1. Introduction

In recent years, sustainable materials have been widely studied and developed especially for construction, highway, and civil engineering. Controlled low-strength material (CLSM) is commonly used as backfilled materials. It would be a friendly environment-cheap material and typically consists of small amount of cement, supplementary, fine aggregates, and a large amount of mixing water. Self-compacting/self-leveling, significantly low strength, as well as almost no measured settlement after hardening are remarkable characteristics of CLSM.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

CLSM can be defined as a kind of self-compacting cementitious material that is in a flowable state at the initial period of placement and has specified compressive strength of 1200 psi (8.27 MPa) (or less at 28 days) or is defined as excavatable if the compressive strength is 300 psi (2.07 MPa) (or less at 28 days) [1]. Recent studies have reported that the maximum CLSM strength of approximately up to 1.4 MPa is suitable for most of backfilling applications when re-excavation is required [2, 3] It is also recommended that depending upon the availability and project requirements, any recycle material would be acceptable in the production of CLSM with prior tests its feasibility before uses [4]. The special features of CLSM can be summarized as follows: durable, excavatable, erosion-resistant, self-leveling, rapid curing, flowable around confined spacing, wasting material usage, elimination of compaction labors and equipment, and so on.

There are several studies on the engineering properties of CLSMs by laboratory experiments [5–10], and numerical analyses of applications of CLSM to civil engineering, such as excavation and backfill after retaining walls [11–13], bridge abutments [14–17], pipeline and trench ducts [18], pavement bases [19–24], and so on. All these studies reflect requirement of the identification of mechanical constants of the CLSMs. Though it is known that the Young's modulus of CLSMs lies between soil and commonly used concrete, precise determination of engineering material properties of CLSMs (even for soil and concretes) is a questionable and difficult problem. For example, modulus of elasticity is evaluated by experiments using secant modulus of stress-strain curve or estimated from empirical formula of Young's modulus with 28-day compressive strength or weight of concrete.

Besides, artificial neural networks had been widely applied to various engineering [25], especially to civil and construction engineering [26, 27]. Alternately, several studies were conducted on the application of inverse problems in structural and geotechnical problems [28–32].
