A new simplified Hypothesis B method for calculating the consolidation settlement of ground improved by vertical drains

Abstract

Vertical drains are widely used in soft ground improvements to accelerate the consolidation process. This paper develops a new simplified Hypothesis B method for calculating the consolidation settlement of a soil layer improved by vertical drains under the instant and ramp loadings. As a comparison, the traditional Hypothesis A method is also used to calculate the settlement.Then, a fully coupled finite element consolidation analysis is utilized to examine and verify this simplified method and Hypothesis A method. For the instant loading, Carrillo-Barron method and Zhu-Yin method are used to obtain the average degree of consolidation for vertical drain system. Typical parameters, such as over-consolidation ratio (OCR), smear zone, and space ratio of vertical drains, are considered. It is found that the calculation results from the new simplified method in this study agree well with finite element simulations, and relative errors are in the range of 0.1% to 12.3%. Comparatively, there are obvious differences between the calculated results from Hypothesis A method and finite element results. Carrillo-Olson method and Zhu-Yin method are utilized to obtain the average degree of consolidation for the vertical drain system to consider the ramp loading. Equivalent time is determined from half of the construction period to calculate the creep compression under the ramp loading. The accuracy of this simplified Hypothesis B method using both Carrillo-Olson method and Zhu-Yin method is acceptable with the relative errors less than 9.4%.

A new simplified method for calculating consolidation settlement of multi-layer soft soils with creep under multi-stage ramp loading

“…However, this delayed creep strain can also be used in the over-consolidated state in the new simplified calculation method with the same creep parameter and "equivalent time," whereas a new value of the "secondary consolidation" coefficient is defined in the traditional Hypothesis A method for the soil at the over-consolidated state (Feng and Yin, 2018).…”

“…Thus,  is adopted as the parameter to evaluate the expressed creep settlement during the consolidation stage. When the soil layer is within 10 m, 0.8   is suggested (Yin and Feng, 2017;Feng and Yin, 2018). However, this simplification may overestimate the creep compression during the early stage of the consolidation of thick soil layer (e.g.…”

Modelling the time‐dependent behaviour of granular material with hypoplasticity

“…Many geotechnical structures such as embankments, retaining walls, slopes, and tunnels show time‐dependent behaviour to some extent . The time‐dependent behaviour of fine grained soils such as clay and silt has been studied extensively in the past . For granular soil, however, the study on the time‐dependent behaviour has started only recently.…”

“…[1][2][3][4][5] The time-dependent behaviour of fine grained soils such as clay and silt has been studied extensively in the past. [6][7][8][9][10] For granular soil, however, the study on the time-dependent behaviour has started only recently. Clayey soil, usually referred to as isotach material, follows a classical deformation pattern with time.…”

Development and Verification of a New Simplified Method for Calculating Settlement of a Thick Soil Layer with Nonlinear Compressibility and Creep

“…is the coefficient of "secondary" consolidation. For the over-consolidated soils, a smaller value of e C V  will be taken in practice (Feng and Yin 2018). In Hypothesis A, "secondary" consolidation occurs after the "primary" consolidation, therefore, there is no need to consider the coupling of the consolidation and creep.…”