to that of vertical pile groups. To demonstrate the importance of the findings, a five-storied portal frame structure supported separately on vertical and batter pile groups were considered and analyzed for El-Centro Earthquake (1940) time history. The difference in structural response considering vertical and batter pile groups is highlighted.

Nonlinear modeling of soil deformation modulus through LGP-based interpretation of pressuremeter test results

Soil deformation modulus is an essential parameter for the analysis of behavior of substructures. Despite its importance, little attention is paid to developing empirical models for predicting the deformation moduli obtained from the field tests. To cope with this issue, this paper presents the development of a new prediction model for the pressuremeter soil deformation modulus utilizing a linear genetic programming (LGP) methodology. The LGP model relates the soil secant modulus obtained from the pressuremeter tests to the soil index properties. The best model was selected after developing and controlling several models with different combinations of the influencing parameters. The experimental database used for developing the models was established upon several pressuremeter tests conducted on different soil types at depths of 3–40m. To verify the applicability of the derived model, it was employed to estimate the soil moduli of portions of test results that were not included in the analysis. Further, the generalization capability of the model was verified via several statistical criteria. The sensitivity of the soil deformation modulus to the influencing variables was examined and discussed. Moisture content and soil dry unit weight were found to be efficient representatives of the initial state and consolidation history of the soil for determining its deformation modulus. The results indicate that the LGP approach accurately characterizes the soil deformation modulus leading to a very good prediction performance. The correlation coefficients between the experimental and predicted soil modulus values are equal to 0.908 and 0.901 for the calibration and testing data sets, respectively.

Braced Excavations: Temperature, Elastic Modulus, and Strut Loads

Relationships between strut loads, earth pressures, temperatures, and the measurements provided by strain gauges are presented in this paper. A braced excavation up to 20-m deep, 9–20 m wide, and > 650-m long constructed in competent glacially derived sand, silt, and clay soils (including glacial till) provided a significant amount of data for analysis. The excavation was supported by soldier piles and lagging with pipe struts and was covered with decking during construction. A direct correlation between incremental changes in strut load and temperature was observed during the course of the project. The few existing relationships between strut load and temperature were reexamined and were found to produce back-calculated elastic modulus values that were either without comparison or inconsistent with data from field tests and published sources. The relationships derived as a result of this work are supported by limited case-history data from other published sources and are consistent with practical application of elastic deformation concepts and published soil modulus values.

Settlement of Circular and Ring Plates in Very Dense Calcareous Sands

Plate‐loading tests were carried out on very dense calcareous sand for the construction of the new telecommunications center complex in downtown Kuwait City. The tests were conducted at the foundation level, which was located 18 m below the original ground level. Circular plates 0.3 m, 0.61 m, and 1.28 m in diameter, and a ring plate of 1.28 m outside and 0.68 m inside diameter were employed. The tests were intended to provide reliable soil modulus values for the estimation of the settlement of a 55‐m diameter ring‐shaped raft of the 370‐m tall antenna tower. Several factors affecting settlement were examined. These include soaking or ground wetting, the size of the loaded area, and load cycling or repetition. The load‐settlement response of the ring plates and the full plates are compared.

Three-dimensional finite element analysis of pile groups under lateral loading

The analysis of a group of foundation piles under horizontal load is difficult because the system is strongly three-dimensional in nature. Also the materials of the piles and of the soil have very different stiffness properties and the piles and pile cap respond primarily in bending deformation while the soil acts initially as an elastic half space. The rapid expansion in mainframe CPU and memory capacities now allows full 3-D analysis of small groups of piles connected by a stiff pile cap. The types of elements used to represent the pile shafts and the pile cap need to be selected carefully to ensure compatibility with the surrounding soil elements. Meshes were constructed to model a single pile, and two- and three-pile groups, all subject to horizontal loads. After preliminary verification, the meshes were used to calculate deflections, pile axial forces and moments, and pile/soil pressures, for the two- and three-pile groups. The two main variable parameters were the spacing of the piles, and the overhang height of the pile cap above ground. The soil modulus values were then modified in the case of a two-pile group in order to evaluate the effects of strain-softening and of pile/soil separation. It was found that the overall stiffness of the group decreased, and the bending moment at the head of the front pile became greater than in the rear pile.

Discussion of “ Pile Horizontal Soil Modulus Values ” by Trevor David Smith (September, 1987, Vol. 113, No. 9)

Discussion of “ <i>Pile Horizontal Soil Modulus Values</i> ” by Trevor David Smith (September, 1987, Vol. 113, No. 9)

Discussion of “ Pile Horizontal Soil Modulus Values ” by Trevor David Smith (September, 1987, Vol. 113, No. 9)

Discussion of “ <i>Pile Horizontal Soil Modulus Values</i> ” by Trevor David Smith (September, 1987, Vol. 113, No. 9)

Closure to “ Pile Horizontal Soil Modulus Values ” by Trevor David Smith (September, 1987, Vol. 113, No. 9)

Closure to “ <i>Pile Horizontal Soil Modulus Values</i> ” by Trevor David Smith (September, 1987, Vol. 113, No. 9)

Settlement of Single Piles in Nonhomogeneous Soil

An analysis, previously developed for evaluating the settlement of a pile in homogeneous soil, is extended to the case of nonhomogeneous soils. Comparisons with finite element solutions suggest that the analysis gives solutions of adequate accuracy for practical purposes. A series of parametric solutions is presented for a pile in a Gibson soil in which the modulus increases linearly with depth. The analysis is also found to be applicable to piles in a layered soil, except in the case where the pile is founded in soil that is more compressible than the overlaying strata. A simple approximate method is described for using the available solutions for uniform soils to calculate the settlement of piles in nonhomogeneous soils. The determination of soil modulus values is then examined briefly, and finally, some comparisons between measured and theoretical pile behavior are presented to indicate the possible practical consequences of assuming a soil profile to be nonhomogeneous rather than homogeneous.