A knowledge of artificial fill, or simply "fill," is useful when considering either the purchase of developed or undeveloped property in Malibu, or anywhere else for that matter. Fill is listed in the typical Seller's Disclosure Statement as one item of a number of conditions of which the seller may be aware concerning the property in question that reasonably would be of interest to a prospective purchaser. Almost all hillside properties have fill, but in many instances, the seller either is unaware of the fact or professes to be so. The presence of fill in a property is especially important where a purchaser is contemplating some sort of addition or remodeling that would impose additional loads on existing foundations in an area underlain by fill. In some instances, an uncertified fill presents a potential risk to a neighboring property that the purchaser would "inherit." This is especially a matter of concern in properties in Malibu and elsewhere in southern California, developed before about 1960, because fills then generally were not placed under controlled conditions. There are many such "uncertified" fills in Malibu.

The construction of artificial fill under controlled conditions was first codified in California as a result of the promulgation by the City of Los Angeles of its first grading ordinance in 1956. Similar legislation followed soon after by Los Angeles and Orange counties, and from those ordinances specific building code standards for grading were developed. Now most California counties require such controls and have, or are in the process of adopting, standards set forth in Appendix Chapter 33 of the California State Building Code. Although prior to 1956 certain techniques may have been employed by contractors with or without the advice of a soils engineer, there was no legal requirement controlling grading generally and fill construction in particular. Scullin (1983) presents a somewhat dated but nevertheless excellent introductory treatment of the use of artificial fills and grading in general as practiced in California.

Grading sections of modern California building codes contain standards relating to fill design and construction. Generally, codes require fill be placed on a relatively strong surface that has been "scarified," i.e., prepared by removal of vegetation and weak surficial materials. Further, there are certain limits in fill texture and lithology. If the surface has a slope, it is "benched," i.e., terraced, to produce a stair-like configuration so that the fill can be compacted over a level surface. This greatly reduces the probability of gravitational slide movement along the fill base which was a problem in earlier fill construction practice that allowed placing fill directly on an unbenched slope. Also, good construction practice requires placing the fill in "lifts" a foot or so thick which is most efficient for adequate compaction.

The degree of compaction obtainable for a specific fill material depends primarily on its texture and an experimentally determined optimum moisture content. Fill materials are such that above or below a certain moisture content they cannot be as well compacted for a given amount of compaction energy. This is determined in the soils engineering laboratory through repetitive trials at varying degrees of moisture using a specific control volume and compactive effort. This procedure, first established in 1933, is referred to as the "Proctor compaction test" (Taylor, 1948, pp. 552-539). Accordingly, geotechnical engineers now commonly develop laboratory Proctor test data using American Society for Testing Materials (ASTM) Standard Test Method D-1557 as a reference to determine the degree of compaction that must be obtained in the field as a result of the grading operations. The California State Building Code (Sec. 3305) recognizes a variety of tests suitable for determining the degree to which fill has been compacted in the field. This degree of compaction is referred to as the in-place "density," by which actually is meant the in-place unit weight. The tests determine whether the degree of compaction is the code-required 90 percent. or more of maximum density at optimum moisture content.

The earliest problems of fill construction were due to: [i] failure to scarify the underlying surface to receive the fill; [ii] failure to require a specific degree of compaction leading to fill settlement and slope failure; [iii] placement directly on a slope, i.e., without benching it, thereby creating a sloping contact subject to sliding; [iv] failure to provide a subdrain thus allowing for a buildup of hydrostatic head within the fill thus reducing its shear strength. Malibu's Building Code, its Guidelines for the Preparation of Engineering Geology and Geotechnical Engineering Reports dated February 2002, and its Site Grading Policy, provide standards for artificial fill construction similar to those used in other California jurisdictions.

Returning to the buyer's concerns, the best way to determine if there is fill in a property. other than research of agency records, is through site examination by an engineering geologist . Furthermore, if such fill is present and would affect the buyer's contemplated use of the property, the best way to determine the significance of this with regard to the value of the property is to consult with a geotechnical engineer regarding the geologist's express concerns.

* * *