*Article* **Experimental Investigation on Small-Strain Sti**ff**ness of Marine Silty Sand**

#### **Qi Wu <sup>1</sup> , Qingrui Lu <sup>1</sup> , Qizhou Guo <sup>2</sup> , Kai Zhao 1,\* , Pen Chen <sup>3</sup> and Guoxing Chen <sup>1</sup>**


Received: 12 April 2020; Accepted: 14 May 2020; Published: 21 May 2020

**Abstract:** The significance of small-strain stiffness (*G*max) of saturated composite soils are still of great concern in practice, due to the complex influence of fines on soil fabric. This paper presents an experimental investigation conducted through comprehensive bender element tests on *G*max of marine silty sand. Special attention is paid to the influence of initial effective confining pressure (σ 0 c0), global void ratio (*e*) and fines content (*FC*) on *G*max of a marine silty sand. The results indicate that under otherwise similar conditions, *G*max decreases with decreasing *e* or *FC*, but decreases with increasing *FC*. In addition, the reduction rate of *G*max with *e* increasing is not sensitive to σ 0 c0, but obviously sensitive to changes in *FC*. The equivalent skeleton void ratio (*e*\*) is introduced as an alternative state index for silty sand with various *FC*, based on the concept of binary packing material. Remarkably, the Hardin model is modified with the new state index *e*\*, allowing unified characterization of *G*max values for silty sand with various *FC*, *e*, and σ 0 c0. Independent test data for different silty sand published in the literature calibrate the applicability of this proposed model.

**Keywords:** marine silty sand; small-strain stiffness; Hardin model; binary packing model
