Graniterock’s monumentally mobile crusher

By |  May 14, 2019
he Krupp has been operating at Graniterock’s A.R. Wilson Quarry since the late 1980s. Photo courtesy of BuildWitt Media Group.

he Krupp has been operating at Graniterock’s A.R. Wilson Quarry since the late 1980s. Photo courtesy of BuildWitt Media Group.

The A.R. Wilson Quarry, owned and operated by Graniterock, is nestled in the quiet, tree-covered hills of Aromas, California.

From Graniterock’s headquarters in Watsonville, California, located near Monterey Bay, the quarry is a 20-minute drive through strawberry fields. The 2,000-acre quarry sits squarely on the San Andreas Fault, aiding in the pre-fracturing of hard rock material.

Graniterock is family-owned, founded by an M.I.T.-trained engineer named Arthur R. Wilson whose company began mining in 1899. Those who drive by the Wilson Quarry today likely have no idea some of the largest pieces of heavy construction equipment in America toil away day and night to produce millions of tons of aggregate each year that provide for California’s infrastructure.

In fact, according to Graniterock, the Wilson Quarry is one of the largest hard rock quarries west of the Mississippi River.

Demand dictates change

Aggregate products of all types – from base rock to concrete and asphalt products to rail ballast – exit the quarry by truck and railcar every day. Thanks to automated loading and ticketing systems, trucks depart all hours of the day, seven days a week.

The site’s current production exceeds 5 million tpy, with reserves available to mine at least another 100 years. Big production, of course, requires big iron, and Graniterock’s Wilson Quarry exemplifies this notion to a tee.

In the late 1980s, the Bay Area experienced an enormous building boom. Demand for aggregate skyrocketed, and Graniterock’s primary crusher struggled to keep up. Back then, Graniterock’s crew members ran their stationary crusher as hard as they could during a 12-hour period, making repairs over another 12-hour stretch before starting production all over again.

The primary tower at the A.R. Wilson Quarry sends coarse rock to the secondary crushing circuit. Photo courtesy of BuildWitt Media Group.

The primary tower at the A.R. Wilson Quarry sends coarse rock to the secondary crushing circuit. Photo courtesy of BuildWitt Media Group.

But in addition to experiencing higher demand, Graniterock at that time needed a reliable solution to fit the company’s mine plan. The plan in the 1980s called for a mobile primary crusher close to the mining face.

Graniterock’s answer to this dilemma came from thyssenkrupp, the German-based company that provided a monumentally unique crushing solution: “the Krupp,” as Graniterock employees refer to their machine, weighs 750 tons and is said to be the largest self-propelled rubber tire crusher in the world.

Shipped from Germany, the Krupp began crushing at the Wilson Quarry in the late 1980s, and it hasn’t stopped since. The crusher’s enormous cone chews through 3,000 tons of granite every hour.

The mining process, like most aggregate operations, starts with drilling and blasting. Graniterock employs a 20-ft. x 20-ft. pattern, so blasted material is as coarse as possible while keeping material under the Krupp’s 3-ft. maximum.

After blasting, two Caterpillar D11T dozers push fragmented granite toward the mouth of the Krupp. Ideally, the Krupp’s feeder is positioned within 50 ft. of the face.

Two Caterpillar 992K loaders tandem load the feeder from both sides, and the crusher runs 10 to 13 hours at night due to power requirements.

For a machine that’s worked at a maximum output for three decades, maintenance is relatively straightforward. Graniterock staffs a team of full-time mechanics who stay on top of the Krupp’s maintenance needs. Certain parts, such as the pans, chain and mantles, are replaced every few years during scheduled shutdowns.

Crushed 10-in.-minus granite makes its way from the Krupp to the secondary crusher thanks to a two-mile-long overland conveyor. A primary tower sends the coarse rock to the secondary crushing circuit, and fines are moved to a wet plant. The Wilson Quarry dramatically reduces water consumption because of a plate press plant that separates water from the fines.

Also, the quarry has a two-week to one-month inventory goal for most products.

Moving the crusher

PhotoWeighing 750 tons, Graniterock’s massive crusher produces more than 5 million tons of aggregate each year for the San Francisco Bay Area. Photo courtesy of BuildWitt Media Group.

Weighing 750 tons, Graniterock’s massive crusher produces more than 5 million tons of aggregate each year for the San Francisco Bay Area. Photo courtesy of BuildWitt Media Group.

The Krupp rarely moves far, but it was set to make one of its most significant moves ever earlier this year to 120 ft. below sea level. The Wilson Quarry has steadily grown deeper, and the Krupp is now sitting on material ready to be mined.

Graniterock construction crews worked for several months to build the conveyor and electrical infrastructure necessary to move the Krupp to the bottom of the pit, where 30 years of aggregate waits to be mined. Quarry management contracted a heavy-haul company that plans to use self-propelled modular transporters to gently transport the behemoth machine in one piece over three days.

Graniterock’s Krupp crusher and the Wilson Quarry are sights to behold. The high-quality aggregate products and excellent safety record make the operation an example for the rest of the construction materials industry. Graniterock and the Krupp will continue to produce aggregate for the San Francisco Bay Area and beyond for decades to come.


Aaron Witt is managing director of BuildWitt Media Group.


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