Estimating Deformation Modulus and Bearing Capacity of Deep Soils from Dynamic Penetration Test

Shihan Shan,Xiangjun Pei,Weiwei Zhan,Antonello Troncone

doi:10.1155/2021/1082050

Shihan Shan, Xiangjun Pei + Show 2 more

Open Access

https://doi.org/10.1155/2021/1082050

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Abstract

The dynamic penetration test (DPT) and the Menard pressuremeter test (PMT) have been widely used in geotechnical survey of deep soils for megadam foundations in western China. The DPT measures are not well utilized due to the lack of correction factors and of empirical relationships for deep soils. This study investigates the relationships between the corrected DPT blow counts ( N 120 ′ ), pressuremeter modulus (EPMT), limit pressure (pL), deformation modulus (E0), and bearing capacity (fak) derived from the PMT results. Meanwhile, a nonlinear regression model is developed to predict the DPT correction factor (a) based on the raw DPT blow counts (N120) and the rod length (L) by integrating the available correction factors for shallow gravelly soils suggested by the code provisions and the deep soil data in this work. It is concluded that the proposed DPT correction factors match well with the code suggestions and the new compiled dataset, and the corrected DPT blow counts can be used to reasonably predict the engineering properties of deep sand and clay soils. Although the proposed correlations need to be tested among different soil types and regions, the results shed the light on in situ geotechnical tests and data utilization for deep and thick overburden.

Highlights

Many megadams have been constructed on the valleys in western China to utilize the hydropower resources. e dam foundations are usually placed on the deep and thick overburden soils, which demand engineering properties of deep soils that are deeper than 20 meters
E dynamic cone penetration test (DPT) is widely used in the geotechnical survey in river valleys consisting of deep and thick overburden soils because of its characteristics of easy operation, wide applicability to different soil types, and relative low cost. e test consists of repeatedly dropping a hammer weighing 1177 N (120 kg) from a height of 100 cm onto an anvil that is connected by 60 mm diameter drill rods to a solid cone tip with a diameter of 74 mm and a cone angle of 60° [3]
Each hammer drop has potential energy that is theoretically equivalent to 1177 J. e number of blows by the hammer needed for the cone to penetrate the 10 cm strata is the counted N-value (N120). e dynamic penetration test (DPT) has been widely applied in Chinese geotechnical practices for foundation design since 1970s [3]

Summary

Introduction

Many megadams have been constructed on the valleys in western China to utilize the hydropower resources. e dam foundations are usually placed on the deep and thick overburden soils, which demand engineering properties of deep soils that are deeper than 20 meters. Is study attempts to expand the DPTcorrection factors for deep soils and to use the corrected DPT blow counts to predict deformation modulus and bearing capacity of deep soils. For these purposes, a database consisting of 74 pairs of DPT and pressuremeter test (PMT) results is compiled from a geotechnical survey project for a dam designed on a deep overburden site in southwestern China. Sublayer III-2: it is located at the middle of Layer III It majorly consists of dark-gray clay and silt (see Figure 3(c)). According to USCS, this soil is classified as lean clay with the group symbol of CL (see Table 1)

B5 B4 B3 B2 B1

III-1 III-2 III-3

Results

Empirical Relationships Using the DPT Blow Counts